Skin

After a second round of studs, hundreds of gussets, several rows of blocking, and the completion of the roof dormer, we are ready to put on the sheathing, and the house will go from a skeleton to having skin. The sheathing for this house will be 1/2″ CDX plywood and will serve multiple roles. The plywood skin braces the house against lateral loads like wind, on this project it will act as the air barrier sealing the house against air moving between the inside and outside of the structure, and it is the substrate supporting both the weather resistive barrier (house wrap) and siding or in our case the battens that support the siding.

Structural Bracing

Before, in a different post, I discussed the let in bracing that we used on the interior walls and the reasons we chose to build those walls that way. What I haven’t mentioned is that as the house got taller and more levels were added it was apparent that there is a lot of flexibility in tall walls with let in braces. I mean a lot. Finally on the roof finishing the framing details at the top of the house a couple people moving around up there would produce enough swaying everyone anywhere in the house could feel it and it was likened to a boat at sea. Very flexible. As the plywood was nailed on, each completed wall section made the house more rigid, and when every surface was finished the motion was gone. Very rigid, just like houses ought to feel.

We started putting on the plywood at the top of the house and worked down. This allowed us to utilize the open wall studs as support for our scaffold jacks. Moving down in 8 foot increments, we could do two courses of plywood before moving the scaffold jacks. At the bottom of the wall where the wood meets the concrete foundation, our last course is a 2′ strip of pressure treated plywood as added insurance against rot for the sheathing that is closest to the ground.

The first few boards of sheathing installed

The first wall is completely sheathed, you can see the treated plywood strip at the bottom

Sheathing as Air Barrier

One of the goals in an energy-efficient house is to minimize the transfer of air between the space inside the house and the outside. This requires a clear distinction for where inside air stops and outside air begins. I have generally used the sheathing to define the separation. I find this line to be cleaner than using the drywall, which is another option, to insure a complete barrier.

For this house, without a pitched roof, we just need to seal the plywood box composed of the sheathing and the roof decking, tied into the foundation wall, which has already been sealed, to create our air barrier for the walls. I chose a sheathing tape for the job on this project. On other houses we have used caulk and duct mastic to seal the plywood joints, and it seems to work well, but with two trips around the house the time required was unattractive. On a house previous to this one we switched and tried Siga Wigluv tape, and I have used the same tape on this project. It is very expensive tape. 70 sheets of plywood for the sheathing and about 18 for the roof deck is $700 in tape to seal the joints, but we can do it when the sheathing goes on, one trip for both nailing plywood and taping joints, which speeds things considerably. For us I think the caulk and mastic is probably cheaper, including the labor, but the lost time for the extra steps has a cost that better business people than me could likely quantify, and my confidence in the tape is much higher than the caulk and mastic. The Wigluv is crazy sticky, and flexible, lifetime of the house kind of sticky.

I plan to get the house sheathed, housewrapped and get the windows and doors installed and get a blower door test to see how we’ve done and identify places we need to seal, before the insulation and siding get in the way of corrective measures.

Another view of the north side

Plywood completed along the back

And the front

The front photo shows some things that depart from traditional framing practice, and are a nod to establishing a continuous air barrier. First the parapet for the front roof is already installed when this photo is taken, but the sealing tape is visible up to the parapet, but not on it. We sealed the wall sheathing to the roof deck before the parapet was built, so that the parapet is outside the air barrier where it ought to be. If we had run the exterior wall to the parapet height and sheathed continuously to the top of the parapet, air sealing the area on the wall above the roof deck would have proven to be much more complicated. Also, there will be a porch coming off the second level on the front of the house. The opening in the center of the house in the last photo is the door that enters onto that porch. We haven’t framed that porch yet in order to maintain the air barrier formed by the sheathing and tape. In fact the porch won’t be framed until the house wrap AND the battens for the rain screen are complete, allowing for the air barrier, rain barrier, and the air space behind the siding on the house to be continuous and not interrupted by the porch framing. Something we will talk about later.

The windows have arrived as well as all the products for flashing the openings. Next post I will discuss prepping for the windows and the installation, the roof is going on soon as well, but that might need a separate discussion.

Two Walls

Where we are now on the project, with the roof framing on and decked, most houses would be ready for sheathing or likely sheathing would be finished and the framing pretty much done, but for us there is a second wall to build outside the first one.

Rain

It is always good to get houses dried in and safe from weather in as short a period of time as possible. With less swelling and movement, and less effort to dry the framing after the house is enclosed, houses built with less exposure to rain are favorable. Sometimes the weather and scheduling cooperate for this to happen, this spring has not been a cooperative time. So when we start on the second wall when we could be getting the house in the dry and 3 more inches of rain fall over a weekend my sense of urgency heightens, and I start to regret the complexities of my little house. In a month, typically one of the dryest, where twenty days in we’ve gotten about seven inches of rain, a month that averages three, I force myself to remember the house will be covered soon and it will dry out and the second wall is integral to the whole concept, lots of insulation, little foam. Here’s a spoiler alert, building two walls is about twice as much work as building one. Maybe more.

Twelve Inches of Insulation

The whole purpose of building two walls is to fill the space between them with insulation. In our case it will be twelve inches of cellulose giving us a wall with an R-value somewhere in the low 40’s, but super insulated houses are put together in a variety of ways. A standard stud wall covered in a bunch of foam can yield walls with R values approaching 60, but the building has to be covered with 8 inches of foam to see performance like that, and I have already written about why that approach wouldn’t work for us, mainly we don’t like foam. Another method also starts with a traditional wood frame wall and after sheathing another frame is added. I have done this with a 2×6 wall attached to the sheathing of a 2×6 wall, an even more insulated version attaches a 12 or 14 inch I joist to the sheathing of a framed wall. I can see the value in that approach, especially in time savings, but we would have had to sheath both walls, which I think would cost as much as the time saved, and I joists aren’t cheap. The method we are using does two things that are important when it comes to insulation, first it provides a lot of space. Since the insulation performs generally in a linear relationship to its thickness, more is better. Doubling the R-value of a wall reduces the energy loss by half, with caveat that the rest of the components of the building envelope, namely windows and doors, need to keep pace. Secondly, it separates the interior surface from the exterior. With the two walls, a continuous blanket of insulation rests between the interior framing and the exterior framing. This differs from a standard single frame wall where the stud touches both the interior surface (usually drywall) and the exterior surface (usually osb sheathing) and bleeds energy from one to the other, because wood is not nearly as good an insulator as, well, insulation.

On our site we were severely limited in the footprint available for building. Building to the full extent of the available space we have a structure that is 16 feet by 29ish. The twelve inches of wall thickness versus say a more typical 6 inch wall represents more than 100 square feet lost to insulation. I only say this because for us it was a balance between sufficient insulation without losing too much floor space. Going through the trouble and expense of building two walls, it is likely better to get more insulation out of the prospect; expanding to 16 or 18 inches of thickness would involve the cost of some more insulation and some exterior surface, small expenses relative to the second wall. Again make sure the windows keep up.

Lots of little pieces

Our walls are built with an inner load bearing wall that uses 2×4 studs on the lower floor and 2×6 studs on the upper floor (because of the wall height). The outer wall is 2×4 studs. Because it sits on the foundation wall the outer walls starts about 3 feet higher than the inner wall. The two walls are staggered with the inner wall breaking at the floor system and the outside wall extending 5 feet or so past that point breaking at a plate and then a second level of studs extending to the roof deck.

the lower half of the outer wall is in on the left, both the lower half and the upper section are in on the right. the dividing plate is visible about midway up the wall.

The roof deck ties the outer wall back to the structure at the very top of the building and of course it is tied to the plate on top of the foundation wall. Between those two points we used a lot of 3/4″ plywood gussets spaced 2 foot on center vertically to tie the two walls to one another.

There are a couple nice things about the two wall system. First only one side of each wall receives a finished surface, so if there is a width discrepancy between a stud and the plate they just have to be flush on the finished side, the other side will only see insulation. Similarly when we needed to switch to 2×6 for the upper inside wall we attached an extra band to the floor system and extended the additional stud width into the insulation cavity. We didn’t need to use 2×6 on the lower wall just because the upper wall needed them. Also the walls could be plumbed and straightened independently. So small errors through the floor system, for example, didn’t need to transfer through to the outer wall, we just set the plate in the middle of the outer wall to a string and tied it back to the inner wall that had been plumbed and braced, doing this again at the mid-point of the studs we were able to achieve a very flat outer wall surface.

To tie the outer wall to the inner wall we used 3″ x 11″ x 3/4″ plywood gussets nailed to aligned studs in each wall. There are a lot of gussets. We had form material from the foundation walls we were able to get the gussets from, 800 in all.

The outer wall is finished to the roof deck and we have started the gussets between the two walls. the gray color of the gussets is concrete. the gussets are made from the form material for the foundation walls

This shows the outer wall complete in the back and the many gussets in place to tie the two walls together.

 

With the outer wall completed (except for some blocking) our next framing task is the roof dormer for the stairway access to the roof and the sheathing. The forecast calls for few dry days. Sometime next week we ought to be ready for some roofing, finally a dry house!

Framing the Roof(s)

With the second level walls framed, plumbed and braced it is time to frame the roof or actually roofs. On top of the two different height walls are two separate roofs, framed with different materials. The lower roof will be the planted roof, built up with multiple layers of waterproofing and drainage material, topped with 12″ of soil. The upper roof is the roof that supports the dormer that covers the roof access stairs, with the remaining area, about 8′ x 14′ serving as a patio. The different uses and associated loads of each roof dictated the size of the framing material needed. In the case of the planted roof, covered in saturated soil, the loads required a 16″ I joist, for the other are, just serving as a patio, only a 12″ I joist was needed. The deeper the joist, the more insulation that can be packed in, which is a good thing, and I would have prefered to use 16″ joists on both roofs, but that additional 4″ would have put the rear section of the house beyond the maximum allowable building height. So we have to be satisfied with an R value of about 50 including the foam tapers on the top of the deck for that roof, where the planted roof will be more like R70.

More Cantilevers

Step one: install the LVL’s that will hold up the upper roof and cantilever the lower roof over the bay window

Since the bay windows project from the building without bearing directly on the foundation, their weight being carried by cantilevered flitch plates at their base, they are not able to carry the loads from the planted roof. So to support the load from the portion of the roof that sits above the bay window we employed double 16″ LVL’s cantilevered over the bay. The double LVL’s served as the rim along the entire front and southeast side of the roof.

The cantilevered LVL rim boards

The beams join at a corner of the building that is suggested by the rest of the walls, but not realized until the roof comes together over the bay window. This creates an interesting play of triangles: the two corners of the window projecting from the main building and the roof projecting over the center of the window like a ship’s prow. This will become clearer when the second outer wall increases all three projecting points and even more so when the sheathing solidifies the mass of the building.

We also needed a set of double LVL’s across the transition between the lower roof and the upper roof. Because of the orientation of the dormer for the roof stairs, the joists for the upper roof had to run back to front. This necessitated a beam across the building at the roof transition. The lower roof joists don’t bear on this beam, they run side to side with both ends landing on a wall, with the exception of the joists over the bay that hang from the previously mentioned cantilevered beam.

Getting the lower roof joists into place

Planted Roofs

It is easy to write about the process of building the roofs, placing framing members and revealing the puzzle pieces that will go together to make the whole. In the end this is what building a house is, a series of steps and layers that culminate in a place where people live. It is also easy to get lost in those steps, to substitute process for purpose. In our case I think it is worthwhile to discuss the purpose for the planted roof.

Not everyone loves green roofs, the value that they add to a sustainable design is debated. Engineers tend to point out that the benefits they provide are available through other means. Their contribution to reducing urban heat islands can be accomplished with high reflectivity roof materials. Their mitigation of storm water run off can be handled through infiltration systems on the ground. Because dirt is not a very good insulator, planted roofs don’t really add to the energy efficiency of buildings, except that the plants on the roof, supplied with sufficient water, will provide evaporative cooling through transpiration. Better and cheaper to increase the insulation on the roof to improve the efficiency of the building, and insulation will perform during both the cooling and heating seasons. And using potable water to irrigate plants on the ground is wasteful enough without adding irrigation to the roof.

I agree with all that I just wrote, and there are good studies to back it up, but there are a couple of reasons, general to building and specific to this project, why we decided a planted roof was purposeful and included it in this house.

Water

It is hard to assess how much of building is directed toward managing water, water from the sky, water from the ground, water in the air. Maybe it is just in the Southeast, but I don’t think so and here we are mostly spared the problem of frozen water, thank God. Anyway it is a lot. The conventional wisdom and vernacular architecture in the South embraces steeply pitched roofs to shed rain water quickly off the house. I have found, though, over many years of repairing houses it seems more damage is done by the rain water after it leaves the roof than from the time it spends on the roof. Overflowing gutters, splash from the eaves, flooding foundations, all lead to problems for houses. When I built my first flat-roofed house I never noticed the water that left the roof, it was collected behind a parapet, drained into a downspout, then through underground pipes and finally flowed onto the ground forty feet from the house. The roofing material was a heat sealed membrane that was user-friendly and durable. The one drawback was that the leaves from nearby trees tended to collect at the screens for the roof drains, but at least when you have to clean them you are standing on a (nearly) level surface. So the only thing better: a flat roof where the leaves don’t matter. A filter of soil and the other layers of the planted roof negate the ability of accumulated leaves to clog the outflow for the roof. As opposed to a traditional roof that encourages the rain water to flow off the roof as quickly and directly as possible, dragging with it any debris that has landed on the roof, the planted roof slows the rain, absorbs and retains some of it, and filters it through a broad area before releasing it slowly to the roofing to convey it away from the building. It may seem counter-intuitive, but part of my no maintenance scheme included the planted roof. I was going to garden somewhere, why not accomplish roof maintenance at the same time I was planting or weeding.

The Garden

My musings on water management made the idea attractive, but the reason for the planted roof is the desire for garden space on a piece of land so small its hard to escape our own shadow. We have always had gardens, frequently unruly, sometimes very productive, sometimes less so, a garden is part of who we are and I have nearly arrived at the place that I believe if land isn’t going to be left to its own and return to what here would be a subtropical deciduous jungle, it ought to grow food. The house dominates the lot, add a parking space, walkways, space for our aging dog, consider the north side lost in the shade of the house, bamboo and a struggling pecan tree on the adjacent property shade some of the narrow strip to the south; even so we will plant the front hill with blueberries and strawberries, we will put some blackberries on the fence line. But the roof offered an unobstructed view of the sun, and though small, plenty of space for a generous kitchen garden. The roof is where we will have our cooking herbs and spring lettuce. Every garden we have ever had has been an evolutionary project and this will be as well. I see some years with sweet potato vines cascading down the walls, while beans grow on a trellis above them, maybe our virgin roof top soil will even produce a zucchini before the squash borers kill the vine.

Watering the Roof

One drawback to planted roofs is that they almost certainly need irrigation. Maybe not always and not as much with the carpet of sedums that often make up green roofs, but with plants like tomatoes that are thirsty in the ground, watering will be a necessity on the roof. I didn’t want to take an idea that is borderline sustainable and throw it clearly on the wrong side by watering our roof with potable water. To avoid this we needed to get our irrigation water from somewhere other than the tap. My first choice is stored rainwater, and we have some roof area that will not be planted that can be collected during rain storms and used during the hottest months. Several hundred gallons of stored water can last a few weeks without rain as long as the irrigation is efficient and there is plenty of mulch. We will have a 300 gallon storage tank under the porch with a pump to lift the water to the roof, and a subsurface irrigation system to put the water where it is most needed. The water keeps the plants alive and makes the garden viable, but during the hottest months it also provides the one energy benefit of a planted roof, evaporative cooling.

We did get the roof framing done and moved on to building the outside wall, things are wet now, but next week looks clear. A good week’s work and we’ll be close to the end of the framing

Here the roof is fully decked, ready for the rooftop dormer and the completion of the second wall

 

Going Vertical

With the floor system finished and the subfloor (and finished ceiling) installed it is time to make this thing look like a house, or at least look like the house that it is.

Two wall heights, Three ceiling heights

As I have said earlier, raising walls is one of the absolute joys of construction. Tilting a wall up, looking at the top plate overhead and a cloudless blue sky beyond, is a singular moment, emblematic of the entire effort, and makes me feel that I am lucky to have a job where I get to work outside. And makes me forget about carrying buckets of gravel in the rain a month before.

Our plan is to get the second floor interior walls up and straightened before working on the outer walls. There are two different wall heights on the second level, 10′ 4 1/2″ in the front and 14′ 10 1/2″ in the rear. This is for a couple of reasons. First the higher wall in the back is needed to allow for the loft. With 7′ being the minimum ceiling height allowed, 14′ 10 1/2″ gives us enough for two levels plus a 2×6 floor system and a little extra for ceiling covering and such. Because the planted roof is on the front section and that overall roof package, framing, insulation, and planted roof paraphernalia, is 30″ thick, the wall height below it needed to be lower. The stairs from the loft to the roof also open on to the front section so having it lower than the back requires fewer steps to get up onto the roof.

Here is a section showing the floor levels, roof levels, and stairs between them.

A vertical section of the house, showing the stairs, floor levels, loft, and roof access.

There was one difficulty in building the tallest walls on the deck and raising them into place, the walls are about as tall as the building is wide. And once one side was in place there wasn’t enough room for the other side to be laid flat. The last of the tall walls we framed were at least not long so we built them where we could, stood them up, and wrestled them into place.

First wall up

The three front walls in place

The first rear wall up

everything up, windows framed in

 Old Methods, New Face

We worked last Saturday because the weather was good and we hadn’t gotten much done on site for much of the week. I worked the full day, everybody else split half shifts to preserve some of their weekend. In the afternoon Woody came in after we had gotten the rest of the second level walls up and started to plumb corners in the AM. He and I finished plumbing corners and framed in window rough openings. At some point during the day, in the course of conversation, he pointed out that one of the things he liked about the house was that though it is a fully modern design it uses old framing methods to get there. It was something I hadn’t thought about, but he is right, let in 1×4 bracing disappeared with the advent of plywood, and balloon framing with fire codes and pre cut framing and small trees, and we’re using both in this house, and I don’t think I have ever used either method before, mostly because I’m not old enough.

I have built another double stud wall house, but that one was sheathed twice, once to brace the walls and then again to hold the siding. I didn’t want to do that and so needed another way to brace the interior wall and 1×4 braces let in to the studs satisfied. We can insulate around them so the stud cavity between the two walls is uninterrupted, they brace the walls against lateral loads, and they use a whole lot less material than plywood sheathing. And we are going to fully sheath the exterior wall with 1/2″ CDX plywood, mostly to hold siding, but also the exterior wall has a full foundation under it and though it won’t carry the bearing loads of the building, it will be subjected to other forces on the building like wind loads and it will act in concert with the interior wall (because they are fully tied together) to handle these loads.

The balloon framing is really only used on the loft framing, though the double wall acts a little like a balloon framed wall. For the loft floor we are going to use a let in 1×4 on the back wall of the house that the loft floor joists will rest on. The joists will also be nailed into an adjacent stud. Balloon framing multi story houses disappeared from common building practice long before framers quit using let in bracing, I guess because the studs had to be so long. It made sense for the loft floor because it simplified the framing of the back wall by allowing the entire rear section of the house to be framed to the same height, and again serves to allow the insulation to flow fully through the framing cavity. The main floor system was platform framed and we placed foam blocks against the band joist so the amount of insulation wouldn’t lessen at the floor system. That won’t be needed at the loft floor which won’t create an obstruction within the wall.

Balloon framing does create the need to address a common problem of the past, the potential for a fire within the wall to jump floors because the framing doesn’t create a full barrier between the floors. This is the aspect of the double stud wall that behaves like a balloon framed wall. The goal of the double stud construction is to provide a continuous insulation layer, with no bridges of framing for heat to move through. In order to achieve this there is no framed fire block between the floors, a block that would also be a thermal bridge. Instead the wall cavity is completely filled with dense pack cellulose, which in addition to the many other wonders of cellulose serves as a fire block, partly due to the fire retardants in the insulation (borates mostly, not like fire retardants in pillows and furniture) and also due to the lack of air flow through the material.

So fully modern, yes, but leaning on older techniques that were properly suited to accomplishing our overall goal

Getting off the ground

Sometimes it seems like the whole construction effort up to the point where we are now is a long slog just to get up and out of the dirt. In multi story projects once you get the first floor system above the slab completed, the next bit of framing, raising walls, is as good as construction gets. As a friend said, who saw us after most of the second level walls were in place, ” It’s like you build the whole house in a day,” and it kind of feels that way. Before we got there though we had to frame the second level floor.

Framing as finish

A few things about the floor system that are atypical: first, we are not going to cover the floor joists underneath with a ceiling making the joists and subfloor the finished ceiling for the first level, second, there is a significantly cantilevered corner, and last we are going to pour a 1-1/2″ thick concrete slab on the subfloor to serve as the finished floor for the second level. I am going to admit I am not sure that having the joists and subfloor as the ceiling will be the greatest idea. It will provide a lot of spider habitat, which makes for much dewebbing or a cobwebby house. Both the joists and the subfloor are southern yellow pine which even clear finished will be a relatively dark surface, on top of the recesses of the joist bays being shadowy anyway. On the plus side since the interior walls and ceilings are going to be a 1/2″ formaldahyde-free birch plywood, leaving the downstairs ceiling open saves both the plywood and the labor that would be needed to cover it, and I have always liked southern yellow pine, and not just the old stuff, as a finished surface. Here is another opportunity for me to show one of my laminated detail drawings.

this shows the framing details for the transition between the first and second levels

This shows the 2x 12 blocking used at the wall plates to close the joist cavity and provide a transition between the wall plywood and the subfloor. I filled the space between the floor system band joist and the blocking with 2″ of sheet foam before we sealed that cavity so that we would not reduce the insulation at the floor system.

The 2×12 floor system with blocking and foam

As pretty and even as the drawing looks, framing lumber can confound the best of intentions and teaches us why we cover it when we try to leave it exposed. The joists varied from 11″ to 11 5/16″ which would challenge even a drywall ceiling. In the end we culled a few, planed a few, and ripped blocking to keep it consistent. And reminded ourselves often that the intent was to leave the framing exposed. The one place where we will cover the ceiling is the downstairs bathroom. I haven’t decided what will cover it yet, but I am sure I don’t want either floor joists or birch plywood to serve as the shower ceiling. It is not going to be tile either, too sanitorium, so we’ll figure that out in a couple months.

The Cantilever (and the notch)

installing the beams that support the cantilever

There are a few things that happen when you design two-story structures. One is that once you have designed one of the floors you have to come up with a way to design the other floor using the same area and shape. In larger houses this can frequently end up with trying to find some use for the extra square footage dictated by the space above or below. In smaller houses where space is more of a premium using all the area available is easier especially when the plan is opened up, on one level specific uses are partitioned and defined, on the other the same area and space is used in a single open room comprising several uses. That is somewhat how we got to our design, and it is the notch out of the lowest level that dictated how the different levels would be used, the notch that I added early in design to get at least one parking space off street. Our plan is inverted, the bedroom is on the (almost) entry-level, with the kitchen, living, dining above, and this was driven in large part because the private portion of the house was more suited to less square footage than the public portion, and with the notch making the lower level about 30 square feet smaller than the upper it made sense to put the bedroom on the lower level. There was a cascade of serendipity that followed this decision. The loft above the second level was accessible and connected to the main living area, the kitchen could inhabit a space with a low ceiling under the loft, the roof which will serve as both kitchen garden and outdoor dining is closer to the kitchen than the bedroom with this configuration. The notch though required the cantilever if we were going to regain the space for the second level and keep the parking area free of a support post for the walls above. This is an instance where an engineered wood beam served well. Though we are limited in how low the beam can be placed (no lower than flush with the bottom of the floor system) and still maintain headroom under the cantilever for the parking area, we are not limited in how high the top of the beam can be as it can extend up into the second level inner wall as much as necessary. Expecting that a double 16″ LVL might be needed this was exactly my plan, to allow the beam to occupy the bottom 4″ of the second level wall, the engineering only required a double 12″ LVL, which very conveniently allowed the subfloor to finish nearly flush with the top of the beam and the bottom plate for the second level wall to be placed on the top of the LVL’s and the subfloor with no stud length adjustment. The fully loaded deflection for the cantilever is a tiny 0.08″. There is one downside to the cantilever: it provides a thermal bridge. The joists and beams are a direct path for heat transfer between the interior and the exterior, something the framing plan for the rest of the house was designed to avoid. This occurs at the bay cantilevers as well. In both cases I will use sheet foam on the undersides of the cantilevers to provide a thermal break. Again more foam, but again a limited amount in an area that would be hard to insulate another way.

Upstairs Concrete

This was not my idea actually. Mary proposed this and I was resistant, cost and difficulty mostly, I had planned on the subfloor being the finished floor. But the design is intended to capture passive solar in the winter, and for that the added thermal mass of the concrete floor would be a benefit. It will weigh more than a wood finished floor, though not as much as one might think. Lightweight concrete weighs about 120 pounds per cubic foot so pouring the upstairs floor 2″ thick will add 20 pounds per square foot to the floor system, something the 2×12’s spanning 14 feet can easily handle. There are still a few details to work out around the stairwell where the edge of the concrete will be visible, but we won’t want to see the edge of the subfloor. This gets especially sticky where the landing to the loft sits on the second level floor. I had always planned on the screened porch floor being poured concrete, part of the no maintenance plan. That is a much more difficult prospect than pouring the concrete inside, even more so considering that I am planning a plywood formed structural slab; a subject of a future post I am sure.

Sleeping Nine

This goes hand in hand with a goal I didn’t list earlier but has always been part of the idea behind the project, that the house ought to offer a graciousness of living, a vague statement for sure, but one that encompasses, welcoming guests, entertaining friends, affording privacy when needed, those things beyond shelter that a house can offer. You don’t only use a house daily, but you also use one monthly and yearly. Meaning, we don’t just need a place to do the things we do every day, cook and bathe, sleep, eat, or watch some sort of screen, but also the things that happen less frequently, friends come for dinner or for the weekend, I occasionally make beer, Mary cans, sews, sometimes makes giant banners. All of those activities and others need to be able to have space for us enjoy richness in our lives. So although we can pare down much superfluous stuff, and we have, there are still going to be some things that need storage and activities that need a place to happen. I am mainly talking about this because in balancing all of these different needs for the house, I often looked at the nine sleeping spaces as lost storage that we could use. In the end we have kept them, because of all the things we want to keep in our lives when we shrink the size of our living space, relationships with the people who are important to us has remained the highest priority. So we needed space to welcome them and make them feel comfortable.

No mattresses on the floor

The number nine comes from the meeting of two families, ours with four people, and good friends of ours who visit and stay frequently. There are five in their family. Part of the graciousness I was speaking of before includes not putting a bunch of air beds on the floor for our guests to sleep. Also we didn’t want to put our own bed away during the day. I felt like there was sufficient space in the design to have an actual bedroom, even if it’s small. This isn’t 300 sq. ft. after all. The space is small enough though that putting a bunch of air beds out would be awkward, so we wanted a better more built-in solution. Additionally, at least for the next several years, our girls will come home for more extended stays, between semesters or during school breaks and they will need something that will act more like a bedroom space and provide them some privacy. But they will have to put their beds away during the day.

The count stands at two, our bedroom, one queen sized bed. Excluding the bathroom and the 1/4 bath (we will talk about that eventually) the house only has four “rooms” and 1 interior door, the one to our bedroom, but it does have spots that are separated somewhat from adjacent areas that serve as natural locations to convert into sleeping areas. The office area, it really should have a different name but it would have to be very long to accommodate all of the things that will go on in there, so we will call it the office, is the other room on the lowest level. Mostly it will hold our desk and computer, a drafting table and storage for officey things. A set of storage shelves will be located along the wall the office shares with the entrance door, this will also house the drafting table, which will be hinged so that it can be stowed. Once the drafting table has been put away a full size murphy bed will fold down out of the shelf unit. This space will offer a good bit of privacy, even if it doesn’t have the separation of a door, but will also be a location that will see a lot of daily activity.

Now we are at four. There is a loft above the kitchen. It will serve as a landing midway to the roof access door and as a sitting area separate for the main living room. The TV will go here. We haven’t had a TV for years, we watch plenty of stuff, but mainly on the computer. I have to admit I feel a little lame saying this, but I am looking forward to sitting on a couch to watch a movie. That couch will be in the loft and it will be a full size sleeper. I think there may end up being a curtain to separate the loft from the rest of the second level space which will provide some privacy for sleepers, or TV watchers.

That gets us to six. This is the hardest one. In the living room area above the office there will be more storage on the wall beside the stairs. This will end up being deep storage, 2 feet or so to house a variety of things. The entire storage unit will pull off the wall and slide 7 feet away from the wall exposing a full size murphy bed hinged horizontally on the wall. If you are reading this blog about a small house, it is likely you have seen the videos online of the convertible apartments where partitions slide around in various configurations to reveal ever more spaces and functions. It will be like that but just one partition. Here again a curtain can be pulled across the open end and with the shelf unit on one side will complete a very small room. This will unfortunately block access to the screened porch, but it should be easy enough to move that it won’t prove to be to a problem. I figure the sliding storage may end up being the hardest carpentry project in the house; I am sure it will be the subject of later posts when it is underway. I hope they are not frustrated and angry posts, lamenting my decision to try this. We will see.

Eight down. The last spot would be one for a small young person. In the loft above the sleeper sofa we will hang a ship’s bunk. Narrow and high this would be a bed of last resort, but available.

One good thing about tucking the sleeping spots throughout the house is it has naturally allowed for privacy by separation. I can imagine when the girls are home, the loft and living room partition would be their choices for crashing, but I am sure that we will learn lot about how the space will work when we are there.

No Maintenance

There are a lot of good reasons not to paint houses. And one of the best is that you will have to do it again and again, and if you don’t your house will look bad and fall apart. I have learned about myself that I prefer making new things to fixing old ones and so forcing myself to choose between painting my house or letting it fall apart, I am going to choose a third option: no paint. I want to be clear I am not advocating for vinyl siding here. But what cladding options are there for houses that don’t require any maintenance? What material can you leave outside for decades and never do anything to it ever and it will last?

Rain Screens

Before I go into the material that will go on the outside of the house I want to talk about what goes behind it. Pretty much every house today is constructed with a weather resistant barrier under the siding. Asphalt felt or house wrap or some proprietary integral house wrap like Zip system is behind the cladding preventing water from getting into the wall. Several years ago we built a few houses that had dissimilar and nontraditional siding materials, and we turned to rain screen construction to simplify the waterproofing details. These were open rain screens, a UV resistant WRB flashed appropriately at all junctures, vertical battens attached to the wall, the siding attached to the battens creating an air space between the back of the siding and the WRB where water can drain to the ground and air can circulate to dry the back of the siding and the WRB. The open part of the open rain screen is the spaces that are left between the individual pieces of cladding. Durable wood planks applied horizontally, aluminum composite panels, cement board panels or planks, with 1/4″ to 5/16″ spaces between the pieces. I have looked at how much water is behind the pieces lowest on the wall draining down the WRB during driving rain and it is not much, a few drips. You don’t really try to keep the water from getting behind the siding, you just make sure that when it gets back there it has a clear open path to exit at the bottom of the wall, siding stays well ventilated so it can dry on all sides. I always knew this house would have its cladding on a rain screen. That is the first step toward durability.

Naturally durable exterior materials

There are some really cool commercial claddings like Trespa and the previously mentioned aluminum composite panels that will hold up outside for a long time, but the budget of the project eliminated those. Excluding those leaves masonry, metal, and possibly a durable wood, but it is asking a lot of even the most durable of woods to last without some protection from the sun and rain.

I have had a couple projects recently where Cor-Ten in some form was considered for building cladding. Cor-Ten is a steel alloy that rusts on its surface, but doesn’t continue to rust and degrade, enabling it to survive in the elements unprotected for a long time. We never ended up using it, though. I have used other types of metal siding, painted and galvalume roofing panels with gasket screws and T-panel siding with good result and like them as building siding. They are pretty affordable depending on the product, and especially so if you include the money not spent on painting.

Brick, stone, block, and concrete are traditional materials that have been used on the exterior  of buildings for almost as long as there have been buildings, but for me, on this project, I was looking for a different feel, something less massive and imposing.

That leaves durable woods. Wood shingles obviously are a traditional application of exterior wood cladding that doesn’t have to be painted and will hold up in very harsh climates, but like the masonry, shingles just didn’t capture the what I wanted for the house, but having decided on metal, Cor-Ten actually, I also didn’t want the house to only be metal. It needed variety and something to soften the box car aesthetic of the Cor-Ten. I was trying to find a way to incorporate wood, avoiding tropical hardwoods for the obvious reasons, but still not wanting to have to maintain the siding.

This is going to be an experiment

Recently and old process for preserving wood siding has become trendy, especially among modern structures. I don’t remember the Japanese name of the process and am not gong to look it up, and put it here as though I do. It involves charring to varying extents an already durable wood siding, and then applying the siding to the wall with the charred side to the elements. The charcoal on the surface being basically inert protects the wood underneath from sunlight and rot. Traditionally a native cedar or cypress was used, but apparently any rot and water-resistant wood is supposed to work. I don’t know anybody who has actually done this, and although the concept seems sound really am not sure how this would behave in the southeastern US. But it allegedly protects wood for a long time. I decided I would try this. This may be a colossal mistake, and my effort to not paint may turn into residing the failed charred wood portions of the house, but I am hoping that with good species choice, the advantage of a rain screen installation and a few precautions it has a chance of working.

Native wood

In looking for a wood species to use I wanted something that was grown locally. Cypress and cedar are both native to Georgia and durable woods suitable for exterior use. But both eastern white cedar and cypress are harvested out of coastal and south Georgia, and by most accounts not in a way that manages the resource well. We are lucky to have a local lumber supplier here that has started cutting and drying locally cut trees, so I talked to him about getting white oak to char and use as siding. White oak isn’t a species commonly thought of for exterior uses, but it’s tested durability outside is excellent. So the first level will be clad with Cor-Ten 4′ x 8′ panels and the second level with be charred local cut white oak. As an additional protection for the white oak we will seal the cut ends and the back before installation. We will see how it goes.

Meeting Standards

Mary and I have lived and built in Athens’ historic districts since 1992. I realize that a builder expressing frustration with a historic preservation process is cliché, but I will say that after building the two homes we lived in that were within historic districts, having the opportunity to design and build our house outside of historic preservation oversite sounded good to us. It was a requirement, actually, of whatever lot we were going to buy and build on.

Of course, there are standards, other than historic preservation, and outside of building code, that must be met in the construction of homes, and a desire to reduce the complicating factors of boards or commissions, led me to attempt to design this latest house completely within the zoning standards. This sounds like I am a scofflaw trying to reform, but the zoning standards for the zone where our house would be built require a lot to be no smaller than 5000 sq. ft. Ours is less than a third of that. On a lot this small, where design options can be extremely limited, gaining some relief from setbacks or other requirements can provide needed flexibility. I tried to stay within the rules, it didn’t quite go that way, and I ended up before the Hearings Board asking for variances in the end.

Designing within the lines

The greatest regulatory hurdles in Athens to building on very small lots are the building setbacks from the property lines, which limits the building foot print, overall building height, which functionally limits the number of stories, and the requirement that every single family house has to have two off street parking spaces, which at its smallest would consume 325 sq. ft. Setbacks first. The very first lines I put on a piece of paper in this design were the setbacks, those mostly became the exterior walls. Six feet for the sides, fifteen in front and ten in back. Needing to orient some walls to capture southern light, I took advantage of a setback encroachment that allows bay windows to project 2 feet into the setbacks. This gave us our southern exposure and gained a little volume for the interior.

Wanting at least one parking space that was not on the street we took a notch out of the northwest corner of the foot print to allow a narrow spot where a car can pull fully off the street; the code allows for two available on street parking spots to count as one off street spot which would give us our second required spot. That lost area on the bottom floor was regained on the second level by a cantilever over part of the parking area.

Finally the house, with two levels plus a loft, exceeded the maximum allowable building height of 25 feet. To accommodate this I placed the first level 2 feet below finished grade, ending up with a finished building height of 24′ – 4″. Using nearly all of the available space on the lot and building as tall as we are able got us to 1023 sq. ft. which is just over the required 1000 sq. ft. minimum house size in Athens.

What I got wrong

I submitted my site plan assuming we had covered all of the necessary requirements. A day later I got a message from the planner who was working on my permit that the plan did not have the necessary two off street parking spaces, and after further discussion I came to understand that there weren’t any spaces on the street that met the criteria to substitute for the lack of on site parking. I needed a variance to proceed. I have done variances in the past and felt this would be a simple and sure argument. When I turned in my variance request application though additional planners reviewed the site plan and determined that my setbacks were measured from the current right-of-way lines, that is the property lines, not from the future right-of-way lines.

A moment to talk about future right-of-way. Future rights-of-way are additional corridor width that the city has determined may be required in the future for street widening, some streets have specific future right-of-way widths based on assessments of likely future needs. Every other street has a future right-of-way of 50 feet regardless of how narrow or unused the street is, no matter the extent of the encroachment of existing houses. Our lot has frontage on two streets, one a relatively busy residential thoroughfare, the other little more than an alley, and measuring from the future rights-of-way of both streets reduced the buildable depth to about 10 feet. Including future right-of-way is something I know, but in practice the planning staff will only require site plans to show it and setbacks to be measured from it about half the time, probably less. And in fact, this time had the parking issue not come up the original planner was set to approve the plans. This added two more variances to the project, requesting a reduction in both the front and rear yard setbacks.

And in the end

It all worked out. Two and a half months and six hundred dollars later the plan was approved as drawn.

Energy Efficient Design

The Plans

Floor plans of the first level, with the bedroom and office, and second level, the main living area.

The plan of the loft area and the site layout

A vertical section of the house, showing the stairs, floor levels, loft, and roof access.

And a perspective drawing from the “front”, south corner of the house.

View from the south, with the screened porch, bay projections and roof access shown.

I draw by hand, so even though the plans may look like they are from a high school project, I swear I am a professional.

One of the initial goals of the project is that the house would be net zero or as close as we can get, given the limited roof area available for solar generation. Small houses are inherently efficient, but still have to heat water and refrigerate food, wash clothes and dishes. Behavior can have a significant impact on the energy use of many household activities, we hang laundry out to dry, for example, which in the south works year round. But in designing to reduce energy use I concentrated on the building envelope and passive solar potential.

Foot Thick Walls

I like cellulose insulation a lot, and use it on almost all of my projects. Besides being a good insulator, it has very little embodied energy, fills wall cavities well, and buffers water vapor in the wall. I am ambivalent about foam; spray foam is certainly useful and I have used it frequently (open cell) for roof lines and band joists. I also use sheet foam under and at the edge of slabs, for roof tapers and even over sheathing for added insulation. But I am skeptical of foam as well; though spray foam is a good air seal, the standard installation, which is expensive relative to cellulose with a separate air barrier, produces about R20, going beyond that is really expensive. Sheet foam is difficult to recycle and I think that if our goal is to build a more sustainable house the materials generally ought to be able to return to a natural state.

Between cellulose and foam, in applications where they work more or less equally well, I will choose cellulose; so on this project, where I wanted a highly insulated wall, from the beginning I planned on building a double stud wall, 12″ thick, filled with dense pack cellulose. One disadvantage of double stud construction is the thermal bridge formed by the joists and rafters passing through the wall to the exterior bearing wall. To eliminate that problem, the interior wall will be the bearing wall, allowing an insulation layer to extend uninterrupted around the entire building. This requires bracing the interior wall for shear strength,  accomplished here by let in bracing. The exterior wall I will sheath with 1/2″ CDX plywood taped at the seams to act as an air barrier and a substrate for the cladding. I was proud to have worked this out, and then found that, of course, someone had already come up with this. Robert Riversong in Vermont has been doing a very similar construction for decades; he calls it a modified Larsen truss. The 12″ of dense packed cellulose will insulate the walls to about R40.

But there are areas that are difficult to insulate without using foam. The main level will be a slab set 24″ below grade poured within a 3′ concrete knee wall that will be in line with the exterior frame wall. Under the slab will be insulated with 4″ of EPS with 2″ of EPS extending up the knee wall. The roof will be framed level using 16″ I joists with the 1/4″ slope formed by foam roof tapers that will vary from 1/2″ to 3″, and a 2″ layer of XPS foam on top of the roof membrane, insulating the roof to an average of about R75.

Extremely Efficient Windows and Doors

Before I talk about the windows, I want to admit that I understand that triple glazed windows don’t make sense in Georgia. With Georgia Power charging 11 cents per Kwh, we’ll never make back the difference in cost over double glazing. A difference I don’t even know because I didn’t find out. What we are using is Intus triple glazed Eforte tilt/turn windows and doors. The average u value is around .14. Mostly I did this because I wanted to, but at the same time the R value of the windows and doors has a disproportionate effect on the overall R value of the wall, and with limited solar capability we need to reduce our load as much as we can, and super airtight super efficient windows and doors will help with that.

Passive Solar: Getting a little back

This is fairly well understood: southern facing high solar heat gain glass with an overhang above that blocks the high angle summer sun but lets in the low angle winter sun. Minimize your eastern and especially western glass, if you have western or eastern glass make sure it is very low solar gain. This last bit is especially true in the South where high summer afternoon temperatures coupled with sun blazing into a western window can make a room uncomfortable. The sun you do want to come in needs something to warm that can hold a lot of heat to temper the heat gain.

In designing the overhang you get to pick the date the window will be fully shaded by manipulating the overhang projection and its height above the window. But here where it can be hot well into September you really want to block not only mid summer sun but most of the early fall and late spring sun too. Full shading of southern facing windows a month on the summer side of the equinoxes seems like a pretty good balance here. Which means that from April 20 to August 20 no direct sun would come through the window. But with all the worry about the summer heat here we actually have more heating degree days than cooling degree days in Athens, making capturing a little extra heat from the winter sun worthwhile.

Our lot is oriented 45 degrees from north/south making south-facing windows hard to come by, and opening up every side of the building to direct sun; even more so in the summer with the northeast and northwest sides exposed to early morning and late afternoon sun. To overcome the lack of a southern wall I designed two bay projections placed at 45 degrees to the main walls to have southern windows. One is a small triangular bay with tall narrow windows, the other a broad bay cutting across the southeast corner of the building with large windows. Both bays have high solar gain glass. The rest of the windows in the house are on the northeast and northwest walls and have low solar gain glass. There are no windows facing southwest and the door to the southeast is under the screened porch roof. The second half of the system, the thermal mass, is handled by concrete slab floors on both the first and second levels.

Heat, and oh yeah, Humidity

Building Science Corp published some studies a while ago about highly insulated houses in Houston they worked on as part of the Building America program, if I remember right Pulte was the builder. It turns out that when you super insulate houses you don’t need to run your air conditioning very much. But cooling systems don’t just cool, they remove humidity, and if they aren’t running because the thermostat says it’s not hot, they’re not pulling water out of the air even if it’s humid, and in Houston, in the summer, apparently it’s humid (I’ve never been there). They went back and installed dehumidifiers to correct the moisture issue.

Athens is humid enough in the summer to have the same problem. So the cooling system for the house will be a mini split with a head on each level. Mini splits can pull a lot of water out of the air and can have a dehumidifier setting to continue pulling water out even when they aren’t cooling, and they are about as efficient as you can get in an air source heat pump.

Solar

With the house taking up much of the lot, and a car taking up some more, there won’t be much outdoor area left for garden or patio or really anything. So we are utilizing as much of the roof for outdoor space as we can. Roughly half will be planted, herbs and vegetables mostly; the other half will be a patio seating area and the structure that will enclose the stairs and door for roof access. That uses all the roof area so to fit solar we will set the panels on a structure that will go over the seating area. The panels will provide some shade for the patio and be out-of-the-way. That is still a limited space, but should fit two solar thermal panels for water heating and six 60 cell PV panels. Because the array is so small I will get the most efficient panels I can find, LG is making a 300w 60 cell panel. That would still only provide 1800w max output. Net Zero? It’s not a lot of power, we’ll see if we get there.

Starting the design

I have trouble remembering exactly how we started down this path, but the gist of it is that we had built and moved a couple times, going from a small house (1200 sq. ft.) to bigger to bigger again, ending in a 3000 sq. ft. house with a full basement. After our daughters left home we generally used exactly 3 of the rooms in the last house. I tell this story to people and that seems pretty common, We decided we wanted something smaller, more efficient, both in size and energy use, but didn’t have a firm idea of how that would take shape. Several years earlier, a house burned a couple blocks from where we lived, pretty much to the ground. After it got cleaned up, all that was left were the remnants of a foundation and a 6′ plank fence charred from the fire; the owner painted “for sale” and a phone number on the fence, and it sat that way for years. I thought about that lot occasionally, looked at the dimensions online, figured rough scenarios for siting a house, which amounted to drawing in the setbacks and placing the building on them, on all four sides. Between 2008 and 2011 we weren’t ready to move and didn’t have any extra cash for buying property, but when we started to think much more seriously about a move, that lot was still sitting vacant; the portion of the fence with the phone number had fallen and was gone. Figuring it was probably still available, I started to really work out a plan that would work on the lot.

The criteria that drove the plan: We wanted the house to be super efficient, net zero as a goal, but achieved primarily through efficiencies, there wouldn’t be much roof area for solar so the house needed to require very little energy to operate. The design needed to meet the zoning requirements; I didn’t want to have the uncertainty of requiring variances in order to build the project. I really wanted the house to be maintenance free once it was finished, no painting, no cleaning gutters; I like building houses, but have learned over many years and several houses I do not like maintaining them. And here is a big one, though it would be small and have only one permanent bedroom, our girls would be coming home from school for breaks and we have good friends who visit from Atlanta often, there are five of them; the house would have to sleep nine comfortably. Last we wanted to do the whole thing, land and all for around $100,000. We’ll see what “around” means as we get further into it.

Each of the criteria will be the subject of its own future post, but now I’ll show a couple photos of the lot before construction. I’ll add the plans and a perspective drawing at the next post.

A view of the lot from the east

A view of the lot from the west