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Design

The most exciting thing lately has been the shower. Over the last two weeks our tile setter has been working hard and doing a beautiful job tiling our shower.

Andrea and I decided to invest a lot of our savings from building our bathroom DIY into some nice finishes. Such as expensive, high-end tile. We found out later that the tile we picked out is truly an exclusive item: the factory in Italy went out of business, and we bought the last seven boxes of tile available anywhere.

Since we had a lot invested in the tile, finding a good tile setter was critical for us. We needed a pro who knew how to properly waterproof the shower. If the shower were to leak, our pretty and very expensive tile would have to be torn out to effect a repair. Our tile is irreplaceable, so a shower failure is not an option. We want this shower to outlast us.

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The last couple weeks have been fits and starts. Basically finishing up the exterior insulation and installing the strapping.

I used 3/4" plywood "straps" screwed through the foam into the studs. The straps serve as attachment points for the siding, which I will put on next.

Finishing the foam was a laborious process. All the seams of the foam had to be taped. If I couldn’t tape them for some reason, I had to fill the gaps with spray foam. This was important to make sure there were no air leaks (or at least as few as possible).

To give an idea of how meticulous the air sealing has to be, here is what I did to seal around the sewer cleanout. I first sprayed expanding foam, then waited for the foam to cure before I trimmed it and finished with tape.

I had to use 6" long screws to attach the strapping. It was a little nerve-wracking to drive these screws through thick foam, but I only missed a stud three times. I had to use a corded drill; the cordless drivers could only drive a few of these at a time before the battery power gave out. I almost overheated the drill, too.

At the top and bottom of the walls I had to put insect screening. Once the siding is on, there is a continuous air space between the siding and the foil-faced foam. The concept is called a “ventilated rainscreen“. The siding can be a little leaky; any moisture that gets behind will run down the foam and out of the wall, or evaporate. This improves the durability of the building by reducing water intrusion and extending the life of the siding and, in the case of the wood parts, its paint or stain.

The air gap also allows the reflective foil facing to serve as a radiant barrier. This is pretty important in a hot climate like ours. It reflects a lot of solar energy away from the building in the summer time.

This is the aluminum insect screen at the bottom of the wall. It wraps around the strapping. When the siding goes on, it prevents bugs and other critters from crawling into the air space between the siding and the foam.

I started installing the foam insulation on the exterior walls this past weekend. I took a couple pictures this morning but it was difficult to get good shots. The glare from the sun reflecting off the foil facing was blinding!

One layer of foam. A second, thicker layer will follow.

There will be two and a half inches of polyisocyanurate foam insulation board on the outside. It’s predominantly in two layers. The first layer is an inch thick, and is tacked to the framing with cap nails. The second layer is an inch and a half thick, and is temporarily held in place with long screws and plywood washers until we install the 3/4″-thick plywood strapping. We use 6″ screws to secure the strapping to the framing.

Two layers installed, with all seams covered with foil tape to prevent air and vapor intrusion.

Later, once all the strapping is installed, we’ll attach the siding to that. We will put corrugated steel siding on the north and south walls, and redwood lap siding on the east and west walls.

So far I’ve got the north wall insulation complete, most of the east wall, and the first layer on the south wall.

The foam insulation is fairly expensive, but there are many advantages of the foam insulation over conventional batts:

  • The continuous foam on the exterior eliminates “thermal bridging”, which is what happens when you insulate only between wood studs. Wood studs are terrible insulators.
  • The foam has a foil facing which serves as a radiant barrier. Put it in the sun and you can feel the heat reflected back at you. This is invaluable in a hot, desert climate.
  • Foam has a higher insulation value per inch than batt insulation. If it’s thick enough, you can eliminate batt insulation entirely and leave the stud bays open, thereby facilitating utility maintenance in the eventual remodel.
  • Batt insulation is difficult to install properly, especially if you have pipes or wires in your wall. To get the rated insulation value, batts have to be installed darn near perfectly.
  • Foil-faced foam is waterproof and impermeable, so it serves as both a moisture barrier and a vapor barrier. If installed on only one side of a wall, it makes the house more resistant to moisture. Just be careful not to create a “moisture sandwich” by installing impermeable surfaces on both sides of the wall. By choosing to use polyiso on the exterior, I can’t use a waterproofing membrane on the walls of our shower.
  • Foam insulation board doesn’t itch or release cancer-causing fibers into the air for you to breathe. It’s extremely easy to cut, handle, and install.

I chose this design because I wanted thin walls, and I wanted to be able to run utilities like pipes and wires in exterior walls. I am able to have a high-performance structure framed with 2X4s instead of 2X6s; in a bathroom, those inches really count.

This next weekend, Caleb and I will finish the foam install and the strapping.

Our bathroom addition isn’t going for any sort of “Green” certification, but I am trying to make it as “greenish” as possible. I’ve definitely had some Green Building Fails, like the foundation using seven cubic yards of concrete. That’s seven cubic yards of carbon into the atmosphere for a piddly bathroom, compliments of yours truly. I definitely could have done better!

But it vastly exceeds insulation requirements for our climate, is sited for passive solar, is built using durable materials and methods, specifies no mechanical heating or cooling, specifies energy-efficient or low-water-use appliances and fixtures, provides a permanent greywater reuse system, and it even calls for a rain barrel. Perhaps it will look cool enough that future owners won’t decide it’s ugly and tear it apart for remodeling.

Most of those green features really don’t add much to the cost of the addition. Some even qualify for rebates and tax credits. But sometimes trying to find stuff is a real pain (try asking a local lumberyard about Forest Stewarship Council-certified lumber). Trying to determine what really is environmentally responsible versus what is simply “greenwashed” is a challenge, too.

Given that, I think our addition should qualify for some kind of Green award after all. Maybe if I give my kids some markers and green construction paper they’ll make one for me. (They’ll have to learn how to spell first.)

I took last week off, and Caleb and I made rapid progress. We finished framing, sheathed the walls and roof in plywood, got most of the tar paper up, insulated the roof and one wall, and installed the metal roof. Whew!

A view of the framing from the northeast.

I used pressure-treated lumber to frame the shower area. It is regular lumber treated with stuff that bugs and fungus don’t like. Why do this, you ask? The foam insulation I plan to install on the outside of the house is vapor-impermeable polyisocyanurate (building science nerd-speak for fancy foam board). Because the foam board doesn’t allow any moisture to pass to the outside, the building has to dry toward the interior. Since the interior is a humid shower, I wanted some insurance against rot and termites. We didn’t use plywood around the shower, either. Confused? Good. Just know it’s awesomely over-thought.

This is the roof deck shortly before we finished nailing on the plywood. We tried installing the plywood on the roof before installing the plywood on the walls, but the structure was very wobbly. The plywood really provides incredible strength. We were using a nail gun that shot smaller nails than are in the code book, so we had to use extra nails. There are thousands of nails in this little room!

View from the southwest, with plywood shear panels in place.

This is what the room looked like when we called for inspection. The inspector needed to see that all the plywood was nailed on properly and in the right locations. We mostly passed. Which is to say, we slightly didn’t pass. One panel didn’t provide enough shear bracing for the west wall (it’s the one right in front of you, to the left). Long story short, there was some confusion about what I thought I permitted and what was actually allowed. But the inspector was cool and said we could continue, we just needed to show that we had provided adequate shear bracing before we put up drywall.

The roof sheathed and covered with tar paper.

I was glad to move on to roofing. After shooting thousands of nails I was really tired of plywood. The roof is pretty unusual: the insulation is on top of the roof deck. Four and a half inches of polyiso foam over felt over plywood. And steel on top of all that.

The roof covered with polyiso insulation.

The thick foam provides a little more insulation value than is required by code in our area. There will be another six inches of rock wool insulation between the rafters below, making a fairly superinsulated roof. Cozy!

Roof with purlins and metal roofing going on.

We installed the galvalume roof ourselves. A local metal roof manufacturer measures the roof deck and fabricates all the pieces, then delivers them. They provide some basic instructions and loan you a few necessary tools. Installing the roof was pretty easy. There was some cursing over the waste vent pipe flashing, though.

We finished the roof as it was getting dark, so no pic yet. But it’s purdy.

We’ve finally started our master bathroom!

We’ve been dreaming of this moment for a long time. Four people in a one-bathroom house is pretty tight. It’s even tighter when that one bathroom is about the same size as most walk-in closets in new homes. Now that we have a permit and have started, we can almost taste the water in the soon-to-be lavatory faucets! I can almost feel the lack of wind in my face from not having to go outside to do the laundry!

We used white marking paint to show where we would remove existing concrete, and to mark the limits of the excavation.

A shot of the bathroom laid out in paint.

We had to dig down below the existing foundation so the new footing would flow beneath the old one.

The previous owner sunk a 4X6 post in concrete. Like, eight bags of it. He used the post to hold up a speed bag. I think he was afraid he might knock it down with a mighty blow.

We had to dig the post out and used a sledgehammer, a heavy bar, and a jackhammer to try and reduce the size of it. We found rebar and copper Romex in the concrete.

We estimated the post weighed around 600 pounds. Caleb is around 200 pounds and would stand on one end of the post, which balanced on the edge of the hole. We managed to roll the post out of the hole, stand it up, and roll it out of the way, The entire time we were dealing with this monstrosity, we kept asking ourselves, why? Why did somebody think they needed 600 pounds of concrete to hold up a post? One 80-pound bag would have been fine.

After we dug the footings, we had to raise the level of the ground inside the building. Because the house is in the floodplain, various levels of government required us to ensure the new bathroom would be 12" above the flood elevation, which happens to be precisely equal to the bedroom floor elevation. So we will have two steps up into the bathroom. Alas, no ADA wheelchair accessible entrance from within..

As we dug the southern footing, we encountered a giant concrete box that had been filled in and buried. I suspect it is the old septic tank, as our house was on septic until the seventies. We also found a variety of abandoned plumbing lines.

We removed all the concrete in front of the back room. We needed to remove most of it to make the connection to the existing sewer line. I also wanted to run a greywater line from the laundry, sinks, and shower to our fruit trees, and that needed to go under the patio too. It sloped toward the house anyway. We re-poured it with positive slope away from the house, and made the back door wheelchair-accessible in the process.

After the plumbers came and went. We have separate drains for sewer and greywater, so there is a lot more pipe than is usual. Arizona is a desert, so it only makes sense to reuse the water from sinks, washing machines, and showers to irrigate the landscape. Arizona has wonderfully progressive greywater laws and incentives so it is easy to do.

The forms are up.

We used a pumper truck to get the concrete all the way to the bathroom. It made the pour a LOT easier and faster than using wheelbarrows.

After a parade of inspectors and concrete guys came and checked everything out in prior days, the pumper truck operator took one look at our forms and said they wouldn't hold. And they didn't. As I watched them blow out, my life flashed before my eyes. It took seven cubic yards of concrete to do the job, and I envisioned a giant useless lump of rebar-reinforced concrete in my back yard. A permanent testimony to my DIY foolery. But it worked out. The concrete guys were awesome. The top stayed square and true, and the finishers were able to strip off the forms and straighten the sides. At the end of the day I had eaten a large slice of humble pie, but was better for it, and everything worked out fine.

There it is! A beautiful finished slab, thanks to an awesome crew of helpers, some professional and some not. I'm looking forward to framing!