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December was interesting. Wifey was in hospital for a planned surgery. It was supposed to be 3-5 days for recovery before being discharged home. It turned into two surgeries, fifteen days in hospital, and two weeks at her parents’ before coming home. Thankfully she was discharged before Christmas, so we didn’t have to have Christmas dinner in the Tucson Medical Center cafeteria. We expect her home this weekend; she’s doing well and we’re excited to have her back in the house!

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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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We passed a whole bunch of inspections over the past few days, yay! We’ve now passed all our inspections pre-drywall and are now on the downhill slope. We decided to hire out the drywall and tile, since both can be quite time-consuming and the cost savings over DIY are not that much relative to, say, plumbing.

Presently I am installing batt insulation in the ceiling; I have to be done by Friday because that’s when the drywallers come in. I’ve only got the evenings to work, though; hopefully I can work fast when it’s 8pm and I’ve already spent all day in the office or chasing kids at home.

Also working on the greywater line. It involves digging a lot of trenches. The ground is really hard so it is conducive to very big and very sore muscles. I hired Caleb’s brother Daniel to do most of the digging so I could just lay the pipe. He gets the muscles and I get black ABS cement on my hands.

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.)