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.
This weekend we installed the three clerestory windows and the door.
The shed next door proved to be a handy platform for installing the windows. I built a sturdy scaffold from extra 2x4s and plywood and leaned it onto the shed roof.
The windows are of the awning type, which means they are hinged at the top and open with a crank. The screens go on the inside, though they aren’t installed yet. I will install them after construction is complete so they don’t get torn. They are aluminum-clad wood windows and very energy efficient units. Installing them was pretty easy, except that the self-stick flashing doesn’t stick to tarpaper very well. Nothing a few staples couldn’t fix.
Door viewed from shower area
The door is really pretty. The light that comes through in the morning is very cool. I can’t wait to take my morning showers in here!
The door is extremely heavy. It is a fiberglass door (we didn’t want a wood or steel door in a shower area) but the weight comes from all the glass. It is triple-paned, which was necessary to meet energy efficiency requirements. Since I was careful to make sure the stud on the hinge side was plumb during framing, the door was not difficult to set. The hardest part (other than wrastling its bulk into place) was installing the lockset, which required some modifications to the stock bore.
Well, as of today, the addition is “locked up”… literally. Hooray! A major milestone achieved. Next week: lots of foam insulation.
This past weekend I tried to get a head start on framing. So without expecting any
laborers friends or neighbors to be able to help, and knowing I’d be out of town the following weekend, I ordered a truckload of lumber and had it delivered. Meantime I got started on sill plates and flashing.
I installed copper termite flashing under the sills. It is supposed to make termites easier to detect by forcing them to tunnel out into the open. It's also pretty.
Between the termite shield and the sill is a foam gasket to stop air leaks.
Some of the anchor bolts were awkwardly placed. Some are where studs should go. This one was a tight fit under the stack cleanout. I couldn't get the sill plate to fit between the top of the bolt and the cleanout. I had to use a grinder to cut off the top of the bolt.
I had to chop off the overhang because the new addition is taller than the room we're attaching it to.
I managed to frame a little over one wall. My neighbor helped do the short wall; the tall one I had to do solo.
I spent a lot of time doing the stud layout. It was made more difficult for two reasons: pipes and anchor bolts. Some of the anchor bolts are where studs should go, as is the greywater pipe for the washing machine. I can’t move the pipes or anchor bolts, so I either have to adjust the stud placement or notch the studs to fit over or around the anchor bolts.
Since the south windows are eight feet up, the view is of trees and blue sky. The window placement is great for passive solar heating in the winter, too.
This is the view from the back patio, with the bedroom to the left. The building on the right is the shed, so you can see there is a sort of outdoor hallway to get behind the new bathroom. I'll put a gate back there to create a sort of secret garden. Don't tell anyone.