We've been asked lots of times why we are foaming the outside of our house, why so many layers, and many more questions! I thought I'd take the time to explain everything!
When we started this adventure back in 2012 when we bought our land, Scott started researching the best ways to insulate to best keep the cold air out. In the process he came across the Cold Climate Housing Research Center in Alaska (
http://www.cchrc.org/). What he discovered is a method of adding rigid foam boards to the outside of your house. The method calls for insulating 2/3rds on the outside and only 1/3rd on the inside.
Here is how I interpret it: Imagine building a traditional house.... you have your walls, then the sheeting goes up along with your Tyvek wrap. But after that, traditionally, you would add your siding. When the cold winds arrive, the cold air penetrates through the siding, the sheeting and through the wall studs. Traditionally, the insulation on the inside then blocks some of that cold air. However, you only put the insulation between the wall cavities, not over the wall studs. Now I'm not a scientist, but I don't believe wall studs have much R Value to them. So logically it makes sense when using the foam.
After our walls, sheeting and Tyvek went up, the next thing we did was add 4" of foam (two 2" sheets) to all the exterior walls. Another thing Scott discovered were these, approximately 3" diameter, plastic 'washers' that you screw into the foam. The screws hold the foam sheets in place and the plastic washers keep the screw from sinking completely into the foam. We used ~2,000 of these plastic washers.
For each layer of foam, we wanted to be sure the screws sank into the studs/trusses, so we marked (with a T Square and permanent marker) where each of the studs were. This was VERY time consuming. If we had it all to do over, we should have pre-marked everything and pre-cut everything before we even rented the lift. When we had thing ready to go, it didn't take long at all to get them up!!
After the foam was marked, each layer went up - one right next to the other. Once the lower layer was on, the layer above it was staggered so the seams overlapped. All visible seams on the outer most layer were taped with either Tyvek tape or metal foil tape. Also, for each layer of foam, we needed a longer screw!! We ended up with 3", 6", 8", 10", and 12" screws!!
All the walls had a total of 4" of foam on them. However, the roof had 8" of foam (4 layers).
Once all the foam was up, we needed something for our siding and roofing to lag into. That's where the 1x4's (16' long) came in. We used 10" and 12" screws to lag these into the studs/trusses as well. They were spaced 1' on center apart. The edges of the roof line and the corners of the house we had to cover the layers of foam that did not have a stud or a wall under them (that way there is something to screw the roofing/siding into on the corners), so we added 12" wide strips of OSB.
Foam facts. The 2" thick, foil backed foam that we used has an R Value of 13 for each 2" sheet. So our outer walls are R26 (traditional roll in fiberglass insulation is only R13). Our roof, with 4 sheets, is R52.
The reason we are using so much foam is because the CCHRC has done extensive research and suggested 2/3rds of the insulation is on the outside.
With that said, we aren't even close to being done insulating!! Our plan, as of right now, is to spray foam insulate everything inside for a base layer sealing everything even tighter (especially since we had to put so many screws into the studs/trusses). Once we get the base layer of spray foam in, then we are also going to roll in traditional fiberglass insulation (in the walls) and probably use the blow-in insulation inside the trusses (that's still up for debate).
***Side note - we may only spray foam the inside wall cavities and not add any additional insulation. Scott just informed me that from his research the 2/3rds outside 1/3rd inside rule is so you don't have condensation issues on the inside of the walls. So we don't want to exceed the 1/3rds R Value of insulation (R13) in the wall cavities. So, he said we may only be using the spray foam and not the roll in insulation. He thinks we will be flashing the roof first with spray foam and then, depending how 'thick' the spray foam gets will depend if we add any more insulation to that.***
The more insulation, the cooler it will be in the summer and the warmer it will be in the winter! It stinks that the cost is so high up front, but hopefully it all pays for itself in the long run. But we will keep you posted as to what our energy bill is like this winter and next too!
Our goal is to ONLY heat using a wood burning stove and to occasionally supplement using our 2 portable infrared electric heaters.
Foam Lessons Learned - We spent nearly $4k in screws!! Next time, we are going to see if we can just get 8" or 10" thick pieces of foam (saves us time and $$). If we can't, Scott said we can glue the sheets together then only have to use the long 10/12" screws instead of 4+ layers of screws. Also, we will pre cut and measure everything before we rent the lift (we thought we'd have everything done in 3-4 days, 1 week tops - well 3 weeks and 3 days later we returned the lift). We will be sure to level all the areas around the house before getting the lift next time. This isn't something we thought to do and the lift requires a level ground. The front of the house (mountain facing side) was the most frustrating because the ground sloped so badly that Scott actually put a ladder in the lift to reach the top. Finally, and the funniest/scariest part - foaming the roof can be slippery business!! Scott's body hurt after the first day trying to traverse the roof, so I suggested he take off his shoes and socks!! And it worked! He had very little problems walking on the roof then.
Also, Scott just informed me that next time for our future additions onto the house, he will be using either 2x4's or 2x6's instead of the 1x4's - the reason is 2 fold - first this gives more area for him to sink the screws into and second, when he's walking up and down the roof, there is more of a ledge for him to walk on. Also, the 1x4's are very flexible and using the 2x4's/2x6's provides more of a level surface to attach the siding/roofing too - when driving the screw in it is really easy to have the screw go in too far creating a 'wavy' board making low spots. We had to be VERY careful of this!
Here are all the pictures of foaming our house. I'm a visual person so hopefully these will help connect the dots if you still aren't sure what I was talking about above. Remember, click on the first one and then you can scroll through them - it will make the pictures bigger this way. Enjoy!!
OH!! A funny story - we went to Kapor Lumber to get all our screws. The 72 year old owner of the store told us, 'Looks like you two will be screwing all weekend!!!' I about died! He made my day:)
Something you will notice in the pictures - the foam at the tops of the walls and some corner pieces (especially near the edges of the roof line) are taller than the walls. We did this for 2 reasons, one on purpose and one purely accidental - The foam on the roof added 8" to the height of the walls, so we wanted the foam on the walls to cover the edges of the roof foam. Also, this 'lip' provided Scott a safety if he slid down the roof (happened many times!!).
