Well, Weatherseal Insulation Company just spent the last two days spray foaming, caulking, and firestopping the house in anticipation of drywall. So, I thought I would take a second to talk about the various insulation strategies used in the house.
First off, let’s start with the biggest limitation: this house is a traditional wood framed house. When people think about insulation, they generally think about what’s in between the studs (fiberglass, cellulose, foam, ect), but not actually the studs themselves. For instance, a 2×4 stud wall can have an r value of 13 for the insulation, but the studs themselves have only an r value of about 4. Cumulatively, all those studs are like a big hole in your house.
So, there are great technologies out there, if installed properly, that don’t give you that thermal breakage. We just finished a S.I.P framed house (which is foam sandwiched between osb on the inside and outside). There is also thermasteel panels, superior walls and ICFs among other options.
But, again, we did not use any of these options for the simple reason of cost. I hope as these there options gain more and more market share, the cost will come down, but it still can be a little prohibitive. The SIP manufactures make the pitch that it is about the same cost, for the extra material cost is covered by how much you save in labor costs. But, honestly, I build relatively small houses, and the three of us have become pretty efficient in framing up a house.
Anyway, to counteract this limitation, we do a bunch of things: One is to wrap the entire exterior in 1/2″ rigid foam board, which acts kind of like a blanket over the entire house and doubles the r value of all those studs.
Another thing we do is value framing techniques, which I feel most builders around here are pretty hip to these days. I took all these pictures to show what that means, but I think I’m going to hold back on posting them as this post is probably dry and boring enough.
But, in a nutshell, it means limiting the amount of wood in the exterior wall as much as possible to increase the whole house r value of the house. Some of the strategies weuse include ladder blocking, stacked framing, 24″ on center stud spacing, insulated headers, minimized cripples, one stud corners. Again, thankfully, a lot of builders have made this the norm.
Another consequential item when it comes to framing is that we are building are roof systems out of manufactured wood i joists (tjis). These have the same profile of a steel I joist, in which you have a top and bottom wide flange separated by a long narrow vertical member. In the case of the TJIs, the vertical member is only a 1/2″ thick meaning the roof system has an extremely low level of thermal breakage when you spray all the foam in there.
As far as actual insulation, we have been using an open cell foam spray foam for the walls and roof. While the idea of recycled newspapers (cellulose), or recycled blue jeans (demim batt insulation) sounds cool, I just don’t think you can beat the performance of foam. Anecdotaly, our experience is the difference is night and day. Basically, spray foam expands and hardens and fills every crack and void to make an air impermeable barrier. Cellulose or fiberglass works by trapping and slowing air movement.
The only other thing to add on the foam is that not all foams are the same. To be honest, I’m still trying to increase my awareness, but we have been using a polyurethane foam rather than a polyiso as it has a much higher r value per inch. The big thing is it maintains it’s air barrier, vapor barrier and r value properties over time. For example, celullose can settle leaving holes up top.
The product claims it is made sustainably made from renewable resources, but if you dig deeper, only about 20% is renewable (namely vegetable oil), so it seems like there is room to grow in that regard. Another reason we have switched to 2×6 walls instead of 2×4 is that we don’t have to spray the whole 2×6 wall cavity with foam to get an extremely high performance house. (Basically a 5.5″ thick wall is only 2 percent more effective than a 3.5″ thick wall at heat flow reduction). The upshot is if properly installed there should be no waste if done right. However, in a 2×4 wall, they have to overspray and then trim back the foam flush meaning you end up with all these garbage bags full of extra foam. Honestly, we did a house where this technique was used and the installer probably left with 20 garbage bags of trash, which is extremely disheartening.
When it comes to indoor air quality, I do know the foam contains zero formaldehyde, cfcs, hcfcs, hydrocarbons, or penta bde. Also, the one material I use when building a house and that most builders use is the OSB sheathing (the chip board stuff that goes on top of the studs and give shear strength) and honestly, I just think that stuff really off gases. But, by sealing in the wall cavaties with foam it should stop any offgassing to the inside of the house.
I’ll try and write a post about indoor air quality at some point, but we have a bunch of strategies to maintain a healthy house.
Alright, running out of steam. Really quickly: The Weatherseal company has had superb attention to detail on my houses, including caulking any piece of framing that touches one another as well as where framing touches the ceiling and floor to prevent air infiltration. To some extent, this is redundant in my system with the exterior taped foam board, but it’s nice insurance.
We are also using high performance low e-4 Andersen windows. The only bad thing I have to say has nothing to do with the performance but that the exterior is vinyl, which in terms of the manufacturing process, is pretty bad for the environment. Contrast that with Pella, Marvin, Jeldwen, Loewen which are all wood aluminum clad. My only defense is that I bought all the windows from two separate builders that screwed up their order (wrong color), so I see it as effective reuse.
Lastly, the first floor has a concrete slab in order to capture, store and emit heat collected from the sun as were trying to do more and more with each house with passive heating and cooling strategies. The big thing to say about that is that concrete will slowly leach the heat. So, even though the slab is at at minimum 18″ below ground already and the exterior of the slab is completely insulated, we laid 2″ rigid foam board under the entire the slab.
The other big heat loss for concrete slabs is around the perimiter. To solve this, we used the Superior Wall XI foundation system (www.superiorwallsva.com) around the perimiter of the house. This precast concrete foundation has 2″ of rigid foam imbedded into it. We then poured the non loadbearing concrete slab inside of that, avoiding any heat loss. The other bonus of this foundation system is that it is wider than our walls and is 3’6″ off the concrete floor. So, we plan on building a little ledge on top of it around the 1st floor, which will be a great place to set drinks down or maybe have small sculptural pieces of art.
I think that’s it for about now. More power to you if you actually read all this. Hopefully, moderately coherent.