Insulation details

With all the remodeling going on we haven’t given up on our super insulated goal. All the downstairs 2×4 walls were furred out to 6.25″ thick. Each bay was filled in with a layer of 0.75″ foil-coated EPS foam board, followed by 2″ foil-faced R-max foam board, followed by 3.5″ high density fiber glass insulation (total: R31). We attempted to maintain the air seal (which is basically perfect on the second floor), by spray foaming the edge of every foam panel and between studs and gaps. The band joists received a similar treatment of layered foam inserts and spray foam.

Foam panel cut-to-fit

We hired out all the fiberglass work including R30 batts under the house. The ceiling bays had twenty inches of blown-in insulation, for a minimum of R60. Most windows were spray foamed into place or tucked with insulation scraps. Lee needs to spray foam the light fixture boxes in the top attic before it’s blown with loose insulation, but otherwise we are nearing the end of the endless insulation.


We also sound insulated with fiberglass batts between the two floors and added rock wool batts to the laundry room, office, bathroom and master bedroom walls. The laundry room is in the center of the house, so we insulated there to reduce the echoiness of the whole house. The office insulation was particularly important, since Lee works from home. Now Sidney and all her friends can practice playing the drums and bagpipes and it won’t disturb him.

Sound deadening

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9 Responses to Insulation details

  1. Woody says:

    I’ve read where a house can be too tight with insulation that fresh air exchange becomes a concern.

    • lee says:

      Yes, this is certainly possible. Back in the dark days of the 1980’s there were a string of issues related to tight houses. The techniques for building a air-tight house were still new and nobody knew how they would react. Canada actually built some test houses, monitored them for air quality and moisture in the walls, and then subsequently figured out how to fix them.

      At this point, most issues related to air quality have been resolved. (Europe’s Passivhaus standard is way ahead of the U.S. on this front.) On the whole, most new builders still aren’t building sufficiently tight homes for it to matter, but for those that are the ASHRAE 62.x standard provides recommendations about minimum fresh air exchange. For our house, based on ASHRAE 62.2 we need 40cfm of fresh air or about 4.5 whole-house air exchanges per day. This can be done by automating an exhaust fan and providing a vent for the make-up air. When everything is done, I plan to have the house blower-door tested to see what the natural “leak” rate is, and if we won’t hit 40cfm I’ll look into a solution.

  2. Snowbrush says:

    I had the same thought as Woody, and it also occurred to me that it might be especially important to have good air-intake while all the fumes from all the building and insulating materials off-gas. One reason I have five peace lilies is that they’re among the best air cleaners, but all houseplants contribute.

    • lee says:

      It certainly has that “new house smell”, although that seems to be the low-VOC paint. Fortunately, we are heading into the spring and there will be more opportunities for opening the windows soon. I’ve always liked the idea of plants as air cleaners (i.e. Biosphere 2), but I’ve read that the effect is quite small unless you basically live in a greenhouse. This might actually apply to you!

      • Snowbrush says:

        Yes, “live in a greenhouse” might apply to me as I have 40 plants in my bedroom, and would like to have more if I could figure out how to work them in. As for how many you need, I should think that some would be preferable to none, and what I’ve read didn’t suggest that it would take scores of plants to do any good.

  3. Snowbrush says:

    On the other hand, I don’t mean to discount the importance of good insulation. After we put it inside our walls, we could sit near those walls in and not feel a chill. Lee, at one point, you mentioned the crack under our front door. I rather like that crack for the reason I mentioned in my first comment. Of course, in really cold weather, it might not be a bad idea to have something to stuff it with temporarily.

    • lee says:

      This is why most extremely tight houses have a mechanical system for ventilation. A naturally leaky house will be ventilated too, but the effect is stronger when you least want it. When it’s extremely cold outside, the warm air inside presses harder on the ceiling to leak through the cracks and wind force cold air in on one side and out on the other. An HRV/ERV by contrast is barely affected by the weather outside and delivers a measured amount of fresh air each hour. Sometimes they are set up to run more slowly when the outside conditions fall below a certain temperature.

  4. ShimFarm says:

    It looks like you have done a great job. Do you still intend to heat with wood? And do you need some kind of back-up heat (such as baseboards) as well?

    • lee says:

      Yes, we still plan to use the woodstove, although less so I’d guess since it’s no longer burn-wood-or-freeze. By code, a wood stove can’t be the only heat source, so we’ve installed a minisplit heat pump with a head on both floors. There are also two in-wall cadet heaters and a bathroom kick heater to provide supplemental heat to the rooms furthest from the heat pump heads. I don’t think we’ll need the cadets, but I haven’t recalculated our heat loss rate given all the new windows.

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