New house build, how would you insulate it?
I have been studying this for three years and still can’t make up my mind!
The house is in-slab heated, (the slab is already poured and was insulated with 3 inches of Type II EPS which worked very well). Framing will start in the spring because the weather and contractor delays set us back four months. The house build site is in zone 5a at 8500 ft. in Fremont County, Colorado. It is a single story, 12″ deep double stud walls, 10ft tall walls, 5300 sq ft (yes it had to be this big, my wife is now quadriplegic and we had to have room for kids, therapy, live-in caregivers, etc.), Alpen Zenith ZR9 windows have already been purchased. There won’t be exterior insulation, but there will be a 1.5″ rain screen on the exterior walls and a vented attic (thank you Martin). The exterior walls will be normal OSB (we can’t afford zip system), but will be taped and rolled at the seams, then wrapped with Tyvek commercial D. We can’t afford and don’t want to use spray foam except where it is needed around the perimeter. This week I found that there is a qualified dense pack cellulose installer in our area so we can use any or all of the available insulation types. I haven’t been able to source some of the more obscure insulations like Spider. We have a fairly tight budget but want to hit a goal of R40 walls, and R60 to R80 in the ceiling with as long a life-span as possible. There is one area of vaulted ceiling truss’ over the living room which we could use SmartBaffles between the rafters all the way up or rigid foam etc.
If this was your house how would you cost effectively insulate it for longevity in 2024.
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Replies
Hm. What’s the heating type? Can you include a ducted heat pump? You’re probably well past the point of “cost effective” insulation unless you’re paying out the nose for propane or something. Closer to code minimum walls is what you want if you want a good investment. The attic with R-60 cellulose is perfect.
Since you already have double stud walls, you really don't have a lot of options as to how to insulate this -- going with double stud has already taken you in that direction. I would try to go with dense pack cellulose as a first choice here, otherwise I'd go with fiberglass. Mineral wool would be nice, but would cost a LOT more with a double stud wall, for relatively little added benefit over what you'd get using much cheaper fiberglass. Depending on how the walls are built or being built, you might be able to use batts or rolls of fiberglass, or you might be stuck using loose fill.
R60 of blown cellulose in a vented attic is perfect. I wouldn't change anything there, I'd only advise that you airseal the attic floor prior to insulating, and make sure you have baffles at the eaves to both limit wind washing and also to make sure the cellulose doesn't clog up your soffit vents. Be sure to get as much insulation over the exterior top plates as you can -- that's a weak spot when insulating this way, and is often insulated to less than ideal levels.
Bill
Having lived in Colo. off and on for many years and having
designed, built and lived in 3 double wall houses at over
7000 feet for more than 26 years I think I can speak from
experience. I don't know anything about your window plan
but if you are planning to achieve significant heating from
solar gain, you live in a "Goldilocks" environment. It's easier
adjust the overhang length there than in more northerly
locations - if you don't know how have someone (your architect
or engineer) calculate the proper length of overhang given
the top of window distance below the bottom of the overhang.
Set it to keep the sun out from about mid May to about mid
October for your Latitude. Free heat all winter in a relatively
cold dry climate. In the houses I built the required overhang
came out a little over 2 feet (but I was a little farther south).
Lets talk wall design - the best double wall system I have ever
seen (not the cheapest but the best) is a double wall with 2
or 3 inches of foil faced polyiso in the center - built this way.
2x4 inner wall 16" OC with fiberglass bats - 3" polyiso (fastened
to the interior face of the exterior wall - 2x6 exterior wall 24"
OC with fiberglass bats - Actual R-value = about 38 (nominal R
about 48 but nominal R ratings, though popular, are worthless)
Note total wall thickness (stud face to stud face) Exactly 12"!
Here is a second variation - might be cheaper
2x4 wall inner wall 16" OC with fiberglass then
3.5" of fiberglass (installed on edge, horizontal) against 2" of
polyiso fastened to the interior face of the exterior wall -
then a 2x4 exterior wall 16" OC with fiberglass bats -
actual R-val will be about 35 and the total wall thickness
Stud face to stud face will be 12" (NOTE you build the interior
wall 3" from the interior face of the polyiso to compress the
horizontal fiberglass a little)
Either of these walls will go over R 40 if you replace any of the
fiberglass sections with mineral wool. The advantage of this
wall construction is that they can dry to both the inside and
outside and no moisture or air can pass through the center -
in addition the polyiso is protected from physical damage
and thermal degradation due to temperature drop.
My brother currently lives in one of these designs in the
Woodland Park area and loves it.
"Set it to keep the sun out from about mid May to about mid
October for your Latitude. "
Just a comment about this. Mid May is about 55 days after the spring equinox. The day in the fall with equivalent sun is July 26. Mid October is about 25 days after the fall equinox, the day in the spring with equivalent sun is about February 23.
One more thing! When I built my houses and when my brother
built his we found it easier to build the exterior wall of the
double wall first (and get the roof on) and then insulate the
exterior wall and then build the interior wall of the double wall
later (as if it were merely any other interior wall). Some contractors
will balk at this sequence.
Best of Luck!!!
Given a choice between fiberglass and cellulose, I would almost always use cellulose. Fiberglass is TERRIBLE if you ever have to get in do to any maintenance, etc. It can't be good to have all those fibers loose filled in an attic and potentially getting into the environment via venting.
I didn't say anything about attics and all of my houses were
actually built with cellulose in the attics.
gstan,
What made you think he was replying to you?
How many spray foam installers have you contacted? I would shop around more. In my market (Central NY) mineral wool is about $1.00-1.20 per sqft and closed cell spray foam is $1.40-2.00. I wouldn't think a $0.20 would break the bank and it would be help quite a bit with your air tightness, which some would argue is more important to comfort than just adding extra R Value.
With spray foam especially, it's important to note the cost per square foot at a given thickness of material. Convention is to price spray foam in "board feet", where one "board foot" is a 12" square of material 1" thick.
It is NOT necassary to use spray foam to have good air sealing. A careful job of air sealing the "old fashioned way", using caulk and canned foam will do a good job too. Using spray foam as an air sealing step is similar to using textured coatings over all the drywall in a home: the textured coating covers up sloppy tape/mud work, and hides an otherwise less than great drywall job. Spray foam can certainly help with air sealing if the other "air sealing" steps were done sloppily, but in a well-built house where care was taken in air sealing details, spray foam doesn't really offer much aside from extra cost.
If really high levels of air sealing are desired, I would insulate with batts and/or dense pack, air seal the old fashioned way, avoid the use of spray foam, and use the savings from not using spray foam to pay for an Aerobarrier crew to come out and do their thing.
Bill
I never got any e-mails from this thread so didn't respond. Thank you for the input. I can still do pretty much anything as the framing won't start until the snow melts and we got over two feet up there today. The plumbing is in the slab for a double stud wall and that is the plan. Based on other discussions in the forum the plan is to use CDX on the exterior taped and rolled and carefully detailed. Tyvek Commercial D for the WRB, 1x4" furring is now quite a bit cheaper than 2x4" studs and 3/4" ripped plywood so the rain screen will be 3/4". The insulation will be Dense Pack Cellulose in the 2x6" load-bearing wall slightly overpacked. Then another layer of DPC to fill the thermal break and the 2x4" interior non-loadbearing wall. Then a smart VB before the drywall. To reinforce the interior VB I will do as much sealing of the drywall layer as is practical. That should give R48, humidity isn't a problem here and the ERV system should maintain a good interior humidity level.
I am considering running 3 inches of recycled Polyiso in two staggard layers horizontally in the thermal break and leaving the 2x4" stud wall free of insulation so plumbing and electrical are easy. There are no qualified Dense Pack installers in the area, but after about 20 YouTube videos I am confident in doing that myself with my crew, heck if it goes well we might start offering the service to others, we are licensed.
The heating will be in-slab, with primary heat being a self-engineered evacuated tube solar array with an industrial heat transfer fluid into a phase change underground heat storage tank. It is designed to only have a couple of panels exposed in the summer for DHW, it will have a robust heat dump, and if the water temp is below the high setting my solar electrical system will auto divert to heater elements in the heat storage tank once all other loads are satisfied. The backup heat will be a propane-fired high-efficiency wall-mounted boiler that I hope will only turn on a couple of times a year. The attached picture is the insulated pipe loop I ran out to the solar array. When completed it had 1" noodles and two inches on the bottom and sides and then 4 inches of high-density ground-rated EPS on top of the pipes.
Would you guys use 3 inches of taped recycled polyiso in the thermal break as an interior air barrier or just fill the thermal break and the 2x4" interior wall with dense pack?