Minimizing Spray Foam in new Construction in Zone 2/3
My wife and I will be building our dream house about 45 minutes west of Austin, TX, in the Hill Country which is Zone 2, but technically, the county we’ll be in is Zone 3 (so right on the border of Zone 3) and still within the “warm-humid line”.
While we’ve built 2 other homes before in the Midwest (never south of Wisconsin), we’re trying to take a more active role in identifying some of the products used in building this home, including insulation.
A spray foam insulation would be “easy” but we’re trying to avoid that where possible given it’s carbon impact, the chemicals used, questionable longevity, open vs. closed, etc.
For the purposes of this question, we’re looking for alternatives as we know a HFO blown foam could be an option.
I’ve read about the “Perfect Wall” with interest from Building Science Corp, but left wondering what to do specifically.
The Perfect Wall | Building Science Corporation
What would others recommend we do?
We’re considering a mineral wool product for external (like ComfortBoard) and internal wall insulation. We’re trying to build this thing very air tight (PH levels), and will have a dehumidifier and ERV.
Facts:
* Slab foundation.
* Mix of façade from stone to possibly cement board or a durable painted steel product.
* Metal roof.
* Probably Huber’s ZIP, with liquid flashing
* Maybe T-Stud? Although thermal break may be unnecessary with use of external insulation.
* Code says R-15, but we want the house to be closer to double that in the walls.
* I’m very sensitive to “external noises” so having more insulation (and air sealing, etc.) will ideally lead to consistent temperature comfort and noise comfort.
* Strongly Considering doing 2×6 walls. (Builder concerned about anything deeper as we’d need to increase the size of the foundation, which will mean more concrete — which definitely isn’t a win for the environment).
* Bug/termite unfriendly (we’re planning on some borate treatments that would help with wood, but not necessarily tunneling termites that I’ve seen pictures of burrowing in foam products)
* (We’re going to have an extensive PV system and battery backup and make sure that everything is freeze-proof given the recent tragedies in the area)
* I don’t know if folks use cellulose or similar products in higher humidity areas, like zones 2/3 (it’s what we have in our Wisconsin home).
I’ve read so much about smart vapor barriers, air barriers, read Musings of an Energy Nerd, bought Building Science books, read extensively the forums and articles here and on Fine Homebuilding ….
Our builder is game to try something new — novel, modern (like new products). He’s very concerned about the ability to get the house air tight. So, I’m concerned about that and moisture control (as we have both issues in our current Wisconsin house).
I’ve read 475’s suggestions for their ideal wall for inspiration.
I’ve read about flash & batt and the comments seem mixed over time.
I’m a software developer by trade and own a saw, so by no means a building science expert, but I want to learn! 🙂
Please help and thanks!!
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Replies
You want 2x6 walls, dense packed. Cellulose works just as well in warm climate as it does in colder places plus it does make for a quieter building.
In warmer climate, going crazy on insulation is never worth it but the additional material cost of 2x6 24OC vs 2x4 16OC is so small that it is the cheapest extra insulation you can add.
On a slab on grade, the extra foundation thickness for 2x6 wall is noise in terms of overall concrete use, I would not worry about it.
SPF should be designed out for any new build. Not only is it expensive but a pretty high enviromental footprint. Simple taped sheathing and a solid ceiling air barrier is all you need for good performance.
No need to try anything fancy. I would keep the build simple and make sure your builder pay attention to air sealing details. Getting this right will get you much better performance any fancy materials such as Zip R or T-studs. Make sure these details are on the drawings and they are followed to the T.
P.S. Make sure you get an independent HVAC engineer to size your mechanical system and use actual building construction parameters with the above improvements taken into account. You don't want your builder or their HVAC install do this as there is a good chance the units will be WAY oversized causing efficiency and comfort issues.
Thanks so much! What are you referring to by a "solid ceiling air barrier?"
I was concerned about moisture with cellulose mostly because I couldn't find many people talking about using it in zones 1 & 2 (it's not the easiest web-search to do).
Good point about the HVAC -- we know we'll want some zones too because of the layout of the house and our usage patterns.
Do you have any opinions about what might be "upgrades" from what you're suggesting? We want this to be a "great performance" house when possible -- especially since we "saved money" on our current house on things that in hindsight, we wished we'd upgraded (and are not cost effective to change now).