Dr. Joe Lstiburek Discusses Building “Almost” Net Zero Ready Homes
rockies63
| Posted in General Questions on
Here’s a great paper from the Building Science Corporation website about how to build net zero homes. Dr. Joe provides building sections and details on how to construct residential buildings in all climate zones, and there are also links to Govt programs discussing Net Zero building as well as to the Pacific Northwest National Laboratory for additional sections.
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This is good stuff. I liked this part in the preamble:
"Yup, if you build new homes to comply with the 2021 International Energy Conservation Code (IECC) you 'officially ' comply with the Department of Energy 'Zero Energy Ready Home Program (ZERH)'. Okay, there are few other typical 'government' things (see https://www.energy.gov/eere/buildings/zero-energy-ready-home-program) but I never thought we would get as far as we did. Nice job United States of America….
"Build to the 'code' …. Build to the 2021 IECC… and you also qualify for the 45L Tax Credit….(see https://www.energy.gov/eere/buildings/section-45l-tax-credits-zero-energy-ready-homes).
"Do this and add about 5kW to 7.5kW of PV to the typical house and you are at 'net zero energy'."
Net zero is on the brink of going mainstream.
I feel deeply indebted to Joe L. for his work, but sometimes he makes my head swim. Not long after asking if it is time to retire vented attics, we now have them featured in many of the assemblies. His article chronicling the evolution of air-barriers pointed out the drawbacks of using drywall as the primary one, but there is. Poly faced batts in crawlspaces also make a comeback, and structural sheathing has disappeared for most climate zones, including those prone to high-wind damage and earthquakes.
I like the cost of a taped rigid WRB (even given additional bracing requirements) and airtight drywall but would you be comfortable with this wall assembly?
I think the holy grail for Dr. Joe is the universal assembly, one that works in all climates. Material science isn't there yet. So he's looking for a small number of assemblies to cover every situation. Turns out that doesn't really work either.
DC,
There are things that appear to go against his past advice, or just seem odd.
- Vented crawlspaces make a comeback in zone 5, and the insulated floor is sheathed on the underside against rodents - although the space is fully enclosed.
- In zone 4, the poly-faced batts continue from the inside of the stem-walls across the crawlspace floor, making the space unusable. Why a masonry foundation there and not elsewhere?
I wish the document explained the reasoning a bit more.
Vented crawlspaces are necessary where flooding is an issue - high ground water tables... they are also popular for folks who hate concrete slabs and concrete foundations. Wood piles are making a comeback. Hey, don't blame me. I just try to make things work. You want to build using green jelly beans....I will help you...we call those folks clients...our job is not to kill them, make them sick, or kill the building or make it sick.
The point was to show many options are possible.
The point was not to show every option.
You want to use concrete...go for it...you want to use blocks...go for it....you want to make the carbon cult happy...use wood...
Most crawlspaces are not used for much anymore...if you want to use the crawlspace for storage then design it to do so. The batt insulation is a low cost way to meet the energy codes. If you want to store stuff then replace the horizontal blanket insulation with rigid insulation and place some pavers on it. You folks are clever and most of you figured that out already. The key is controlling the temperature of the condensing surfaces...but you all know that already....
By the way I do not have a holy grail besides trying to avoid doing stupid things...I am still struggling with that...
A response from one of my pantheon of building science heroes.
Better than my very first post here some decades ago that provoked John Straub into calling what I suggested "nutty".
I feel honored to be on the same thread.
“You want to build using green jelly beans....I will help you...we call those folks clients...”
Classic.
Why not use the zone 7/8 roof design minus the interior rigid for all climates?
In warmer climate, go for diffusion vent, for colder soffit to ridge venting. Change the rafter size (lumber to I-joist/truss) if more insulation is needed.
Anytime I've priced out exterior roof rigid install it was much more expensive than spray foam. Pushing unvented roofs will simply mean a lot more spray foam in new houses which is the last thing we want.
I also think in zone 4 and 5 walls, 2x8 without exterior rigid is the way to go for higher R values.
Hello,
This is a massive change on the crawl space. So I'd like to see some argument on this.
The picture shows a vapor barrier sandwich on the crawl floor.
1" dirt/sand/concrete for thermal/ignition barrier mentioned, which almost no one ever does for crawl space code and manufacture rigid foam protection. That's positive. However, I am not sure we are 100% on tape on the poly is currently 100% permanent. Any thoughts? It seems this would be critical as no place is more likely to take water into a house than a crawl space.
Spray foam is heavy in those designs.
Not something to celebrate both for this website or for the intent of saving energy to save the planet.