Feedback on Assembly Plans for New Build
Hi all! We are in the planning stages of our new house build. It’s a one-story, all-brick, about 2400 sf build with an attached garage. Our priority for this build is good moisture management and mold issue avoidance. We will also have 16 inches of overhang all around the perimeter of the house. Site location is about 30 miles from the gulf. This will be an all-electricity-operated house. If we would have any gas lines it wouldn’t be within the walls of the building envelope.
Have since done a lot of research with no background in construction at all, but definitely getting great information and learning. That being said, I am still quite confused on how to apply what I am reading to the details of our house project. We don’t have $$$ millions to put on this venture, so trying to find better-practices building choices and solutions for a good build that are practical and at a more moderate price point. Watched loads of Matt Risinger’s video also.
So far, we know that we are going with 2×6 stud framed walls and a conditioned attic space where the mechanicals will be placed, and looking at higher performance windows ≥ R5. Also looking into using an ERV, VRF with dehum setup for mechanicals. Our builder uses spray foam insulation quite regularly on their builds but granting our reasons for building this home (medical mostly) they are open to other setups if deemed feasible. Doesn’t help that lumber prices are 3-4x higher than normal.
I know there are lots of factors, but from a simple standpoint, would this be an ok setup:
Floor = Do we really need a subfloor with Advantech or plywood? We want to go with LVP but are hearing reviews about tile being the best choice for mold avoidance and to not use plasticky vapor barrier because those trap the moisture and give environment for mold to thrive and party; have found some info on the Delta FL dimpled product that supposedly pushes back the moisture back into the slab foundation by equalizing the vapor pressure. Can I just get away with Delta FL and Tuck tape sealing the joints over the slab foundation and install floating LVP flooring on top of it and call it good? Tile and sealed concrete just seems to cold and hard on the joints and feet.
Wall = all-brick cladding, with ample airspace behind it, then exterior foam insulation, Zip sheathing, 2×6 wall studs, and then spray foam for cavity insulation in between studs, followed by drywall painted over with latex paint (to provide semi-perm vapor barrier class III). What brand would be best as exterior foam insulation: Poly-iso? for its reflective/radiant heat barrier properties, XPS? Although being in our area termites might be an issue and foam insulation is a great meal for them so no bueno on that? I am curious also on the Rockwool products for both external and internal insulation due to its various properties (bug repellant, water properties, noise reduction, fire resilience, etc). Don’t know which of these products shrink over time though.
Roof = With this having a conditioned attic in climate zone 2, it has been proposed to use spray foam. Since we are leery of off-gassing potentials from spray foam, what other things can we use instead of spray foam? Perhaps use a radiant barrier to reduce the delta on temperature; would an ice and water shield be also beneficial? What radiant barrier product would be best? Also, lighter colored roof shingles? What about Permalock aluminum shingles (which the HOA architectural board gave approval of)?
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I'll venture an opinion on a couple of things.
Instead of trying to manage moisture in the way you outlined, I'd focus on preventing moisture from migrating through the slab. You should read Martin's article on slab design if you haven't already (https://www.greenbuildingadvisor.com/article/polyethylene-under-concrete-slabs).
I'm going through a similar exercise with my CZ3A new-build. FWIW. I'm going with a slightly modified approach (based on a post from Carl Seville). I'm spec'ing the four inches of gravel but only installing rigid foam at the perimeter. I'm also following his recommendation to use the Polyguard Term System since termites and carpenter ants are an issue.
With this strategy, I'm less concerned about moisture migrating through the slab. Even so, I will probably opt to put down a layer of plywood wherever we decide to use wood flooring. (FYI. It's important at this stage to determine how you will manage HVAC in the home.)
For insulation, I'm going to try to avoid spray foam. If you have environmental sensitivities, I would go with rockwool batts or cellulose. Standard ZIP on a 2x6 wall with rockwool batts is what I'm specifying for my own build. I'm going to try to use a ventilated approach in the homes cathedral ceilings, but this (and the band joist) is one area where I might allow water blown closed cell in combination with air permeable insulation.
I noticed your exterior cladding is brick. No doubt this is an aesthetic choice. But with your sensitivities, I would be extra careful about ensuring that the contract includes a sufficient gap to promote drainage. Cement siding over a sufficiently deep rain screen would be more forgiving (and probably cheaper).