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Input on a New Design-Build

beedigs | Posted in Energy Efficiency and Durability on

Hi all! Need help pls! We are doing our first custom build here in hot and humid Houston (zone 2) with the priority of durability, good moisture management (no mold problems), and good indoor air quality due to family member(s) having environmental health issues such as mold sensitivities.  It is a 2300sf 1-story full brick house with slab-on-grade foundation.  Overhang is at 16 inches. We are aiming for an all-electric home and switching to induction cooktops, heat pump clothes dryer, and ERV system in lieu of the standard HVAC system to help make this home more efficient.  Also going for a conditioned attic space. After researching quite a bit I still can’t fit the puzzle pieces together.  Unfortunately, we had already signed up with a draftman (and paid him) when we found architects that would have been a better fit for us.  Since we didn’t want to start over with the design we just need some guidance in some decisions while still keeping budget in mind. 1) We think this wall setup would be ok – 2×6 studs with zip r3, plus xps rigid insulation and spray foam cavity insulation.  Would the zip r3 be enough WRB or do we need something else on top of that for efficient water shedding? Would Polyiso be better since it has the shiny top layer that reflect heat? any other suggestions on efficient setup for said climate?  Zip seems to be a good product but what is making us hesitant is its potential to not deliver its intended functions because of poor installation by contractor (tape not put on right, creases that allows pooling of moisture, tape might not being able to handle the shifting of the house later on, tape needs to be applied in clean and dry surface which not all contractors would take the time to ensure and follow through on.  Also, I’ve heard of doing weep holes on top and bottom of brick wall, not just the bottom; is this good advice? 2) Do we need a subfloor installed above the concrete slab on grade foundation before installing flooring of choice?  We are thinking of LVP but have heard mixed reviews about it not being a good idea because it traps any moisture coming up from the slab and being a good idea because of its waterproof qualities?  Is there anything besides Dorkin Delta-FL that we can install before putting flooring on that will provide a vapor barrier and capillary break from moisture coming from the slab and not jack up costs as much as the Delta -FL? 3) In the bathrooms, we’re trying to see if there are better products to use besides the traditional tile and grout because grout has its cons.  Chanced upon a laminate bath and kitchen wall product called FIBO wall which is supposed to be better than using tile and grout.  Please share your opinion on which direction we should go. 4) How do we address the roof setup for our needs as described earlier?  Use the brown Zip sheathing, put an ice and water shield on top of that before installing the composite shingles? 5) With building science application in mind, which would be our: a) water barrier – Zip R sheathing b) air barrier – Zip R sheathing? c) vapor barrier – ?? d) thermal barrier – External rigid foam insulation and spray foam cavity insulation besides the one I mentioned? I might have missed something. If this was your build, how would you set this house up given the details I shared?  What other things would you add or take out to make this a great build?
Anybody used Aerobarrier with great success?
Thanks so much!

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Replies

  1. Steve Knapp CZ 3A Georgia | | #1

    Beedigs,

    If you haven't already, read https://www.prettygoodhouse.org/, search GBA for posts on the "pretty good house," and watch the BS & Build Show on Yahoo (https://www.youtube.com/channel/UCvAmHSecglp-u-DTFQlU8Tw).

    Even if you stuck with your draftsman, you really need to seek out a builder who specializes in efficient homes. There are a million details to get right, and you are not in a position to manage that part of the process.

    As far as your specific questions, here is my non-expert input.

    1) ZIP is a great product from everything I've read. I'm considering a similar stackup (ZIP R-3 on 2x6 framing with air permeable insulation) for my next house. Note that you don't have to have exterior insulation in your climate zone. So you could use standard ZIP or another material. As you noted, proper installation is critical, which is why it's best to go with whatever your builder and he/her subs are familiar with. You want a continuous air barrier tied to a contractually or code-mandated metric.

    2) What matters here is having a robust vapor barrier (6+ mm poly or similar) under the slab. If you are installing LVP, I suspect it can go directly on the slab. But check the manufacturers installation requirements. If I were installing wood, I would want to put down a plywood subfloor. (Note your draftsman may need to account for the thicker floor if you go this route.)

    3) I would ask this one as a standalone question. There are lots of ways to build a bathroom that performs well. I would tend to favor a well-established process over a new introduction.

    4) Here again, there are lots of ways to build a high-performing roof. The best/cheapest solution is often a vented attic with lots of cellulose. But that might not work if you have a complicated roof or areas with cathedral ceilings.

    1. beedigs | | #2

      thanks so much! il try to post the bathroom question separately...we are going with a conditioned attic..have u heard bout aerobarrier? wonder if that would be a good idea to do before drywall to seal microleaks

  2. Steve Knapp CZ 3A Georgia | | #3

    I wouldn't want to count on it as a way to solve an otherwise sloppy construction process.

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