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A few question about my build.

bigdaddygb | Posted in General Questions on

I am building our retirement home here in Macon, NC zone 7 or 7a can’t remember. We have been working with our architect who is great and has done all the craziness I came up with on paper. So here is a list of everything we came up with after watching several building shows and seeing what they did and applied it to our house.

crawl space Foundation – Fox blocks
crawl space pad – 2″ of ips foam under 4″ of concrete pad with vapor barrier coming 18″ up wall glued down.
normal pressure treated sill plate with EPDM rubber gasket ( rubber because I have seen how the plastic pink foam breaks down really fast.)
2×6 wall construction with board and batten siding on top of ( considering) zip r-6.6 sheathing, with 2″ of CCF followed up by 3.5″ or r15 rockwool. This should net a r-value of 33 on walls. I have been considering plywood with 3″ of rigid foam board since the floor joists according to my engineer seem to be cantilevered over the foam of the fox blocks.
Roof has 7/16″ zip with 2″ of IPS foam and then Carlisle WIP300ht peel and stick, followed up by 3/4″ battens laid at 45 deg. for Steel standing seam roof panels.
Unvented soffits, as both crawl space and attic are conditioned spaces.

Am I missing any thing you could or would suggest. Is there something that would be poor design on my part and cause issues down the road? Attached is a picture of the wall section for my house. Everyone I have talked to here says man that’s over kill, I am working toward being very energy efficient as I hope to be running off just solar, and wind in the future here.

Thanks For any help you can provide.
G

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Replies

  1. user-2310254 | | #1

    George,

    Macon, North Carolina, is in CZ4. (See here for more info: https://www.greenbuildingadvisor.com/article/climate-zone-map-including-canada). On the wall, you don't need the two inches of closed cell if you are already installing ZIP R-6. I'd save some money and just install rockwool or another air permeable type of insulation in the wall cavity. In the crawlspace, I'd go with a thinner (two inch) rat slab and use the saving to install a couple of inches of rigid foam on the walls.

    On the roof, are you planning to install insulation above and below the sheathing? If only above, you need a much thicker layer to get to R-49. (See here for more info: https://www.greenbuildingadvisor.com/article/how-to-install-rigid-foam-on-top-of-roof-sheathing).

    1. bigdaddygb | | #2

      Steve yeah sorry, I forgot in the attic I am planning 5.5" of CCF in roof rafters inside+ all that I mentioned in drawing on top. Also the reason I chose the 2" of ccf in walls was to help seal off any air intrusion, along with caulking the sill plate and the bottom plate as well. I'd rather bring in filtered air rather with an air exchange unit than air run though dust filled cavities. Trying to make as air tight as I can. We had one house drawn up a 3200 sq ft rancher and got engineering done on it and got quotes from 400K to 800K to build it. the quote for the supplies was 260K .. so we down sized to our 2200 sq ft pick to get a house built that still fits our needs

      1. Expert Member
        Akos | | #3

        For a new construction you design spray foam out not in. It is expensive and not very environmentally friendly. There are much simpler, cheaper and easier ways to air seal. Taped sheathing adds very little cost, with a bit of care it is easy to get a house that is passive house level of air tightness.

        Your drawings show a vented roof but your description is for an unvented one. If unvented, the peel and stick should go above the deck, this way it can serve as both air and vapor barrier. Plus you won't need the fancy HT version, the cheapest non-granular one works just as well. You can use regular synthetic underlayment above the foam under the metal.

        I have seen this strapping at 45deg, but I can't see what extra it does unless you are in deep snow country. Most metal roof panels have enough ribs and striations to allow for enough airflow that any condensation there can dry. I would keep the strapping perpendicular and simplify your install. Also check your roof panels are rated for this type of install, not all are.

        You will need to tie the roof air barrier and sheathing air barrier together somehow. With rafter tails, this is one of the few areas best done with spray foam. One of the larger two part kits can do your rim joists and this area.

  2. charlie_sullivan | | #4

    I'm confused about the picture you included. It doesn't match what you are describing. For example, it shows blown-in insulation on the attic floor, whereas you are talking about insulating at the roof. Is that what the architect proposed and you are wanting to do something different? What don't you like about R-60 on the attic floor?

  3. bigdaddygb | | #5

    Yes his drawing needs to be adjusted. It was right then we made a change to the foundation and think he reverted to an old version of when he first started. But it is as I described it. The whole idea of a conditioned attic as I understand it is to eliminate moisture in the attic area, as well as to eliminate dust buildup under the insulation as well. My family have allergies pretty bad some times and anything I can do to control the incoming dust and dust transfer inside I want to do. That's why I have closed eves, and yes it shows ridge vent which is wrong also. The roof area over the sheathing is open for ventilation under the steel panels to help even more with moisture and condensation evaporation.

  4. charlie_sullivan | | #6

    If you get the air sealing between the attic and the conditioned space right, there's no concern about dust in the attic affecting the occupants. And a vented attic is pretty much the best design there is for avoiding moisture problems.

  5. user-2310254 | | #7

    George,

    I think you would benefit a lot from partnering with an experienced builder who understands how to build an efficient and healthy home. There are a thousand things you have to get right, and it's nearly impossible for a home owner to oversee those details.

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