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Type of insulation? And should I have a vented attic or not?

user-6813968 | Posted in Green Building Techniques on

I am building a new construction home in North Carolina in climate zone 4. I have the plans almost done and I have a builder. The builder will work with me but does not have experience with building energy efficient homes. I will be building a 2090 sq ft single story 3br 2 ba 2 car garage home no basement and will build on a slab with a 12″ poured stem-wall foundation. Roof will be a 12-6 hip style with asphalt shingles. Framing will be 2X6 on exterior walls. I plan to build an energy efficient home with wood stove as primary heat with in floor heat secondary and split unit AC with condenser outside and and multiple evaporators inside. I also plan to install an ERV system to assure fresh air in the home. Also wil have a propane gas stove for cooking. Also plan to use copper plumbing and on demand propane water heater. House will be on a well and garage will have a utility room for installing ERV/water heater/well pressure tank. House will have 9″ ceilings except cathedral ceiling in living/family room and an 11″ raised ceiling in the entry way. My primary objectives are keeping the house dry to prevent mold and energy efficiency. My question is primarily about insulation and mold prevention. Here are my questions.
1. Should I have the air seal in the roof or the ceiling?
2. Should the attic be vented?
3. Will I need to have makeup air for the range hood over the propane gas stove.
4. What type of insulation should I use in exterior walls and in the attic.

I have attached my house plans and the type of in-floor heat with GEO insulated slab.

Thanks for your advice

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    User-6813968,
    Q. "Should I have the air seal in the roof or the ceiling?"

    A. Every house needs an air barrier. The air barrier (or air barriers) should be adjacent to the insulation. If you are insulating a flat ceiling (for example, the floor of a conditioned attic), the air barrier is usually on the interior side of the insulation. (Most builders use drywall as the air barrier in this location.)

    If you have an insulated sloped roof assembly (a cathedral ceiling), the air barrier is either located on the interior (again, drywall is common), or the exterior (for example, using taped plywood sheathing), or near the vent channel (using ventilation baffles installed in an airtight manner) -- or, even better, your roof assembly will have two air barriers (one on the inside of the insulation, and one on the outside of the insulation.)

    Q. "Should the attic be vented?"

    A. The answer to that depends on where you put the insulation. If you install the insulation on the attic floor, most building codes require the attic to be vented.

    Q. "Will I need to have makeup air for the range hood over the propane gas stove?"

    A. The answer depends on the cfm rating of your range hood fan. For more information on this issue, see Makeup Air for Range Hoods.

    Q. "What type of insulation should I use in exterior walls and in the attic?"

    A. Here is a link to an article with recommendations on walls: How to Design a Wall.

    Here is a link to an article with recommendations for attics: How to Insulate an Attic Floor.

    -- Martin Holladay

  2. Expert Member
    Dana Dorsett | | #2

    By "...split unit AC with condenser outside and and multiple evaporators inside" are you talking about a ductless multi-split system?

    If yes, all multi-splits are heat pumps, which would automatically give you zoned back up heating for the wood stove. If sized for the ~2 ton cooling load (run and aggressive Manual-J, don't wing it), there are several 2-2.5 ton 2-4 zone (4 evaporators, when operating in AC mode) options out there. The efficiency and cost of heating with a decent multi-split is half the cost of condensing propane boilers for under floor heat in most markets, and less than a third the operating cost of electric resistance heating for the under floor heat.

  3. Anon3 | | #3

    Vent it.

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