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I am remodeling a house in Sacramento, California.

Tg8zQmYhMk | Posted in Energy Efficiency and Durability on

I have stripped it down to the subfloor of its original foundation. I am interested in making it very energy efficient. I am thinking of 2×6 walls with a R-22 fiberglass batts, 2-coat stucco over 1″ foam board, and a layer of 3/4″ polyboard under the sheetrock at all exterior walls. R-8 flex duct and HVAC units of 90% ++ efficiency to be in attic. I am considering spray foam insulation to be applied underneath solar board with a light colored comp or metal roof on top. Attic to be tight unvented type. Should I consider additional foam above roof sheathing with a additional layer of sheathing or would this be both too costly and not very effective ?? Should I consider still insulating the ceiling with a additional layer of R-19 since the spray foam will give me about a R-20 ??

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  1. Danny Kelly | | #1

    I certainly cannot answer all these questions as I am still learning the building science behind high performance homes but may be able to tell you a few things to be careful of. First of all your climate is very important so answers vary quite a bit. My experience is in Charlotte, NC which looks like is somewhat along the same latitude as Sacramento - we have a mixed humid climate - I would assume since you are so close to the coast you are about the same.

    2x6 walls and 1" foam is a great idea. I am not familiar with polyboard but sounds like it could be a vapor barrier as is most exterior foam boards. I would not put a vapor barrier on both sides of your wall - need to allow your wall to dry to one side or the other - so would invstigate this product.

    By solar board are you referring to a radient barrier like techshield or something? A light roof, radient barrier, and spray foam is a pretty good roof system. I would skip the extra foam above the sheathing =- going to get to a point of diminishing returns on investment and again installing a vapor barrier which should be studied prior to installing. Our insulation companies here would recommend not insulting the ceiling since you are trying to semi-condition your attic anyway.

    Be sure your HVAC unit is variable speed and will run to dehumidify when needed in such a tight house.

    Hope that is somewhat helpful - good luck

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