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Community and Q&A

Gut-rehab envelope assembly advice needed

Gary Ingram | Posted in Energy Efficiency and Durability on

I am a new forum member and have found a lot of useful information on a wide variety of topics. I am looking for advice on a gut rehab of a 1,035-sq-ft single-story duet starting in the August timeframe. Bottom line, we want to make sure we spend our time and money wisely but also spend dollars now for insulation, air sealing, etc. rather than giving the money to the utility company long term.

A few details about the project:
– We are in zone 3B boarding 3C (Livermore, CA).
– Roof assembly from outside in: Asphalt shingles, 15lb felt, 5/8 in. full sheet sheathing, 4 in. of open cell sprayfoam (non-venting attic)
– Wall (2 x 4) assembly from the inside out: 5/8 drywall airsealed, RC1 (sound control), Roxul mineral wool (R13), 1/2 in. OSB, Tyvek, 1 in. polyiso (R6.5) taped, 1×3 straping, Hardieplank fiber-cement lap siding, Milgard Tuscany windows with 3D Max option (U-Factor .30)
– Floor assembly from inside out: Tile (all floors), Schluter Ditra, 5/8 plywood (for strength), 3/4 particle board, 6 in. open cell sprayfoam

Thanks in advance.

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  1. GBA Editor
    Martin Holladay | | #1

    Since you didn't ask any questions, I'm assuming you just want feedback on your plan.

    California builders are governed by California's energy code, Title 24. I am not a Title 24 expert. However, your planned ceiling insulation doesn't meet the minimum requirements of the 2012 IRC, or, for that matter, most building codes.

    In your climate zone (Climate Zone 3) you need a minimum (according to the 2012 IRC) of R-38 ceiling insulation.

    To meet this minimum requirement, you would need 10.5 inches of open-cell foam, not 4 inches. Your planned insulation is only rated at about R-15.

  2. Gary Ingram | | #2

    Thanks Martin. Yes, we are looking for confirmation on the selection of materials, the order of installation, and that we have (as you pointed out in the roof insulation) an appropriate quantity/value. I will look into the title 24 requirements. I will post specific questions as we get closer to construction dates since we will be doing most of the work ourselves and our goal is to heat the home with a candle and cool it with an ice cube - lofty expectations :)

  3. Bruce Friedman | | #3

    Given you goal of such a tight house please don't forget mechanical ventilation. You will need/want to breathe clean air.....

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