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Remodel Insulation – Starting fresh. Stripping drywall, siding and roofing.

jetlaggy | Posted in Green Building Techniques on

Howdy community,

I bought a very funky 1960’s ranch home in Climate Zone 5b (Salt Lake City) with the plan of reconfiguring it for my needs after a year of living in it and figuring out my ideal home. I am trying to make a big dent in my energy consumption because this area has a massive need for heating and cooling. The natural ventilation season is brief as it goes from 20 F to 100 F and back pretty quickly.

-Trusses currently cover the entire 85 x 25 structure. Low pitch, only about 4 ft of attic crawl space. Vented. Ice dam city.
-Planning to replace 30 ft of trusses with beam and rafters to give living area more headroom
-Planning to remove shingles and install metal roof

-2×6 exterior walls with pink batts under sheathing. Basically your standard 1960’s house.
-Planning to redo interior drywall to replace electrical and improve insulation
-Planning to replace dated siding with something new and low maintenance

Given it’s a good opportunity to go above and beyond code, I don’t want to look back on this and think I should have added more insulation when I had everything down to the studs.

What wall assemblies would some of you recommend?

My original thought was spray closed cell between cavities for air tightness, then add 4 inches of rigid above deck and outside the sheathing. Here to see what people would do in my situation. Thanks.

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  1. brendanalbano | | #1

    A good starting point would be to look at the insulation required for condensation control, as well as code minimums, to establish a baseline.

    For your 2x6 walls in climate zone 5, the standard recommendation for condensation control is to install a minimum of R-7.5 continuous insulation outside the sheathing. 2" of mineral wool, EPS, or Polyiso will cover you there. Check out the opportunities to source reclaimed foam in your area as well. If you want to go above and beyond, you could bump that 2" up to 4".

    For your roof, 40% of your insulation should be either rigid insulation above deck, or closed-cell foam in the cavities. For a code-min R-49, that could be 4" or 5" of foam or mineral wool (depending on type) on top for R-20, and R-29 worth of fiberglass, cellulose or open-cell foam in the ceiling. Keep the ratio of above deck to below deck insulation the same, and boost the total insulation up to R-60 if you want to go above and beyond.

    Closed-cell foam is a great problem solver, but it's expensive and many kinds are blown with blowing agents with high global warming potential, so the more you can minimize its use the better. If you can establish your air-barrier at the wall and roof sheathing with tapes, membranes and goops, that's the most ideal.

  2. user-2310254 | | #2

    Air sealing is a good first step. See this article and the links in the sidebar:

    Are you sure the walls are 2x6? 2x4 would be much more likely for a house of that era.

  3. jabloz | | #3

    Continuos rigid insulation is The way to
    I'm remodeling my own house in Staten Island NY
    And have 2 layers 3inch 15R on top of old wood plank gaps sealed with expanding foam roof 5 inch closed cell between truses
    and no regular heating yet
    3000W electric heater gives me 67 F
    No insulation between studs
    All this fiberglass insulation just creating condensation

  4. GBA Editor
    Martin Holladay | | #4

    It would be very unusual for a 1960s home to have 2x6 studs. I'm guessing that either (a) your house actually has 2x4 studs, or (b) your house was built in the late 1970s.

    An older home with roof trusses usually uses trusses that don't provide enough room for insulation near the eaves -- in other words, they aren't raised heel trusses. If that's the case in your house, it's a strong argument in favor of installing exterior rigid foam. For more information, see How to Install Rigid Foam On Top of Roof Sheathing.

    If you plan to install 4 inches of rigid foam on the exterior side of your wall sheathing, why would you install closed-cell spray foam between the studs? The spray foam is expensive, and it limits the ability of the wall assembly to dry to the interior. You may want to read these two articles:

    How to Design a Wall

    Installing Closed-Cell Spray Foam Between Studs is a Waste

  5. jetlaggy | | #5

    Thanks guys. I stand corrected and the exterior walls are 2x4. I had to dig up some pictures of putting in the in law apartment to verify. Also great articles.

    To reach at least R38 roof and R20/13+5 walls (and hopefully beyond) it sounds like exterior may be the only way. Assuming we did 4" outside of the sheathing, would you then just use Roxul between the studs? How would the overall wall R value look?

    Also, I understand the cathedral portion of the roof will be similar to the walls but thicker. How about the existing truss portion? Keep that vented and lose a lot of the rigid foam benefit? Otherwise how could you get enough insulation under the deck between the trusses?

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