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Insulating with siding

michaeldrehl | Posted in General Questions on


I have aluminium siding on the exterior of my house. I was replacing the exhaust vent and noticed that the aluminium siding was placed on top of the older asphalt shingles siding. 
So there is plywood and the asphalt siding and then there is another plywood and on top of the plywood is the aluminium siding. 
On the inside, I have wall cavities, and then plaster and lath and then on top of the plaster, I have sheetrock. There are small 1/2 inch wooden beams between the plaster and the sheetrock. 

I was thinking of insulating with cellulose in the wall cavities. Since there are apparently two sidings installed, I am not sure insulating would be a good idea since the house won’t be able to “breathe”.

Any thoughts?

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  1. GBA Editor
    Martin Holladay | | #1

    It's always helpful to tell us your climate zone or geographical location -- advice can vary depending on climate.

    Briefly, in most climate zones, filling your stud bays with dense-packed cellulose won't cause any moisture problems with the layers you describe.

  2. michaeldrehl | | #2

    Hello Martin,
    Thank you for your kind response.
    My apologies. I am in zone 4 in northern NJ.

  3. Expert Member
    Dana Dorsett | | #3

    In zone 4A it's fine to have a low-permeance asphalt shingle on the exterior with cellulose in the wall cavities. The key things that have to be right right are...

    #1 window flashing has to be properly diverting any bulk water out to the exterior.

    ...then much further down, but still somewhat important...

    2# interior side wall finishes can't be super-low permeance, such as vinyl or foil wallpaper. (Latex paint on wallboard or plaster is fine.)

    Aluminum siding is inherently back-ventilated and that keeps exterior moisture drives fairly limited. Even wind-driven rain blowing by the aluminum siding drains & dries quickly to the exterior. Asphalt shingles are fairly low permeance and aren't usually a very good approach to insulated walls in heating dominated climates. But with any reasonable drying capacity toward the interior it's not particularly risky in a zone 4A climate.

  4. walta100 | | #4

    It sounds like you have an older home be certain you do not have any old knob and tube wiring in any wall you want to insulate as it will create a fire hazard.

    It could be difficult to hide the holes needed to blow the insulation in from the exterior unless you are replacing the aluminum siding.


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