Insulation against roof deck leads to roof failure

Fiberglass insulation against roof deck plus moisture = roof failure

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Humid air is moving up through the wall cavities an condensing on the roof deck.

2 thoughts on “Insulation against roof deck leads to roof failure

  1. Dear Tedsenergytips,
    Interesting Thoughts, The ductwork in my attic has insulation that is deteriorating. Replacing it all would be in excess of $1000. A friend suggested an alternative might be to not replace the ductwork, but to instead just fill the entire attic with insulation.

    Is this a good or bad idea?
    Great Job!

    • That’s essentially the solution I took in my own attic and it worked great. I had cellulose blown in and it covered everything. The tops of some of the ducts peek out from the insulation, but overall, mostly it’s covered, providing much better insulation than the inch or two used in insulated ducts.

      There are a couple considerations:
      – if you have soffit vents, you’ll want to prevent the insulation from covering up the openings. This might involve installing a piece of cardboard or other blocking material to stop the insulation from spilling down onto the soffit vents. You might do this in conjunction with installing ventilation “chutes” (often made of foam or cardboard) that directs the air from the vents up along the underside of the roof sheathing.
      – It’s messy! Blown fiberglass or cellulose gets everywhere, which is why it’s pretty good for insulation retrofits. But, once you have a foot or two of insulation on the attic floor, it makes it very difficult (and somewhat dangerous) to navigate the attic. And when you do have to walk through it, it will cover you in the material.
      – In addition to the mess, it hides everything. So if you have to trace a wire or something else on the attic floor, blown insulation makes this difficult. Not impossible, but difficult.
      – If you’re going to do any construction, like adding lights, installing a bath fan or even something as basic as running a wire for cable TV between rooms (and through the attic), do these projects before you add insulation.

      Hope that helps. Cheers!

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