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Community and Q&A

How do you keep a continuous air barrier in a vented attic over a porch?

ecoecompany | Posted in Energy Efficiency and Durability on

This duplex is being built in zone 4C (see photo). The vented attics are going to be blown with cellulose.

My concern is the part of the attic that extends over the front porch. The porch roof will be cedar car decking. The plans don’t call for any insulation or air barrier in this part of the attic – just cardboard baffles at the exterior wall plane to hold the cellulose in place.

Are insulation or an air barrier needed there?


  1. GBA Editor
    Martin Holladay | | #1

    There is no need to install insulation above your porch roof.

    However, you do need to have a physical barrier (an insulation dam) at the edge of your attic floor, to contain the insulation installed there, and to make sure that the insulation doesn't spill into the porch area. Your contractor could use plywood scraps, OSB scraps, or rigid foam to make this insulation dam. The dam should extend from the top plate of your exterior wall to the top of your planned insulation depth.

    It's a good idea to seal the edges of each rectangle of material used as part of your insulation dam. You can seal the edges with caulk or canned spray foam. You'll be sealing these pieces to the top plate below, and to the sides of your joists, rafters, or trusses on the sides.

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