How to Install RoofingFoil™ Under a New Shingled Roof
You may have heard that a radiant barrier can't go under a shingled roof because there's no air gap between the deck and the shingles. That's true for existing roofs — but if you're building new construction or re-decking, you can install it in a way that outperforms traditional radiant barrier decking like TechShield™ or Solarboard™ by nearly 20%.
Installing under new decking
The perforated (breathable) foil is installed across the top of roof framing before the deck boards go on. It drapes down naturally between rafters, creating an air space on both sides of the product — above and below the foil. Perforated material is used in this special application because the layers above the roof decking will be solid, vapor barriers so a vapor barrier isn't needed below the deck too.
Roll out the foil across the open framing
Before any decking goes down, roll Original AtticFoil® (the 60" wide is a great width to use in this application) horizontally across the roof framing, starting at the eave and working toward the ridge. The foil will naturally sag between rafters — this is intentional and creates the air gap above the foil.
Fasten to the framing
Staple or nail the foil to each rafter as you go. Plastic cap roofing nails are preferred, but staples work well here since the deck boards will compress and secure the foil from above.
Overlap each row 4–6"
Overlap each successive row by at least 4" as you work up the roof to keep the barrier continuous.
Install the deck boards over the foil
Lay your plywood or OSB decking directly on top of the foil. The deck compresses and holds the foil against the rafters at each board edge, while the foil sags freely between rafters — preserving the air space that makes this method work.
Foil rolled across open framing — the sag between rafters creates the air gap above (and below) the foil. In this application you are using a perforated foil product since you are adding it below the decking, in the attic space.
Install roofing felt and shingles as normal
Once the deck is down, continue with your standard roofing process — felt underlayment, then shingles on top. The AtticFoil® material is now permanently in place between the framing and the deck, with air space on both sides.
The natural sag of the foil between rafters is what creates the air space on both sides of the barrier.
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