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Wood shingle roof and an energy retrofit

I have a wood roof to replace on a 300-year-old house in a historical district. The house is also in serious need of an energy retrofit.

Wood is more expensive (the HD Commission has a record of approving asphalt based on cost, so it is a choice), but may provide options not found with asphalt or other coverings, since, by design, shingles and skip sheathing must dry to the outside; sheathing condensation issue evaporates.

Any thoughts/research about how to best use this advantage?

Asked by Ev Hyde
Posted Mon, 02/10/2014 - 17:01
Edited Mon, 02/10/2014 - 17:35

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3 Answers

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1.
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Ev,
There is no building science reason why asphalt shingles won't work. The choice is one of aesthetics and your budget. The only other factor to consider is fire safety: wood shingles are more flammable than asphalt shingles.

You didn't tell us whether your roofing will be installed over a vented, unconditioned attic or whether it will be installed over a cathedral ceiling. If the roofing is installed over a vented, unconditioned attic, the roof sheathing will dry readily to the interior, so the roofing has no need to be vapor-permeable.

If you are installing the roofing over a cathedral ceiling, the details are a little trickier -- but it is still possible to design a roof that functions well, even if you choose asphalt shingles.

Answered by Martin Holladay, GBA Advisor
Posted Tue, 02/11/2014 - 07:01

2.
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Thanks for the response. The roof has several configurations; a story and half, with cathedral; another part is gambrel, with 'cathedral' under steep sections and unvented flat ceiling under low slope; a third small section is 'flat'. (This <1" sealed roof will be re-roofed with some membrane.) But my thought was that a wood roof, including skip sheathing, has greater drying possibilities than other coverings and underlayments which trap moisture. So there might be more options for a from the top energy retrofit.

Answered by Ev Hyde
Posted Tue, 02/11/2014 - 14:46

3.
Helpful? 0

Ev,
You are right that a wood shingle roof "has greater drying possibilities than other coverings and underlayments." That doesn't necessarily imply, however, that other types of roofing won't work fine.

If you are planning a "from the top energy retrofit," it sounds like you want to install rigid foam above your roof sheathing. If you do that, your wood shingles aren't going to help the entire roof assembly dry, because your rigid foam will be a low-permeance vapor retarder.

Answered by Martin Holladay, GBA Advisor
Posted Tue, 02/11/2014 - 14:55

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