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Metal roof with exterior fasteners OK for school?

My school board is discussing a new roof for our building. We recently insulated our attic space and want to prevent any possible ice dam water infilitration with our new roof.

It was suggested that we look at using, ice/snow membrane adhered directly on the roof deck followed by 1-in. strapping -- installed vertically -- and then agricultural type metal roofing (exterior fasteners) to finish. The idea being that the membrane would be the primary defense on moisture entering the buiilding and the metal roof would be ventilated by the air space from the strapping to provide a truly cold roof.

We are in mid Vermont in a relatively snowy location.

We are looking for comments.

Thanks,
Adrienne

Asked by Adrienne Raymond
Posted Wed, 11/07/2012 - 15:46
Edited Thu, 11/08/2012 - 08:25

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4 Answers

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1.
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Adrienne,
As long as the roofer is familiar with this type of roofing, it should work well. The only trick is flashing penetrations properly (as well as detailing valleys).

I hope that the insulation contractors paid attention to air sealing the ceiling plane of your school before adding insulation to the attic floor.

Answered by Martin Holladay, GBA Advisor
Posted Wed, 11/07/2012 - 16:43

2.
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We actually had spay foam installed to the underside of the roof, but we are concerned with the valleys and eves as they were somewhat difficult to reach for the foamer.

Answered by Adrienne Raymond
Posted Wed, 11/07/2012 - 19:54

3.
Helpful? 0

Adrienne,
If your spray foam contractor wasn't able to reach all of the areas of your roof, that's bad. Especially if the valleys and eaves remained unfoamed -- those are the most critical areas for preventing ice dams.

You may want to consider installing a layer of rigid foam on top of the roof sheathing in light of the fact that the spray foam contractor did an imperfect job.

Investing in a layer of rigid foam would be a much better investment than investing in the Ice & Water Shield. If your spray foam contractor had been successful and had actually sprayed all of the underside of the roof sheathing, you would not ordinarily want to install Ice & Water Shield. Instead, you would want ordinary #30 asphalt felt underlayment, so that the sheathing could dry out if it ever gets wet.

Answered by Martin Holladay, GBA Advisor
Posted Thu, 11/08/2012 - 06:46

4.
Helpful? 0

THe foamer did get in those spaces he just wasn't sure he got as much coverage in the smaller spaces. I suppose that is some of the confusion for local roofers we have spoken to. The Ice and Water Shield was suggested because of the use of the "ag. style" roofing materials. Thinking that some water would penetrate after a few years of contraction and expansion. Also assuming the space left by the 1" strapping would allow a small amount of snow blow in. IE the Ice and Water Shield is the "real" water stopping material and the vented overoof is supposed to solve any ice damming type melt. I appreciate your comments, thanks.

Answered by Adrienne Raymond
Posted Thu, 11/08/2012 - 07:53

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