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What are the fasteners for roof exterior rigid insulation (4.5 inches)?

I am looking to use a detail similar to 4-05055 - metal roof/unvented/cathedral/exterior 4.5" rigid insulation. I have a few questions on the assembly:
1- are the layers of rigid insulation adhered together?
2- what type of fasteners are being used to go thru the first layer of sheathing, thru 4.5" insulation, 2nd layer of sheathing and into rafters? spacing? (I am located in NY - 90 mph ground wind)
3- do you know a relative comparison between this detail and using a SIP panel - cost? installation? structural?

Thank you!

Asked by Linda Zwart
Posted Wed, 07/23/2014 - 09:11
Edited Wed, 07/23/2014 - 10:33

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2 Answers

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1.
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Linda,
If you want to compare costs between two different construction methods, you have to cost them out. If you have never done a construction cost estimate, you should probably contact a contractor for bids.

If you have two layers of rigid foam above your roof sheathing, you should stagger the foam seams. There is no need to attach the layers together, but the top layer should be well secured with long cap nails or long screws and roofing buttons.

Cap nails can be purchased in a variety of lengths up to 8 inches.

Some suppliers of long screws include:

Answered by Martin Holladay, GBA Advisor
Posted Wed, 07/23/2014 - 10:38

2.
Helpful? 0

I used Windlock's "Wind Devil" system on my house ... its a very good quality phillips head fastener - the heads do not erode like most fasteners upon installation and so can be easily backed out for replacement and reused - the cap is also very strong and good quality mateiral. An 18V cordless driver with Windlocks phillips chuck works great.

Make sure the fasteners penetrate the deck 5/8" into the rafters. Since you have significant stand-off distance from the rafter faces, and you are working at an angle (i.e. pitch), setting the fasterners takes careful attenton to keep them perpendicular and in line with the joists

http://www.wind-lock.com/cat-25-1-5/Fasteners.htm

Answered by flitch plate
Posted Wed, 07/23/2014 - 11:37

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