metal roof over purlins vs plywood

Guest User
7/29/2010
I have an R-Panel Roof on a metal frame home. The roof is attached to purlins at 2' spacing. i'm getting some quotes to replace with standing seam metal due to some leaks and signs of trouble (screws have been replaced already, lots of silicone on screws, and some leaks). the ridge is about 80' across. both roofers want want to rip off the existing R-panel. One roofer says 5/8" OSB with reflective backing is needed as decking before a snap system can be laid down over some other layment material (felt). (24 gauge metal) Another roofer is proposing that the new roof go right over the existing purlins. (24 gauge with 1-1/2 seam crimped by machine, 18" seams) My question is: can the 24 gauge metal span those purlins and not deform when walked on? how much added insulation will the wood decking added? ie - the inside ceiling are vaulted and they tend to heat up somewhat. I'm going with a very high reflective index (76) and hope this helps improve things. Thanks. Bill
Todd Miller
Classic Products, Inc.
7/31/2010
The information on going over purlins needs to come from the roofing manufacturer. Adding decking will increase efficiency. Increasing ventilation will also help.
Guest User
11/29/2010
Hope this is not too late. NO you do not need to deck the house first. We frequently install (24 ga. BattenLok, WeatherLok) standing seam panels over purlins between 4' to 5' centers. I would add 3" blanket insulation under the panels for extra R-value, it is relatively inexpensive about .25 a sqft.
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