Todd Miller - Roofing Expert

Expansion and Contraction

A homeowner from Texas asked:
I am currently have a galvalume standing seam roof installed on my home. I am seeing lots of oil canning and asked the installer about it. The metal roof is being installed over shingles using a sharkskin underlayment. I noticed that the crew doing the installation is screwing down the pancake screws as tight as they can and I brought this to the installers attention. He tells me that they can not tell when they are hitting the plywood decking. Can the screws be tightened too tight and can this be the cause of the oilcanning?

Also, on the flashing at the side wall, the flashing was put on top of the siding with a piece of trim board put on top of the flashing and then the trim was caulked with a laytex caulk. Was this done correctly or am I going to have problems with that later down the road?

Should I be seeing the pancake screws coming thru the decking in the attic? I live close to the Texas coast and I am concerned these panels could come off in a hurricane like the one that came thru last year—-Hurricane Ike.

Any help you can give me on this would be greatly appreciated.

My response:
Most manufacturers test with screws that penetrate 5/8″ thick decking … most will say it is also acceptable for them to go at least 1″ into thicker decking.

The wall flashing sounds okay … it is nice to remove the siding and flash behind it but in some cases that just isn’t very possible or practical.

Yes, the oilcanning could be caused by over tightening the screws.