Replies

1. GBA Editor
   Martin Holladay | Sep 17, 2015 06:35am | #1

   John,
   Manufacturers of through-fastened steel roofing accommodate thermal expansion by including ribs or corrugations in the metal panels. As these panels expand, the metal between the screws expands, and this expansion is accommodated and disguised by the ribs or corrugations.

   Through-fastened metal roofing sometimes makes a squeaking or popping sound when the sun hits the panels. These sounds indicate that the metal is expanding. If the thought of a roof that occasionally makes these noises bothers you, choose a different roofing.

2. 
   ranson | Sep 17, 2015 08:27am | #2

   I'm not worried about squeaking and popping. I do see how the corrugations and short width relieve pressure along the narrow axis of the panel. However, along the length of the panel, where it expands most and is braced by the corrugations, I'm concerned about the force on the fasteners. A lot of standing seam panels use clips that allow the panel to slide along its length. How do the fasteners in a through-fastened panel bear this force without pulling out?

   (Thanks for updating the title. I noticed the error after I clicked submit, and couldn't figure out how to change it.)

3. GBA Editor
   Martin Holladay | Sep 17, 2015 09:57am | #3

   John,
   The short answer is that, although expansion and contraction probably puts a strain on the roofing screws, the screws seem able to handle the stress, and the neoprene washers seem to keep these roofs leak-free, even when expansion and contraction forces end up slightly enlarging the fastener holes.

   I'm put on a lot of these roofs, and haven't yet had an example of a leak caused by expansion and contraction forces.

   I've heard of some roofers who prefer to install two overlapping panels -- for example, two 12 foot panels instead of one 22-foot panel -- because of the concerns you raise. That's always an option. I've installed 18-foot panels without problems.