Todd Miller - Roofing Expert

Strapping or No Strapping

Question from June in New Hampshire:
Greetings: – We are in the process of contacting contractors regarding the installation of a metal roof on our home and with each contractor that comes to the house we are getting more and more confused:

1. should it be installed over the existing asphalt or strapping
2.
Standing double locking seam- DOes this tend to sweat ontop of asphalt shingles?- one contractor states yes – the other recommends using it?

My response:
Thanks for investigating metal.

1) Some products CAN be installed on strapping. Very few MUST be installed on strapping. Most products CAN or MUST be installed on solid deck. If you currently lack attic ventilation and have difficulty achieving it then there is good reason to consider strapping but you must choose an appropriate product and you may wish to install vertical strapping followed by horizontal and then actively venting the resulting chamber.

2) A double lock panel should not pose any special issues in comparison to other styles.

I hope this helps some. If you have special circumstances that need to be considered please let me know.