Or copy this URL:
https://www.metalroofing.com/spirit/comment/4792/find/
The building code allows metal to be installed over one layer provided the building offical approves so check with him. Second you need to choose a system that is designed and tested to go over that material and perform at the low slope. Most have certain criteria and do not allow a direct application.
At the same time you need to consider why the old roof failed and it was probably because there is inadequate ventilation and you need to address that at the same time to get the best performance out of your new roof.
Go to our members page, choose a product and contact the manufacturer for its fit for use or look up their product approval which should indicate if this application is permitted and how it is installed.
12/9/2004
Dura-Loc Roofing Systems, Inc.
12/9/2004