Underlayment needed between zip system and ribbed metal roof?
user-7418476
| Posted in Construction Techniques on
The roof will be installed soon on our new house and our builder suggests there is no reason to put an underlayment between zip panels and the ribbed metal roof. Do we go along with this?
Thanks
Replies
You will be better served to attach the metal panels to sleepers allowing a 3/4" air/water/drainage plan for the panels. The Zip will provide a good air/water barrier, but the sleepers will ensure a dry roof for ever. Also the air gap will cut down on heat build up in the attic (but more important in a cooling climate (climate zones 1,2,3)
Matt Risinger has a great blog on youtube and one of his videos is on the installation of a metal roof over sleepers.
First thing I'd do is ask the manufacturer of your metal. Likely to have install instructions on their website. I assume by ribbed metal you mean with exposed fasteners which will likely have a leak or two long term. Actually I'd not expect the sleepers to make much difference but if your deck is 7/16" sleepers will provide better screw holding performance. Heat build up in the attic is a whole 'nother issue..
A builder's favorite line is "you don't need that." According to Huber, taped Zip panels are suitable under a metal roof. But metal roofing is relatively expensive and intended to last a long time, so the insurance of an additional layer of underlayment seems like it might be worth it. Just be aware of how the permeability of the underlayment impacts your roof system, as the zip sheathing is considered vapor-open but many roof underlayments are vapor-closed.