Roofing without sheathing
We are currently doing a retrofit that includes a vented attic with lots of cellulose. The baffles will be ripped PIC with FG facings. The current roof is metal over 2×3 (actual) battens with no underlayment. In the next year or two we will need to replace the roofing. For some of the other details we are working out now, I want to make sure I know how we will be handling the roofing when it comes time. So here is the catch, do we need to sheath if we already have the battens? So far I have come up with 4 options:
A) Underlayment over the battens then metal roofing. Would rather have the battens on top for ease, so…
B) Remove the battens, notch them for draining, add underlayment, reinstall battens, add metal roof. Not sure how easy they will remove and its a lot of work.
C) No underlayment – just let condensation drip
D) Extend the baffles to the ridge with underlayment strips stapled between rafters. Condensation would be directed to the soffit which doesn’t seem ideal.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Matthew,
Step one is to investigate local code requirements. New buildings are required by code to have roofing underlayment -- but in most jurisdictions, a re-roofing job doesn't have to follow code requirements.
My advice is to install solid sheathing and underlayment, followed by roofing. It's the best way to handle condensation, and makes it possible in the future (if it's ever needed) to convert the vented unconditioned attic to an unvented conditioned attic.
Martin, thanks for the feedback. I will take another look at sheathing.