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I have a 1997 double wide mobile home with shingles and a 3 1/2 on 12 pitch roof with vented soffit, but no ridge vent and 75% of the celing is cathedral. The 7/16 osb has some rot and some interior leaks. So I'm going to strip off shingles and repair the rotted deck. The celing doesn't appear to have a vapor barrier and the insulation thickness is questionable (from what I saw replacing a bathroom exhaust fan) so I would like to (perhaps) blow in more insulation while I'm repairing the deck. My plan is to repair the deck, add sythentic under layment and counter batten over top the underlayment with 2x4's and install my standing seam metal. My question is the metal mfg is ok with their product being over battens or solid decking so should I just replace the osb with 5/8 or 3/4 plywood or continue with my batten plan? I'm also uncertain if a ridge vent is possible with the mating design of each half. Thank you!!
I would not mind seeing some sort of space between the metal and the roof deck. I am concerned that you could drop the roof deck temperature enough to cause condensation that didn't occur before inside the attic. Battens would help create that space ... or you could also use a breathable synthetic underlayment (Vent3 is one I like for its high PERM rating) and then an entangled mesh product ... this allows moisture to drive out and the airspace created by the entangled mesh helps prevent dropping the roof deck temperature too low and also gives a space for moisture that is driving out.
So are you recommending breathable synthetic underlayment with battens on top? or or breathable underlayment on top of 5/8 or 3/4 plywood then metal. Sorry for the confusion!!
My suggestion is breathable underlayment over the decking followed by battens and the metal ... or you could use an entangled mesh product instead of battens. Thanks!
Are recommending breathable synthetic underlayment and battens on top? Or plywood, synthetic underlayment then metal. Sorry for the confusion!!
Could I just use a spacer under my horizontal batten at each truss to space it off the deck instead of running full length vertical ones?
Thanks todd, I appreciate you're time and advice!!
My suggestion is breathable underlayment over the decking followed by battens and the metal ... OR you could use an entangled mesh product such as Dry-Tech instead of battens and install the metal panels over it. Now, you have also mentioned the possibility of "cross battens" or similar. This would be placing vertical battens over the decking and underlayment as "sleepers" over the rafters and then your horizontal battens over those. That is certainly a nice idea and would enhance things by allowing air flow up the decking beneath the horizontal battens. You also could probably use spacers as you suggested. All this said, you need to also make sure that what you're doing meets local building codes.
I'm having trouble with finding the vent3 in stock. Could you recommend some other equivalent underlayments. Again I appreciate you taking the time to help me, thanks Todd!!
I think you will have a tough time finding any breathable in stock at a local big box or lumberyard. I am sorry. They just aren't used very often. I generally rarely see a need for them except in situations where traditional ventilation is extremely limited. Breathable underlayment by the way are not a "cure-all" but they can be helpful toward creating a system that works. GAF has a product called DeckArmor that is probably most likely to be in stock. It has a breathability rating of 16 PERMS. Vent3 is made in the UK and stocked in OH by RoofAquaGuard ... with a much higher PERM rating. In the interest of transparency, I will say that RoofAquaGuard is a part of the company I work for. I do see that Menards offers a product called Hydra, also 16 PERMS. A company called Proctor from the UK was perhaps the originator of these types of products but I doubt you will find it in stock anyplace.
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