
If these are just plain pine boards and not treated lumber, the normal practice time would be to install right over them. You could paint them if you want to.
Painting them would offer some protection. Otherwise, unfinished would not be unusual.
My apologies for the delayed response. The situation you describe is of course not a conventional metal roof installation with which our organization has worked thousands of times. However, I do think there will be times when ambient humidity is high and it cools down at night that you will end up with condensation on the underside of the carport cover. My feeling is the enclosed section may be slightly less prone to this. It all depends on temperature and moisture levels and whether dew point is reached.
Thanks Joseph. Unless I am mistaken, Emma did not ask about condensation. However, my answers were influenced by that thought. Treated lumber has chemicals that do not behave well with many metals, especially if you add moisture / water to the mix. As far as using strips of underlayment, I just didn't see that as being worth the effort. It wouldn't stop condensation and that condensation would still drip down the sides of the wood. Now, that said, Emma is in Tucson I believe which doesn't have huge issues with condensation but it can happen. I am not sure where you are located.
Joseph, as Todd mentioned the chemicals in treated lumber are corrosive to GALVALUME or AL/ZN alloys. I suggest using Galvanize coated steel to avoid reactions with the chemicals in the wood.
I am building my house in Tucson and am not sure how to treat the porch roof! The main roof is insulated, then decked with OSB, and then covered in self adhering underlayment with corrugated fastened on top.
However, the porch is only roofed with pine board purlins spaced out (skip-sheathing) AND will be visible from below, so the boards and metal want to be visible!
My question is what to do to the purlins. Should I finish then with anything before laying metal? OR should I try to cut strips of tar paper or other underlayment to protect them from the metal?? I'm worried about them degrading over time... Is there a best practice for this scenario?
Thanks in advance!!
thanks Todd. One other caveat is that I am using some clear polycarbonate panels in a few sections of porch roof for increased light. Would that advice still apply for unfinished pine under clear panels getting cooked by the desert sun??
I'm planning to build an open carport using 7/8" corrugated metal roofing. Similar to Emma, I would like to install the corrugated over continuous 2x4 purlins leaving them and the corrugated exposed and avoiding sheathing and underlayment. My question is if this method will result in condensation, even in a completely open-air environment. I am located in Massachusetts. A portion of the roof will extend over an enclosed, unconditioned shed, with airgap between the bottom of the walls and the ground and I'm wondering if purlins are acceptable in the open carport portion, are they also acceptable over the enclosed shed portion. Thanks for your help!
Hi There,
Following up on a question I asked earlier in the week regarding leaving the underside of a corrugated roof on a carport open. I am wondering if I should be concerned about condensation on the underside, even though the underside is exposed to the elements and the roof is not covering conditioned space. Thanks!
Thanks Todd, that's helpful. I do have one quick follow up question - isn't the exposed corrugated from the underside with purlins basically the same condition Emma describes in the first post on this thread? If not, how is my proposed condition different?
Thanks again.