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Considering replacing a 23 year old screw down metal roof. The existing roof has an asphalt paper underlay and would rather go with a better product. Most of the roof except the porch is a 45 degree slope and there is no attic. Under the asphalt is OSB board 8" rafters with batt insulation and then drywall scrim coated ceiling. Worried about condensation with different underlays with this set-up. I do have soffit vents but not sure how much good they do with batt insulation between the rafters. Am wanting to get roofing quotes but need to make sure they are giving me a good system that will last. I have read the roof will outlast the asphalt underlay. BTW roof has three dormers. Here are some images of the original roof install. If you need more info let me know. Thx.
1/7/2023
Have you ever checked to see if you have had high moisture levels or condensation? Based on what you've told us, I feel you are at risk as things are. Just trying to figure out if there are indeed existing problems. Here's a webinar that I'd suggest you watch in order to understand some of the dynamics that are at play: https://www.youtube.com/watch?v=NYwD9CWveKY
Isaiah Industries, Inc.
1/7/2023
Thanks for the reply. Very interesting video. I have not checked condensation levels. Without removing drywall it is very inaccessible. I recently noticed what appears to be a small water stain line that I would bet is at a drywall joint within a few feet of the peak in the ceiling. It is actually a very light brown line about a 1/4"-1/2" wide and at the most 3-4" long. Barely noticeable. I cannot see any noticeable problems on the roof at or above it on the outside even with the help of a large camera zoom lens. No other stains on the ceiling throughout the entire house. We recently experienced the coldest temperatures I have seen in my 20 years up hear in western North Carolina and with a 25 mph wind we well in the negative temps. I had thought maybe condensation had formed high up maybe even under the ridge cap, dripped down thru the insulation to the drywall and then to the first joint. The ceiling is sealed very tight from the living area below. Whatever I do with a new roof I don't want to make the condensation problem worse for sure. I have one of the larger roofing contractors that covers our region coming out to do an estimate. Hopefully he has some expertise in this area.
1/8/2023
I am concerned what may be going on. I realize that tests / checks will be invasive though. One way to do it from the outside would be pullout resistance tests up near the ridge. My concern is that you really don't have a vapor barrier between the living space and the area beneath the roof. Once moisture gets into that area, it will condense on cold surfaces. One of the realities of a metal roof is it will create a cooler roof deck, increasing the chance of condensation. This situation is always worst at the peak because of the way warm air rises and warm air carries moisture. My thought is that ideally you will remove the old roof, check the decking condition, replace it as needed, and then install a vented cold roof on top of the existing followed by another layer of decking and the new roof. Now, yes, that is a lot to do. If the current decking turns out to not be in bad shape, I would suggest installing a breathable underlayment over the deck and then an entangled mesh to create a thermal break between the new roof and the decking. Feel free to call me if you'd like to talk this through. 1-800-543-8938 ext 201
Isaiah Industries, Inc.
1/8/2023
Agree with the breathable underlayment for sure and the mesh sounds good. When they replaced the screws on the roof about 6 years ago they told me they all "bit" good which they explained meant there was not any serious rot underneath. I noticed looking at the pictures they stapled the batt insulation backing to the bottom of the joists hopefully leaving some available circulation above. I am going to remove one of the soffit vents and if need be remove a section of the soffit and see what kind of air space I have between the insulation and the deck. I am no expert but I would think if I had a big condensation problem it would have showed up earlier than at the 23 year mark especially with more/larger stains on the ceiling. If the ceiling is sealed tight from the living space how does moisture get in from the living space below? They scrim coated the entire ceiling throughout the house and other than a few penetrations for ceiling fan electrical boxes it is really tight. I love my metal roof but maybe shifting to a shingle roof with my situation may be more cost effective if it is less likely to cause condensation.
1/8/2023
Thanks. Good thoughts. I think you're understanding the dynamics well. The airspace beneath the decking, unless vented, really doesn't accomplish a lot. It would still be a place for moisture to collect and condense potentially.
One thing to think about is will anything potentially be done to the house down the road to make it more airtight such as new windows or doors? That will increase the potential for condensation.
I do think that switching to a metal roof without exposed fasteners is helpful. Any exposed fasteners over time that may leak a bit would introduce more moisture into the roof assembly, increasing the potential for condensation.
I feel like if no major changes are planned to the house and no major issues are currently found, then switching to breathable underlayment (still using ice and watershield if required by code on the perimeter) and the entangled mesh or some other way of creating a thermal break between the metal and the roof deck will create a good long term solution for your home.
Isaiah Industries, Inc.
1/9/2023
If condensation is a concern but you still want to make your full roof area watertight, you can nail in a 30# felt and go over this with a High Temp self-adhered metal underlayment.
1/9/2023