Our home is a double wide that does not have an attic. Built in 1970 with an original cedar shake roof that was leaking a couple years ago. I replaced the roof with asphalt shingles. When replacing the roof, I pulled up one of the plywood sheathing panels and noticed fiberglass batting that looked about 4" thick, just basically laying on top of the plywood ceiling panel on the other side of the rafters. The rafters are 2x6. So there is about a 2" space between the roof sheathing and the batting. I didn’t think much about it and proceeded to install felt and shingles. As I said, there is no attic, just a 5/8" plywood ceiling on the under side of the rafters. Since reroofing, moisture has been collecting on the ceiling, of coarse causing mold at the peak. I used one of those laser temp sensors to measure the temp differences and noticed the peak of the ceiling is about 10-15 degrees hotter than the middle of the ceiling. I added ceiling fans to keep the air circulating and this has helped a lot but doesn’t address the issue. I also should mention that there is no moisture barrier on the ground under the home either. I’m not sure how much a part that plays in the problem, but it’s probably a huge source of moisture. What are my options to resolve this issue? Is it a must to strip the roof and sheathing off to stuff the rafter spaces with thicker batting? I’ve thought about cutting a hole in eack ceiling space and having insulation blown in on top of the batting, but besides being a lot of work, probably not the best idea. I’m going to put a moisture barrier under the home for sure, but I doubt that will resolve the ceiling moisture problem. I’ve wondered if installing ridge vent would help, but there is no way to install intake vents as there is no soffit on this house. I’m guessing the old cedar roof insulated the roof enough to not create this problem. Any advise would be greatly appreciated.
If you go the insulation route go with sprayed in foam.
If you want to get some sort of intake and use a standard ventilation system you can use a product called smartvent or edgevent.
Many local building codes (CA), as well as major shingle manufacturers, require compliance with a minimum 1-inch airspace between insulation and roof sheathing.
A main contributor to your problem is unfortunately the asphalt shingle material itself. Wood shake does a great job of insulating and ventilating any moisture that may have crept up that way. Moisture can travel up Your asphalt shingle is absorbing a lot more heat. Poor Insulator Diffusion usually carries moisture from a warm place to a cold place. Hot roof = Interior ceiling moisture
Ceiling fans will address the interior climate, but the moisture is caused by an unvented roof system. And, a moisture barrier under the home will not adequately address everyday home uses such as cleaning ourselves and clothes.
- Do not add insulation to the “2’ airspace”
- A proper combination of eave and ridge venting is a candidate for this. I like the “eave venting” products/methods @Axiom brought up. For this to work, the 2" airspace must remain
I just keep getting up,
Thanks for the info. Would I have to re-shingle the roof to install those eave vents? I’m hoping I could carefully peel up the row at the top of the vent, slip it under and re shigle over the bottom of the vent. This is in sunny So Cal, near the coast, so it gets plenty of sunshine and humidity too sometimes.