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PepperDog
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# Posted: 16 Nov 2020 05:19
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Greetings. I have a small recreational cabin I built by myself next to a waterfall on the edge of a cliff overlooking a river in the Olympic Rainforest. I have no building experience or knowledge at all, so everything was done by trial and error. It's small enough that I didn't have to worry about permits or codes and it's totally off the grid.
The main part of the cabin is 8'x8', two stories. The second floor has a corrugated metal roof (I love the look of it) that I attached directly to 2x4s. It's strong and secure and looks beautiful and my cabin is wonderful and everything I've ever dreamed of. I absolutely love it!
But, now that it's colder outside, the roof has developed condensation issues. I've done some research and discovered I built it wrong, should have put OSB underneath it, etc. etc. etc. I can't go back and undo my errors; I need to figure out how to fix it. What would be the best way to deal with this? I'm thinking about installing rigid foam insulation boards between the 2x4s, which are spaced roughly one foot apart. And then maybe a plastic vapor barrier under that or running another thin sheet of rigid foam insulation under the 2x4s and rigid foam.
Would this work? Do I need to have ventilation holes and where would I put them? Along the insulation layer? Or underneath in the main cabin area? None of the cabin is insulated yet, in part because there really hasn't been any need, and also because of limited resources. It rarely falls below freezing, and my little propane space heater does a great job.
Whatever I do, it has to be done by me and my battery power tools. And, everything has to be carried in by hand. (If you want to check it out, I've blogged my experience at https://www.river-song.com/.)
Thank you.
Metal roof condensation
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My cabin
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Bruces
Member
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# Posted: 16 Nov 2020 05:40
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One of the great things about metal roofing,is yes you can actually remove it and re use it ,so climb up there ,unscrew it ,do what you need to do ,and screw it down afterwards .You can’t do that with shingles .
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Brettny
Member
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# Posted: 16 Nov 2020 06:38
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Yea I would remove the roofing and start over. 2x4s layed flat like that for rafters is not a good idea. Theres no strength in them layed down. If your useing them as strapping that's fine.
I would remove the metal, put down foam board then strapping.
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toyota_mdt_tech
Member
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# Posted: 16 Nov 2020 07:58
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Remove metal roof, install a good plywood underlayment, dont use OSB, use real plywood and then a good 30# felt layered to shed moisture down and out, screw the roofing right back down.
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PepperDog
Member
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# Posted: 17 Nov 2020 13:10
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Thanks for your comments. An engineer friend reviewed my plan, revised it a bit, and it will get me through winter. I will have to hire someone to redo the roof for me this summer. With carpal tunnel and arthritis, it's too big of a job for me alone. But, I'm planning to add another 48 square feet this summer, anyway, so this will be a good time to do it.
I know using 2x4s flat is not accepted practice. I researched load bearing capacity before I laid them that way. Where my cabin is, I don't have to worry about snow load, just falling trees. If a tree falls, it doesn't matter how strong my roof is. The whole thing will be a pile of matchsticks. However, with a 2x4 every foot, the roof is strong and can support several people without even flexing. In addition, according to the snow load calculators I used, it should be able to support at least six inches of very wet snow. Laying them flat gives me an additional two inches of headroom, which is important with me being 6' tall. But, since I have to hire someone to redo the roof anyway, I'm going to see about raising the roof another foot this summer.
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Desim
Member
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# Posted: 19 Nov 2020 09:21
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Going to mention that I have had several garages with what is commonly called double bubble foil insulation.
Love it! not much insulation value but it keeps the interior as cool as ambient temp. and stops condensation.
Still have to pull the roof off but it can go against the roof itself and will have a white side facing interior.
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paulz
Member
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# Posted: 19 Nov 2020 11:39
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Quoting: PepperDog Greetings. I have a small recreational cabin I built by myself next to a waterfall on the edge of a cliff overlooking a river in the Olympic Rainforest.
Sounds disgusting! 
Going to do a metal roof carport next year, glad you brought this up.
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gwindhurst
Member
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# Posted: 19 Nov 2020 11:43 - Edited by: gwindhurst
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You could use closed-cell spray foam insulation directly onto metal roofing. You can purchase DIY kits.
For example: https://tigerfoam.com/sprayfoaminsulation/order-products/spray-foam-kits/
-OR-
http://www.sprayitgreen.com/
Also, here's an article regarding "hot roofs":
https://www.structuretech.com/blog/hot-roofs-minnesota#:~:text=Why%20are%20they%20cal led%20'hot%20roofs%3F'&text=When%20spray%20foam%20is%20applied,are%20often%20called%2 0hot%20roofs.
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PepperDog
Member
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# Posted: 26 Sep 2021 20:24
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Update: I went ahead and hired a professional roofer. We removed the corrugated metal and installed OSB decking, 2" foam board insulation, roof felt, furring strips, and then reattached the original corrugated metal over the top of all that. It's now well insulated and I shouldn't have any issues with condensation now. Thank you for all your comments! I learned a lot.
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toyota_mdt_tech
Member
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# Posted: 27 Sep 2021 15:48
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Did you flip rafters up or still laying flat?
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PepperDog
Member
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# Posted: 27 Sep 2021 17:11
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I left them laying flat. I consulted with two engineers and two experienced carpenters, and all agreed because the roof span is so short (8') and the rafters are only 9" to 10" apart (one every foot), it's strong enough for the area. We rarely get snow, so I designed it to support 8" of very wet snow, just in case. This past winter, we actually got a foot of snow, and the roof held up great. With the new decking, it's even stronger.
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