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Princelake
Member
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# Posted: 1 Apr 2021 06:57am
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Hey guys, I’m finally moving forward with my build this year even though the price of lumber is insane. I’m looking to see where I can cut costs. I’m thinking of strapping the ceiling with 1x4s and put metal down. I run the risk of condensation so I was thinking before the metal goes down put synthetic roofing felt or even house warp on the trusses first so moisture can run down and put before getting to my insulation. When it’s raining it’ll probably be louder in the camp. Anything else to consider? Also locally the price of osb plywood is $43 and the price of smart panels are only $34. If I used the smart panels then sided the cabin afterwards would I need house warp on the smart panels? Would I be creating a space for moisture to get trapped?
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Brettny
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# Posted: 1 Apr 2021 08:16am
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You will need synthetic roof felt made for metal roofs no matter how you sheeth or strap the roof. Plywood roof sheething dosnt make it so you dont have to use an underlayment at all. It may hide the fact that you have moisture between the metal and plywood though. But cold plywood above not enough insulation can move the surface that condensation down to the surface between the insulation and plywood. I guess what I'm trying to say is plywood vs strapping should be considered more of a sheer product than a insulation, waterproofing or venting.
Have you priced out the difference in the following.
Plywood roof sheething with fiberglass insulation vs strapping and spray foam.
Spray foam allows you to get a far superior air seal and more R value in a smaller space. I have done alot of research on metal roofs and cathedral ceilings. The end all be all is really just to spray foam them. You can also use a "wrap and strap" method where you put foam board on top of the rafters and metal on that.
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gwindhurst
Member
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# Posted: 1 Apr 2021 09:04am
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I installed metal directly to 2x4 strapping and used a DIY spray foam kit. My discussion on that starts here
https://www.small-cabin.com/forum/6_9681_1.html#msg140543
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gcrank1
Member
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# Posted: 1 Apr 2021 10:18am
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Will you have any heat stacking issues? We recently had some great posts regarding making a breathing air space between the metal roofing and the roof deck. Were I roofing my place I would be doing it.
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Brettny
Member
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# Posted: 1 Apr 2021 03:41pm
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I believe when you spray foam directly on the back of the roofing or on the back of the underlayment you dont need that air space. Il have to look up if you need an underlayment between and where to spray.
The theory with no underlayment was there is no gap and no gap means the cold surface is the outside of the metal roofing. This cant be done with bat insulation because water permeates through bats.
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ICC
Member
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# Posted: 1 Apr 2021 04:56pm
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If you spray enough thickness of foam directly to the metal roofing underside that is all that is needed to prevent condensation. The foam will air seal and be the required barrier.
However the osb or plywood does more than provide a flat surface to secure the roofing panels to. The osb or plywood is a structural element. Some but not all metal roofing is rated as structural. Most, especially off the rack at a big box store is not meant to be used as a structural component.
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gcrank1
Member
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# Posted: 27 Nov 2021 03:54pm
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Ime, 'there aint no easy (money) run'
and 'if it sounds too good to be true it probably is'.
That said, IF no money needs be invested out of your pocket give it a go. If anybody wants you to 'ante up' to be involved, RUN!
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toyota_mdt_tech
Member
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# Posted: 27 Nov 2021 09:49pm
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I have metal roofs on all my structures at the cabin area, I follwed mfg specs, they wanted strapping every 2 feet or underlayment ie sheeting and then a 30# felt. I used the felt underlayment. All my areas under my roofs are not insulated, my cabin has an attic, dry climate, no moisture, same for container roof and of course, my shelter is wide open.
Look at the roofing you plan on using, in the guide they have the mfg specs, screwing schedule etc.
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