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DJR
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# Posted: 20 Nov 2020 11:16am
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Hey all, I'm new to the forum. Did some searching to see if anyone has posted about a similar situation, but didn't find anything. We bought a 20X24 cabin a couple of years ago. Northern MN, no insulation in the floor or ceiling. It has a cathedral ceiling.
Looking up at the cathedral ceiling, you see the underside of the 2X6 tongue and groove that forms the roof deck. The T and G is attached to a log beam at the peak, two other log beams about half way down, and then it rests on the stud walls. There is no plywood on top of the T and G. The roof is finished with tar paper and metal.
As you can imagine, we go through a lot of firewood trying to keep the place reasonably warm. The cabin sits on posts and is not skirted. I'm exploring ways to insulate the roof.
I don't want to work from the inside of the cabin since we love the look of the T and G and the log beams and posts. I'm considering pulling the metal off, laying rafters on top of the T and G to create a cavity, insulating in between them, decking with plywood, then reinstalling the metal. Any advice would be appreciated.
By the way, insulating the floor from the underside is not practical since the lot is sloped and one side of the cabin is almost on the ground. Pretty tough to get under there. I am also thinking about skirting to reduce airflow under the cabin in the winter, possibly with removable panels to increase ventilation in the summer as someone else on the forum did.
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ICC
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# Posted: 20 Nov 2020 01:59pm - Edited by: ICC
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Quoting: DJR I'm considering pulling the metal off, laying rafters on top of the T and G to create a cavity, insulating in between them, decking with plywood, then reinstalling the metal.
You're on the right track, but use foam sheets rather than infilling between new 2x material.
I am assuming the roof is structurally sound.
Decide how many inches of foam you want or need. Either by you deciding what R-value you will use or if meeting code is important go by the climate zone guide for your location. There will also be a minimum R-value to ensure that the roof will stay warm enough inside to eliminate any concern about moisture condensing on the inside surface of that decking material; varies with climate zone.
Sheet foam insulation should be installed in two or three layers with all the seams staggered from one layer to the next.
The top layer can be either sheathed with a 1/2" or 5/8" OSB or plywood or 2x4 (laid flat) can be inlaid into the top foam layer, positioned to simulate rafters. The sheeting or 2x4 are secured through the foam to the bottom layer of T&G 2x6 decking. You just have to select the proper screw length to prevent penetration of the visible 2x decking.
Fastenmaster makes a series of screws called HeadLOK. They are available in lengths to 18" IIRC. They have self-drilling tips and use a "star" drive; like a Torx but their own special drive size. You can find the screws in many online locations; buckets of 250 screws make the price reasonable. Download link to a document on HeadLOK use.
The metal roofing can then be screwed to either the top sheets or the inset 2x4. Because the roofing has already been used installing the metal over sheathing would be best.
There are a few different ways to ensure the roof assembly is air sealed and water sealed. They can be found online. Google can help find....
such as
https://basc.pnnl.gov/resource-guides/above-deck-rigid-foam-insulation-existing-roofs
or
https://www.greenbuildingadvisor.com/article/how-to-install-rigid-foam-on-top-of-roof -sheathing
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AKfisher
Member
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# Posted: 20 Nov 2020 06:06pm
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ICC has good info on your roof being insulated.
For your floor, can you remove the flooring, plywood and insulate that way? Could also get some pluming or wiring done that way as well.
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fiftyfifty
Member
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# Posted: 20 Nov 2020 06:54pm
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Here is 1 idea: https://baileylineroad.com/insulating-a-cabin-roof-and-floor/
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DJR
Member
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# Posted: 21 Nov 2020 10:39am
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Thanks for all the info! I'm talking to a contractor friend and he steered me in the same direction. That leads me to two more questions. 1.) To vent or not to vent. 2.) How to keep carpenter ants out of the foam. I've already had problems with ants in the tongue and groove ceiling. I've read that they love to tunnel through the foam. It seems like that would potentially defeat all the seam taping and create a wonderful conduit for moist air which would then lead to rot.
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