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Borrego
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# Posted: 7 Jul 2018 11:13am
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I've got a friend that I'm going to help build a cabin next season out in the desert, so I'm drawing up plans right now.
Trying to figure out how to:
1) do the overhang..... 16' x 20' building, we will have exposed rafters inside (4x8's at 32"OC w/ 2x6 TG, so they will run over 2 ft on the high and low ends (shed roof). I don't want to do the typical 'outlooker' thing because the flat 2x4's would be visible inside. I thought about running 'purlins', 4 x's and set the rafters on top, but I'm not crazy about that.
Also don't want to scab on the side outlookers because we want a 2 ft eave and they'd be too heavy.
2) Insulation - The way I'm doing the ceiling does not allow for insulation, so I'm looking into using rigid insulation on top....some of it now has a R value of 7 per inch.....any comments/ideas?
I figure some one on here has to have done this.....Thanks for the help in advance!
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toyota_mdt_tech
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# Posted: 7 Jul 2018 03:52pm
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I did my roof over container with no outlookers. I just ran the large 4X6 for top plate, extended it past to overhang point and just put a rafter in there on top of it to ridge board which was a 2X6.
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Borrego
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# Posted: 7 Jul 2018 06:28pm
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Quoting: toyota_mdt_tech I just ran the large 4X6 for top plate, extended it past to overhang point and just put a rafter in there on top of it to ridge board which was a 2X6.
Thanks....that's what I meant by 'purlins'...I was feeling it would raise the roof too high, a 4x8 on top of a 4x6....but it certainly would work. How does it look?
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toyota_mdt_tech
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# Posted: 7 Jul 2018 06:42pm - Edited by: toyota_mdt_tech
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Quoting: Borrego How does it look?
The 4X6 would raise the roof on the wall, but if you incorporated the 4X6 into your wall, IE trimmed your studs down to compensate for the taller top plate board. How far back you go in would depend on how far out it goes. Mine was 16" overhang going by memory and mine ran the entire length. I did splice it near the center. As you can see, its just an extra rafter for the overhang. The end grain on the exposed top plate and ridge board are hidden with the final trim. Very strong too. I grabbed a few of the pictures I had on hand that would best illustrate it.
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Borrego
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# Posted: 7 Jul 2018 09:48pm
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Thanks Toy, I think that show i will do it.....do you have any input as to how to add insulation on top? In order to show the TG 2x6's underneath, I will have to add rigid insulation on top and then cover that with ply....any thoughts?
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toyota_mdt_tech
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# Posted: 7 Jul 2018 10:53pm
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Can you add it from underside. Sheet top with plywood, then underneath, insulate, then cover with T&G? Add vents at bottom of bays and ridge vent at the top and air space above insulation.
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Borrego
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# Posted: 8 Jul 2018 10:03am
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You mean cut the 2x6's and splice them in between the rafters?
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toyota_mdt_tech
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# Posted: 8 Jul 2018 10:39am - Edited by: toyota_mdt_tech
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OK, seen you want fully exposed rafters on inside. OK, in the log home fashion (same principle), they would sheet the entire rafters on top with 2X6 like you want to do, then rafters all exposed inside along with the T&G. Then on top of the 2X6 T&G you would frame in, just like a stud wall your insulation cavities. Install insulation to meet code, allow breathing, then sheet over that then add 30# felt and roofing. Makes for a thick roof. This can be a thick stud wall basically, maybe even 2X10 or 2X12. But when done, well insulated, super strong too. You could put the end ones it, them space the rest evenly. You could use a 4X6 every 4 feet, would look nice from the inside.
Another option is to just sheet it like I mentioned, from the inside with the T&G, no exposed rafters, insulation between them (you could do the lookouts normally at this point), then install fake rafters over top of the installed T&G from the inside. Use some ledgerlocks or timber locks and secure them to the T&G, this would make it lower cost and quicker.
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Mike 870
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# Posted: 8 Jul 2018 06:56pm
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I did something like what you are wanting to do. I have a timber framed roof, I used rigid insulation on top of the ceiling. I put 6 inches for R39 with no thermal breaks. It worked great, but it was tedious. I wanted it vented as well so I strapped everything down rather than re-sheathing over the insulation, Video: https://youtu.be/viabiXnrcjs
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Borrego
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# Posted: 8 Jul 2018 09:41pm
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Thanks Toy...I will do one of the above, prob with the thick roof....
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