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Thread: Roof

  1. #1
    Member akriverunner's Avatar
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    Default Roof

    I am getting ready to put the roof on my cabin soon and I am trying to decide what to do. The pitch will be 9/12 and I want to put r-38 in the ceiling. I am thinking of using 11 7/8 bci's or maybe stacking a 2x6 on a 2x10 and plating them together with plywood that way I can run the 2x6 longer at the eve. The roof has to be cathedral for the loft and I can't get trusses to where I am.

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    Member 4merguide's Avatar
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    Just go with the bci's.....
    Sheep hunting...... the pain goes away, but the stupidity remains...!!!

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    Member greythorn3's Avatar
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    you cant get any trusses in wasilla? u gotta be kidding me. have you tried sbs?
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    Quote Originally Posted by akriverunner View Post
    I am getting ready to put the roof on my cabin soon and I am trying to decide what to do. The pitch will be 9/12 and I want to put r-38 in the ceiling. I am thinking of using 11 7/8 bci's or maybe stacking a 2x6 on a 2x10 and plating them together with plywood that way I can run the 2x6 longer at the eve. The roof has to be cathedral for the loft and I can't get trusses to where I am.
    Why so very heavy on the roof structure? With a 9/12 pitch, the thing will barely be out of plumb!

    It takes more than twelve feet of fresh snow to equal about 35-pounds per square foot of live load. Your 9/12 roof won't hold that sort of snow depth. After six feet, snowfall becomes WALL load, not a roof load, so I can't see how you'll ever get to even a 40-psf roof load, except with the dead load contribution of materials used, maybe six or eight pounds psf. Have someone capable of roof design do the calcs for you. Save some money, have a good, strong roof, and make the transporation of materials a little easier in the bargain.

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    Member Dirtofak's Avatar
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    Site built trusses worked for me.







    From www.countryplans.com

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    Member greythorn3's Avatar
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    them look great!
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    I am about to do my roof too. I am going with a double 2x10 for the ridge beam and 2x8 for the rafters. I am only doing R-19 for the roof and walls. The cabin is 24x24. I will either do an 8/12 pitch or a 9/12 pitch. My buddies roof let off about 3 1/2 feet this winter while we were enjoying the woodstove, pretty scary makes me wonder. You do not want to hang out on the slide side in winter, you would of been dead when that let go. With that being said good luck to ya and post pics please. What are you doing for a woodstove?

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    Rafter sizing is determined by horizontal span. Pitch has nothing to do with it. Overkill is overkill. Money and effort wasted.

    If the structure is going to be heated 24/7/365 then there's good cause to insulate to R-38. For occasional use cabins that'll only see heat when you're there? Your heating capacity will be greater than necessary and less insulation will work fine. The initial heat-up of a cold cabin has little to do with insulation value. Once you get the mass warmed up you'll have the heaters choked down whether your ceiling is R-19 or R-38.

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    Member dkwarthog's Avatar
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    Quote Originally Posted by Grizzly 2 View Post
    It takes more than twelve feet of fresh snow to equal about 35-pounds per square foot of live load.
    You must be referring to that flaky Florida snow!!!


    Really nice work dirtofak, that looks great.

    Myself, I'm a fan of overkill to some degree. When there is 6 feet of heavy dense snow on your roof and it starts raining, you can rest assured that you got it covered.

  10. #10
    Member akriverunner's Avatar
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    i want r-38 in the ceiling because the cabin will be heated about 6 months a year, i plan on leaving the toyo set at 50 when I'm not there. r-38 is 12" and i need an air gap so i was thinking about 14". i would have to use the simpson hangers that are adjustable on the wall and one at the ridge and one is $8 and the other is $10 so that would be a spendy route. I'm kinda leaning towards a 2x6 stacked on a 2x10 like dirtofak did above.

  11. #11
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    Build your own parallel chord trusses. Simple to build, cheaper, lighter, easier to ventilate, and the thermal separation is a plus as well.

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    Member AKDoug's Avatar
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    Quote Originally Posted by Grizzly 2 View Post
    Why so very heavy on the roof structure? With a 9/12 pitch, the thing will barely be out of plumb!

    It takes more than twelve feet of fresh snow to equal about 35-pounds per square foot of live load. Your 9/12 roof won't hold that sort of snow depth. After six feet, snowfall becomes WALL load, not a roof load, so I can't see how you'll ever get to even a 40-psf roof load, except with the dead load contribution of materials used, maybe six or eight pounds psf. Have someone capable of roof design do the calcs for you. Save some money, have a good, strong roof, and make the transporation of materials a little easier in the bargain.
    Mort- You are a good dude, but you are way off on this. I actually measured/weighed our snow this year and 160" of snowfall (settled to a mere 48") weighed 76# per square foot. When we sell trusses we spec them at 100# snowload. A 9/12 is far from vertical, in fact it is only 36.87 degrees from horizontal. There is no magical point where a roof rafter suddenly distributes all it's load to the wall. Yes, the wall and the ridge carry the load at the ends of the rafters, but you cannot exceed the load carrying capability of the rafter either.

    Anyhow, there is not enough information given in the original post to help decide what would be the best choice for a roof system. If possible, could you post a floor plan with dimensions?
    Bunny Boots and Bearcats: Utility Sled Mayhem

  13. #13
    Member akriverunner's Avatar
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    24x36, rafters running the 24' length I'm doing half the cabin with an 8' wall and upstairs floor and a +- 3 foot pony wall to match a 12' wall for the front half of the cabin. I'm planning on a 9/12 pitch and I need to get r-38 in the roof and have room for a cold air gap.

  14. #14
    Member AKDoug's Avatar
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    With that pony wall, if you are using rafters, you are going to need a load bearing ridge. Otherwise the roof can't resist lateral thrust. To get a load bearing ridge that long, that you can handle without a crane, is going to require several posts or walls that can help carry the load. These walls or posts are going to need a load path all the way down to the foundation. Last winter even my 12/12 pitch steel roof carried over 100lbs per square foot at one point in the winter. For your building that would have meant an astounding 86,400 lbs of snow load!! Do not underestimate that need for a well designed roof. I would seriously look into Mikes' (dirtofak's) roof style.
    Bunny Boots and Bearcats: Utility Sled Mayhem

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    Member Dirtofak's Avatar
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    Just a couple of notes on my trusses. My cabin was 20X32. That meant the long boards had to be 16' long. They are 2X6X16'. 12/12 pitch and it would still build up a snow load on the standing seam metal roof. I cut all the bracing on my table saw before hauling it out. All bracing was glued and nailed. I also cut the squirrel blocks and put the mesh on them. With 2X6, you must use the cardboard insulation barriors to prevent the insulation from blocking the airgap. I sheeted with OSB, 2 rows of *****athane, then tar paper.

    You can also modify them to have a peak roof inside. I chose to limit my ceiling to 7'6" to lower the area to heat. Rustic ties would look awesome for this. Some roughcut would be the ticket.

    I only had to shim 1 truss to make the ceiling flat. It was only off a 1/4 inch. Not bad for an old guy and a hippie.

    My next cabin will only be 16' wide.

  16. #16
    Member akriverunner's Avatar
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    doug do you think if i stacked a 2x6 on top of a 2x10 and pretty much copied what dirtofak did with the bracing and making the peak flat inside it would work? i don't want to have to put a ridge beam in.

  17. #17
    Member AKDoug's Avatar
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    I think you would be good to go, but I do not have any engineering to back that up.
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