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WILL1E
Moderator
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# Posted: 9 Feb 2021 13:02
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So I've started looking at alternative roofs instead of doing a shed roof. I really like the look of these to break up the gambrel roofline and make it look like something other than a barn.
In the permit documentation for that shed, they give details on the roof. How does the gable part work without a ridge beam? I thought for just about any roof besides shed and gambrel you had to have a ridge beam.
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Irrigation Guy
Member
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# Posted: 9 Feb 2021 13:40
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Why not to gable with dormer? To me this is a classic look, much more appealing than gambrel.
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Nate R
Member
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# Posted: 9 Feb 2021 13:52
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They have sort of a truss thing going on, so no ridge beam needed.
Nice to see the calcs shown to give a BI confidence that you're building strong enough trusses....Pretty hard to get DIY trusses approved any other way, I bet.
BUT, notice that they only spec to 30 lbs/sf snow load. (Ground load). Your area requires 40..... (See the dormer truss page....They show 30 PSF ground snow/21 roof snow.)
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WILL1E
Moderator
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# Posted: 9 Feb 2021 14:24
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Quoting: Irrigation Guy Why not to gable with dormer?
I'm 6'5", so the more square footage in the loft that i can walk around in without having to hunch over or duck the better. And i feel gambrel gives me that option.
Quoting: Nate R BUT, notice that they only spec to 30 lbs/sf snow load.
Yeah i saw that. That was going to be my next question as to why it was so low. My assumption was because of the 2x6 roof construction. Also, i don't believe i need to have any calc per BI.
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ICC
Member
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# Posted: 9 Feb 2021 15:34
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Quoting: WILL1E Also, i don't believe i need to have any calc per BI.
That does not mean that the actual physics of a 40 lb snow load is going to take a holiday.
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Nate R
Member
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# Posted: 9 Feb 2021 16:42
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Quoting: ICC That does not mean that the actual physics of a 40 lb snow load is going to take a holiday.
Yeah, and they are looking at 30 lb GROUND snow load, and saying it'll be 21 lbs stuck on the roof. WI requires 40 lb ROOF snow in the northern part of the state.... I believe they do allow for slope, etc to account for less roof snow load, but still...certainly been some roof collapses in the last few years up there due to snow/rain/snow or snow/ice snow loads adding up.
You might consider looking at room-in-attic trusses...maybe chat with the Menards Truss people (online chat) and see what they can do that can accommodate your height...? Maybe they can do a simple triangle truss with small knee walls?
I know they can do gambrel or gable room-in-attic trusses. A 10/12 gable roof 24' span can give you a 12' wide, 7'6" tall room, so I wonder if a smaller span, 12/12 roof, maybe even raised heel?....can get you like 8 or 9 feet wide and 7 feet tall?
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WILL1E
Moderator
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# Posted: 10 Feb 2021 07:59
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Quoting: ICC That does not mean that the actual physics of a 40 lb snow load is going to take a holiday.
Agree..what i was implying is that i don't believe i need to show official calculations.
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WILL1E
Moderator
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# Posted: 10 Feb 2021 08:16
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Back to my thread starter question, i also found it interesting they only use 1 beam to hold the eave walls from bowing out. They then tied all the loft joist to that beam and to ledgers on the gable walls.
Is 1 beam really all that's need to keep the eave walls from bowing out?
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jsahara24
Member
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# Posted: 10 Feb 2021 08:28
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Quoting: WILL1E Is 1 beam really all that's need to keep the eave walls from bowing out?
If you use a ridge beam, or trusses in this situation, it typically eliminates the need for rafter ties....
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Brettny
Member
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# Posted: 10 Feb 2021 08:34
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If your going to do double dormers on a gambrel roof I would just build a 2 story cabin. Essentially that's what your building anyway but making things more complex with a section that's a gambrel.
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ICC
Member
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# Posted: 10 Feb 2021 14:43
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Quoting: WILL1E Is 1 beam really all that's need to keep the eave walls from bowing out?
As jsahara24 pointed out, IF the ridge is a beam, not just a simple ridge board, with proper supports, then there are no horizontal forces from from the rafters to the walls.
Remember that finding a picture of something that someone built does not mean it was correctly designed or correctly built. Building a loft floor with joists in that orientation is not structurally sound.
I second brettny's thoughts on building an actual two-story building rather than building dormers and making your construction more complicated than it needs to be. Professional builders screw up details on dormers.
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gcrank1
Member
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# Posted: 10 Feb 2021 14:52
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How about a split, 1 1/2 story to 2 for the 'loft' and whatever roof you like over the remaining one story?
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WILL1E
Moderator
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# Posted: 11 Feb 2021 08:48
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I think i'm just gonna go towards a standard full length gambrel roof with 10ft eave walls and run the loft joist into the walls with jack studs under them. I'll post some designs soon for feedback.
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Brettny
Member
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# Posted: 11 Feb 2021 09:12
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How wide is the cabin? Generally your roof height would be half of the building width, useing equal length roof rafters for the gambrel. So 16' wide cabin would be 8' high above the top plate. To figure head room you would take roof height, subtract floor joist,sub floor and rafter thickness. Or you could just use the gambrel roof calculator. https://www.blocklayer.com/roof/gambreleng.aspx
I suggest adding a lower gambrel also, moves the drip line away and can help with sliding snow.
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WILL1E
Moderator
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# Posted: 11 Feb 2021 09:39
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16' Yup, did the circle method to get my roof height and rafter lengths. I'm doing the taller walls and dropped loft floor so that i (6'5" tall)can make the most of the space upstairs. Plus, i have a stairs going along 1 eave wall and turning 90deg to a catwalk in the middle of the cabin. So i need head clearance as i go up the stairs.
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Nate R
Member
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# Posted: 11 Feb 2021 10:06
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Quoting: WILL1E Plus, i have a stairs going along 1 eave wall and turning 90deg to a catwalk in the middle of the cabin. So i need head clearance as i go up the stairs.
That gets to be tricky!
Sounds reasonable though!
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