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pxtn
Member
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# Posted: 29 Jan 2025 01:33pm
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I’m renovating a cabin that has a 12/12 roof. The rafters are 2x8 on 24”oc, but they used a 2x8 for the ridge board, as well. That leaves ~2” of the rafter cut end without any purchase on anything. Structurally, I know it isn’t the end of the world, and it hasn’t been a problem for 20 years, but it’s a big deal that needs correction. Especially before an inspector comes around. What are my options? Can I scab a 2x4 the underside to fill that? I’d prefer not to pull the top off and replace the ridge board entirely. Thanks!
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gcrank1
Member
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# Posted: 29 Jan 2025 01:57pm
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How long is that ridge? Any sag in the middle? If so it would indicate the walls are bowing out. Imo, if that isn't happening after that many years there isn't a problem. But Im just a guy with an opinion.
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pxtn
Member
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# Posted: 29 Jan 2025 04:06pm
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24’ ridge. 16’ and 8’. The whole building is perfectly square. Zero sag. It has 2x8x12 collar ties on every pair
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Grizzlyman
Member
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# Posted: 29 Jan 2025 04:30pm
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I don’t know why you couldn’t just fill the gap with a 2x2. It’s not structural so as long as there’s something solid to sandwhich I think it’s be allright. A lot of ridgeboards are even 1x’s
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DaveBell
Moderator
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# Posted: 29 Jan 2025 07:54pm
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It appears from this discussion it is not an issue.
https://forum.nachi.org/t/ridge-board-smaller-than-rafters/39825/15
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DRP
Member
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# Posted: 29 Jan 2025 08:09pm
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There are 2 different things that can be at that location, and there can also be nothing.
In your case that is either a ridgeboard or a ridgebeam.
If there is not a ceiling or ties in the lower third of roof height then the ridge needs to be designed as a beam with the rafter weight hanging from the ridgebeam.
If there are ties or ceiling joists creating the simplest truss, a triangle, then the ridgeboard is simply an alignment aid for framing and it is code to use a 1x. It is not a beam, the triangle is a stable assembly sitting atop the walls.
Triangles cannot change shape, 4 or more sides can change shape... "truss" things.
Store bought trusses are just assemblies of stable triangles, engineered to the slenderest members possible. Rather than a ridgeboard for alignment you tack a strip or two to hold it and use the sheathing for permanent alignment.
Best practice when faced with that situation with a ridgeboard, where the plumb cut at the top of the rafter is taller than the ridgeboard, is to put the ridgeboard low, in plane with the bottom heel of the plumb cut. Then set the finishing scab on top of the ridgeboard and offset the splices in lengths. The dangling heel is the most prone to splitting, that is where the rafter need support the most, make sure the heel is tight, I don't care if the toe is open a little and old timers would to allow for shrinkage. Think about splitting under load. In this case slip one under and shim tight and it'll strengthen it a bit. There should be a tie across from rafter to rafter under the ridge. That is the actual "collar tie", a "rafter tie" is in the lower third of roof height.
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Brettny
Member
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# Posted: 30 Jan 2025 10:15am
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Really a ridge boards only purpose is to hold the rafters while there installed. It's not a ridge beam so the length dosnt matter. My roof dosnt even have a ridge board or ridge beam.
If you have questions call the Inspector.
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DaveBell
Moderator
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# Posted: 30 Jan 2025 11:28am
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From what I read, a ridge beam is required for roof pitch 3:12 and less. A ridge board can be used for 4:12 and higher. I always over build, ridge beam and ties for any slope. Typically a good practice is to use one board larger for the ridge board like 2x8 for 2x6 rafters.
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DRP
Member
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# Posted: 31 Jan 2025 06:06am
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Here's a bit from that chapter;
R802.2 Design and construction. The roof and ceiling assembly shall provide continuous ties across the structure to prevent roof thrust from being applied to the supporting walls. The assembly shall be designed and constructed in accordance with the provisions of this chapter and Figures R606.11(1), R606.11(2) and R606.11(3) or in accordance with AWC NDS.
R802.3 Ridge. A ridge board used to connect opposing rafters shall be not less than 1 inch (25 mm) nominal thickness and not less in depth than the cut end of the rafter. Where ceiling joist or rafter ties do not provide continuous ties across the structure as required by Section R802.5.2, the ridge shall be supported by a wall or ridge beam designed in accordance with accepted engineering practice and supported on each end by a wall or column.
R802.4.2 Framing details. Rafters shall be framed opposite from each other to a ridge board, shall not be offset more than 11/2 inches (38 mm) from each other and shall be connected with a collar tie or ridge strap in accordance with Section R802.4.6 or directly opposite from each other to a gusset plate in accordance with Table R602.3(1). Rafters shall be nailed to the top wall plates in accordance with Table R602.3(1) unless the roof assembly is required to comply with the uplift requirements of Section R802.11.
R802.4.4 Rafter supports. Where the roof pitch is less than 3:12 (25-percent slope), structural members that support rafters, such as ridges, hips and valleys, shall be designed as beams, and bearing shall be provided for rafters in accordance with Section R802.6.
& etc, there is a lot to study in that chapter.
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