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rick7033
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# Posted: 21 Jun 2023 05:08pm
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I've got a 12' x 16' sunroom. I have a roof w/ a 6.75/12 pitch, with a 12' 2x8 ridge board, 10' 2x8 rafters 16" OC, and 16' 2x8 ceiling joists 16" OC spanning the room. One side is tied into the primary house wall, the other a 16' gable end exterior wall. The other two bearing walls are exterior as well. All exterior walls have sliding glass doors with 2 2x8 headers.
I would like to eliminate the ceiling joists and do an open room. I will probably still install collar ties near the top for a flat section & safety factor as well.
I calculated out I need a single 2 x 16 ridge beam or 2 2x10s to span the entire 12' section as a ridge beam. I was thinking about butting a 2x8 section directly under the existing 2x8 ridge board and then bearing these down to the existing house exterior wall and the gable wall as well.
Are there any issues with this or should I double up 2 2x10's underneath the existing ridge board?
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ICC
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# Posted: 21 Jun 2023 11:27pm
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I am curious how the calculation to determine the size of the ridge beam was done. ??
Constructive comments are difficult when we don't know the snow load, the lumber species or grade....
As well as the ridge beam needing to be sized properly there is the question of the size of column supports and the foundation those columns are bearing upon.
While adding, butting, another 2x8 under the existing ridge board may seem viable there are issues that may not be obvious. Two same size, boards edge stacked like that do not necessarily have double the strength of one. In other words a true 2x16 is stiffer than one 2x8 stacked on another. A load applied to the stacked 2x8 will cause slipping at the interface of the two 2x8. That could possibly be restrained with mechanical fasteners. However I do not know how to calculate that. A factory glulam beam has no slippage of fibers when a load is applied (within design limits).
Quoting: rick7033 I will probably still install collar ties near the top...
Collar ties are an important component for a gable roof assembly when it comes to keeping the ridgeline connections from separating. I only mention this a many people confuse their purpose woth rafter ties. https://www.nachi.org/collar-rafter-ties.htm#:~:text=A%20collar%20tie%20is%20a,permit ted%20to%20replace%20collar%20ties.
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rick7033
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# Posted: 22 Jun 2023 05:45am
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Thanks ICC -
Here's the site I used to calculate, it was the site that actually gave me the idea to do a single ply.
https://learnframing.com/wood-beam-calculator/
I used 15 psf roof load and 30 psf snow load. We rarely get any snow here in southern va, so I didn't douple up for a live load. Used #2 Pine as a safety factor too.
The other part I like about this idea is that w/ a 2x8 rafter and a 2x8 ridge board, my rafters don't fully bear on the ridge board. This would fix that. If I go w/ 2 2x8s for the beam, I will likely add a 2x2 to fill this gap and then notch the existing rafters to get a full 3" bearing. make sense?
Thanks,
Chris
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Brettny
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# Posted: 22 Jun 2023 09:09am
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To put a ridge beam in you basicly need to rebuild the structure. You also need a post going from the beam to the foundation. What is the foundation under that side? The other side of the beam is the house correct? How would you attach it to the house and add support?
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ICC
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# Posted: 22 Jun 2023 11:31am
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Quoting: rick7033 idea is that w/ a 2x8 rafter and a 2x8 ridge board, my rafters don't fully bear on the ridge board. This would fix that. If I go w/ 2 2x8s for the beam, I will likely add a 2x2 to fill this gap and then notch the existing rafters to get a full 3" bearing. make sense?
Yes, I wondered about the rafter point bearing when I saw the rafters and ridge were the same size. Adding a 2x2 would help that.
Or if adding a pair of sandwiched doubled 2x8's as a beam under the ridge board, use a third 2xsomething in the middle of the sandwich and have it extend up against the lower edge of the ridge board.
Make sense?
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ICC
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# Posted: 22 Jun 2023 11:33am
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I had not seen that calc before. Looks good. The numbers more or less agree with one I have access to.
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