Gable roof covering patio beam sizing

[Shawnbunchofnumbers]

Long time lurker, first time poster...

Hey all,

I'm sizing a beam carrying rafters and ceiling joists for a gable patio roof that is 24' wide. If my ceiling joists act as rafter ties, my ridge is a ridge board, the max my 2-2x12 can span is 8-1 per R602.7(1)

If I support the ridge at both ends so it serves as a ridge beam, can I use R602.7(3) and calculate my depth from post face to centerline of beam and justify the 12' span that table would give me?

Appreciate any insight anyone can give, big fan of this community helping the industry forward!

 

[steveray]

Don't entirely understand what you are saying, but supporting a ridge board does not make it a beam.....I believe the 602.7.3 table is intended for shed roofs, but I am sure you can make it work for whatever if you can figure the tributary correctly...

 

[Genduct]

Long time lurker, first time poster...

Hey all,

I'm sizing a beam carrying rafters and ceiling joists for a gable patio roof that is 24' wide. If my ceiling joists act as rafter ties, my ridge is a ridge board, the max my 2-2x12 can span is 8-1 per R602.7(1)

If I support the ridge at both ends so it serves as a ridge beam, can I use R602.7(3) and calculate my depth from post face to centerline of beam and justify the 12' span that table would give me?

Appreciate any insight anyone can give, big fan of this community helping the industry forward!

I don't understand how the Ridge BEAM ( not Board) is carrying the Rafters AND Ceiling Joist?

Is your Roof Only 24 wide X 12 ft (the Ridge Bean dimension) and 12 ft rafters ending at What, A wall or another joist/ girt or ?

Would it help you if you just considered the Ridge Beam like the center girt that is holding up Floor Joist?
At the end of the day, it is close to the same situation

 

[Mr. Inspector]

Need to know what code is being used, ground snow load, how high the rafter ties will be (1/3, 1/4, 1/5, 1/6 of the way to the ridge from the top wall plate), what your ridge beam size and the length of the ridge beam span.

 

[Shawnbunchofnumbers]

I don't understand how the Ridge BEAM ( not Board) is carrying the Rafters AND Ceiling Joist?

Is your Roof Only 24 wide X 12 ft (the Ridge Bean dimension) and 12 ft rafters ending at What, A wall or another joist/ girt or ?

Would it help you if you just considered the Ridge Beam like the center girt that is holding up Floor Joist?
At the end of the day, it is close to the same situation

The ridge is not carrying the ceiling joists, just the rafters. My question concerns sizing the beam at the tails of the rafters where it also carries ceiling joists. The reason I bring up the ridge is because it being supported at each end by the house wall/post seems like it would then carry half of the tributary width of the rafter (1/4 of the overall roof width if you just consider the one side of the roof)

Need to know what code is being used, ground snow load, how high the rafter ties will be (1/3, 1/4, 1/5, 1/6 of the way to the ridge from the top wall plate), what your ridge beam size and the length of the ridge beam span.

2018 IRC, 10psf snow load, with rafter ties in the upper-third. Assume ridge beam span is adequate although IRC doesn't seem to have prescriptive sizing of ridge beams (I digress)

If the rafter is supported at the ridge, as opposed to being tied to the other half of the roof and only bearing on the outside [walls] beams, would R602.7(3) assume the load more accurately than R602.7(1)?

 

[Mr. Inspector]

Sorry but i don't have the '18 IRC, we still use the '15. I'm sure the '18 still only allows rafter ties to be use on the bottom third. But if using a complying ridge beam for support, rafter ties are not needed but the ridge beam would need to be engineered. So you might as well have an engineer design the whole roof.

 

[steveray]

Very nice easy way to understand load paths:

https://www.beamchek.com/AcrobatFiles/IntroLoadPath.pdf

 

[e hilton]

. My question concerns sizing the beam at the tails of the rafters where it also carries ceiling joists.

Isn’t the “beam” at the tails of the rafters called the top plate of the exterior wall?

 

[bill1952]

Isn’t the “beam” at the tails of the rafters called the top plate of the exterior wall?

It is but I think in this case, it's all header with columns at the ends. Living with a middle post would sure make it easier.

Interesting one next door. Columns at the corners, and a ridge beam load is transferred by a gable beam. Nothing amazing, but interesting.

We need a drawing from the OP to help, but it seems a simple problem.