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Old 06-05-2007, 04:17 PM  
xdissent
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Default Cathedral ceiling support?

Hey guys, so I'm mid-renovation on my home and have hit a bit of a stumbling block. Basically my house is a two story, but the entire 2nd story has been converted out of attic space (my guess). The second floor is built on 2x10s at 24in spacing that meet the top of the second story walls and serve as ceiling rafters for the first floor, and (i assume) cross ties to keep the roof from collapsing outward. My project is to rip out one of the 2nd story walls (parallel to the roof line) and add a railing for a loft style overhang over the first floor - featuring a cathedral ceiling which follows the roofline from the wall up to the top cross tie. I dont know if it's important, but the second floor is also supported by first-floor walls it seems. Above the second floor, I have also noted 4ft long cross ties which also form the top of the ceiling for the 2nd floor. The roof rafters (long boards that create the roof line and support the roof decking - sorry if I got the term wrong) are long 2x4s. I am already planning on adding 2x10 rafters along side the 2x4s to create a larger insulating space, probably not with a continuous board though. My questions: Am I detracting from the strength of the roof by doubling each 2x4 with 2x10 segments? Should I even be concerned with the strength of an approx 13 ft long piece of roof supporting itself and 2x10 pieces? I just hear about roofing today utilizing either 2x10s or similarly strong pieces of lumber instead of the 2x4 rafters of yesteryear. Am I being too paranoid? I think the angle of the roof is near 45deg if that matters and like is said, the roof and ceiling will run unsupported except at the ridge board, the top cross tie (approx 4ft in length), and the top of the exterior wall, where it also meets the floor joists/ceiling ties.



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Old 06-05-2007, 04:42 PM  
mudmixer
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I think you should have had professional opinions before you got into everything. - You are guessing and assuming too much (with a few I don't knows thrown in).

It could have saved you a lot of grief and money. Maybe it is not too late.



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Old 06-06-2007, 10:58 AM  
glennjanie
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Welcome to the community XDissent:
I would first put a glu-lam beam under the ridge,support each end of the beam, connect the 2 X 10s to that and run them down onto the top plate of the wall. Now the roof is held by the 2 X 10s rather than the 2 X 4s and the glu-lam beam will keep it from squatting. You will need to get rid of the collar ties (4' long) to get the beam in place. You need to insulate with batts that will leave at least 1" between the insulation and the roof deck, ventilate between each rafter with a couple of 2" holes at the bottom and Vent-A-Ridge at the top. Its called "ice house" insulation. You will end up with a breath-taking open feeling and I think it will look good.
Glenn

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Old 06-06-2007, 06:24 PM  
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2x10 segments for rafters will add enough weight alone to cause problems. Rafters must be full length, continuous, one piece design or they must have adequate support under the splices. A cathedral ceiling leaves no opportunity for additional support.

This alone makes your project dangerous to you and the long term effect could be structural failure. Load distribution and breaking points can surprise a person in a standard roof where the load is equal from side to side. Add a heavy side with 2x10 spliced rafters and you have a potential for serious and sudden failure, possibly collapse.

I have to agree with Mudmixer, get someone in there with experience and knowledge of sound construction practice. Maybe an engineer. The project you are considering will have to be done in certain order and with careful consideration of what could happen as you go.
The laminated beam at the ridge may support the weight but it offers very little side to side resistance to deflection and you will still need a way to tie the top plates of the walls in place to prevent collapse from spreading.

Too much at risk and too many unknowns for a person who isn't familiar with this type of construction.

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Old 10-03-2007, 12:36 PM  
scottyf
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Quote:
Originally Posted by xdissent View Post
Hey guys, so I'm mid-renovation on my home and have hit a bit of a stumbling block. Basically my house is a two story, but the entire 2nd story has been converted out of attic space (my guess). The second floor is built on 2x10s at 24in spacing that meet the top of the second story walls and serve as ceiling rafters for the first floor, and (i assume) cross ties to keep the roof from collapsing outward. My project is to rip out one of the 2nd story walls (parallel to the roof line) and add a railing for a loft style overhang over the first floor - featuring a cathedral ceiling which follows the roofline from the wall up to the top cross tie. I dont know if it's important, but the second floor is also supported by first-floor walls it seems. Above the second floor, I have also noted 4ft long cross ties which also form the top of the ceiling for the 2nd floor. The roof rafters (long boards that create the roof line and support the roof decking - sorry if I got the term wrong) are long 2x4s. I am already planning on adding 2x10 rafters along side the 2x4s to create a larger insulating space, probably not with a continuous board though. My questions: Am I detracting from the strength of the roof by doubling each 2x4 with 2x10 segments? Should I even be concerned with the strength of an approx 13 ft long piece of roof supporting itself and 2x10 pieces? I just hear about roofing today utilizing either 2x10s or similarly strong pieces of lumber instead of the 2x4 rafters of yesteryear. Am I being too paranoid? I think the angle of the roof is near 45deg if that matters and like is said, the roof and ceiling will run unsupported except at the ridge board, the top cross tie (approx 4ft in length), and the top of the exterior wall, where it also meets the floor joists/ceiling ties.
Sounds like you need a structural engineer. Let me see if I understand whats going on. The second floor is supported by 2x10 @24" o.c. floor joists. The roof consists of 2x4 @?" o.c. rafters with 2x? rafter ties. If the rafter ties define the second floor ceiling plane, then you are talking about a tray ceiling and not a cathedral ceiling. You are looking to sister 2x10s to your rafters to gain insulation space and would like to square off a portion of the roof to gain headroom along the exterior wall.

A structural engineer will let you know if the rafters and ties are sufficient and will create a plan for framing out the "overhang" that you are looking for. I'm guessing that service will run you about a $1000. If I understood it all correctly.


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