cathedral ceiling


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Old 08-13-06, 11:06 AM
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cathedral ceiling

I understand the basics of ceiling joists holding the walls from being blown out when adding a center peaked roof. What keeps the walls from being blown out when you do a cathedral ceiling and there are no ceiling joists?
Thanks, Joe
 
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Old 08-13-06, 12:17 PM
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cathedral ceiling cathedral ceiling

One method is to use scissor trusses that resist the spreading and convert the roof loads to vertical loads at the walls and still provide some open feeling to the structure.

The only problem is when you have wind or unsymetrical vertical loads (snow, wind suction). Then, the vertical wall has to have enough lateral strength to resist the horizontal load at the top of the wall. Unfortunately, a wood frame wall has little horizontal strength, so some bracing or load reduction could be required.

If you replace a traditional wood framed roof system with a system that gives you a "non-flat" ceiling, you will need engineering advice to alter the roof framing with collar ties (if possible), a new truss system or whatever can work for your home.

The cheapest way to build is wood frame, trusses or joists for a flat ceiling and cover everything with vinyl siding or brick veneer, When you start changing the structure after it is built is gets a little complicated and you usually need help to make changes

Dick
 
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Old 08-14-06, 04:59 AM
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Some cathedral ceilings are supported by replacing the ridge rafter with a ridge beam. If the ridge of the roof can't move downward, it won't push the walls out. The principle load is on the beam.

If you are attempting to convert an existing structure, Dick's right, you need to consult an engineer.
 
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Old 08-30-06, 08:15 AM
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Okay, many thanks. As I suspected this will require some engineering work to develop a good solution. One other question. I have been told that as an alternative to collar ties, you can remove every 2 out of every 3 ceiling joists and use the two removed joists as sisters on the 3rd remaining joist. So if I have 12 ceiling joists, I can remove joist 1, 2, 4, 5, 7, 8, 10, 11 and use them as sisters to joists 3, 6, 9, 12. What remains is a "cathedral" ceiling with 3 large beams at the original ceiling height. True?
Thanks.
 
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Old 08-30-06, 10:11 AM
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In response to your question about removing 2/3 of the ceiling joists (to sister with those that remain) - the answer is: it depends. Removing those joists increases the span between joists from what is probably 24" o.c. to 72" o.c. - the area between joists will still have rafter loads pushing them out. How your wall is constructed, and its ability to resist/transfer that load over the wider span is deciding factor.

Before you cut anything, consult an engineer.

I looked back through the post, and didn't see it mentioned, but are you sure your roof/ceiling was stick-built? If it was built using trusses, you cannot just remove the bottom chord (equivalent to ceiling joist).
 
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Old 08-30-06, 10:31 AM
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Thanks. The ceiling/roof is stick built. My township prohibits truss construction.
Agin, many thanks.
 
 

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