cathedral ceiling supported by cables ?
we are cathedraling a ceiling in a 50 yr old house – 12/12 L shape – the part we’re doig is 16 x 20, with about 12 ft till it hits the valley, 2x6x11 rafters 24 oc.
a builder whom I trust said I could avoid a big load bearing ridge by just tieing the walls together with a couple 3/8 aircraft cables, hidden in faux beams….
is this for real…?
Replies
Wellllll, talk to an engineer for a specific answer.
Yes, in general, the function of ceiling joists (to tie the outside walls together so they aren't pushed out by the force of the rafters) might be able to be done with cable. The questions would be how often? how attached? how big a cable?
This is not a time for a seat-of-the-pants guess, IMO.
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"Doubt is not a pleasant condition, but certainty is absurd." Voltaire
""we are cathedraling a ceiling in a 50 yr old house - 12/12 L shape - the part we're doig is 16 x 20, with about 12 ft till it hits the valley, 2x6x11 rafters 24 oc.""
""a builder whom I trust said I could avoid a big load bearing ridge by just tieing the walls together with a couple 3/8 aircraft cables, hidden in faux beams....""
""is this for real...?""
Yes,it can be done.I've see it done a few times. This has to be designed by an Architect or Engineer without a doubt.
An engineer will be your best friend here - risky just saying "yes" to you. But, yes, all the same. You will need the top plates to be engineered if you intend the plates to take the 'moment', or beefed-up joists if you intend to use them. Around here 4' is considered max distance between lateral supports - possibly 6' if you can prove it strong enough. So think more than "a couple".
BTW, why not go for heavy rods with welded plates that attach to the structure, and make features of them? But if you are building false beams around wires, why not have structural beams that serve the purpose in any case?
All the best...
To those who know - this may be obvious. To those who don't - I hope I've helped.
I'd be concerned with cables that there is no resistance against lateral forces pushing against the walls from high wind. This could cause minor problems with creaking and drywall pops, or more drastic problems.
thanks for your replies - they echo my concerns...
as to using real beams, how large would they need to be to do the job and not sag? the client doesn't want a vertical support to the ridge, but is ok with a couple 45 degree legs. hoping for just 2 beams, thinking that the valley at 12 ft does a pretty good job of tieing the walls together there...
>>"as to using real beams, how large would they need to be to do the job and not sag? the client doesn't want a vertical support to the ridge, but is ok with a couple 45 degree legs. hoping for just 2 beams, thinking that the valley at 12 ft does a pretty good job of tieing the walls together there..."
For the beams would need to know your local design loads and snow loads as well as the size and shape of the roof.
For the 45's (I'm assuming at the intersection of the el), to support the beams the members would be acting as both columns and girders, and those member would transfer thrust forces to whatever they were tied in to so you'd end up having to keep that assembly from spreading as well. You definintely need the engineer.
What I'm envisioning is an el shaped structure with cathedral ceiling over both wings and no partitions holding it all up (am I even close?). For materials, sounds like a job for . . . steel.
"Let's get crack-a-lackin" --- Adam Carolla
""as to using real beams, how large would they need to be to do the job and not sag? the client doesn't want a vertical support to the ridge, but is ok with a couple 45 degree legs. hoping for just 2 beams, thinking that the valley at 12 ft does a pretty good job of tieing the walls together there...""Toledo,No one here can possibly answer this. You have to get an Architect or Engineer to look at this first. There are a million things that has to be taken in consideration with this.This is a big job just with lumber you want to use cables. You have a valley there also. Right now, is the valley being supported underneath with vertical 2x's down to a wall?If so will those supports be coming out?All valleys don't have to be supported naturally when they're framed for a cathedral ceiling because there's nothing underneath and the valley is designed to support itself.When it's not designed they have to be supported underneath down to a wall.If you remove a support that valley might not be able to handle what you want to do.Tell your builder friend to give you his Architect. This is way out of your league and anyone else's to try and figure this out.Around here Homeowners can draw they're own plans and give it to the town. No need for an Architect. Your case this is not just a simple remodel. You need someone in there to design this, Period!
Joe Carola
Yes, in theory an appropriate set of cables/rods/beams tying the two sides together will do the trick. They of course have to be SECURELY anchored to structural members at the eave joint in such a way that the lateral force will be transferred to the rafters evenly. This may require the installation of a small "sideways" beam at the eave. (In other words, you can't just drive screw eyes into the walls and tie the cable to that.)
These cables/rods/beams will be in tension. They don't require any strength against bending other than that required to support their own weight and to support any other loads you decided to place on them.
This is the sort of thing that needs engineering. Even if an engineer's stamp isn't required, someone with sufficient engineering background needs to work out the numbers.
(Of course, since this is a cathedral ceiling, flying buttresses would be the more historically pure way to deal with the problem. ;))
I'm of the "sideways" beam school of thought. uniform loading of the sidewalls is critical, assuming that there will only be 3 or 4 cables to resist lateral force from the roof.
In theory, with sufficiently stiff side beams, tied together at the end walls, one could do away with the cross-ties entirely.Of course, this ends up being as much trouble as a ridge beam, if not more, so I suspect it's rarely done.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
>>In theory, with sufficiently stiff side beams, tied together at the end walls, one could do away with the cross-ties entirely.
Better than theory, you are 100% right on. It's called a ring beam. Very frequently used on non-rectangular buildings (rounds, octagons, etc.) and on buildings with lofted roof structures but too small for the hat truss thing.
"Let's get crack-a-lackin" --- Adam Carolla
Edited 9/16/2006 7:34 am ET by philarenewal
thanks again for all your ideas -
got an engineer out, and he said the cables would be fine with a little reinforcement - ie. big plate washer for the I-bolts, sufficiently sized rafter clips, reinforced turn buckles, and reinforced top plates.
he also ok'd my original idea of a couple beams 1/3 up the rafter, with all the same reinforcement, and skipping the cables altogether - this idea was for some reason glossed over by my builder friend and the clients, but now seems the option of choice...
BUT, I began to wonder again when I asked the engineer for his suggestion about reinforcing the top plates, this being a remod with certain limitations, and he said:
a) glue a 1in x 3in strip to the interior face of the double top plate (huh?)
or b) glue 2x4 blocks to the plate and rafters of each bay (?)
so I'm wondering, maybe we accidently got like a train driver kind of engineer instead of a structural kind....or he has tremendous faith in glue...these ideas just don't seem to add that much resistance to thrust....
any thoughts...?
Given what the engineer suggested, I'm thinking the entire wall isn't all that long?
If that little voice in your head says a bunch of 2x's glued to the plate between the rafters or a 1x3 along the inside won't do, listen to that little voice. It's usually right. Likely won't collapse but will the engineer be there along side you to fix all the cracks and pops in the drywall after each strong wind or after the snow melts each spring?
"Let's get crack-a-lackin" --- Adam Carolla
Edited 9/19/2006 8:06 am ET by philarenewal
the wall is 20ft long , though only 12ft to the valley rafter of the rest of the L-shaped house, which I think ties that point in fairly well...
the ceiling will be v-groove, so no drywall to crack at least...
your point about the engineer not being responsible is well taken, as he merely offered his opinion and certainly didn't stamp the plan, since there is no plan, - I walk in every morning and say "what's changed now?"
it's an interesting job, but I'm beginning to long for a nice dull one for a while...
Here is what I did on a similar situation. The room is 16x34 with a 12-12 pitch. Framed very poorly. I used 5/8" rod and turnbuckles (McMaster Carr) along with 3" angle. I backed up the top plate and rafters with a 2x8 and a 2x6. The walls were almost 2" out of plumb and bowed. By sloooooly using the turnbuckles I was able to bring the walls back to plumb. Fake beams will cover the lovely iron. Lots of work but I had to gut the house to fix the bad framing, plumbing, wiring, etc.
wow - that's some serious stuff, nicely done -
I have the benefit of currently plumb walls - hope they stay that way....
we installed the beams today to bypass the cable idea - got another curve thrown at me when the clients selected these 6ishx8 ish hand hewn beams salvaged from a log cabin in kentucky....lots of "character" to these beasts....
this is an interesting job, though sometimes maddeningly so....