supporting cathedral cieling

[JOHNNY J.J.]

:? Hi everyone. Me and a few people at the church I attend here in Cleveland, Ohio want to take our old caretaker house and tern it into a youth center. The building is 32 feet wide by 50 feet long. It is 12 foot 4 inch high at the center of the gable roof, and 8 foot high at the extr. walls. The rafters are 2 x 10 - 16 inches on center. There were no ceiling joists. There is a weight bearring wall running the length of the building. What we want to do is remove the center wall to open it upcathedral ceiling style a large space. I was kicking around an idea of constructing a beam laminated out of 2 x 12's and installing 2 sheets of 3/16 steel plate inbetween the2 x 12.

[Tom R]

If I'm understanding you correctly, I would think you would need to go with 'exposed' collar beams maybe every 64" at about the 10' or 10'-6" point, but let's hear what the others have to say.

[doyle]

If there is a load-bearing wall down the center of the building, then I would assume there are angled rafter supports resting on that load-bearing wall??

In order to remove that load-bearing wall, you want to put beams in to support those angled rafter supports?

If so, I would say the laminated 2x12's you propose using will work, but you will have to have posts every so far supporting said beam. Maybe even 2 to 4 foot sections of wall every so far.

There's no way you will have a totally open floor space since you will have to rest the beams on 'something'. I don't see a completely open cathedral ceiling either, since there is already an issue with the load beaaring center wall.

A local engineer can tell you exactly what kind of supports you will need, as well as how long and what kind of a beam. This will be fairly inexpensive to have him give you this info. Perhaps there's already an engineer in your congregation?

[JOHNNY J.J.]

Thank you gentelmen on the information you provided me. since we are wanting to go with a wide open floor plan without posts or walls. I think we will probably go with the open collar beams athight of 10'. Now is there a formula to calculate the size lumber I will need for this project ? :)

[davidshackelford]

I dunno of any special forumlas, but I would just use the pythagareom theorem, and if needed, some trig forumulas (using roof pitch) to find the collar tie length. Note: to be able to use the pythagoream theroem, you'll need to "split" the triangle formed by the rafters and collar ties into two triangles as shown:

(I hope this shows up right)
/|\
/ | \
/ | \
/----------\
/ \
/ \
/ \
| |
| |
| |
| |
------------------

I just realized...I hope that both "sides" of your roof have equal pitches.

Good luck!

-David

[Tom R]

The lengths would be about 16' at your 10' height, the widths should probably be the same or maybe 1 size smaller than the widths of your roof rafters. The purpose of these is to prevent your walls from bowing outward under a snow load (or even just the roof load). But is there an existing ridge beam with 'opposing' rafters on each side? Even if this is the case, you would have to install the collar beams 'as' you removed the wall. This is a DANGEROUS job, especially on a building that size. I'm a contractor and there's no way I'd tackle it without the written recommendations of a structural engineer. You need to do the same.

[Tom R]

Seems like you would also need some kind of 'intermedate' supports (from above) to keep the 16'ers from sagging. The engineer will know.

[JOHNNY J.J.]

Is it possable, to build from the inside, to incorperate the rafters already in the roof into a scissors truss system. this way we can still have the open floor plan we want, but also increase the stringth of our roof?

[Tom R]

Why do I get the feeling this thing's gonna be a 'skyscraper' by the end of the month. :lol: Just kidding. I would think you could with some gusset plates, I don't know if it's all that necessary, might be more of a question for mjpliv (he's our online 'designer-at-large').

[mjpliv]

Using the collar ties at a height of ten feet sounds like a possible solution to your needs. If you are concerned about them sagging add a king post back up to the ridge. The one piece beam option may not be feasible because of the length, cost and the loads generated at the bearing ends. It would necessitate excavating the foundation at the bearing points and adding reinforced concrete pilasters to the foundation walls and under-pinning the existing footings with expanded, reinforced concrete pads. More than likely, a 50' beam would need to be fabricated from a very large steel section or an engineered wood product such as a gluelam, LVL or paralam beam. The support columns at each end would also need to be engineered. The bearing points will need to support in excess of 25,000 pounds each.

I would strongly suggest you use the services of an enginner to evaluate your roof structure and design the size and spacing of the collar ties. There might be a requirement to reinforce the top plate using steel angles if you do not provide a collar ties for each rafter pair. Most building codes require a "method of restraint" for all rafter ends which means a collar ties, floor/ceiling joist or a wall plate rigid enough to push back against the rafter with at least the same force as the rafter is pushing out.

Also, this sounds like a "commercial" project where occupancy loads dictate a higher degree professional design input.

[JOHNNY J.J.]

THANK YOU MJPLIV. I WILL BE TALKING TO AN ARCH. ENGENIER IN THE NEXT FEW DAYS. AS OF RIGHT NOW WE ARE LEANING STRONGLY AT THE EXPOSED COLLAR TIES EVERY 32"/ EVERY OTHER RAFFTER, 10' HIGH. :)