collar ties explained?

troycalm

i am building a summer cabin for my family...
It is a 900 sf floor with a 550 sf loft i ordered the plans online and have had no problems until now.
Roof plans call for 2 2x12 scabbed together for the ridge beam (30 ft span) and 2x10 for the rafters 16 oc.Plans call for 2x6 collar ties 48in oc, a min of 3 ft from the roof peak.
my confusion is the 48 oc does that mean 48in apart, ie only every forth rafter???????
can someone enlighten me
The cabin is 30ft by 30ft with exposed ceiling and no ceiling joists just collar ties and for some reason this doesnt seem like it will be enuf strength and support for a 6/12 roof maybe im wrong..

Thx in advance Troy

Joe Carola

Why don't you call the Architect who drew them. He would be the one to know.

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Joe Carola

AtlanticWBConst.

48" OC ... sounds about right, that is usually the minimum spread for collar ties; Collar ties do not support vertical loads. Their function is to keep rafters from spreading apart.

I posted this on a previous inquiry regarding collar ties:

"Collar ties are not installed for vertical loads, they are installed to re-inforce the rafters and roof structure from upward wind pressure and roof loads that can cause rafters to spread apart outward.

To illustrate: Take 2 playing cards, or 2 books, and lean them end to end to form an "A"....Where is the weight load? At the peak and at the bottoms. They support each other....there is no downward or vertical weight load under the areas of the 'A' form."

This Link has a good illustration on the end of the page:

http://tpub.com/content/engineering/.../14069_213.htm

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troycalm

thank you atlantawbconst that answered my question,that just doesnt seem like it would keep the walls from spreading.
as for Joe i have contacted the drafter and his reply has always been
2x6 collar ties 48in oc ,min 3 ft from peak he had never elaborated on 48 in

thx again
troy

joasis

Sounds interesting...from the framing description, that roof is going to weigh a lot. What pitch on the roof and how are the walls framed? Seems to me the architect is inviting a wall "sway out" problem.

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AtlanticWBConst.

J. You know, your right. I was only looking at the title of the post and answering the collar tie question (Collar ties explained)
- It was late.

30' x 30' is a wide spread... I'd seriously think about getting the design checked-over and also consider web trusses instead of rafters ...

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joasis

At the very least, with the dimensions stated for the rafters.....it probably needs something like a fabricated timber frame truss, at least on the 10 and 20 foot mark. This must be way up north to need 2X10's for rafters every 16 inches...wow.

After re-reading this, I would say this needs a serious checck from another source......of course, there is no rule against over built.

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troycalm

slope =6/12
run=15
overhang=1ft
heel= 6 7/8
seat= 3 1/2
common=1 1/2 x 9 1/4
ridge= 3'' x 11 1/4"
fascia= 3/4" x 9 1/4
ridge allowance= 1 1/2
adjusted run=14-10 1/2
this is being built in arkansas

Zero Punch

troycalm was only concerned with the coller tie spacing I bet there are also wall ties on 48" oc. Maybe he'll get back and let us know.

troycalm

Yes my concern was how to space the collar ties 48oc now i understand that but no there are no wall ties in the plans..
http://www.cabin-plans.com/store/mer...gory_Code=COZY

gary

The house that I build has a catheral ceiling its about 18 feet high and a span of about 26 some feet. When I put collar ties in I installed on every rafter ( funchion of collar ties has already be explained) then when I was ready to put in v-groove knoty pine I had plenty of nailers plus the added strenght (heavy snowloads). Roof in front of the house is 8/12 and the back is 11/12 with shingles so there was concern about pushing the walls that rafter were setting on, I installed a 6x8 hemlock beams this was build in an A, the horz. beams set on the plate and are fasten with two angle irons 4x4 these bolt thru the beam and thru the plate, where the beams meets in the middle I used diamond plate (diamonds towards the beam) this plate also holds the two beams that are at 45 degree angle from center up to the roof rafters, to bolt this together I used threaded rod when painted flat black the nuts on both ends look like bolt heads. to tie all this in I placed two beams on each end on top of the horz beams and ran them along the roof rafters and bolted a heavy collar tie to both sides. where the horz beams and these beams meet I again used diamond plate. I have a very nice beam thru the center of our big room and have tied opposing walls to keep them from spreading from heavy snow loads. You have been given some very good advise, one I believe was going to talk to a contractor, find one who builds post and beam they work with all the time and could give you the best way to do this. One last thing if you use v-groove knoty pine put in the house on sticks for several weeks that way when you install it will stay in place and not move around, high ceilings trap a lot of hot air install a paddle fan to push back down.
Gary

Big Dave

From looking at the plans on the link the loft area will keep the back wall from bowing out and the way the front rafters hang out over the front wall will help some. In a worse case scenario I would run two beams spaced evenly from the front wall to the loft area at the loft floor height to keep the front wall from bowing out. This will give a little bit of visual interest plus allow you a place to put some hidden lighting that can be focused on the ceiling above.

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mt232

Took a look at your website....your work is incredible!

Big Dave

Thank you very much. I'm still trying to improve though.

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