Removing Collar ties
I am new to this board and would like some advice about possibly removing collar ties in my attic. I added a second floor to an existing ranch house. The span along the middle of the house is 24 feet wide by 40 feet in length. My carpenter installed collar ties at every other rafter about 4 feet up from my attic floor. I would like to know if I can remove them, or possibly just cut them shorter and move them up closer to the ridge. I have no idea if this is possible, but I would appreciate if sombody could help me out.
The span is 24' wide
The length is 40' wide
The rafters are 13' long
The rafters are 2" x 8"
The ridge is 2" x 12"
The rafters are 16" apart
Collar ties are 4' down from ridge
Collar ties are 9' 7" long
Collar ties are 2" x 6"
The distance from floor to ridge is 6' 5"
The rafters run the same way as the floor joists
It is a perfect triangle design
It sounds like overkill. As long as you keep the ceiling joists, (Attic floor beams) in you can move them up. These are there to keep the rafters from pushing the walls out, but the ceiling beams also do that if nailed properly. You can replace them with 2x4s and move them up to save 2 more inches.
1.) Add knee wall framing and collar ties to each side (sandwiching) the rafters at a higher location.
2.) Create plywood gussets and install them at a higher location on EACH rafter.
Do not move them so far up that you defeat the purpose of the collar ties...
I would recommend that you have someone knowledgable, view the rafter layout on site to see if there are other structural areas that could be affected ... BEFORE you start to do anything up there.
Collar ties are generally for the benefit of the rafters, though, and your rafters sound more than big enough. Well, unless your roof is concrete tile and less than 3:12 in slope... you might actually need 2x8 rafters in such a case.
I am using the space for storage only. The attic floor joists are 2" x 10". They are 24ft long. There is no load bearing wall in the middle. I have standard roofing shingles. There is only one layer of shingles.
P.S. The collar ties are only 3 feet off of the floor which makes it very difficult to walk up there.
Th above advice is all correct, but I will add one thing to consider with "knee bracing" a rafter.....you must have structure (wall that will bear the load) under the knee bracing, or you will have problems later with sagging ceilings. It sounds like you won't really have a problem, but do get some advice from a pro...it may be worth a lot to spend a few bucks getting an opinion.
sjrhome is right.
If the rafters are 2x8's @ 16" o.c. in a moderate snow zone, horizontally spanning 12 ft and the attic floor joists are properly nailed to them and also properly nailed where they might lap at middle of the house, then the ties in question are not properly placed and can be moved.
When ties are in the lower part of an attic space they aren't really "collar ties", they're "rafter ties", and are doing the same thing as the attic floor joists which is preventing the top plates of the walls, as well as the rafter bottoms, from spreading. In this case, the ties appear to be redundant.
Proper "collar ties" would be installed in the upper 1/3 of the attic space in order to prevent the tops of the rafters from separating at the ridge. That means they can be installed as high as the bottom of the ridge board at every third rafter pair. Most codes require 2x6 collar ties.
Such a modification would be compliant with the requirements of the 2003 IRC.
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