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I need some help! I’m planning to finish out my attic space…finish surface will be drywall. Rafters are 2×6, 24″oc, no structural ridge, the rafters just butt to each other, pitch is 7/12, the span is approx 16′ with a knee wall about 8′ from the outside wall. Do I need to keep the collar ties? I’d really like to take advantage of full head room and go the the peak with drywall.
Any advice would be appreciated.
Replies
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Yes, you need the collar ties.
As the weight of the roof pushed down, it tends to spread the walls. Collar ties keep the rafters from spreading and pushing the walls out.
Ceiling joists would do the same thing.
Or, you can use a structural ridge beam, not a ridge board, but actually a load bearing beam that's heavy enough to prevent the roof from sagging and pushing the walls out.
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How about boxing them in with drywall or one-bys. You can't get rid of them so may as well integrate them into the design. It's a common practice.
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I need some help! I'm planning to finish out my attic space...finish surface will be drywall. Rafters are 2x6, 24"oc, no structural ridge, the rafters just butt to each other, pitch is 7/12, the span is approx 16' with a knee wall about 8' from the outside wall. Do I need to keep the collar ties? I'd really like to take advantage of full head room and go the the peak with drywall.
Any advice would be appreciated.
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Gortco,
I tried to take the information you gave us and conjure up an image. This is what I got. An eave to eave width of about 32'. A load carrying knee wall 8' in leaving an open center bay about 16' wide. About 9' of clearance from the deck to the peak interupted by collar ties on some plane from several inches to several feet below the peak. If this is correct and I was in your shoes I would discuss the following option with an experienced framing carpenter, structural engineer, or architect familiar with your actual situation. Cut triangles 24" wide and 14" tall out of 1/2" plywood. Nail a triangle in every bay tight on the roof decking. Use a lot of #8 nails. Pull strings to get an exact plane for your mini flat ceiling. Get the strings as close as possible to the bottom of the triangles. Individually cut and fit 2"x4" cross ties to fit between the rafters on the plane established by the strings. Secure them in place by driving more #8 nails through the plywood triangles. Cut more triangles and nail them to the other side of the rafters. When this is completed, go to the Breaktime ENERGY: HEATING, INSULATING, & VENTING A HOUSE board for advice on insulating and venting your roof.
Steve