Can collar tie prevent sagging rafter?

Old 06-30-20, 03:46 AM
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Can collar tie prevent sagging rafter?

My house is like 100yo and in bad shape. Rafters are only 2x4 and sagging. Rafter tie are 2x4 and weak. Ceiling joists are buried deep below insulation and inaccessible, they are prolly weak too. There is a decent load barring wall parallel to the ridge tho.

Roof pitch is about 7.5/12. Rafters are about 14'. Rafter ties are about 12'.

Can I use collar tie around the middle of the rafter to prevent rafter sagging? I don't wanna use the rafter ties because they are too weak. I don't wanna use the load barring wall under the ridge, because it is a bad angle to suppose 7.5/12 pitch rafters. If u brace a rafter to it, the brace would be too horizontal, and not vertical enough to support much weight.

Also where should I put collar tie and what size they should be and is framing nail good enough?
Old 06-30-20, 04:02 AM
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Some pictures would be helpful.
Old 06-30-20, 05:28 AM
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Rafter and collar ties only job is to prevent the house's walls from being pushed out by the roof rafters. They don't provide much to keep rafters straight though they can help a little. The real problem is that your's are already bent. You will even find it difficult to straighten your framing after it's had a hundred years to slowly bend. I would focus on taking out what bend you can remove easily and strengthening the structure to prevent further warping.

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