New Rafters to existing

Old 05-14-13, 07:23 AM
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New Rafters to existing

I would like to know my options for matching existing roof line on a room addition, when my existing rafters are 2x4 and the plans call for 2x8 rafters on the new addition. I don't want to use trusses. Can I simply shorten the the wall height by 4", and coffer or soffit the ceiling?
Old 05-14-13, 01:37 PM
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If the exising are 2x4, why does the new have to be 2x8?

Depending on the span of your new rafters, it is sometimes possible to use a reduced size by simply putting more rafters in. (for example, if rafters are normally @ 16" c/s, putting them @ 8" c/s means that each rafter is only supporting one-half the weight).

If you tried this, you would need an SE to do the figures to justify it.
Old 05-14-13, 03:19 PM
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Welcome to the forums! I would gather your original housing is of truss construction, hence the 2x4's. Definitely as tony.g says, get an engineer in there to determine if you need to install a knee wall below the attachment point, and exactly what size rafter members you will be needing.
Old 05-14-13, 04:36 PM
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As mentioned, you need to have an engineer involved in the process, but, if I understand your question correctly, yes, what you suggested may be feasible. Or, and again, someone knowledgable is going to have to see it first hand, you may not need to lose all of or any of that 4 inches. Depending on how the original rafters were cut, or the trusses configured, the roof pitch, etc., maybe it's simply a matter of how the birdmouths and tails on the new rafters are cut.

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