Remove joist?


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Old 11-04-06, 10:11 AM
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Remove joist?

We have a free standing 14 by 24 ft single garage we want to convert to a hobby room. It has a hip roof with rafters and ceiling joists spaced 24". (all open 2x4 construction). We would like to put a skylight on the roof. All is fairly straight forward. What we would also like to do is remove one of the ceiling joists in the middle of the garage. Is this possible? this would leave a 48" opening between the two middle ceiling joists (not that there is a ceiling but just open joists).

We have a similar building on the property that does not have ceiling joists but does have a ridge beam. The garage, in contrast does not have a ridge beam. Could we add blocking between the existing rafters of the garage at the ridge and does this act the same as a ridge beam even though it is individual pieces of wood?

Also. I'm curious as to what is the purpose of ceiling joists. Is it to add strength to the roof? Keep the rafters from spreading? Could I double the joists up on either side of the one I would like to remove?

Any hints or advice appreciated. Thanks
 
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Old 11-04-06, 10:41 AM
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If I'm picturing it correctly, you could cut out a section of the ceiling joist that is wide enough for your skylight if you doubled the joists on either side, and headed off the cut ends of your joist with a double header that is nailed on both ends to your doubled joists. The same would apply to the rafter you intend to cut, head it off with an inboard header above and below the skylight.

Regarding why ceiling joists are needed, the best way I could explain it is that a triangle is the strongest shape structurally. Without the ceiling joists to hold the walls together, weight on the roof would simply push the walls out laterally. It would be like a triangle with no bottom chord... like two playing cards that are set up to lean against one another.
 
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Old 11-04-06, 11:24 AM
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I appreciate the info. The triangle analogy explains a lot and gives perspective to the physics involved. I find it easier to work through a do-it-yourself project if I understand the 'why' as much as the 'how'.

I don't need to cut into a rafter to install the skylight as the rafters are on 24" centers. I simply want to remove one of the ceiling joists below one of those rafters (the bottom of the triangle).
 
 

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