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Old 08-30-2010, 06:43 PM   #1
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joist cantilever


Bumping out the back of my house 3'-6'' ( 2 floor addition ). Would like to cantilever the 2'x10'' joists that are carrying the 2nd floor beyond the new bearing wall. I haven't submitted plans to code enforcement yet. Would like to grab about 18'' to 24''. How much will they approve ?
Also , must these new 2nd floor joists go beyond the existing bearing wall and be slid in under the bedroom floor boards a foot or so ?
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Old 08-30-2010, 06:50 PM   #2
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Where are you located ?
Local codes may apply
Yes, joists will need to extend in along the old floor joist & be secured to those joists
I went out ~24" & IN about 5'
"Only" supporting bay window, new floor area & roof over bay window



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Old 08-30-2010, 06:51 PM   #3
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The first question they will ask you is if there will be a weight-bearing wall on the ends of the joist cantilever. That point, alone, will severely limit how far out you can go.
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Old 08-30-2010, 07:06 PM   #4
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joist cantilever


Located in S.Jersey. No load above. Looking at the project from the yard you would be facing a gable . New roof rafters will be resting on the short walls. Existing back wall of home carries the old rafters and is guttered. Will be framing intersecting gables and valleys
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Old 08-31-2010, 07:00 PM   #5
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"How much will they approve ?" ----- Check with them.

"Also , must these new 2nd floor joists go beyond the existing bearing wall and be slid in under the bedroom floor boards a foot or so ?" ---- Yes, clear back to next interior bearing, past exterior bearing: maximum overhang length is limited to the depth of the joist if the end of the cantilever supports a load bearing wall or shearwall (Figure 1). When designed for additional loads, cantilevers are limited to 4 times the depth of the joist (Figure 2). The cantilevered joist must be located directly over studs unless the top plates are designed to carry the loads. If the end of the cantilever supports a non-loadbearing non-shearwall, then the maximum overhang length is limited to one-fourth of the joist span (Figure 3). Notice figures: 1, 2, and 3. From: http://www.awc.org/HelpOutreach/faq/...e_Cantilv.html

“Yes, joists will need to extend in along the old floor joist & be secured to those joists
I went out ~24" & IN about 5'” "Only" supporting bay window, new floor area & roof over bay window ------- Wrong, Dave. With any roof load above, it is now a bearing wall: http://resourcecenter.pnl.gov/cocoon...er/article/125

No scabbed-on shorter joists for a cantilever, unless engineered, that would put abnormal/additional loads on the existing joists and rely on the type/amount of fasteners.

Gary
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Old 08-31-2010, 07:56 PM   #6
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Quote:
Originally Posted by GBR in WA View Post
I went out ~24" & IN about 5'” "Only" supporting bay window, new floor area & roof over bay window ------- Wrong, Dave. With any roof load above, it is now a bearing wall: http://resourcecenter.pnl.gov/cocoon...er/article/125


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Which I guess is why I said "Only" supporting
Supporting means it load bearing




Last edited by Scuba_Dave; 08-31-2010 at 09:43 PM. Reason: removed comment
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Old 08-31-2010, 09:31 PM   #7
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Hey, relax fella.... pointing out to people the difference between loaded or not and not to tack a 7' joist on with a 2' cantilever. Only going 5' back putting an up-lift load in the middle of a long joist rather than all the way back to interior bearing. DIY'ers would think that is acceptable and the way to do a cantilever, coming from someone with your post numbers- it must be correct. Even nailing another joist alongside is a weak way to cantilever, unless it runs the whole way back to interior bearing.

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Old 08-31-2010, 09:37 PM   #8
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Sorry...hot & humid today
Bad day trying to get some siding finished up
Poor wording & explanation on my part
I consider any cantilever as load bearing on the outside point

The joists actually do extend in along existing joists
Each goes in as far as possible before coming up against either the chimney or cross joists



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Old 09-02-2010, 10:15 PM   #9
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Thanks everyone for the info. Sorry I haven't responded sooner. Meeting with an architect next week.
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