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Old 02-03-2012, 05:44 PM   #1
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ceiling span vs. joist size


i have a small room portion that is 9 x 10 ft. it is on the top floor and right above it is a slightly slant roof, i.e. no attic in between or anything to be walked on or carry any weight whatsoever.

i was gonna set the ceiling joists along the 9 ft side, naturally. previously there were 2x4 joists there. for the ceiling i was gonna use just simple drywall and the lighting fixtures would not be of significant weight either (e.g. 4 small 4" recessed lights).

my questions are whether the 2x4 size would suffice over that span and is 16" an OK distance between two adjacent stud centers.

thanks

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Old 02-04-2012, 06:05 AM   #2
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ceiling span vs. joist size


Assuming that there would never be anything on the roof but roofing, I would say NO!! That roof would sag considerably. Figure roughly 1" per foot, and that is for #1 framing lumber. A 9' span would need at least 2x10's.

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Old 02-04-2012, 07:41 AM   #3
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ceiling span vs. joist size


I wouldn't run out and get a permit for such a little job.

You need 2x10 for insulation anyway.
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Old 02-04-2012, 08:00 AM   #4
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Quote:
Originally Posted by Joe Carola

I'm sure you wouldn't. Eveyone job this guy has done needs permits and inspections and he doesn't get them and admits it.....
I didn't know he has other things going on, maybe that really do need
permits.
I just can't see paying more for the permit than the job is going to cost.

Last edited by titanoman; 02-04-2012 at 12:01 PM.
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Old 02-04-2012, 08:38 AM   #5
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ceiling span vs. joist size


Permitted or not, 2x4s will sag. Maybe this will help:
http://www.awc.org/calculators/span/...eversecalc.asp
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Old 02-04-2012, 09:06 AM   #6
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ceiling span vs. joist size


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Originally Posted by ratherbefishing
Permitted or not, 2x4s will sag. Maybe this will help:
http://www.awc.org/calculators/span/...eversecalc.asp
One of the options in this calculator is the selection of incised lumber. What is that?
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Old 02-04-2012, 10:45 AM   #7
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ceiling span vs. joist size


http://www.fpl.fs.fed.us/documnts/pdf1998/winan98a.pdf
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Old 02-04-2012, 11:21 AM   #8
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Originally Posted by joecaption
Thanks.
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Old 02-04-2012, 12:08 PM   #9
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ceiling span vs. joist size


Quote:
Originally Posted by Joe Carola

And I can't see why people want to help people do illegal structural work when these people don't care about codes permits and inspections...
Maybe the job is real small, doesn't put anybody in danger of anything.
Maybe some people are on such a tight budget they can't afford to unnecessarily apply for a permit on a little improvement.
There is a place and a time for permits, and it's not up to me to make that determination.
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Old 02-04-2012, 02:15 PM   #10
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ceiling span vs. joist size


the reason i thought it'd be OK to go with 2x4 again is that the old 2x4, when i took them out, and they were pretty darn old, my estimate is late 60s or early 70s based on the previous ownership and some pieces of old newspaper i found tucked in gaps instead of foam/insulation, were in very good condition and not sagged. they were pretty darn straight. but i had to take them out because i needed to work on a ledger they were nailed into, i.e. replace it.

why do i need 10" for insulation yet 2x4 on the wall is enough depth for wall insulation?

finally, i am aware of the inch per foot rule and i used it for building my deck and i understand it is needed for structures that carry weight but all this ceiling will be carrying is 4 small recessed lights and drywall.
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Old 02-04-2012, 02:45 PM   #11
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ceiling span vs. joist size


Quote:
Originally Posted by amakarevic
the reason i thought it'd be OK to go with 2x4 again is that the old 2x4, when i took them out, and they were pretty darn old, my estimate is late 60s or early 70s based on the previous ownership and some pieces of old newspaper i found tucked in gaps instead of foam/insulation, were in very good condition and not sagged. they were pretty darn straight. but i had to take them out because i needed to work on a ledger they were nailed into, i.e. replace it.

why do i need 10" for insulation yet 2x4 on the wall is enough depth for wall insulation?

finally, i am aware of the inch per foot rule and i used it for building my deck and i understand it is needed for structures that carry weight but all this ceiling will be carrying is 4 small recessed lights and drywall.
Because since heat rises, you lose most of it through the ceiling.
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Old 02-04-2012, 02:49 PM   #12
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ceiling span vs. joist size


well, none of the existing last floor ceiling joists are 2x10 in my house. the roof is a simple one sided slant and the higher side has 2x8, the lower side has 2x6. and this is from 100 years ago. i am not so concerned about 6" thick insulation not being sufficient, that's the least of my worries, heck there used to be much less in the part that i demolished and now renovating.
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Old 02-04-2012, 04:06 PM   #13
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ceiling span vs. joist size


Quote:
Originally Posted by titanoman

Because since heat rises, you lose most of it through the ceiling.
So in hot climates, are narrower (shorter) ceiling joists recommended so as to contribute to cooling the space?
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Old 02-04-2012, 04:24 PM   #14
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let me make one HUGE clarification: these joists ***ARE NOT HOLDING THE ROOF*** they are just holding the ceiling under the roof, i.e. drywall and lights, that's it. the roof is already in place and there is between 4-5 (tapered side) and maybe 10" clearance between where the ceiling sheetrock ought to be and the inside of the roof. the roof and the rafters are already in place but i'm not using it to hang drywall cause i want it to be level with the rest of the room. so this is sort of underceiling. i think using the same strength as for something that would carry lots of weight (inch per foot rule) is plain foolish, there has got to be a simple calculation.
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Old 02-04-2012, 07:32 PM   #15
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I sent you a link for the simple calculation. It says (assuming Douglas Fir) that you can use 2x6s for ceiling joists. Unless you are trying to reuse your old 2x4s (and I can undestand that), 2x6s don't cost that much more. If you are trying to reuse your old 2x4s, just space 'em 12" OC. The insulation can be taller than the joists, so you can still use R-30 (code here) if you want to.

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