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Old 12-09-2006, 11:35 AM   #1
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Question about ceiling joists in a garage


Hey all. My house had a garage which, apparently, rotted down to the sills because scraps of those are all that is left of it. Anyway, I want to build a new one (using the existing concrete foundation) but a couple of details in drawing out the plans for the permit have me stumped.

The garage will be 16' x 16' in size as that is just a bit smaller than the slightly out-of-square slab (measured from the outside of the unfinished walls). Since the attic will not be used for storage (only ~31" of headroom at the ridge) it seems that I can just use 2x6's 24"OC for the joists if they are #2 or better southern yellow pine. My big question is - do I need 7 or 9 of them??? That is to ask, are the joists which would sit directly on the top plates at either end of the garage be redundant/unnecessary? If it helps to know, the walls will be framed with #2 SPF 2x4's 16"OC with a single PT mudsill and doubled top plates. Yes, I understand that this going with 9 joists only costs another $25 or so, but if they aren't necessary I'd still like to know. Thanks!

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Old 12-09-2006, 01:46 PM   #2
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Question about ceiling joists in a garage


9 is still the magic number, why would you want to run 7? I assume you are not putting in a ceiling? If you are in Tampa, you need to remember that building codes are based on acceptable practices, whether you think you need them or not, and acceptable is 24" on center.

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Old 12-09-2006, 03:29 PM   #3
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Question about ceiling joists in a garage


Thanks for the reply joasis.

So I will need to put a joist on top of each end wall just like the rafters, then? I don't offset the first joist 24" from the top plates of the end wall?

It's not that I "want" to use 9 or 7 joists, or that I am trying to argue with the building code, rather, it's that I trying to determine the correct number of joists. Yes, I know that 24" OC is fine - a table in the FBC said it was - but that doesn't explain whether I need to have a joist at each gable end wall. Common sense says no: a joist is for spanning an open space unsupported; the top plates in a framed wall would have no need of a joist, then.

But I could be wrong, and if I am I will cheerfully draw 9 joists for my submission to the City of Tampa building department.
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Old 12-09-2006, 05:16 PM   #4
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Question about ceiling joists in a garage


You doing any overhangs on the ends?
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Old 12-09-2006, 06:19 PM   #5
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Yes, Mike - 1' out on either gable end using fly rafters and lookouts.
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Old 12-09-2006, 07:17 PM   #6
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I see what you are getting at now....I should have thought about your post for a few seconds....no, you can delete the end joists, and then 7 would be the number, ...sometimes I have to switch my brain into gear.....when we frame a gabled roof instead of using trusses, we lay the end joists down to make the nail flange, but we still count them.
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Old 12-10-2006, 07:32 AM   #7
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Yeah, that was what was stumping me in the first place - it's totally obvious if using trusses but for conventional stick framing I wanted to make sure. The funny thing is that if the span tables required 2x8's for the joists then I was going to specify trusses, but because SYP 2x6's are able to span the 15' 5" inside distance with a good 4" to spare, stick framing looked far more attractive than having trusses made up. And can't you just imagine the truss manufacturer yawning over the size of this order??? You need how many trusses, son? Nine???

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Originally Posted by joasis View Post
when we frame a gabled roof instead of using trusses, we lay the end joists down to make the nail flange, but we still count them.
That nail flange would be for the interior ceiling, correct? Would it be okay to lay a 1x6 down on the top plate with the gable end wall studs sitting on top of it, or does the nail penetration requirement demand that the gable end wall studs sit on 2x material?
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Old 12-10-2006, 08:45 AM   #8
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Question about ceiling joists in a garage


I would use 2X, but that is your choice...the 2X here is cheaper then a 1X anything.
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Old 12-11-2006, 04:27 PM   #9
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Question about ceiling joists in a garage


Quote:
The garage will be 16' x 16' in size...
allpraisebob,

My garage is 18' deep leaving only 1' front & back with a 4-door sedan parked inside. Make sure that you will be satisfied with the 16' depth before proceeding.

...Christopher
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Old 12-12-2006, 07:47 PM   #10
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Question about ceiling joists in a garage


Thanks for the help so far. I have just one last question before sending the plans in to the building department...

The existing driveway terminates into the existing garage slab on the far right so that's where I'd like to place the garage door (which will be 8'W x 7'H). The headers to span that distance need to be doubled up 2x10's at least sitting on 2 jack studs per side. Code requires that there be a minimum of two 1/2" anchor bolts per wall and that they be no closer than 8 bolt diameters (4" min.) from the wall end. Unfortunately, the code does not say how close the anchor bolts can be to each other or whether a wall with an interrupted mudsill (ie - one with doors in it, be they entry or garage) needs a minimum of two anchor bolts on either side of the header or not. If nothing else, the requirement that the anchor bolts be no farther than 32" apart seems a bit difficult to satisfy when an 8' wide garage door is in the plans?! So, my last question is, how big does the narrow piece of wall need to be that will serve no other purpose but to hold up one end of the garage door header (1 end stud, 1 king stud + 2 jack studs, and enough space for the anchor bolt(s))???

I'm beginning to understand why so many people take their chances and not pull a permit in the first place!!!

Any further help appreciated!

And Christopher, I know that 16'x16' is a tight squeeze for using the garage for cars, but I'm pretty much stuck with it because that is the size of the existing slab and even though it is far closer to the property line than the minimum 7' setback required these days it is "grandfathered in" - I'd be foolish to not take advantage of it, especially since concrete is going for $110/c.y. here these days...

Last edited by allpraisebob; 12-12-2006 at 07:50 PM.
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Old 12-14-2006, 08:27 AM   #11
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Question about ceiling joists in a garage


I've set anchor bolts as little as 3 inches apart to satisfy
picky inspectors. This was on the gulf coast, where the
inspectors are understandably picky about anchor bolts,
strapping, and tie-downs
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Old 12-14-2006, 09:00 AM   #12
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Question about ceiling joists in a garage


Well, Jbob, it's exactly that sort of twsited logic I'm trying to get a handle on here. Wood doesn't get any stronger from putting more holes in it so I would think riddling your mudsill with anchor bolts 3" OC would simply lead to it splitting right down the middle when stressed enough.

However, if 3" OC is the minimum distance permissible (giving a 1" gap between the washers), and any given section of mudsill requires a minimum of two anchor bolts, then it would follow that the narrowest wall section one could build would be 4" (to the first anchor bolt) + 3" (to the second) + 4" (to the other wall end), or 11". Should only one anchor bolt be needed then the minimum width of a wall section would be 8", correct?

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