Author Topic: Framing loft floor and Rafters  (Read 4051 times)

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rwalter

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Framing loft floor and Rafters
« on: July 19, 2005, 11:15:04 AM »
I am building a 20'x32' gabled roof 1 and 1/2 story cabin. I still am framing the first floor walls. The roof will have a shed dormer in the loft. The span of the loft is 19'. I used 3d architect to design my plan. I was planning on running the lofts floor joist cross the width and tie them into the rafters. That would require me however to build the rafters on 12" OC to match the floor joists which are 2x12 Doug Fir. I noticed in the framing overview in 3d architect and they had the floor joists running perpendicular to the rafters. They accomplished this by placing a three double "beams”  or joists across width, one at the point where the cathedral ceiling ends and loft floor starts, another one in the middle and then one on the end wall. They then hung joists on joist hangers between them.  Now I would rather frame my rafters using 2x10’s on 16” OC or 24” OC. The span of the rafter is only 10’ so load wise I am fine at these larger spacings. I choose 2x10s obviously to allow for insulation factor needed in the cathedral ceiling area. Now if I frame the loft floor joists on 16” OC they will not meet code, the code I must meet states that I must meet 40/10 Live/Dead loads. Therefore I am stuck at the 12” OC for the 2x12 floor joists if I run them across the width and tie them in to the rafters.

Any suggestions? Here are my thoughts


1.)      Framing the roof and floor joists on 24”OC. Build beams using the 2x12’s for the floor joists. The beams would be made up of two 2x12’s with ½ inch plywood glued and nailed in between. Would this work and allow me to space the floor joist on 24”OC and still meet the 40/10 load requirements? I’ve been trying to find a free beam calculator online but have yet to come across anything decent
2.)      Frame the floor perpendicular to the roof rafters as per the framing model on 3d architect.


Thanks
« Last Edit: July 19, 2005, 11:16:20 AM by rwalter »

rwalter

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Re: Framing loft floor and Rafters
« Reply #1 on: July 19, 2005, 09:25:00 PM »
Well it looks like I might have found the beam calculator that I was looking for. I plan on framing the floor joists/beams on 24" centers along with the roof rafters.

Down load the following software. Very nice.
WWPA Lumber Design Suite 2.0

http://www.wwpa.org/_techguide/suite.asp

If I am running the software right it looks like a 2 piece constructed 4x12 beam, on 24" OC using #2 doug fir will span 20' 2" at a 40/10 Live/Dead load with a L480 deflection rating.  I found this calculator when i decided to check out the WWPA's web site. The doug fir I purchased came from Boise-Cascade and it has WWPA grading stamps on it to boot!

Bart_Cubbins

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Re: Framing loft floor and Rafters
« Reply #2 on: July 19, 2005, 10:09:36 PM »
Maybe I don't understand, but I don't see why you can't have your joists 12" OC and your rafters 24" OC, tying them in to every second joist.

rwalter

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Re: Framing loft floor and Rafters
« Reply #3 on: July 19, 2005, 10:28:20 PM »
Bart,

Having not framed that many buildings, only a few small sheds, I was not sure how that would be framed. Would you have every other joist  toe nailed to the wall plate. Now I am sure there must be some form of blocking but I am having trouble visualizing the ends at the walls if I frame it that way. Thats why I started thinking about these other ways.

Bart_Cubbins

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Re: Framing loft floor and Rafters
« Reply #4 on: July 20, 2005, 10:00:21 AM »
The way I'm picturing this is that you're going to rest both the joists and the rafters directly on a double wall top plate, and nail sideways to attach the joists to the rafters.

Then yes, you would toe-nail down the ones that aren't next to a rafter. The floor sheathing will brace them upright against the ones that are nailed to a rafter. Blocking is a good idea. It will add some strength, keep the insulation in place, and gives you something to nail siding/trim to if you go with open rafter tails.

Doubling up the floor joists at each rafter should also work fine.  If the joists are strong enough for a 12" spacing they should also be strong enough when doubled up at 24" OC. The only thing is that your floor sheathing would have to be thick enough to span the extra distance. I wouldn't bother with gluing in the strip of plywood. You could just nail one joist to each side of each rafter. If you want the floor to be a bit stiffer, you could sandwich a 2x4 in the middle, flush with the top of the 2x12s.

hope that helps

Bart

Offline PEG688

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Re: Framing loft floor and Rafters
« Reply #5 on: July 20, 2005, 04:47:10 PM »
I'd concur with Bart , your loft floor sheeting choice  should drive the spacing .  In a small loft maybe you want to use 2X6 T+G , good floor , attractive ceiling , the dbl joist look like beams if you wrap them , if your going to drywall the lid under the loft and use 3/4 sheeting / floor go to the 12" oc option with the anti rotations blocks . HTBH  ;)PEG

   PS  The T+G will always filter some dust through it , so that might be a though on that type of ceiling . If your kitchen is below it , and the kids are playing in the loft , you'll be salting dinner, with dust .
When in doubt , build it stout with something you know about .

Offline glenn kangiser

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Re: Framing loft floor and Rafters
« Reply #6 on: July 20, 2005, 06:26:57 PM »
I did a variation of what PEG is talking about around 15 years ago.  I had 1x12 pine siding -smooth that had a groove at 1x6 (center) and ship lapped sides-  I put it face down on the joists then put a 3/4 x 4' x8' chipboard flooring underlayment over the pine and carpet over that.  Nice knotty pine office ceiling with carpeted floor in bedroom above.  I applied cement on the joists under the pine to eliminate squeaks.  Right or wrong -never any problem.  Many of the old houses I have seen had a layer of 1x3 appx t&g diagonally with another layer of it straight over top.
« Last Edit: July 20, 2005, 06:28:15 PM by glenn-k »
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Offline PEG688

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Re: Framing loft floor and Rafters
« Reply #7 on: July 20, 2005, 06:48:54 PM »
Great idea  Glenn :)I'll keep  that in mind for potential later use .   We're all smarter than  :o Oh thats your line  8)  HTBH  ;)PEG    Guess that's John's line , but it was general to specific  :D
« Last Edit: July 20, 2005, 06:50:54 PM by peg_688 »
When in doubt , build it stout with something you know about .

Offline glenn kangiser

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Re: Framing loft floor and Rafters
« Reply #8 on: July 20, 2005, 07:08:54 PM »
It made a very solid floor - I used balloon framing on this one as I thought it looked like a good idea.  I was real happy with it.  We still have the house - my son says it was in 1987 or 88.  Shows you what I know.

Seems like it was a relatively cheap way to do it.  I built it on the ground painted it and craned it up on the weekend.  I think I did it so fast I may have forgot to get a permit  --can't recall for sure-- not absolutely - failing memory and all :-/
"Always work from the general to the specific." J. Raabe

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Offline PEG688

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Re: Framing loft floor and Rafters
« Reply #9 on: July 20, 2005, 07:17:47 PM »
  Gee I though you told me to get the permit  :-X??   Ya I'm sure ::) ::) someone got one  :-[, some time  :-[ HTBH  ;)PEG
When in doubt , build it stout with something you know about .

Offline PEG688

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Re: Framing loft floor and Rafters
« Reply #10 on: August 12, 2005, 06:59:18 PM »
  Bump to ya Pioneergal . Was on page four .
When in doubt , build it stout with something you know about .