open beam loft/ need help

dug · December 12, 2009, 01:38:24 PM

I plan on building my loft using tongue and groove 2 by 6 and open beam design. Rough sawn joists will span the 20 ft. width and be supported by a center beam. What is the appropriate spacing for the joists in this situation. Is 48 in. OK, or 32 better (16 in. spacing on wall framing)? I am not one who desires a floor stiff enough to park a truck on, a little spring is fine with me.

What would be appropriate size lumber for joists in this situation (no code here)?

Also, where do you start the joist layout (from end wall)? I realize you need a nail surface at the end, but do you start with one of the rough sawn joists right against the wall?

Hope all this makes sense. Thanks!

Redoverfarm · December 12, 2009, 04:44:20 PM

Quote from: dug on December 12, 2009, 01:38:24 PM
I plan on building my loft using tongue and groove 2 by 6 and open beam design. Rough sawn joists will span the 20 ft. width and be supported by a center beam. What is the appropriate spacing for the joists in this situation. Is 48 in. OK, or 32 better (16 in. spacing on wall framing)? I am not one who desires a floor stiff enough to park a truck on, a little spring is fine with me.

What would be appropriate size lumber for joists in this situation (no code here)?

Also, where do you start the joist layout (from end wall)? I realize you need a nail surface at the end, but do you start with one of the rough sawn joists right against the wall?

Hope all this makes sense. Thanks!

Dug if I am not mistaken 48" is acceptable for 2X6 T&G. I went with 32" instead. On the joist you will need to let in a ledger on the wall to give you a nailing surface on the ends of your T&G. I didn't and wasn't long being told I should have. I used double 2X6 blocks nailed to the studs. It would have been acceptable by somes standards to just add cripples to support but again the best is to let in the ledger or in your case the joist.

On the joist sizing it is best to go with the charts on the span and load dependent on your species of wood. Mt. Don is pretty good with the numbers and maybe he will chime in on that part or offer suggestion on the rest. Mine was a 16' span with 4X8. Just keep in mind the "wiring" when you decide where the beam placements will be. I cut a channel mid center on my beam top to run overhead wires for lights and fans. If not you will have to have exposed wires or hidden by a metal channel.

December 12, 2009, 09:05:49 PM

Dug maybe this will help.

http://www.awc.org/calculators/span/calc/timbercalcstyle.asp

MountainDon · December 13, 2009, 12:13:03 AM

The absolute maximum spacing for the loft joist beams would be 48" and that's with using good quality T&G 2x material. 32 to 36 inches would be better.

You could start at the end wall with a beam there.

What size beams are you thinking of? (sorry if you've stated someplace before.)

dug · December 13, 2009, 09:28:38 AM

QuoteIt would have been acceptable by somes standards to just add cripples to support but again the best is to let in the ledger or in your case the joist.

I was going to use the let in ledger according to plans, is that right? I am not sure I understand about letting in the joist.

What size beams are you thinking of? (sorry if you've stated someplace before.)

I am not sure because I don't see anything about 32 or 48 in. spacing in the span tables. Were it 24 centers I would think 2 by 8 would be fine (spanning 10 ft.) Is 4 by material usually used in wider spacing?

December 13, 2009, 10:23:53 AM

I used 24" OC spacing for the ceiling joists with 2x6 T&G for the loft floors. I don't consider the 24" spacing necessarily the proper choice but I think it looks fine from both top and bottom, and my loft floor doesn't squeak....I used a combination of nails and glue to install the loft floor.

My penny's worth.

Redoverfarm · December 13, 2009, 11:02:26 AM

Quote from: dug on December 13, 2009, 09:28:38 AM

QuoteIt would have been acceptable by somes standards to just add cripples to support but again the best is to let in the ledger or in your case the joist.

I was going to use the let in ledger according to plans, is that right? I am not sure I understand about letting in the joist.

What size beams are you thinking of? (sorry if you've stated someplace before.)

I am not sure because I don't see anything about 32 or 48 in. spacing in the span tables. Were it 24 centers I would think 2 by 8 would be fine (spanning 10 ft.) Is 4 by material usually used in wider spacing?

Letting in the ledger would be to route out or remove a portion of the wall studs a predetermined thickness to except the heigth and width of your joist to allow a portion to remain sticking out to attach the flooring to. I believe that code has only a certain amount that can be removed. I am sure some who are more familar with the code can instruct you on what that amount would be.

The wider the spacing the bigger the joist needs to be to accept the additional load for that spacing. I guess you get into an area whereas the appearence of the ceiling enters into what material you choose to use verses what could be used if the appearence is not a factor. Again it is dependent on your ceiling heigth on the first floor as to what material you choose to use. I guess what I am trying to say if that it enters into the design phase of building trying to incorporate what you want with what will work. You stated that you were going to use "rough sawn" joist. My mindset is that rough sawn joist are 4X where they could actually be 2X. Sorry about that confusion.

MountainDon · December 13, 2009, 11:52:15 AM

I think that for appearances, 4x with 30 or so inch spacing looks better than 2x at closer spacing. hat's just an opinion.

Generally speaking if you double the thickness of a joist you can double the spacing distance, but that is only talking about the ability of the joists/beams to carry the weight. The sag or flex factor of the flooring has to be taken into account.

As for whether or not to let in the end joists, if you are using something like 4x? for the spans across the open areas, there is no reason you can not use the same size beam at the end wall and not let it in.

John_M · December 13, 2009, 04:52:31 PM

For what it's worth:

My structure is 18 feet wide and I used true 4 x 12 hemlock beams to span the entire 18 feet (with no center beam). I used 2 x 8 T&G flooring spaced at 48 inches on center. It is pretty solid!!

I agree that closely spaced 2x material defeats the purpose of a T&G floor!!!

December 13, 2009, 09:51:28 PM

I like 32" centers it looks good and calculates pretty easy. You said you were using a center beam, that needs to be checked, I'm assuming the joist spans are 10' each.
http://www.awc.org/calculators/span/calc/timbercalcstyle.asp?species=Western+Woods&size=2x8&grade=No.+2&member=Floor+Joists&deflectionlimit=L%2F360&spacing=16&wet=No&incised=No&liveload=40&snowload=-1&deadload=10&submit=Calculate+Maximum+Horizontal+Span
At 16" centers a 2x8 works for a joist, if it's not pushing the limits, a 4x8 will work on 32" centers. 2x6 T&G works well over that setup.

dug · December 13, 2009, 10:43:49 PM

a 4x8 will work on 32" centers. 2x6 T&G works well over that setup.

Thanks, I think this is what I will go with. I could not find how to calculate supporting beam on the link you provided. It will be 12 feet supported by a center post, so a 6 ft. span. I was thinking 4 by 10 or 12 in.

Don_P · December 14, 2009, 07:53:20 AM

The beam is supporting 6'x10'..at 60sfx50 PSF=3000 lbs
At that load and span, guessing that "average" wood will be used, a true 4x8 was the bare minimum, anything above that is gravy. The girder tables in the codebook calls for a double 2x10 or a triple 2x8 if store bought lumber is used.