bedroom loft construction

[diymom]

We have a house with amazing 11'6" ceilings in the bedrooms, and when we moved in I promised my 9 year old I'd build a loft on one side of it for her. (What was I thinking? I'm really not sure, just wanting to help sell her on the idea of moving from NJ to Canada) The idea is for a loft/ balcony area to go over the door to be approximately 4' deep and span the full 14' length of the room. I would like to do this without any posts in the middle if at all possible. What I've come up with so far is ledger boards bolted to the studs on the adjoining 3 walls and some sort of beam along the front to be able to fix my joist hangers to.

Here's where I need help. What size do my ledgers need to be? (2 x 4, 2 x 6, 2 x 8?). Will 2 x 4 joists be enough support across the middle to support the floor? And the big question-- will it be possible to span 14" without posts? If so, what will I need to do?

After I built a playhouse out of old doors for my girls at our last house they are convinced I build anything, I don't want to let them know otherwise just yet :)

[woodall83]

Alot of factors to your question. I'll give you some basic answers. In order to span 14' without posts you need at least a 2 x 10. You'd probably be ok using 2 x 6 for the 4' span but I would suggest 2 x 8 or 2 x 10 because you never know what will go on up there, how many kids, etc. Better to be overkill. You have other choices including I-joists, LVL's, etc. that will change your max joist span. One suggestion would be to use posts at either end against the wall for more support. Or you could "hang" it from the ceiling joists. You have a few options. But I would stay away from 2 x 4's.

[Don_P]

The outer beam supporting 2' of the deck X 14' of length X 40 pounds per square foot =1120 lbs. A double 2x8 of Select Structural Douglas Fir or #2 or better Southern Yellow Pine (SYP) or LVL will work. If you go to #2 SPF I'd kick it up to a double 2x10. Half of that 1120 needs to be adequately supported at each end of the front beam, a post under the beam against the wall would be nice.

A joist is supporting 8" to each side of the joist, so 16" wide (1.33 ft) X 4' long X 40psf= 213 lbs. A #2 SPF 2x4 passed fine, this isn't a "stud" stamp, its a #2 or better stamp. A 2x4 starts to get into trouble around 500 lbs at that span (bending moment squares when span doubles, don't worry much about 2x4 joists or not, the beam with its long span is the gorilla in the room)


The back ledger will be supporting roughly 213 lbs at each stud connection if you are hanging the ledger with no posts along the wall. A 5" ledgerlock screw in single shear is good for about 150 lbs so 2 of these or similar per bearing would do it. (pg 7 of the report below);
http://www.icc-es.org/reports/pdf_files/ICC-ES/ESR-1078.pdf

[Pokey]

Don- i'm just curious why you didn't mention the joists running the long way rather than the short way? I'm no expert in this matter, not even close, i just know if i was building it i would run my joists over the 14' span. Of course this would just be winging it with no reguard for engineering.

Most importantly sounds like a great project! I can't wait until my kids are a little older so i can have some fun projects too!

[Don_P]

Ummm, talk about staying in the box... didn't think of it.

That's easy to check,
IRC table R502.3.1(1) shows #2 SPF 2x8's will go up to 14'11" spaced 12" on center.

Remember to refigure the connection loads on the ledgers, that 1120 lbs is on each 4' end ledger now and needs to be distributed among the number of studs there.

And, you should check where that theoretical 1120 lbs is going once its in the wall, is it a supported, load bearing wall or simply a partition on a scrap of subfloor. Probably not a real issue here but probably worth looking at.