Ceiling joists for a cabin loft

[LatinForLiar]

I am in the planning stage for an upcoming shed/cabin project. It will be 10'x20' on PT skids. Location is Southern Maryland. I'd like a portion of the building to have a loft. Assuming 8' high side walls, and a roof that's reasonably pitched, I'm running into the problem of how to maximize headspace in the loft.

My question is, can the joists be placed below the top plate of the wall, at say 7'? I see at least 2 issues to doing this:

1. the walls will be less resistant to outward forces from the roof. I can't use rafter ties, since this will eliminate the loft space. I could do collar ties, though they'd need to be pretty close to the rafter for the same reason. is there bracing that would be sufficient? Maybe this isn't really a big concern?

2. What sort of framing would be required to support the ceiling joists? I presume I'd need short "cripple" studs and blocking (essentially creating a false top plate), but maybe there is a simpler way?

Any thoughts/insights are much appreciated.

[Don_P]

You can do it the way you describe, or notch ledgers into the studs UNDER the joists, run the joists over the ledgers and tie them alongside to the studs well. At 7' with 2x8 joists spanning the 10' you are so close to the plate that spreading/ bending of the walls is not an issue. If you raise the walls to higher than 8' I'd use a ridgeBEAM and hang the rafters from that, you'll likely need a post in the middle.

Draw it in section to scale with all the framing in, I think your loft is under 5' at the peak with a 12/12 pitch.

[SouthernTier]

I am in the planning stage for an upcoming shed/cabin project. It will be 10'x20' on PT skids. Location is Southern Maryland. I'd like a portion of the building to have a loft. Assuming 8' high side walls, and a roof that's reasonably pitched, I'm running into the problem of how to maximize headspace in the loft.

My question is, can the joists be placed below the top plate of the wall, at say 7'?

I had to deal with something like this in my cabin design.  Don't want to do knee walls, but also want a 22' wide cabin and limit my rafters to 16' long boards (longer ones harder to find).  Then there is the code requirement for 50% of floor space > 5' was also > 7'.  So I lowered the loft joists, but had to limit them to 6" stock, which meant they had to be on 12" centers.  Details here: http://countryplans.com/smf/index.php?topic=12801.msg167800#msg167800 

I have since modified my design to have those joists sit on a girder/beam rather than hang from the sides with simpson brackets.  Also will go with 4x6's rather than 2x6's.  Details here: http://countryplans.com/smf/index.php?topic=12801.msg184944#msg184944

Note, haven't built this yet, but hope to soon.

[LatinForLiar]

I was already planning to do 2x6 joists at 12" oc to save 2" of headspace (sad!). I think it may even be cheaper.
I realize that no matter what I'm going to be hunched over up there (it's for storage).  I just don't want to have to belly crawl.

I suppose if I was notching the studs to accommodate a ledger (2x8 ledger?) I'd want to use 2x6 studs? This seems like a pretty reasonable alternative.

Southern Tier: I'm unclear on your girder/beam design. Is this in the middle for support, or along the sides to support the ends of the joists? If the latter,  won't this require the wall to be quite thick ...at least double? I am assuming it is sitting just inside of a standard 2x4 wall?

[SouthernTier]

I was already planning to do 2x6 joists at 12" oc to save 2" of headspace (sad!). I think it may even be cheaper.
I realize that no matter what I'm going to be hunched over up there (it's for storage).  I just don't want to have to belly crawl.

I suppose if I was notching the studs to accommodate a ledger (2x8 ledger?) I'd want to use 2x6 studs? This seems like a pretty reasonable alternative.

Southern Tier: I'm unclear on your girder/beam design. Is this in the middle for support, or along the sides to support the ends of the joists? If the latter,  won't this require the wall to be quite thick ...at least double? I am assuming it is sitting just inside of a standard 2x4 wall?

The original design had a beefy (6x6 or at least triple 2x6) beam down the middle with joists attached at the end using simpson hangers.  The second design (need to fix the link) has the joists sitting on the "girder/beam".  I put that in quotes because it is not really a girder/beam, but rather the joists would be sitting on the wall, which is a load bearing wall (with additional support columns under it in the crawl space - not shown). I don't believe load bearing walls need to be thicker than standard 2x4 thickness.  That said, there are actually three doors in that wall - a closet door, the door into the bedroom, and than a sliding pocket door for the storage area under the stairs.  But I have 2x6's running the length of the wall above it to distribute the forces.

I haven't done any calcs on this, but I should.  Basically to double check that double 2x6's can bear a loft area of about 3.5' (typical door width) by 11' (half the loft with) or 38.5 SF  (round up to 40 SF).  I think for a loft I'd use 10 psf dead load and 40 psf live load, so they would have to handle 2,000 pounds total or 571 pounds per foot.

Actually, just ran the calc on this online calculator: https://courses.cit.cornell.edu/arch264/calculators/example8.1/ and it said use a 2x8.  I would think a doubled 2x6 would be as strong, but I could be wrong.