supporting timber floor joist along stick framed wall
So in my 30×26 stick framed house we are using 4×6 timber joists for the upper loft floor. they will be set 2′ down on the 10′ wall (creating a 2′ kneewall). they also run the direction of the rafters and will aid with holding the house together.
I am trying to find the best way to attach them to the wall. I intentionally did not build them ontop of the wall and build another short wall ontop of them for fear of “hinging” the kneewall. I am thinking of running them long into the wall cavity and using either truss locks or bolts attach them to each 2×6 stud. (the other end of the joists will be dropped into a summerbeam in the middle of the house) . I am just concerned that these 14′ long joists will need more support than being bolted to the studs- am i overconcerned? Or do i need a ledger block? is it better to let the ledger into every stud or attach the ledger to the face of the stud? if i attach the ledger to the outside, what is a good way to finish the 1 1/2″ ledger board in the room?
Does this make sense?
Replies
Interesting. No pat answers from me, so just food for thought to get the ball rolling. Your concern for the 'hinging' is unfounded ... as the floor is the element that transfers the forces ... just like in a two story house. Probably would have been better to frame half the house 8' and the open section 10' and built your knee wall on the loft deck. ... but hindsight.
Now you have essentially balloon framed your house. I think your joist attachment is OK, but since your joists are 4x, I wonder about the way it loads the stud (on the side, rather than down the center). You've only got a 6" joist spanning 13', right? Is this OK? Seems it might be a bit of a long span. If you think since it is 4x, you've bought a lot more structure, that may not be correct. 4x is more structure, but it's still only a 6" joist ... it's the depth that gives you structure, not the width.
You could let in a ledger on either side of the wall. Seems very doable.
You MAY have to include fireblocking as well. Did you talk w/ your BO about this? He may have some suggestions and/or requirements. Walls over a certain height or that span floor structure often need this.
Another way might be Simpson hangers, but not sure if they make such an animal. They make them for all kinds of applications that you or I haven't even thought of.
Hinging
I don't understand what you mean "your concern for hinging is unfounded". It depends on how he intened to use the space and and how he planned to structure the roof . Not structured properly structured, you could very well have hinging. It seems to me that more info. is needed before making such a blanket statement.
Good point, I assumed stick framed w/ a ridge beam, I think. I stand corrected. It's a whole package, so just thinking of one aspect may or may not be OK w/ the rest of it.
Before the walls are framed
notch the studs to allow a 1x ledger to be installed flush. It supports the joists, it does not stick into the room. This is the typical balloon frame detail and was used before platform framing became common. You need fireblocking in the walls behind the ledger.
I always thought classic balloon framing used a 2x ledger, not 1x. Regardless (I wouldn't follow some balloon framing that I've seen before), I wouldn't use a 1x to set joists on. May not even be code to rest a joist on less than 1 1/2". With 2x6 walls, it's nothing to notch for a full 2x. But I'm not an expert in the framing dept. ... Isn't there someone else in here to lend some food for thought? No offense intended David.
None taken.
2x6 walls are a newer thing, mostly for insulation depth. Typical balloon wall that I have seen is 2x4. and the let-in ribbon is 1x. There are framing diagrams out there on the web if you want to look. Sometimes you see a ledger simply nailed to the face of the studs, but then you are depending entirely on the shear value of the nails to hold the floor up. With a 3/4" thick ledger let into a 2" wide stud, assuming 1500PSI compressive strength in the studs, you get ~2250PSI of bearing at each stud, far more than you can get with nails... plus you can nail each joist to the side of the stud.
One should ask here how the roof will be constructed. Unless there's a substantial ridge beam (with some support in the middle) there will be outward thrust on the walls, and it wiould be unwise to notch the studs.
One would side nail the stud to the joist, though even w/ a let in ledger, right? So the outward thrust wouldn't really be an issue; particularly since the notch is below the tie point.
The notch would weaken the stud right at the point of most stress.
The roof
shouldn't be exerting any significant thrust on the walls. It should either use ceiling joists to control thrust (which the OP has said he is not doing) or a structural ridge. Presumably the OP is having this building engineered. I don't see any advantage in balloon framing but we don't have the whole story. If he's thinking that his plan will help support a roof that's inadequately framed then....
With a structural ridge there should be no out ward thrust so conventional framing would have been sufficient. You should let in a 2x it will be much stronger. What is the joist spacing? the sketch appears to have a joist spacing of 24" oc? did you check a 4 x 6 for this span it appears light to me?
"You should let in a 2x it will be much stronger"
What would be the failure mode of a 1x ribbon?
first i would not nail the ledger i would reccomend a let in ledger. Usually the code requires a minimum bearing so as not to crush the wood fibers. With a 1 x ledger the bearing area is very small. the joist are 4x and they appear to be spaced at 24"oc thus carrying more load than normal. So if there is a 16 foot span with 24"oc and a 50PSF load the wood bearing pressure is around 300psi. with a 2x ledger the bearing area is doubled and the the bearing area is halved.
If you are going to let in the ledger why not go for the 2x ledger it will not be anymore work?
i am just being cautious fact is the ledger is not likley to "fail" but you never know.
No disputing the math
the bigger ledger reduces the load per square area. But, the joists are 4x, which is twice as wide as normal joists, and they aren't spaced much farther apart. The handful of balloon framed houses I have worked on have had let-in 1x ledgers and 2x joists nailed to each stud, and I have never seen anything remotely like a failure. I think he said he's doing 2x6 (5-1/2") walls, in which case a 3/4" deep notch would be 14% and a 1-1/2" notch would be 28%, or slightly over the usual 25% limit on notching bearing studs. If I notched a 2x ledger into a 2x6 stud the inspector here would be staring at it and making me nervous.
I'm pretty sure I couldn't build what he's proposing in this jurisdiction without engineering, so I'd have engineering on all of this and I'd follow it, it would not be my job to figure out the sizes, the notches, etc. Either way I don't see a 1x ledger crushing or folding or anything else, in most cases. I guess if someone puts a 130-gallon soaker tub with 4 people in it, bearing on 3 of the joists, then it might creak a little.
FWIW
my shop is a story-and-a-half building, platform framed. The first floor walls are 9 feet, the second floor bearing walls are 2 feet in some places, and 6 feet in others. No need to balloon frame what he's talking about.....
That's what I thought, too. Eliminates having to fire block, too.
I've seen a number of bearing studs notched for a 2x let in ... we were taught that it was OK. Maybe it's because you aren't just notching and leaving ... you are inserting a full filler back in. We were taught when needing a single 2x header over a small window, you could notch the stud and let in the header and eliminate the jack (short) stud.
Stud
Cotton,
Nail beam to stud, fireblock under beam, put perpendicular stud under fireblock.
KK
Good comments and suggestion
So I like what folks have to say about the let in ledger- will do. Just to clarify for everyone- there will be a structural ridge supported in three places. The load on the described floor system is intended to be a loft. According to the structural analysis program that i have recieved from my days as a timber framer- the 4x6 hemlock (#1 grade) does meet the cut (but i am no engineer). The beauty of building in an area with no reinforced code or building inspector is that i can listen to all the great stuff from here and apply it- but that can also bite in the arse.
Still open to any more thoughts and advice. Thanks