Knee Wall Framing

rstork

I'm finishing the second floor of a cape (2 beds and a bath), dormers already in place. When framing out the knee walls, is there any reason (code or otherwise) why I need to construct with a top plate? The knee walls are not load bearing. Can I simply tie the studs directly to the roof rafters? Other than not having a continuous nailer for drywall, I can't see why I would need a top plate. Thanks in advance for all advice.

R

D.Foster

Is this a knee wall that would create an eve space?? I dont think it would be a problem to do it that way. As far as nailers, the rafters that you are nailing the knee wall studs to would be your nailers at that intersection right?

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Burby

I would think once you connect a rafter to a c/j you make it a bearing point. Any deflection to the rafter/roof would then transfer to the c/j because of both being connected. Then resulting in possible c/j sagging, nail/screw pops to the ceiling below.
Without a top plate you would then also have no distribution of the weight during time of deflection, it would be direct & cause more.
Also how small is this room or size of the rafters that there needs to be no bearing point for allowable rafter spans according to the IRC table?

Are you building from plans or just on an existing home with an unfinished attic space? And how many years ago was this house built?

I take it no plans were submited to the building dept for permitting? With the new IRC, no matter is now loads or wind loads, they are a bit different than pre IRC. Most building Dept try to catch all the missing bracing, bearing, ect for the most part. Some areas still fail to push the new codes, but they are getting fewer & fewer.
That is my opinion, right or wrong, but do give some thought to your project to be sure.

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KentWhitten

a top plate keeps things straight, stabilizes the rafters a little, creates a nailing surface for sheetrock among others. do you need to do it? no. would it be advisable? yes.

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Burby

--=oops si daisy, correction to above:
With the new IRC, no matter is now loads or wind loads. should be if snow

Thank you, now back to normal reading..

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wallmaxx

That's what I was thinking. Like a purlin....it evens out any individual crowns in each rafter by tying them all together.

rstork

Thanks to all for responses. FYI, house was built in '57, 2x8x13' c/j's and 2x6 rafters. I have original plans for house, which called for upstairs rooms and bath, so I know it was engineered/built for this additional framing and the roof loads are already accommodated by the existing structure. But I guess it's true that once studs are tied in to rafters, any additional snow loads will now be dispersed through these knee walls as well. As to local building department, this is a property I own and I'm trying to avoid having to pay $2500-3,000 for an architect to stamp plans that already exist and have to retrofit to current codes when everybody else on the block is grandfathered in. Thoughts?

R

Burby

In the roof system, according to IRC, purlins are permitted to reduce the span of the rafters, but must be continous & supported by 2x4 bracing installed to bearing walls at a slope not less than 45 degrees from the horizontal. The braces shall be spaced no more than 4 ft on center & the unbraced length of braces shall not exceed 8 ft.

What he is suggesting doing is, (if are there now, removing the purlin braces) then creating a knee wall to separate storage space from living space.
This, (because is now a wall, needs to have a double 2x4 plate on the top and a single plate bottom. The knee wall has to be built over an existing bearing wall below. With the rafters sitting on this wall, it does become a bearing wall.
Without bearing below it will be not be to code as well as create problems.
Knee wall should also be tall enough to allow for a 6ft 8in finished clearance once floor & ceiling is completed.

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Timuhler

The topplate is required if the wall is drywalled on both sides and a firestop, but if the area behind the kneewall isn't going to be finished, then it isn't required.

We have done it both ways, but mostly we try to have the space behind the wall finished for storage. So we nearly always put in a topplate (not beveled).

When our plans are engineered, the engineer usually requires blocking between the floor joists below the kneewall. We had one plan that called for trusses, but we stick framed it and had it engineered after. One kneewall he had us shorten and attach those truss clips to keep the wall connected to the rafters, but not load bearing.

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Deicide1

Do the top plate, don't be lazy.


Rip it down with the same angle as the roof and do it the right way.

Timuhler

I don't think that beveling the topplate on a kneewall has anything to do with "the right way". It is an unnecessary step that is a waste of time.

What are the advantages? How are you going to rip that angle? Table saw or circ/wormdrive?

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orson

I'm with Timuhler on this one, although it might give you a warm fuzzy to rip the plate you're just wasting time. You're only going to have a tiny gap behind the drywall at the corner, especially if you run the ceiling drywall past and then butt the wall.

There's no problem with not putting a top plate on. A bit more time consuming by the time you nail all your blocking in.

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Deicide1

How is it unnecessary? In order for the drywall to look good, you either need a top plate on you would need to use a laser level to set the studs accurately.


Why ask me how to rip it down? Use the t-square on your circular saw or rip it with a table saw. If you guys can't handle simple **** like this, then get out of the trade and do something easier.


Also, I imagine this wall is going into an older house...generally in an older house the rafters have some sag to them, so what we do is jack them up where need be and straighten them out. Just be careful not to jack up too much to avoid nail pops in the roof etc...

Tinstaafl

This is going to be one of those discussions where everyone's right (or wrong) depending on the particular circumstances and your own style of building.

While I agree that a top plate will help line up the studs, you'd still need to laser or stringline it to be sure it's really straight.

As for:

It was mentioned earlier in this thread that doing something like that is going to transfer pressure to the ceiling joists below. If I have saggy rafters, I shim the non-saggy ones to match as long as they're not ridiculous. If they are, you need to address the sag by other means, probably sistering them.

neolitic

It will make it easier to make
the drywall look better.
Nine times out of ten, no plates
and you have a wavy angle.

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Deicide1

It's tough to even discuss how the load will transfer, as only the original poster has seen the house, so I won't even bother discussing this.



All in all, do the damn top plate, it would only take 10 minutes to find the angle, rip it down, and nail it up.

WarnerConstInc.

Neo- Put some semi-gloss on it and it looks like you are in the Ocean.

A W Smith

the rafters closest to your gable ends are almost guaranteed to be higher than the central common rafters. What this means is that the drywall on your knee wall is also going to be taller at the ends and look like ****. you would need to find the lowest rafter and run a masons line to both ends and work from that. if its a cape with a 12/12 rise run rip the corner off a 2x6 to a 45 degree and use that as a top plate. Do not attempt to draw up the plate against the higher rafters because in doing so your top plate will pull outward as well as up. Putting a sinking curve in the drywall. Do not attempt to jack the lowest rafters to a common height as well as it will sink the floor as much as it will jack the roof causing the 3/8 inch brittle gypsum boards in the room below to nail pop their gypsum lath nails (tiny heads) that they used for drywall in that era. Once you get your knee walls straight you can either strap down the existing rafters to a common plane using 5/4 spruce furring from gable to gable, or sister the higher rafters to a common plane even with the top of your knee wall top plate. If you are concerned with shrinkage in the lumber of your new knee wall let the last foot of the ceiling drywall float on top of the drywall of the knee wall (ceilings should be drywalled first). you could even use isolation clips for the top plate of your knee wall to break the structural connection just like the method used to isolate roof trusses to combat seasonal truss rise. Myself, I never nail the studs of a knee wall against the side of a rafter.

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D.Foster

Find the angle?? It's the same as the plumb cut,..That is , if he framed the roof he should know. And a chalkline would work fine,bring all your studs to the line. A top plate would follow crowns as well and create waves too.
And from what i have read of Tim Uhler's articles in JLC, he seems to know what he's doing. 9/06 Vol.24 No.12 I don't think you have to explain how to make a bevel rip.

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Deicide1

I don't think I can assume that this guy framed the roof, therefore I said find the angle...how he finds this angle does not matter to me.


I don't know anyone on this site, so I merely answered the guy's question. If he knew the answer than he shouldn't have asked.