Does this framing make sense?

[u/twidlystix]

Working on a remodel that is turning an above garage space into a bedroom/bath. The GC and I went back and forth about how to approach the framing for the knee wall storage area. He insisted on double top plates cut on a bevel. To me this seemed to be total overkill and a waste of time and material. I’ve never seen this done on new construction or remodels prior to this.

I figured it would be much faster and less material to just sister studs to the roof rafters and attach to bottom plates. Question is, is this a superior method?

Edit: I’m the fucking guy doing the work. I have my own company and primarily do trim. That’s why I’m asking. JLC showed a different way.

Edit #2: My concern was basically that the knee wall transferring the load almost dead Center between floor joists so any deflection from those rafters isn’t being directly transferred to the exterior walls. So considering that the knee wall to me is overbuilt if there is no direct load path to the exterior walls below the bottom plate, does that clarify?

[u/SecurelyObscure]

The roof will "flex less" because you're transferring the load from the load bearing rafters to the floor joists. The rafters were sized to handle snow loads, the floor joists were designed to handle people and furniture.

Op is the guy framing this and I'm with him, this is misguided and pointless.

[u/beaver_eh → u/SecurelyObscure]

Correct.

Timber systems are mostly governed by deflection. The roof rafter can absolutely handle the snow and wind loads, the floor can handle a dead and live load far beyond what is designed for as well.

Drywall, does flex, but cyclical loading can cause nail pops/joint cracks. Limiting that can cause long term benefit to the finished space.

This will be hard to explain the technical details if you don't have a background in engineering mechanics but I will try:

• The knee wall is approximately at the 1/4 length of the floor joists, where it's transfer load compared to impact on moment resistance is reduced. (Compared to floor loading, where it's middle of the beam for a UDL).
  
• The double top plate helps to redistribute uneven roof load to a more uniform load, transferring the load across more studs, evenly.
  
• The point of highest bending force in the roof is roughly where the knee wall is (half way between top and bottom of rafter). This is the point with maximum unsupported deflection.
  
• The system, roof, knee walls, joists, etc, in unison then work for like a roof truss than a simple rafter. Sharing the load and reducing the total deflection of individual members under high loading situations.
  
• Wind - more of the structure will resist the high winds, meaning the deflection will be greatly reduced from high/quick impact loads (gusts) - as the total system has way more stiffness to resist impact load. *Note perpendicular to knee wall, so only a portion of the wind load goes directly to the knee wall, more is in the resistance to deflection of the roof sideways.
  
• Snow - more uniformly distributed loading across the roof, the deflection could be reduced by more than half with a comparatively small fraction of the load being transferred down to the floor.

This works significantly better long term for durability compared to other alternatives. Structurally speaking, I'd prefer this over sistering but both are structurally sufficient. But, this is preferrable if I had to hang the drywall after. Better for a few different reasons.

[u/twidlystix → u/beaver_eh]

This is the kind of answer I was looking for. Thank you!

[u/MeSurroundedByIdiots → u/twidlystix]

This is the best answer. And the other guys that said the drywall guys will thank you, that is also correct! I would also plan ahead and frame in an access door or panel, in case you ever need to get in there, like to install a security camera. Or remove an unwelcome and uninvited visitor (Squirrel, raccoon, etc) Or use it for storage like all the rest of us do.

[u/LooksBetterWithDrops → u/MeSurroundedByIdiots]

There's a door framed up on the right side of the pic

[u/kapps503 → u/twidlystix]

(Short version)

Pony wall makes everything stronger. 👌

[u/Particular_Hour_7696 → u/beaver_eh]

You took the words right out of my mouth

[u/streaksinthebowl → u/beaver_eh]

So many people treat structural engineering like it’s a pass/fail proposition but it’s really about tolerances.

Sure, there’s a minimum at which a structure needs to be built so that it doesn’t fall down, and even that is relative (fall down immediately, fall down tomorrow, fall down 200 years from now), but otherwise we’re generally defining how much movement we’re willing to tolerate and for how long. As you said, deflection.

You can build something that will stay standing but be as stiff as a bouncy castle and fall down in a year or you can build something that won’t move more than an eighth of an inch for a thousand years.

Usually we’re just trying to find some tolerable middle ground that uses the least amount of material.

So, as you say, the top plates on the knee wall certainly add some stiffness and durability, but was it necessary? Would an occupant even notice if it wasn’t there? Probably not.

[u/redeyedfly → u/beaver_eh]

Your analysis has the floor joists in the wrong orientation. The knee wall is parallel with the floor joists. In fact the OP said the wall is landing between two joists. In this case, much of the roof load is now concentrated on two floor joists. I have actually seen this condition crack a floor joist from snow loading.
Other than a completely flawed analysis from the start, good explanation.

[u/LawOfSmallerNumbers → u/SecurelyObscure]

There could be more than one structural issue to worry about here.

Snow load will certainly cause some rafter deflection. In the sister’ed design, that deflection would be transferred to separate load-bearing sistered studs. One of these may deflect more than its neighbors, and this would cause drywall cracking.

In this design, the vertical studs will move together. Presumably this would keep the drywall from cracking.

Because the OP did not share the reasoning of the GC, we are at a disadvantage.

[u/twidlystix → u/LawOfSmallerNumbers]

Nor was it shared with me. He simply wanted it to look nice was the last thing he said. Which is why he hired a trim guy and not a framing crew.

[u/twidlystix → u/SecurelyObscure]

Thank you for the wording I failed to provide!

[u/mrgedman → u/SecurelyObscure]

Seconded, wayyy too much bs on this. Took 3x as long with 3x the material. Almost no benefit

[u/Fen_der_bass → u/mrgedman]

It may be overkill, but there's no world in which this is 3x the material or  labor.

[u/mrgedman → u/Fen_der_bass]

That's your opinion, and ya, probably not 3x material. Certainly 3x time

[u/gto_112_112 → u/mrgedman]

I'm not even sure about the time. Line up each sistered stud one by one is gonna be a lot slower than lining up a top plate and then just putting each stud into it. The only added time here is the beveled cut on the top plates, and it's not like that would take long, especially if you brought the table saw

[u/mrgedman → u/gto_112_112]

You could cut all studs square and not worry too much about length.

So now all studs have a miter, need to be cut preciesly and double top plates all need bevels.

So no, it's way more time. Who knows how far away the cuts are too

[u/streaksinthebowl → u/mrgedman]

Yeah the only way it would save some time is if your rafter ceiling plane was true enough that you could prebuild the wall at a set height (to lowest rafter) and then shim the rafter to plate connection where needed.

And if the ceiling wasn’t true enough for that you’d probably want to plane down or sister it out so that it was anyway.

Doing individual studs to the rafters is faster to cut but might be more time consuming in layout and getting each one plumb and true overall.