best way to constuct knee wall to support rafters...
best way to constuct knee wall to support rafters...
(OP)
A client wants to install a new roof on a trailer. He want to increase the ceiling height by about a foot. The lumber supplier told him to build a one foot tall wood stud knee wall on top of the existing wood stud wall and then have the rafters attach to the top of the knee wall. My initial thought was this creates a hinge point type connecting between the proposed knee wall and the existing wall. Am I overthinking this or will this work if the knee wall sill plate is fastened to the existing wall top plate with bolts every 16" o.c. or so?
One other thought I had was to cut thru the top plate next to each stud and sister a 4' long wood stud to the existing stud (3' sistered to the existing stud and 1' of the new stud extending up ). See the attached pdf.
Thanks.
One other thought I had was to cut thru the top plate next to each stud and sister a 4' long wood stud to the existing stud (3' sistered to the existing stud and 1' of the new stud extending up ). See the attached pdf.
Thanks.






RE: best way to constuct knee wall to support rafters...
RE: best way to constuct knee wall to support rafters...
Isn't the situation usually like this?
It is only a foot- maybe just sheathing the ext w/ plywood would work.
I get a lot of these, but much more than 1 foot. The Builder always always claims there is no need to add anything - grrrr.
RE: best way to constuct knee wall to support rafters...
RE: best way to constuct knee wall to support rafters...
RE: best way to constuct knee wall to support rafters...
RE: best way to constuct knee wall to support rafters...
I had thought of the truss leg option and will discuss it with my client but he wants to do everything as cheap as possible and I see him trying to do this himself so the labor won't cost him anything.
So if he doesn't want to go with the truss leg option is a 1' knee wall acceptable (bolt plates together every 16"???) or should I go with the 2nd option of sistering the new studs to the existing studs?
RE: best way to constuct knee wall to support rafters...
RE: best way to constuct knee wall to support rafters...
Depending on the span rating of the plywood, you could potentially do this at every other stud.
If you have a very deflection sensitive wall finish I would probably add in new full-height studs as the strap is somewhat gimmicky.
RE: best way to constuct knee wall to support rafters...
Better check the floor framing of the trailer to see if it can handle the additional load. The floor joists are usually cantilevered out from the chassis of the trailer. You may need to install new bearing walls at the exterior of the trailer under the joists.
Also, I do not like the idea of cutting the top plate to install the new vertical member. The existing top plate resists the chord force for the existing roof diaphragm, and unless you are going to abandon this as a diaphragm, I would rethink this detail real hard.
Mike McCann
MMC Engineering
RE: best way to constuct knee wall to support rafters...
RE: best way to constuct knee wall to support rafters...
Mike McCann
MMC Engineering
RE: best way to constuct knee wall to support rafters...
RE: best way to constuct knee wall to support rafters...
I also don't want to seem like an elitist; But I've been stiffed for payment on more than one "cheap" job, including two trailer mods. If the client is starting with that cheap a base home, there is a higher chance that they will fail to be able to pay you when anything goes wrong and they are faced with the "Finish the job or pay the Engineer" question...
RE: best way to constuct knee wall to support rafters...
GMTO. I did a very intensive project on one of these years ago, got paid bupkus, therefore no more trailer jobs for me.
RE: best way to constuct knee wall to support rafters...
Garbage.
RE: best way to constuct knee wall to support rafters...
They always, always result in a black hole of hours expended, why should I take them, it will only increase my yearly gross by 1% but give me a colossal headache?
I always say, "Sorry, I no longer deal that type of construction..." and tell the owner he can find another engineer by checking into our State Registration Board, on-line.
RE: best way to constuct knee wall to support rafters...
Oh, and TERRIBLE pun intended, should that not have been obvious.
RE: best way to constuct knee wall to support rafters...
Bad job. Bad, bad jobs.
RE: best way to constuct knee wall to support rafters...
I am gathering my talking points about Imperial vs Metric, so look out.
RE: best way to constuct knee wall to support rafters...
RE: best way to constuct knee wall to support rafters...
RE: best way to constuct knee wall to support rafters...
I have a number of frivolous threads going there.
RE: best way to constuct knee wall to support rafters...
RE: best way to constuct knee wall to support rafters...
Me thinks someone doesn't like me!
RE: best way to constuct knee wall to support rafters...
RE: best way to constuct knee wall to support rafters...
The definition of a structural engineer: overdesign by a factor of 1.999, instead of the usual 2.