Installing load bearing stud wall in loft conversion

[panza]

Hi,

I am planning a loft conversion in my 1920's gabled semi. The roof is traditional cut roof with purlins spanning from gable to party wall with a single diagonal prop at mid span onto the central masonry spine wall. I am planning to install new floor joists front to back designed to support load bearing knee stud walls to replace the purlins.

My question is - is it necessary to birds mouth in the top plate of the stud wall into the rafters, or is it possible to simply cut the top plate with a chamfer to suit the slope of the rafters and nail or screw it? Cutting birds mouths into the rafters close to the back of the existing purlins will be difficult due to restricted access.

Thanks

 

[ree]

I dont quite follow what you have or propose - why not post pics?

Often, the purlin is left in place, and the knee wall top plate will go up to the purlin.
Or, screw your top plate to the rafters, and infill between top and sole plates with your studs cut on the angle.
Or, build a stud knee wall with the top plate at the angle, and rear it up into place below the rafters.
Set the wall out to make sure that studs land below each rafter.
Besides always screwing into rafters, you can also use metal Simpson clips.