What are some options for converting a trussed roof into living space?
My understanding (please correct me if I am wrong) is that the following needs to be taken into consideration:
- proper floor joists need to be installed/sistered.
- Knee wall supports need to sufficiently replace the webbings of the truss to support the roof
- space needs to be considered to accommodate proper insulation between the living space and the roof where it contacts
I've seen a lot of systems/contractors that seem to specialize in this in the UK, but I can't seem to find much information for North America. Not sure why that is.
Has anyone done this? Is it at all a DIY proposition (providing proper engineering documents are approved)?
My purely hypothetical method at this point (how far off base am I?):
- install 12" floor joists 16" OC
- install kneewall between current 2x4 truss 'rafters' and new floor joists.
- install top cross-bracing/collar tie (not sure how much/spacing)
- cut joist webbing (!?)
- between knee wall peak, install 12" 'rafters'...these wouldn't be load bearing but act as spacers for insulation and interior ceiling.
- leave gap between original 2x4 rafters and sheathing for ventilation
- insulate remainder 10" of rafters and knee wall
It seems that the above plan would basically be converting the current truss system into a box storage truss, albeit with larger floor joists.
Am I in the ballpark? Again, I'd definitely be consulting with an engineer to do it right. Just trying to get an idea of what it would take.
With the above, I think I'd need to pull off the first layer of sheathing on one side of the roof to bring in the joists. If I had a load-bearing wall mid-span, could one bring up half-joists into the attic directly (since these joists are purely for floor support while the original 2x4's are acting as the ties?)
Some more details of this particular example:
The attic space is 22' on the side parallel to the trusses (28' on the other side). It's a 12/12 roof, so that's a good 11' at the ridge, which even with new floor joists and a 5' knee wall should be plenty of room for a nice space.
The trusses are double cantilever style:
I also came across this in Fine Homebuilding on using welded steel as part of the rafter structure. More applicable for creating cathedral ceilings but thought it was interesting: