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)?
UPDATE:
My purely hypothetical method at this point (how far off base am I?):
- install 12" floor joists 16" OC
- install kneewall between current 2×4 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 2×4 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 2×4's are acting as the ties?)
UPDATE 2:
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:
Best Answer
Yes. Very possible. It has to be engineered though. We have plans to do just this. The drawings and engineering cost around $1000. I wouldn't try it unless an engineer has looked at it, drawn a plan and signed off on it.
For us we are going over a 3 car garage and the roof pitch is 12-12. So a lot of space there. The plan is to remove the drywall ceiling in the garage and install 24" engineered joists (2x4's). We lose a little head room in the garage and the space above, but not much.
Then once the floor system is in place it's much easier to move around. 2x6 rafters installed with collar ties at about 8.5 feet, and plywood gussets with engineered nailing patterns at the peaks. Then cut away the trusses. Doing it for about $80 a foot, and it will add about 500 square feet.