||02-11-2012 06:03 PM
Furring out existing 2x6 rafters
My house was built in 1941. It's 1.5 story with regular gable roof. We are planning on renovating our 2nd floor. I have few questions about the approach i have chosen.
Existing rafters are 2x6 and 15' in length, span is 14'' o.c. The floor joists are 2x8 and joined from two pieces in the middle (each joist basically consists of two pieces). They are 12' in length (each, making total length of a bit less then 24'' because they overlap like 5''). I attached the picture. There are 2x4 collars nailed every other rafter.
I am planning on furring out rafters and ridge board with 2x4 douglas firs, creating an air channel (smth like 1'' from sheathing) along the space between rafters by using plywood wrapped in radiant barrier foil (exterior side), then putting unfaced R-30 insulation and plastic sheeting for for vapor barrier.
I will use simpson hardware. 3x7, 16ga plates for rafters, 6x2 12ga angles for reinforcing rafters to the ridge board, 9x1.5 16ga angles for reinforcing rafters to the floor joists.
Then, since i am adding weight to the rafters, i am planning to reinforce floor joists in the place where they connect together in the middle. I am thinking of using some simpsons plates and corners, and/or bolting them together.
I will be putting new subfloor using 4x8 boards, and then nailing hardwood floor. Also plan to add some knee wall cabinets.
Here are the questions:
1). By furring out rafters I will add weight to the roof structure (wood + metal plates & corners + plywood). Does this pose any structural problems? Should I reinforce the floor joists better (extend it with 2x4, etc.) then with just some hardware metal plates and bolts?
2). By removing collar beams I potentially increasing outward thrust, however, i don't think that those are helping much. The floor joists is really holding those rafters together. Therefore I plan to reinforce those joists. Question is: from what i described above , does it sound reasonable?