Anyway to put a strongback or beam at midspan of existing rafters?
Even like an overhead beam ontop of or above ceiling joist supported at
Then support rafters on that?
It sounds like doubling is a good way to go.
I would try to raise rafters in a group if possible.
"Wayne Whitney" wrote in message
I have a 1910 home in which the roof is grossly underframed, and I
would like to strengthen it so I can install solar panels. The
original 2x4 rafters at 32" o.c. span 12' 3" in plan from plate to
ridge and support the original 1x skip sheathing, 1/2" plywood, tar
paper, and one layer of architectural asphalt shingles. I checked a
couple of the rafters with a string line, and they are deflected about
1 3/8" at midspan.
My plan is to strengthen the roof framing by adding rafters to modern
framing standards. AWC's on-line span calculator indicates that
DF-North #1 2x6s rafters at 16" o.c. will handle the span with 10 psf
dead load and 20 psf live load. Since I don't see any way to attach
the new rafters to the sheathing without disturbing the asphalt
shingles, I am planning to install doubled 2x6 rafters alongside each
of the original 2x4 rafters and sistering them together.
Is there a better way to go about strengthening the roof framing?
To install the new rafters, I will have to remove the deflection of
the existing rafters so the new ones will fit and properly carry the
roof load. I can jack against the ceiling joists over a bearing wall
below. I am tempted to install the new rafters with the crown down to
reduce the jacking required. The roof is hipped, so the ridge is only
16' long and there are only 7 common rafters on each side of the roof.
I'm going to leave the rest of the rafters as is.
What are my chances of getting the existing rafters to move 1 1/2" or
so without damaging the plywood sheathing or ashphalt shingles?
Can I get away with jacking the rafters one at a time, or should I
arrange to jack all seven rafters on a side at once?
In case it is important, the rafters don't bear directly on the
exterior wall plate; instead, there is a flat 1x plate installed on
top of the ceiling joists (2x6s at 16" o.c.), and the rafters bear on
that. I'm planning to install the new rafters on the same 1x plate,
add squash blocks beneath them, and figure out a strap detail to tie
the new rafters to the wall plate.