Hello all
I have a job for some friends coming up and I wanted some advice.
We are going to be adding an addition which is straight forward but the roof pitch is changing from the current house. The drawings show new trusses being “sistered” to the old ones and therefore changing the pitch. Does this make sense? Or should we just frame new roof over old(removing shingles etc from old). New pitsh is 6/12 old is 4/12.
Any suggestions>
Thanks
Tom
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Replies
For clarification - did youmean to say thetrusses are sistered or the new solid framing?
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the new ones are sistered to the old ones.
Nothing "wrong" with it that I can see but how to accomplish it is tricky in my mind. Normally you would be bracing off the line of them all together as you install.So the old ones would be expected to stand up straight with no bracing once you remove the sheathing until the new ones are set. Lots of leap-frogging in that scenario. Doable, but tricky.I am a stick frame guy anyways. The old trusses will act as rafter ties and eliminate need for a ridge beam so you could either let in rafters or lag them in on tiop of sheathing which would allow you to keep the place dried in while whatever is going on.
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Are you saying to build on top with knee walls on top of existing ? That was my first thought but i was concerned about load( roof on roof) Original roof is well done 16" centers. I would like to leave it if possible.
Your last post leads me to believe your old roof is conventionally framed while the new one will be trussed. Is that correct?
I'm building an addition now that sounds exactly like the one you will be doing. The addition will be trussed and I'm overframing the existing roof conventionally on the rest of the house.
To match the two roofs I pulled the sheathing off the overhang, but only just past the existing top plate, cut off the rafters flush with the outside of the building framing and cut a birdsmouth into the top of each of the existing rafters to place a level 2x as a nailer for the new overframing. A top plate on top of the rafters instead of under.
Then you frame your new roof right over the old, cutting the standard birdsmouth to fit on the plate you just attached to the top of the old rafters. You don't even have to remove the shingles if you don't want to and there is plenty of room to add collar ties. This also keeps the weather out of the old portion of the house.
Since the existing rafters are already strapped to the old top plates new strapping would only be applied to attach the new rafters to the old.
When you know the height above plate for you new overframed roof you can then order trusses with a raised heel to match the top of the lumber you will be using for the new overframing rafters. The conventional framing happens after you install the trusses so you can tweak for any inconsistency.
Another benefit of trusses applied up against an existing structure is the instant bracing of that first truss. In my case, the lower third of the truss is right up against gable end framing and is a rock solid starting place for the rest of the run.
Sistering new trusses up against the old makes absolutely no sense at all to me unless I'm missing something.
I would set the new trusses on the addition up to the existing house and then on the existing house cut out the plywood at the plateline far enough back so the rafter clears to set the new rafters in and then at the top install a new ridge and stick frame it. You said that you're changing the pitch to a 6/12, so the new ridge will be higher than the existing ridge.
The sheathing will stay in at the top and hold the existing trusses in place while you frame one rafter on each side. Precut all the rafters first before you take any of the existing roof off.
I do this all the time around here changing roof lines and framing over the existing just for looks. Sometimes we even take off the old roof and just frame a new roof because of the look and higher attic space.
I can’t see why you can't just stick frame a new roof.
Joe Carola
Edited 2/23/2007 6:24 pm ET by Framer