Wife and I are now starting the planning stages of a new house for next summer. A cape (44×32) with a shed dormer on back. The roof pitch will probably be a 9 or 10. My problem is we can’t get 2×10 or 2×12 long enough to span from top plate to ridge. So, I’m wondering if anyone has spliced the rafter over a knee wall? I was thinking of overlapping the two pieces over the knee wall. Of course I’d design the floor joist to carry the load from the knee wall. Anybody have any thoughts?
Thanks
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Replies
If the knee wall is a true bearing wall, then yes, you can frame the roof with two pieces and break up the span. Don't think of it as a splice though.... two seperate rafters... one with a tail on one end and seatcut to land on the bearing wall on the other end. And the other with a matching seatcut for the bearing wall on one end and continuing up to your plumb/ridge cut at the other end. I had a house with a 40 something foot rafter span last spring and it was designed this way.
Thanks, I thought so but never had the chance in stick framing a roof. Every roof in my 35 years on the planet were trusses. I'm actually a bit tired of them and would like to frame my house.
You'll have a lot of framing below which could effect your floor plan to make the kneewa;;s load bearing, or have to really beef up your floor system and have it engineered to take part of that roof load.
Far better to use TJIs. You can definitely get them long enough and they are light to work with. a cut up roof makesa them impractical to detail, but a simple Cape is made for them
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Good idea using TJI's... didn't think of that.
And TJIs are a lot easier to toss around than are 20 ft. green Doug fir 2x12s. Most suppliers can do the engineering for you at no cost.Andy
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I've framed roofs like that where you don't have to worry about the joists below at all or even use a kneewall. You can just use microlam girders that will span from the outside walls to a inside bearing wall or center bearing wall. Then the rafters will sit on top of them. You can use smaller rafters also because of the span.
You have to make sure that the bearing walls are strong enough to support the microlams or you will have to put a footing in the basement with a lally column. Sometimes they can break at the stairwell on each side and then you post down to the girder in the basement or put a footing and column underneath.
Here's a drawing I did a couple years ago.
I built a similar 16 years ago. unbroken knee wall. Built it into a box beam and used it to "hang" the second floor joists from as well as carry the roof loading. 1/2 inch camber built in and still counting. Jim Devier
the Cape we are building in "Adverse Conditions" is a 44 x 32.. with a 10/12 pitch roof
all 2x10 roof framed with large overhangs.. we had no problem getting 2x10 lumber for raftersMike Smith Rhode Island : Design / Build / Repair / Restore
The house we are framing will use I-joists for the main roof. The rafters about 29' long (little less). We get the package tomorrow and start framing Monday. I'll take lots of pics and send some to you if you want. I'm really looking forward to it.