Expert: Dan Griffin - 8/15/2008

Question
I will not know the technical terms but I hope that you can understand what I mean.
We are having a house built and we also wanted the roof to be stick built. The plans are Betzs plans and the roof has several gables and on the back side it has a long span from the eve to the drip edge. In order to get this long span, they nailed two 2x10's together with about 2 feet overlap and it resting on a load bearing wall. But when standing on the ground and getting an eye level on the roof pitch, there is a small dip in the roof at the point where it sits on the wall and where it is joined.
  I have talked to them by phone but with the distance between us, I have not been able to see it. They tell me that it has been corrected by using plywood shims to raise it about 1/2 inch. I don't like  the method they used.    
  What should be done to correct this so it will be structially sound and not have a swag in our roof.
A quick response would be greatly appreciated.
Bobby Turner

Answer
I think I would have let the material lap a bit more than 2 feet and/or have used a dryline or other straight edge to determine when the when the boards were in plane.  All framing materials should be crowned - framing lumber is not necessarily staight, so the arch in each piece should be turned up.  This could cause a slight deflection at the junction area as you describe.  I would expect the deflection to be almost unnoticable, but evidently yours was more susbstantial.  I don't know how many rafters are affected, but you could use an 8 foot 1x4 or 2x4 scabbed along the side of the rafter depression under the roof sheathing which should be more than adequate to straight line the visual depression.  This would require some additional attention to nailing  to make sure everything was well fastened and working as an assembly.