I am going to be adding an ell addition to my 1 1/2 story cape. The new roof ridge will be at the same height as and perpendicular to the original. To make the 2nd story rooms contiguous I will need to remove original rafters and replace them with valleys and with new rafters resized for modern code. I have two questions:
1. How do I support the original ridge while I remove rafters? I not sure I can trust the load bearing capacity of walls on the second floor, so not certain that building bracing up from them would work.
2. How do I account for the size and spacing differential between the new and old rafters? Old rafters are 4×4 at 28 on center, so new/old won’t meet across from each other. Nor would they be the same depth, so the base of the plumb cuts at the ridge would need support by an opposing force.
Thank you for any input.
Replies
Time for an experienced eye...
I think it's a time for an experienced eye to take a look at your situation...too many variables to be of much help on this site. I'm an architect with 40 years in and I would send this to one of a couple of engineers I know that are practical and experienced in light frame construction. If I were you, that's the direction I woiuld go. You could also seek out help from a very experienced carpenter/framer for general advice on how complete your project.
4x4 rafters @ 28"??? Interesting.... One option (depending on engineer's input) would be to "overframe" the existing rafters. Support and reinforce the exising rafters, put a beam in where the old wall was (bottom of beam flush with bottom of rafters and hang them from the side of the beam), remove all the roofing where the new roof will be, and frame the new roof over the top of the existing roof deck. Again, this solution would need an engineers blessing... Also, it wouldn't work if you wanted any kind of cathedral ceiling in the are underneath the intersection fo the two roofs...
4x4 rafters, 28 oc ??
typo?
house is 1815 timber frame so lumber is not standard dimension
Ridge Beam
Timber frame from that era would probably use a rigde beam, so the ridge would be self supporting. But be very careful since some modifications could result in catastrophic failure.
Support
Build a temporary wall under the existing ridge. The floor joists should support this during the course of construction.
On the old side of the valley I would leave 4x4 valley jacks @ 28" oc and add additional 4x4 jacks @ 16" oc. The valley rafter will have to be sized for the rafters on the new part of the roof. The valley jacks on the new side will be the same as the new rafters. They will meet the new jacks on the old side at the valley rafter but project down farther.