Sagging Catheral Ceiling Rafter replacement and insulation

[Eric Kamien]

I live in climate zone 8, ranch house built in '97. I have a partial kitchen catheral ceiling which follows the staircase up to the FROG (Finished Room Over the Garage). This catheral ceiling has no attic (i.e. dry wall ceiling, rafters, insulation in between rafters, plywood then asphault shingle roof on top).

PROBLEM: The catheral ceiling (12' wide x 16') has sagged over the years, before I moved in 2006. The sag can be plainly noticed outside also, spanning across its entire width for the most part.

Questions:
1. What dimension rafters should I use regardless of the current rafter dimensions, assuming they could be presently 2x8s?
- I've been told 2x10"s should be sufficient so that R30 insulation can be used along with baffles for ventilation and nailed against the old exisiting rafters by sistering (& cut) .
2. At what distance center to center for new rafters regardless of sistering against old?
3. Should new rafters be notched on the header top and/or bottom or use A35 (?) brackets for maximum installation strength?
4. When are LVLs a better choice than solid wood rafters?

Appreciate any opinions/thoughts. Eric

[Jim Luttrall]

I can't imagine sagging due to insufficient rafter size on a roof that small. 12' wide should be able to be done with pretty small rafters and I doubt that it would sag uniformly even if undersize.
If you can stand at the peak looking across the ridge of the roof to the other end and see sagging, it is not the rafters fault and putting in larger ones won't solve the problem.
My guess is that there are no rafter ties and the sagging is from rafter thrust spreading the walls and allowing the ridge to sag. A few photos would be helpful.
I know this does not answer your questions, but first things first.

[Mark Hagenlock]

I live in climate zone 8, ranch house built in '97. I have a partial kitchen catheral ceiling which follows the staircase up to the FROG (Finished Room Over the Garage). This catheral ceiling has no attic (i.e. dry wall ceiling, rafters, insulation in between rafters, plywood then asphault shingle roof on top).

PROBLEM: The catheral ceiling (12' wide x 16') has sagged over the years, before I moved in 2006. The sag can be plainly noticed outside also, spanning across its entire width for the most part.

Questions:
1. What dimension rafters should I use regardless of the current rafter dimensions, assuming they could be presently 2x8s?
- I've been told 2x10"s should be sufficient so that R30 insulation can be used along with baffles for ventilation and nailed against the old exisiting rafters by sistering (& cut) .
2. At what distance center to center for new rafters regardless of sistering against old?
3. Should new rafters be notched on the header top and/or bottom or use A35 (?) brackets for maximum installation strength?
4. When are LVLs a better choice than solid wood rafters?

Appreciate any opinions/thoughts. Eric


Unless there is space here for a book, there are too many variables to give an answer that will work for you.....Except the obvious answer, which is hire a contractor. If you don't know the answers to your own (above) questions you shouldn't be building, or rebuilding a roof. I'm not trying to be an ass, but this is not a place to do weekend work.

[Garry Sorrells]

Eric,
Is the ridge beam also sagging/bowed?
Jim has you going in the right direction and Mark is correct in getting a contractor in to give you direction. It may be necessary to jack up the trusses along with the ridge to get things back in place, which may affect your exterior walls. Sagging is a relative term, a little to one person is a great to another. It may be just that the trusses were set in crown down. So get a contractor in for advice.

I think you may be thinking of sistering the 2x10 onto the 2x8 to straighten out the lines which may correct the appearance for now but may not correct the underlying problem in the long run.

LVL can be used for regular framing, but usually is reserved for headers and beams due to cost.

As for spacing of rafters it is a design issue. 16 or 24 is typical. Which is another reason to bring in a qualified contractor for direction.