I assume these are engineered trusses??? I would not do anything, except stopping the progression, without a truss engineer report and certification for repair. Personnally, if it were my new construction home, it would be comming apart and being redone properly, or I would be walking.
It looks like you might have some rafter spread occuring. Do the walls bow out under the dip in the ridge line? Sistering the rafters won’t prevent further rafter spread.
2x6 rafters have a horizontal span rating of about 7 to 10 feet depending on species, grade, snow load, dead load, and spacing. If the home is more that 18’ wide or so at this point, the rafters may be over-spanned. Are you sure those aren’t 2x8’s? I would have a structural engineer look at it if I would you.
All lumber has some camber in it. Usually the framers sight down the piece from one end to see which way the camber runs, and they try to install the, in this case, rafters, with the camber always in one direction. It’s possible this was not done in your house.
Camber is the term for the natural curve in a piece of lumber. They should have all been installed with the curve up. If they were just installed at random without this little bit of care, you might get a roof that looks like that.
If that’s the cae, I don’t know if there’s a cure, or if there is, what it might be.
More info please. Exactly what work was done? Shingles only? Complete tear off? Reshingle over existing shingles? Rafters replaced? Spacing between rafters? Was there any evidence of this problem before the work was performed? Condition of original roofing? Any pictures of original roofing?
Your first post inferred (to me at least) new construction. The story changed. Give us everything you have, so we can attempt to help you.
Either way, I recommend an SE, as pictures are not even close to being there in person.
I just read through all your prior posts. You seem to be having multiple major issues with the house and garage roofs. Did you go with the cheapest contractor, cause you usually get what you pay for. Time to call for professional help.
This is an aesthetic issue…however same can be reasonably fixed, depending on your expectation and amount of money you want to spend, by doing a combination of both adding purlins and sistering rafters with the same size of those currently in place.
For extremely crowned rafters, one may simply have to partially cut the existing rafter prior to sistering… no engineer is required for either of these type of fixes.
i would agree with the contractor. a 2x4 sister will be far superior to a ripped filler. the sister provides a full depth to recieve the sheathing nails and will not be prone to splitting as would a ripped filler that is applied along the top surface of the rafter and ripprd from something too nothing.
I have yet to see a stick roof where the “required” spacing between the sheathing is performed and yet they are fine…what you have is simply bowed rafters…it is an aesthetic issue.
If every home was built to exact manufacturers specifications the price of a home would be through the roof (no pun intended)
Some installations instructions are simply worded to alleviate the manufacturer from ALL responsibilities regardless weather they are wrong.
Unless the sheathing states that it has been sized for spacing, I guarantee that the sheathing is 48" x 96"…now add 1/8" on each side for lets say a 75’ single story home… by the time you get to the other end your spacing is way off…do you want to talk about how spacing will affect the drywall now…you see what I mean.
In other words that 1/8 spacing is BS…those that look for that are the same ones who want to measure that every nail is 6 inches apart on seams (actually had a friggin rookie B.I. check that on one of my jobs).
I have seen allot of stick built roofs with this type of sagging at the ridge line.
One or more of the following factors usually contributed in the cases I have inspected:
1.) Over spanning of the rafters.
2.) Lack of interior support walls typically in large rooms such as a living room or garage.
3.) Poor fitting joints where the rafters meet the ridge board.
4.) Non-uniform and/or unnecessary vertical braces supporting the ridge board. (overlaps with #2 above)
5.) Rafters placed 90 degrees to the rafters causing the exterior walls to spread.
6.) Sagging ridge line due to shortening of rafter caused by rafter sagging.
I have attached a few drawings to help visualize the issues.