I’m guessing water damage as an active factor, or an existing problem like sheathing too thin for wide rafter spacing. All should almost be visible in the attic, I would hope.
Just guessing, you have sheathing sagging. Because of the weight(tile), the span 24", and because the ridges(where the rafters are) seem to line up with where the rafters are from your inside pictures.
I understand this would be defer-ed to a roofer, but I wonder why? Is it as simple as min code material was used? OR Is there a ventilation/moisture problem? Guess that would be for the roofer to check.
Rafters placed too high on the ridge. Or birds mouth ,resting on the top plate,. not cut deep enough. Orrr rafters weren’t properly crowned.Orrrr a combination of all.
Rafters on 24" centers with 1/2" OSB is very common under concrete tile. In California collar ties are usually installed only on every other rafter pair and that condition might mean that rafter pairs without collar ties could sag, but the ridges look uniform up and down the roof… they dont sag more in the middle of the span, in fact they seem to bow up more in the middle of the span. That would indicate rafters with extreme crowns.
With adjacent rafters crowned opposite or moisture-damaged sheathing sagging or bowing between rafters, the roof should look sort of rolling, wavy, rather than sharp, short ridges like that. No sign of moisture on the underside of the seathing? No bowing/sagging of sheathing between rafters visible from underneath?
Did the whole roof look like this or just this section?
Nope… This was two stories up and concrete tile. Both good reasons for me not to walk it. I’ve deferred some broken tiles on the other side of the roof to a licensed roofer and made a note that these ridges should be further investigated.
Yes they were staggered. Here is a picture from the other side.
While the ridges in the original picture look relatively smooth, keep in mind that I am standing on a hill across the street from this house…probably about 60 - 70 yards away from the ridges, so the picture might make them look smoother than they really are.
I’m leaning towards a crowning problem.As in those two rafters should have been culled from the rest and never used because the crown was so great.
You could find out by going in the attic and pulling a string tight along the bottom of the rafters end to end and compare the gap between string and rafter.Then compare to rafters that seem “normal”.