Swayback? roof spreading?

So we have all seen older homes where the ridge is sagging. How do y’all report or talk about this? As with the home yesterday it was a 1940’s built home. No ridge beam, no visible gap between the rafters at the peak, it did have collar ties installed. In my opinion the sag in this ridge was subtle compared to others I have come across. Thoughts?

https://www.nachi.org/forum/attachment.php?attachmentid=126564&stc=1&d=1457889933

https://www.nachi.org/forum/attachment.php?attachmentid=126565&stc=1&d=1457890252

I would call those toothpicks a poor excuse for a collar tie. :wink:
Anyways, the collar tie has nothing to do with the ridge sag.

This is an old building and may be lacking the proper rafter tie down at the lower section we do not see. The walls may be spreading a bit.

The evidence of the skip sheathing tells me that the roof may at one time have had cedar shakes or shingles on the roof, or may still have.
Since I see no nails sticking out through the spaces of the skip sheathing, that would indicate that they added a sheathing on top or may have left the shingles.

In any case, they have added additional weight to those 2x4 rafters and may not be able to sustainably handle the load.

If the rafters are over spanned and over loaded, that would pull the ridge down and create the sag.

Call it out for a qualified building contractor to evaluate the condition and repair.

Those are great points Marcel, thank you.