On Apr 14, 3:16*am, nestork wrote:
Andy:

I read through most of that thread you linked to, and I can't help but
agree that if the sag is between the joists, then adding fasteners
driven into the joists isn't going to help much.

That's because, just like wood, drywall will gradually bend under it's
own weight. *If you look at an ariel photograph of any city after a
rain, you'll see puddles on all the flat roofs. *That isn't because the
weight of the water is causing the ceiling joists to bend, it's because
over the course of time, the ceiling joists have already bent under
their own weight and the weight of the roof. *Heat and humidity
accelerate that process so that steamed wood can be bent to form almost
any shape, including the sides of a piano, violin or guitar or even
woven into rattan furniture.

So, try putting in some additional drywall screws, but keep in mind that
if there's no visible difference, you need to stop there. *Otherwise,
you're going to end up with an unhappy customer that doesn't want to pay
you because you didn't FIX the problem with the ceilings.

--
nestork

The sag is perpendicular to the joists, I will try and link to a scan
of a drawing of the situation below.

https://plus.google.com/u/0/photos/1...Na1iYPS89KVrQE