Interesting - I doubt very much the ceiling's drywall because it takes a lot to make that cardboard split - no doubt it's fibrous plaster or cast plaster. Irrespective of what's causing it, (don't overwater the foundations either) make sure it's not too dry indoors, humidify a little if it's well under say 45% The cracks themselves can be sealed with a FLEXIBLE gap filler, make sure it's a flexible water clean up one, force it in gently with a thin flexible scraper, and you can gently wipe over with a slightly damp cloth to remove any excess (if you work carefully with the scraper there won't be much excess) and see how you go. if it's a white ceiling, you may not need to repaint. There is a boat-building technique to stop cracks, basically you drill a hole in the path of the crack - being round, when the crack reaches the hole, it'll stop. I'd exercise caution when applying this technique, though, not knowing what the ceiling's made of, condition etc. If you drill small holes, say 1/8 inch, (you will need to be accurate with position) you should be safe enough. Do you have access to the ceiling space above? In older places with lathe and plaster and plasterboard, they often sag with time, in extreme situations, you can prop up the sag with a broad piece of plywood, supported from underneath, then up in the ceiling place (after removing insulation and dust etc) pour liquid casting plaster - plaster of paris - over the top of the sagging part, and allow to set (don't pour it into any light fittings, vents or electrics) - this will reinforce/hold up the ceiling, I suppose if you were clever you could reinforce the plaster with some sort of material like you were fibreglassing, even with, say, fibreglass cloth? (you want to avoid flammable materials up there) Then, the idea is, you have a solid, no longer sagging ceiling, and you apply a thin skimcoat over the underside, to seal/cover the cracks.

Munkos, I didn't mean to be so touchy. I think that's a sore subject w/ me; I really mind that I have so few friends. I'm the one who would gladly go help a friend make shelves, anchor them to the walls, fix the caulk, etc. But I don't even have any friends here anymore that *I* could go help *them*--they've all moved away, and I find it harder and harder to make real friends, as I get older. there's way too much rust in the medicine cabinet, I think, to paint over it--and the idea is for it to look NICE; it wouldn't look that good once I finished with it. I think I'll take a stab at finding one the same size. At the very least, I want to thoroughly investigate that possibility before I tackle the overwhelming task of sanding away all the rust and spray-painting the medicine cabinet. I live in an apartment, and there aren't that many easy places to do a messy task like that. I'm trying to help my DS learn some of the handyman type stuff. He's very intrigued by it, and he's finally old enough that I feel he can tackle some of those things w/ supervision. In our household, I'm the handy person. I'm the one who owns the power drill, the electric screwdriver, the saber saw, the belt sander, etc. I'm going to get DH to help me draw up the master list again; we had one earlier, but we need to start over.

A crack like that is usually do to movement / settlement. I see crooked cracks daily as I'm a painter...

Almost would have to look at the wall on the inside to see if integrity is affected. Typically we look at the cracks to see if the wall needs help. There are different crack types and often unless the house continues to settle the cracks are fine but they need to be sealed to keep water out. You would start to see damage inside the house from settlement if the foundation was still moving. If you have a large horizontal crack and bowing involved that is more worrysome as that can lead to wall failure. Slight bowing is fixable with reinforcing pillars and backfilling the gap space or with carbon fiber strappings. I dont like the soil anchor idea of trying to fix it, it doesnt work well. Continued settling of a foundation would require piers to shore it up.