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Q. About ten years ago I had an addition put on my house, about five years later my bathroom ceiling began to crack right at the wall/ceiling joint. In the summer the crack is closed but in the winter it opens up. Now the rest of the rooms in the addition are doing the same thing. Has using the heat during the cold winter caused this? Should I be concerned and what should I do about this? Besides putting crown molding up is there anything else I can do? Any help would be appreciated.
A. Your addition was built around the time that the true source of what's causing your wall and ceiling separations was identified. It used to be written off as natural settlement or shifting.
The phenomenon that is causing your addition to move about in the manner you describe has been identified as truss-uplift. You have pre-engineered roof trusses that provide the frame for your roof system. These trusses are usually fabricated from 2 x 4 lumber into a shape that resembles a triangle with the letter W inside of the triangle. The arrangement is surprisingly strong and you have to have a good grasp of engineering principles for even a glimmer as to just how they work. They transfer the weight of the roof and anything on it such as shingles or snow to the outside walls, usually front and back exterior walls. The bottom of the truss, the flat horizontal leg of the triangle, floats and does not need to rest on anything in the middle for support.
Carpenters build the interior walls separating bedrooms, halls, closets and baths after the roof trusses have been set. They erect these walls and nail them to the bottoms of the trusses to hold everything where they want them. Then drywall hangers a ttach drywall to the bare framing.
Drywallers attach ceiling drywall first then snug and butt the upper wall sheet of drywall against the ceiling sheet forming the right angle of ceiling and wall connection. At some point during this process the house is insulated and insulation is place d just behind drywall, and if it's a ceiling on the top floor, insulation goes on what we might call the attic floor. Here's where trouble starts.
It was discovered that if the bottom chord of the roof truss forms the ceiling joist and the bottom chord is immersed in insulation while the rest of the truss is not, stresses that set up in winter within the truss cause the truss to lift upward to some degree and then settle back down when the weather warms up. It can and will pull anything attached to it along for the ride. I've seen it lift entire walls creating a space at the wall bottom as much as an inch. Normally what happens is that drywall sp lits and nail pops occur near the wall ceiling connection. In the past those who didn't understand the dynamics of what was going on would come back and nail or screw the daylights out of drywall and framing in an effort to stop the movement but it always came back.
Drywall manufacturers recommend if you attach drywall to the bottom of a truss that the attachment should be about 16 inches away from an intersecting wall. If ceiling drywall is installed first then the sheet will ride on the edge of the upper wall sheet so it's not an issue of it drooping over time. It's against a drywall installer's instinct not to nail or screw at that edge so it gets done.
There is a framing clip designed to stabilize interior walls to the truss bottom that allows the truss to move up and down without dragging the walls along with it. I rarely see them used.
When I see the inevitable nail pop associated with this condition I recommend that the nail be pulled and the hole patched. That usually takes care of it. If the cracks are small and recurring then I recommend using an elastomeric caulk, such as tub and tile caulk, that will move along with the drywall and not split open.
If the spaces are such that they really bother you and are moving then attach a piece of trim, such as crown molding, only nailing one side allowing the trim to slide up and down in response to the truss movement. Beyond that there isn't much you can do short of pulling things apart and rebuilding them with movement in mind. As for any creaking, that's the house talking to you but it's not calling for help.