Ceiling and walls are separating
13 March 2004
A. The first thing you need to know is your house is not about to fall down. Situations like the one you describe happening at your house have been around to a greater or lesser degree for decades as homebuilding became more and more sophisticated in an effort to both conserve materials and energy. Most people who put houses together have been behind the curve and tended to inadvertently build things into a modern house that somehow at a later time would surface to confound the owners. Ask those builders whatís going on and youíll hear all sorts of songs and dances that boil down to they just donít know.
Finally, researchers and manufacturers have tried to team up and solve some of these issues but unfortunately the remedies canít be retrofitted into the examples that prompted the modifications.
Your house was built just around the time that the true source of whatís causing your wall and ceiling separations was identified. It used to be called natural settlement or shifting and some frightened folks were so convinced their houses were indeed structurally compromised in some way that they went tramping off looking for lawyers and someone to sue. Thatís how the researchers got involved as expert witnesses began to focus on the issue.
The phenomenon that is causing your house 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 read the plans for the second floor and build the walls separating bedrooms, halls, closets and baths. They erect these walls and nail them to the bottoms of the trusses to hold everything fast where they want them. Then along come drywall hangers who attach 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 placed just behind drywall and if itís a ceiling on the top floor insulation goes on what we might call the attic floor. Hereís 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. Iíve seen it lift entire walls creating a space at the wall bottom as much as an inch. Normally what happens is that drywall splits and nail pops occur near the wall ceiling connection. In the past those who didnít understand the dynamics of what was going on would come back and nail and screw the daylights out of drywall and framing to staunch the movement but it always came back and thatís when the songs and dances about settlement were sung.
Drywall manufacturers recommend that 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 itís not an issue of it drooping over time. Itís against a drywall installerís nature not to nail or screw that edge so it gets done.
There is now available 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 have never seen it used in the field.
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 only nailing one side allowing the trim to slide up and down in response. Beyond that there isnít much you can do short of pulling things apart and rebuilding them with movement in mind. As for creaking, thatís the house talking to you but itís not calling for help.