i live in 40-year-old townhome, Philly suburbs, and recently started noticing some weird issue on the second floor of my house where it connects with the attic.
I laid out perforated radiant barrier on the attic floor some years ago, i also installed roof fan and put in side window for better ventilation (attic had none of these features before). what i started noticing just two years ago is that when the weather is colder and dryer, my second floor ceiling starts moving a bit creating up to 1/8+ crack along the walls. i can see this happening throughout the whole second floor, closer to house center along the direction of the rafters. when weather is warmer and more humid, the crack disappears, so it seems like attic is breathing depending on the season.
My foundation is in good shape, so i'm almost positive the problem is coming from the attic.
Should i try to sister a couple of rafters so they don't get that space to expand anymore, or is this something different? any thoughts on mitigating the problem would be helpful.
You have seasonal expansion and contraction caused by the extreme temperature difference from summer to winter. It's pretty common and sometimes hard to fix.
But - since your problem is following the central wall of the house then fixing it should be fairly easy. Assuming that the rafters are cross braced down towards this central wall - if so, then what is going on is that when hot temperatures cause the bracing to expand, it pushed the bottom of the roof framing system (in this case the ceiling joists of the top floor) tightly against the center wall - closing up any gaps. Then, when things get cold, the roof framing shrinks up a little, pulling the braces away from the wall - lifting the ceiling joists and the ceiling drywall with it....creating the gap.
Fix it in the summer, when the gap is gone. You need to securely attach each joist to the top plate of the center wall below. If the joists are small enough (2x6 or less) you can get 8" long decking screws and drive one through the joist and into the top plate. do this for every joist. Other methods are to get some Simpson angled plates and attach to each side of the joists and into the top plate. Important to note that while you can use nails to attach into the joists from the side you must use screws to anchor to the top of the wall plate - otherwise the extreme force will just pull the nails out.
I have the same problem and have been told that attaching the rafters to the top plate could result in the roof, when it contracts in the winter, pulling the top plate off the wall studs. Interested in your thoughts.
If the movement is limited to the 1/8" space like in the OP's post above, then just attaching the ceiling joists (or bottom cord of the engineered truss if that's the case) will stop the movement and will not affect the interior wall. If the movement is larger than more drastic bracing measures must be taken.
The worst one we ever fixed had 2" to 2 1/4" of movement from summer to winter. They first tried to repair it by installing crown molding during the winter, when the gap was opened. This worked find for the winter and the first summer, as the compression simply shoved the crown downwards. As soon as the next winter hit though the ceiling lifted again, leaving the same gap - only this time it was above the crown. The house was a single-level rancher with a full basement. We wound up making steel rods with threaded ends that ran from the basement, inside the central wall and up into the attic space. At the bottom, the rods ran through cross blocks anchored to the first floor joists. In the attic, a similar cross block ran between each pair of trusses. We installed it during the summer when everything was tight. It's held up fine ever since.
Unfortunately, we are in a two story house and that might not work here. The gap is 1/2 - 3/4 of an inch. How about going into the attic and cutting the first two screws holding the sheetrock to each rafter. Nailing a piece of 2x6 to the top plate between each rafter and then attaching the sheetrock to the scabbed in 2 x 6? Might something like this work? This is a problem we've experienced for years and no one has come up with a solution.
Any kind of spacing or filling will just move the problem a little. To fix it, you have to keep it from moving with the seasonal hot/cold temperature variations that are the cause of the problem.
Since you cannot go through the entire house from top to bottom do the fix as I had outlined in my April 11 post above.
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