What Causes Siding to Become Loose in the Middle of the Wall?
We have often seen a loose course of siding in the middle of an exterior wall of a dwelling (Figure LS-1 and LS-2). In fact, I have seen it on my own home.
What causes this?
If you take a few measurements, you will probably find that the loosened course(s) of siding are at the floor line. In those cases, the course(s) of siding has probably loosened because the floor joist behind the siding has shrunk in depth and shortened the height of the wall ¼ to ½ inches over its 8 to 10 inch depth. The shortening of the wall at the floor joist (usually the second floor) causes the locking tab along the bottom of the upper course to drop relative to the locking slot at the top of the lower course and unsnap from the slot (see Figure LS-3). This allows the upper strip to become loose, stick out from the wall, and be susceptible to flapping during exposure to normal winds.
Unfortunately, the only way to accommodate the shortening is to remove and reset all the siding from the loosened strip (the shortened floor joist) up to the roof line. A less expensive way to repair this is to apply small dollops of a flexible sealant at regular intervals to the underside of the loosened strip to tack it back to the underlying strip. By flexible I mean a sealant that does not become too rigid over time. Care must be taken so that the sealant does not ooze out at the joint. If it does, wipe it up immediately. This repair should hold the siding in place until it is replaced during normal maintenance, remodeling, or a more complete repair is required.
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