How can I tell if a diagonal crack in drywall at the corner of a window or door indicates a structural problem?
Wednesday, June 27, 2018
Behind the drywall in most homes is wood stud framing. The studs have a higher moisture content when initially installed, which gradually drops over the first few years after construction as the wood dries out. There are also seasonal changes in outdoor moisture, plus the occupants of a home add moisture to the interior environment by cooking, showering, washing laundry, and just breathing. Conversely, if a home is unoccupied for a few months, the moisture level will drop.
Changes in moisture cause minor wood movement and shrinkage, which create stresses that often result in small horizontal or vertical hairline cracks around windows and doors. This is normal and sometimes the cracks close back up as the interior moisture increases. Larger horizontal or vertical cracks, when open and tapered, can signal a structural problem.
Diagonal cracks, on the other hand, tend to indicate some amount of structural movement no matter what size. Most diagonal cracks at windows and doors are “tension cracks,” caused by a force puling the two sides of a corner of the opening apart. Tension cracks taper in width as they snake away from the corner.
The less common “compression crack,” which occurs when forces are pressing the two sides of the corner of the opening together, is more significant as an indicator of structural distress. A compression crack, like the one shown below, has a ragged edge, bulges at the crack line, and one side may be higher than the other.
A diagonal crack can be caused by the bowing of the bottom chord of a truss above it, movement in the floor below, or lateral movement of the surrounding wall. One diagonal crack is something to note and keep an eye on, but multiple diagonal cracks, especially when in a cluster at the same area of a home, indicate a developing structural problem that should be investigated by a professional.
Also look for cracks on outside walls nearby, along with floors and ceilings around the opening. Structural distress is often revealed by multiple medium-size cracks rather than a single big, scary one.
Open and close the window or door at an opening with a diagonal crack to see if it binds at any point. Check that the gap between door edge and frame is consistent. Cracked window glass is another symptom of structural movement.
Also, see our other posts How do I recognize serious structural problems in a house? and What are the places to look for structural cracks in a house? and What causes a vertical crack in drywall? and What causes stair-step cracks in a block or brick wall?
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