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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To learn more about exterior walls and structures, see these other blog posts:

• What is the average lifespan of a house foundation? 

• How long does it take for a new house to settle?

• What causes vertical cracks in fiber cement siding planks? 

• What is concrete spalling?

 • What causes raised white lines of residue on a block wall that are crusty and crumbling? 

• What is the difference between soil subsidence, heave, creep, and settlement? 

• How much ventilation is required for the under-floor crawl space of a home? 

• What causes stair-step cracks in a block or brick wall?

• Should I buy a house with a crawl space? 

• Why is my stucco cracking?

• Can vinyl siding be painted? 

• There's cracks running along the home's concrete tie beam. What's wrong? 

• What would cause long horizontal lines of brick mortar to fall out?

• How do I recognize structural problems in a retaining wall? 

• What are the places to look for structural cracks in a house?

• What is engineered wood siding?

• Should I buy a house that has had foundation repair? 

• What is a "continuous load path”?

• What is fiber reinforced concrete?  

• What is Z flashing?

• Should I buy a house with asbestos siding?   

• How can I tell if cracks in the garage floor are a problem or not? 

• What do you look for when inspecting vinyl siding?

• Are brick houses hotter in Florida?

• Why is housewrap installed on exterior walls under the siding? 

• How do I recognize serious structural problems in a house?

• What are those powdery white areas on my brick walls?

• What causes cracks in the walls and floors of a house?

• How can I determine if a house is structurally sound? 

• How can I tell if the exterior walls of a house are concrete block (CBS) or wood or brick?

• What are the common problems of different types of house foundations? 

• What are the warning signs of a dangerous deck?

    Visit our EXTERIOR WALLS AND STRUCTURE page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.