by Brian Dunagan, PE
Are you noticing cracks on the interior walls or foundation of your home? Wondering if you should be concerned? Read this blog, and you will have a better understanding of how and why they occur. (You can always contact an engineer to evaluate any cracks that may have occurred in your home. If you will feel more comfortable by having this assessment done, you should do so.)
To begin, let’s review the materials and systems that are a part of your residence. The typical residence is wood-framed and supported with a concrete foundation. The wood used to construct your home will shrink and expand based on moisture content, will move when loaded by wind or seismic activity, and is supported on soils that may move depending on the soil type and moisture content. The home is then typically finished with sheet rock, plaster, stucco, tile, or other stiff materials. These materials, due to their stiffness in comparison to the substructure, will crack as the structure moves. Building codes have established limits for allowable movement to help reduce cracking in the finish materials. Problems occur when the movement exceeds these limits and cracks are visible in the finishes. However, just because you have cracks, it does not mean the residence is failing structurally. The great thing about wood-framed structures is that they have redundant structural systems that share loads. It is very rare to see a catastrophic failure in a wood-framed home.
Let’s discuss some of the typical cracks you may see in the sheetrock, plaster, stucco or tile finishes in a residence:
1. Hairline cracks less than 1/16-inch-wide at corners, doors and/or window openings, ceiling to wall intersections, etc,. will occur in most homes. These cracks are generally due to small movements in your home that occur from wood shrinkage or expansion, settlement of framing, or small differential movement of the foundation on the soils below your residence. Most of this movement occurs during construction and does not impact your finishes. Sometimes, however, there are circumstances that will result in hairline cracks in your home’s finishes. Most hairline cracks can be repaired and they will not return, or if they do, they are repaired again as a part of regular maintenance of your home.
2. Diagonal cracks from doors, windows, ceiling corners, and/or intersecting walls can mean there is differential movement of the foundation.
3. Ceiling-to-wall separation cracks typically mean there is some differential movement of the foundation or, on rare occasions, truss movement.
4. Foundation cracks can be a result of temperature shrinkage or differential movement. Temperature shrinkage cracks are typically small, less than 1/16 inch. Cracks as a result of differential movement are typically larger and tend to go from smaller to larger dimension along the break.
If cracks listed in items 2-4 exceed the hairline threshold (greater than 1/16 inch) they should be monitored. If they continue to increase in size, they should be reviewed by a licensed contractor and/or professional engineer.
This is a very brief discussion of some of the cracks you may see in a wood-framed residence. If you have concerns, you should consult a licensed contractor and/or a professional engineer.