Definition
Joists are the horizontal beams holding up your floors and ceilings—think of them as the skeleton of your home. When they're damaged by water, rot, or critters, your floor can start sagging or feeling soft underfoot, which is a red flag that something needs attention.
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Joists are critical load-bearing elements and require proper spacing, sizing, and support based on span and loading. Damage to joists—from moisture, rot, insects, or modification—compromises floor integrity. Inspectors assess joist condition by examining crawl spaces, basements, and attics, looking for signs of sagging, cracking, rot, or insect damage. Notching or drilling joists incorrectly weakens their capacity.
Pro Tip
Soft, spongy, or sloping floors are signs of joist problems. Get a structural engineer to evaluate before you buy or start any major repairs.
Example
An inspector in Vermont found severely sagging ceiling joists in a second-floor bedroom, causing the floor above to slope noticeably. Investigation revealed previous water damage from a roof leak had caused wet rot in multiple joists. Repairs required replacing affected joists and addressing the roof source.