What if a Subfloor Gets Wet From Rain?

Subfloor Damage

• Rainwater, if left standing on the subfloor during home construction or over cracks or openings on the main level, can saturate the subfloor over time and lead to water damage. Water damage can weaken the wood of the subfloor, causing it to sag, bend or even deteriorate. Subfloor wood that has experienced water damage may be wet to the touch and feel spongy, exhibit a darker color than normal, or may even splinter or break if exposed to light pressure.

Health Risks

• A wet subfloor can develop mold, a fungus that feeds off organic matter. Mold spores float through the air within your home, and will settle and thrive on surfaces that offer organic matter and water. People with mold sensitivity can develop allergies, eye or skin irritation, nasal stuffiness, wheezing and other health-related problems. Removing the mold source as quickly as possible is crucial in stopping such symptoms and preventing them from worsening over time.

Building Risks

• A wet subfloor can crumble, break away in places or collapse. Since the first floor relies on the subfloor for added support, a failing or broken subfloor can cause the first floor to bow down and become unlevel. Heavy items, such as refrigerators or large furnishings can add additional pressure on a top floor and cause it to sink. In extreme cases, the surface floor can partially or fully collapse.

Replacing the Subfloor

• Replacing any areas of subfloor damaged by rainwater entails cutting the subfloor boards 3/4 inch deep across the top of the nearest joist and continuing the cut to the next joist. Cutting two more times across -- to complete the square -- will allow you to remove the damaged section. A flat prybar can be used to remove ringed shanks, or the nails that hold the plywood beneath the subflooring to the joist. New 2-by-6 boards can be used to replace the removed boards, and new pieces of plywood can be cut to size and secured to the boards and joists with ringed shanks.