Crawl Space Moisture and Flood Damage in Snellville

Where does crawl-space water come from in a storm?

Mostly from the vents and the grade outside, when the yard is saturated and runoff finds the lowest opening.

In Snellville the yard is often waterlogged after a heavy summer storm, and the ground around the house holds the water above the level of the vents. When the grade slopes toward the foundation, runoff collects along the wall and seeps through the gap where the masonry meets the soil. The vents are then below the water line, and the water enters them with no effort at all.

Creek water is a separate case. When a creek comes out of its bank near the house, the crawl space can fill from the outside through the foundation wall, and the water is then mixed with silt that settles across the dirt. The record of the water line on the outside of the wall is the best guide to which path was used.

How does the moisture in a crawl space reach the floor?

Through the joists and the subfloor, which wick the water up and hold it against the finish.

Wood that sits in damp air for days takes on moisture at its base and keeps it there. The bearing points, where a joist rests on a beam or a pier, are the worst place for it, because the water collects in the seat and the end grain soaks it up. The subfloor above is the next layer, and a subfloor that has been damp from below can cup and loosen the nails long before the finish shows a stain.

The floor finish is usually the last thing to show a problem, because it sits above the damage. A hardwood floor or a sheet floor can look dry on top while the joists beneath it still read wet. That is why the crawl space is measured from below rather than the floor being judged by eye.

• Check the bearing points where the joists sit on beams and piers
• Read the end grain of the joists at both ends of the span
• Look at the underside of the subfloor for staining or a raised grain
• Note any nail heads that have lifted or rusted

What should a vapor barrier do after water has been in the space?

It should be lifted, cleaned or replaced, and it should lie flat on the ground with its seams sealed.

A vapor barrier keeps ground moisture from rising into the crawl space, but it works only while it is in one piece and lies on the ground. Water that stood under it or floated it up leaves silt in the folds, and a torn or creased sheet holds water against the soil. Once a barrier has been wet, the question is whether it can be cleaned and relaid or whether it has become a source of its own.

On a dirt floor the barrier is laid over the ground and anchored at the edges, with the seams overlapped. On a concrete slab that is part of the crawl space the barrier is usually checked for a gap at the wall. This page does not give a product or a standard, because the work depends on the house. It describes the check that is made after water has been in the space.

• Lift the sheet and remove any silt or debris from under it
• Replace a sheet that has torn, cracked or been creased into a fold
• Lay the sheet flat, overlap the seams and anchor the edges
• Check that the barrier does not block the vents' airflow

What is left to repair after a crawl-space loss?

The joists, the subfloor and the finish that rests on them, in that order, after the space is dry.

A joist that has been wet at its bearing is checked for rot, and a sound joist is dried and left in place. A joist that is soft or split at the end is reinforced or replaced by the person who is responsible for the structure. Subfloor that has cupped is removed where it is loose, and the finish above is replaced only after the readings have settled.

The vents are checked as part of the repair. If the vent openings are too low for the grade, or if the screens are blocked with silt, the water will come back in the next storm. Regrading the soil away from the foundation or adding a drain is a separate piece of work, and it is planned while the space is still open.

When is the right time to check a crawl space after a storm?

Within a day of the water going down, and again after the first dry week, because the joists dry more slowly than the floor.

A first look can be made as soon as the access is safe, while the water is still visible and the readings show how far it went. A second look is made after the drying has run for some time, because the wood at the bearing points takes longer to give up its moisture than the air around it does.

The owner keeps a note of each visit, the readings and a photograph of the low corner. A crawl space that is checked in the same place each time shows whether the drying is working, and a space that is still wet at the second look is not closed up until it is dry.