Crawl Space Drainage System Installation

Crawl Space Drainage System Installation

Some crawl spaces are damp. Others take on water. The difference decides whether an encapsulation needs a drainage system before anything else goes in.

A damp crawl space has high humidity, condensation on ducts and a musty smell, and the vapor barrier, sealed vents and dehumidifier handle it. A crawl space that takes on water is a different situation. After a heavy rain there is standing water on the ground, a tide line on the piers or the foundation wall, silt patterns where water has run, or a section of the floor that never dries. In southern Virginia and northern North Carolina that usually comes back to red clay soil. Clay does not absorb water. It holds it against the foundation, and the water finds its way through the block wall or up through the ground at the low side of the house.

Laying a barrier over that hides the problem. The water still comes in, sits under the plastic, and keeps the wood above it humid. So where the inspection finds water entering the crawl space, a drainage system goes in first.

The system works the way water already wants to move. A trench is dug along the inside of the foundation at the low side or around the perimeter, depending on where the water arrives. French drain material goes into the trench and is routed to a sump basin set at the lowest point. A sump pump in the basin lifts the collected water out and discharges it away from the house. A battery backup for the pump is optional. We recommend thinking about it, because the storms that put the most water under a house are also the storms most likely to take the power out, and a pump with no backup stops working exactly when it is needed.

With the drainage handled, the rest of the encapsulation follows in order: insulation on the foundation walls, 20 mil poly across the ground and up the walls and piers, sealed vents, a new insulated access door and a dehumidifier sized at 70 pints per day per 1,000 square feet. The drain system sits beneath the barrier, so the water is collected and pumped out while the space above stays sealed and dry. We obtain a building permit and inspection for every encapsulation job, and the drainage work is part of that.

Not every crawl space needs this. If your inspection shows a damp space rather than a wet one, we will say so, and the encapsulation goes ahead without a drain. If it shows water, we will show you where it comes in and explain why the drain has to go in before the barrier does.