910 Crawl Space Pros

Crawl Space French Drain

What the work involves in Wilmington and the Cape Fear region, what it costs, and the situations where it is the wrong thing to buy.

Last updated: 2 August 2026

  • ASTM E1745 reinforced liner
  • IRC R408.3 closed crawl space
  • Class I vapor retarder (<0.1 perm)
  • ICC-ES certified flood vents
  • Written scope before work starts

910 Crawl Space Pros provides crawl space french drain across Wilmington and the Cape Fear region. A crawl space french drain is a gravel-bedded perforated pipe that intercepts groundwater at or near footing level and carries it to a sump. It is the right answer where water arrives through the soil rather than over the surface.

What we do on the first visit

Determine whether water is arriving at the surface or through the ground, because a french drain solves only the second. Then check footing depth, clearance and the route to a sump location.

Washed stone, and why fines ruin a drain

The pipe is the visible part; the stone around it does most of the work. It must be washed — screened clean of fines — because the fine material in unwashed stone migrates into the perforations and clogs the pipe. A drain built on unwashed aggregate can silt up within a few years and there is no practical way to clean it.

Filter fabric wrapping the stone keeps surrounding soil from doing the same thing over a longer period.

Interior versus exterior

An exterior french drain intercepts water before it reaches the foundation and is the more thorough approach, but it means excavating the perimeter of the house. On a crawl space foundation the cost rarely justifies it.

An interior drain at the footing collects water that has already reached the foundation and removes it before it surfaces in the crawl space. For the large majority of Cape Fear properties this is the proportionate solution.

Fall, and what happens without it

The pipe has to run at a consistent fall toward the sump. A flat run holds standing water in the pipe, which silts and eventually blocks. On a long perimeter this is the detail that separates a drain that works for twenty years from one that works for three.

What's included

  • Assessment confirming water arrives through the soil, not over the surface
  • Trench to footing level at a consistent fall
  • Perforated pipe bedded in washed stone
  • Filter fabric to keep soil out of the aggregate
  • Connection to a sealed sump basin
  • Backfill and reinstatement
  • Vapor barrier installed over the finished system
  • Return inspection after the first sustained rain

DIY, cheap quote, or done properly

Most of the price difference between quotes is not labour — it is which of these steps the quote silently leaves out.

DIY Cheapest quote Done properly
Liner 6 mil builder sheet, laid loose 6–8 mil, taped seams, not fastened to walls Reinforced 12–20 mil to ASTM E1745, sealed to piers and walls
Groundwater Not addressed Sealed over — water ends up under the plastic Drainage and sump first, liner second
Humidity control None, or a household dehumidifier on an extension cord Undersized unit, condensate draining to the soil Unit sized to cubic footage, pumped to a proper discharge
Vents Left open, or foam blocks pushed in Covered, not sealed Sealed and detailed so the space is genuinely closed
Wood already affected Bleach from a spray bottle Surface treated, moisture source left in place Growth removed, framing treated, dried, then sealed
What it costs $300 – $900 in materials $1,500 – $3,000 $4,200 – $14,000
How long it holds A season or two Often fails within a few years Liner life measured in decades when water is handled first

How french drain work runs

  1. 01

    Assess and measure

    Humidity, moisture content in the framing, standing water, clearance and access — photographed throughout.

  2. 02

    Written scope

    Line by line, in the order the work has to happen, with a price against each component.

  3. 03

    The work

    Water handled first where present, then the fix itself, then verification.

  4. 04

    Verify and hand over

    Post-work readings recorded and left with you, along with the photographs.

Get crawl space french drain priced for your home

Free on-site assessment across Wilmington and New Hanover, Brunswick and Pender counties.

Call (910) 886-2018 Get a free quote

Crawl Space French Drain questions

How much does a crawl space french drain cost?
Typically $1,500–$5,000 depending on the perimeter length and clearance. Low-clearance crawl spaces cost more because the trench is dug lying down.
French drain or sump pump — which do I need?
Usually both. The drain intercepts and collects the water; the sump and pump remove it. A drain with nowhere to discharge to only relocates the problem.
Will a french drain fix a musty smell?
Only if the smell is coming from liquid water. If the crawl space is dry but humid, the smell is a vapour and ventilation problem, and the fix is a liner and conditioning rather than drainage.
How long does a french drain last?
Properly built on washed stone with filter fabric and consistent fall, decades. Built on unwashed aggregate or laid flat, it can silt up within a few years.

Related services

Crawl Space Encapsulation

A sealed liner across the floor, piers and walls, taped and mechanically fastened, with the vents closed and the space dried. It is the full system, not a sheet of plastic laid on dirt.

Crawl Space Insulation

Wall insulation for a sealed crawl space, or subfloor batts for a vented one. Which is correct depends on whether the space is closed — installing the wrong one traps moisture against wood.

Crawl Space Waterproofing

Stopping water getting in, before anything gets sealed. Grading, downspout extensions, perimeter drainage and a sump where the water table demands it.
Call (910) 886-2018