French Drain Cost in Cary

Water around a foundation is behind many crawl space and foundation problems in Cary. French drains intercept and redirect it.

This guide covers types and published costs.

Types

Exterior drains run along the foundation or yard; curtain drains intercept water uphill; interior or crawl space drains collect water at the perimeter and route it to a sump or daylight.

Published costs

Published 2026 estimates put French drains at $500–$18,000, about $10–$100 per linear foot, with crawl space drains about $25–$35 per foot and exterior drains $500–$10,000 total. Sump pumps add $500–$2,000.

Clay soil considerations

Clay drains slowly, so drains need proper slope, fabric and gravel and a reliable outlet. Grading away from the house is often the first fix.

Code connections

For closed crawl spaces, R409 requires grading to low-spot drains or sumps, kept separate from gutter and foundation perimeter drains.

Permits

Ask the Town whether your drainage work needs a permit.

Neighbors and stormwater

Redirecting water must not create problems for adjacent lots or the street. If your drainage issue involves a shared swale, an easement or public stormwater, contact the Town before work.

Planning a drainage project

Start by watching where water goes during a heavy storm: downspouts that dump next to the foundation, low spots that pond, and slopes that send neighbors' runoff toward your house. Extending downspouts and regrading soil so it falls away from the foundation are low-cost first steps. If water still collects, a curtain drain uphill can intercept it before it reaches the house, and a crawl space perimeter drain with a sump can remove water that gets inside. Ask contractors where the drain will outlet, how they will keep it from clogging with clay fines, and how lawn and landscaping will be restored. A drain that ends in a buried pit with nowhere to go will fail in Cary clay.

Budgeting and getting bids

Use the published ranges below as a starting point, not a quote. Ask each contractor to identify the cause of the problem and break out drainage, moisture control, structural repairs, engineering and permits so bids compare fairly. Be cautious with proposals that sell expensive systems without explaining the cause. For larger projects, an independent engineer's evaluation before bidding helps define scope. Plan for wood repairs found after work begins, and add a contingency of ten to fifteen percent.

Choosing the drain type

Angi's 2026 French drain guide breaks costs down by type: interior drains at $5,000–$18,000, exterior drains at $500–$10,000, curtain drains at $1,000–$5,000 and yard trench or deep drains at $2,000–$10,000, with crawl space drains averaging about $25–$35 per linear foot. Curtain drains intercept water uphill before it reaches the house and often cost the least. Interior drains collect water that has already entered the crawl space and route it to a sump.

Clay soil installs

Angi notes that clay soils make trenching harder and raise labor costs. In Cary's clay, a drain's success depends on slope, a fabric-wrapped gravel envelope that keeps fines out of the pipe, and an outlet that actually discharges, either to daylight downhill or to a sump pump. A drain that ends in a buried pit in clay often fills and stops working.

Inspection and permits

Angi lists drainage permits at about $50–$200 where required and inspections at $100–$300. Ask the Town of Cary whether your drainage work needs a permit, especially if it is combined with structural or crawl space work. Call 811 before digging so underground utilities are marked.

Maintenance and lifespan

Angi says a well-installed French drain can last 30 to 40 years. Clean-outs at turns let you flush the pipe. Keep the outlet clear of leaves, mulch and soil, and check that the sump pump cycles during heavy rain.

Planting trees with aggressive roots near the drain can clog it, and adding mulch beds over the trench can slow surface intake. If water returns after a few years, a camera inspection can show whether the pipe is crushed, clogged or poorly sloped before anyone digs.

Comparing bids

Ask each bidder to state trench length and depth, pipe type and diameter, gravel volume, fabric wrap, outlet location, whether a sump and pump are included, restoration of lawn or hardscape, and permit handling. Prices per linear foot mean little without those details.

Drain outlets and neighbors

Under North Carolina's general drainage principles, you should not redirect concentrated water onto a neighbor's property. Plan the outlet so water leaves your lot along its natural drainage path or into an approved structure, and ask the Town of Cary whether stormwater rules apply when work changes how water leaves the lot. Document the outlet location on a simple site sketch for future owners. Ask whether the outlet will need periodic clearing and how to reach it. A quick check of the outlet after the first few heavy storms confirms that water is actually leaving the system and not backing up.

Published crawl space and foundation cost estimates

Sources: Angi: Crawl space repair cost (2026); Angi: Crawl space dehumidifier cost (2026); Angi: French drain cost (2026); Angi: Structural engineer cost (2026). Figures are published national or regional estimates compiled by those sites, labeled as estimates; they are not quotes and not prices from any provider on this site. National published estimates; Cary crawl spaces with low clearance, standing water or extensive wood damage price toward the upper end. Engineering and permits are often separate.

Local rules and code references

• NC Office of State Fire Marshal, Codes: Current and Past: the 2018 NC State Building Code remains the enforced edition; the adopted 2024 NC Residential Code (which keeps R408 Wall Vented Crawl Spaces and R409 Closed Crawl Spaces) takes effect only after the certification process set by S.L. 2025-2.
• 2018 NC Residential Code §R409 Closed Crawl Spaces, the edition currently enforced (text published by Johnston County Building Inspections): closed crawl spaces: sealed walls, a 6-mil vapor retarder with 12-inch laps, floor graded to a drain or sump at each low spot, and mechanical drying such as a permanently installed dehumidifier rated at least 15 pints per day with condensate drained to daylight or a pump.
• Town of Cary Residential Permits & Inspections FAQ: lists foundation repairs, and closing or sealing a crawl space, among residential projects that require a building permit, quoting the NC State Building Code requirement to obtain a permit before altering or repairing a structure.
• NC Board of Examiners for Engineers and Surveyors, Foundation Repair Guidelines (rev. 10/22/2024): state board guidance: a PE must be in responsible charge of foundation evaluation, pier count and location, repair design and completion certification.

Code text and department procedures change; confirm current requirements with the jurisdiction before work starts.