Licensed, insured, and built for Fairfax County's wet clay soil
Crawl Space Drainage Solutions McLean VA that keep your floor dry
Crawl Space Drainage Solutions McLean VA means moving water out from under your house before it rots joists, feeds mold, and drives your heating bill up. We install a crawl space drainage system in McLean, Virginia for homeowners in Chesterbrook, Langley Forest, and West McLean whose vapor barrier is floating in two inches of water. Call (571) 773-0698 and we'll be under your floor this week.
Live phone supportUpfront optionsBacked workmanship
What's included
What's Included in Our Drainage Scope
Every drainage job we quote in McLean includes the source fixes, the drain itself, and the verification readings. Encapsulation, dehumidification, and mold treatment are quoted separately because not every home needs them, and we'd rather tell you that than pad the invoice.
Full Crawl Space Inspection
Boroscope, moisture meter, and thermal imaging camera survey with photos. We map low spots, water entry points, and existing damage, and you get the report the same day.
Exterior Water Source Fixes
Downspout extensions, splash blocks, and regrading recommendations. This is the step most contractors skip, and it's the reason their drains fail within a year.
Perimeter French Drain
4-inch perforated pipe set in washed 3/4-inch gravel on a measured 1% pitch, wrapped in filter fabric. Hand-dug in low crawls so we don't damage joists or ductwork.
Sump Basin and Pump
Cored basin with cast-in-place liner, cast-iron or stainless pump, battery backup, and high-water alarm. Discharge line runs 15 to 20 feet from the foundation.
20-mil Vapor Barrier
Reinforced encapsulation liner laid over the gravel bed, up the walls, taped at seams, and terminated at the sill plate. Sealed edges keep soil gas and moisture out.
Post-Install Verification
Pump float tested three times, moisture meter readings at 24 hours and 30 days, and thermal images of the finished space. All documentation goes to you in writing.
Service overview
Crawl Space Drainage Solutions McLean VA: What We Actually Do
Crawl Space Drainage Solutions McLean VA is the category of work that intercepts groundwater and surface seepage before it pools under your floor. In practice that means a perforated perimeter drain set in washed gravel, pitched to a low point, tied to a sump basin and pump, and finished with a sealed discharge line that dumps 15 to 20 feet from the foundation. We trench by hand in tight crawls, lay 4-inch corrugated or rigid PVC, and backfill with 3/4-inch washed stone so the pipe never silts shut.
Most McLean crawl spaces flood for one of three reasons: clay-heavy soil that sheds water sideways instead of down, a downspout dumping within 3 feet of the foundation, or a grading slope that pushes runoff toward the house. We see it constantly in Chesterbrook and McLean Hamlet, where 1950s and 1960s split-levels sit on shallow footings. If you've been searching crawl space drainage near me and finding nothing but vapor barrier installers, that's the gap we fill.
How we workWe verify the cause, compare realistic options, and confirm the repair before we leave.
The service timeline
How Our Crawl Space Drainage Installation Works
The process flexes to the condition, but these checkpoints keep decisions clear.
Inspection and Mapping
We crawl the whole space with a boroscope and a moisture meter, map the low spots, and check the exterior grade and downspout discharge. A thermal imaging camera shows us where water is entering behind the foundation wall. You get photos and a written plan the same day, usually within 90 minutes on site.
Water Control First
Before any pipe goes in, we fix the source: extend downspouts, correct negative grade, and seal visible foundation cracks with hydraulic cement and polyurethane injection. Skipping this step is why so many DIY drains fail within a year. This phase takes one day on most McLean properties.
Trench and Drain Install
We hand-dig a 12-inch-deep trench along the low perimeter, line it with filter fabric, and set 4-inch perforated pipe on a 1% pitch to the sump location. Washed 3/4-inch gravel goes over the top, then the fabric wraps closed so fines stay out. Two technicians, one to two days.
Sump Basin and Discharge
We core a basin into the lowest point, set a cast-in-place liner, and install a cast-iron or stainless pump with a battery backup. The discharge line runs through the rim joist and dumps 15 to 20 feet downhill from the foundation. We test the float three times before we call it done.
Vapor Barrier and Verification
A 20-mil reinforced encapsulation liner goes over the gravel and up the walls, taped and terminated at the sill. We run a Santa Fe or AprilAire dehumidifier set to 50% RH, then meter the space at 24 hours and again at 30 days. You get both readings in writing.
Tools & methods
Tools and Methods We Use on Every Job
Purpose-built equipment, used by trained technicians, so the job is done accurately the first time.
Moisture Meter
Reads wood and concrete moisture content before and after work. We meter every joist and log the numbers so you see the change, not just hear about it.
Thermal Imaging Camera
Shows temperature differentials that reveal hidden water entry points behind foundation walls and under subfloor. Catches leaks a visual inspection misses.
Boroscope
A flexible camera on a 3-foot probe that lets us inspect behind rim joists and inside wall cavities without cutting anything open.
Santa Fe and AprilAire Dehumidifiers
Sized to your crawl's cubic footage and set to 50% RH. Condensate lines run to the sump so you never empty a bucket.
Dri-Eaz and Phoenix Air Movers
High-CFM drying equipment used after water removal. A wet crawl dries in 48 hours with air movement instead of two weeks without it.
HEPA Vacuum and Air Scrubber
Captures mold spores and fine debris during cleanup and remediation. Keeps the rest of the house from getting what was under the floor.
Fiberlock and Concrobium Treatments
Antimicrobial coatings and encapsulants applied to framing after cleaning. They seal in residual staining and stop regrowth on treated wood.
Use cases
When McLean Homeowners Call Us for Drainage
These examples show how the service framework adapts rather than forcing every call through one repair.
Langley Forest: From Mold to Market-Ready
A home going on the market got flagged for mold on the joists and a musty odor in the living room. The buyer's inspector noted moisture at 21% and visible fungal growth across roughly 200 square feet of subfloor and framing. → We fixed the grading, installed drainage and a sump, HEPA vacuumed and treated the framing with Fiberlock, and added a Santa Fe dehumidifier. Post-remediation air testing came back clear, and the sale closed without a credit.
West McLean Rancher: Cutting the Dehumidifier Bill
A rancher had a dehumidifier running 20 hours a day and still couldn't get below 65% RH. The north side of the crawl had negative grade, and a downspout was dumping 2 feet from the foundation. No standing water, but constant damp. → We corrected the grade, extended the downspout 14 feet, and installed a 38-foot drain to a single sump. Relative humidity settled at 48 to 52%, and the dehumidifier runtime dropped by about 60%.
Problems we solve
Crawl Space Problems We Solve in McLean
Water under a house shows up in ways homeowners don't always connect to the crawl space. Here are the four we get called about most in Fairfax County, and what's actually happening.
Standing water after every heavy rain
We intercept the water with a perimeter drain on a measured pitch to a sump basin, then fix the exterior grading and downspouts that were feeding it. Most McLean installs are dry within 48 hours of the pump test.
Musty odor drifting up into the living room
We remove the water source, HEPA vacuum and treat affected framing with Concrobium or Fiberlock, then hold the space at 50% RH with a Santa Fe dehumidifier. The odor clears within about a week.
Vapor barrier floating on a puddle
We pull the old liner, install drainage underneath, and reinstall a 20-mil reinforced barrier over the gravel bed. The liner goes on top of a working drain, never instead of one.
Rotten sill plate and soft joist ends
We fix the moisture first, then sister or replace affected joists and sill plates with pressure-treated lumber. Repairing structure over a wet crawl just means doing the job twice.
Pricing process
What Crawl Space Drainage Costs in McLean
$3,200 - $8,500 depending on crawl size, drain length, and sump configuration
Crawl Space Height
Crawls under 24 inches require hand-digging and shorter tools, which adds roughly 15 to 25% to labor. Above 36 inches, we can work faster and the price drops accordingly.
Linear Feet of Drain
Most McLean homes need 40 to 80 feet of perimeter drain. Each additional 10 feet adds pipe, gravel, fabric, and labor, so the total scales with the footprint of the house.
Sump and Backup
A single cast-iron pump with a cored basin is the base. Adding battery backup and a high-water alarm runs a few hundred more, and it's the upgrade we recommend most in Fairfax County.
Customer reviews
What McLean Homeowners Say
★★★★★
“Our 1962 split-level had standing water under it every spring. TerraVault dug the perimeter drain by hand because the crawl is only 22 inches tall, set a sump with battery backup, and put a 20-mil liner over the gravel. Six months later the floor is dry and my joist meter reads 13%. The musty smell upstairs is gone too.”
★★★★★
“We had two other companies quote us a vapor barrier and nothing else. TerraVault actually fixed the grading and extended the downspouts first, then installed the drain. They showed me thermal images before and after and gave me moisture readings in writing. Cost was right in the middle of the three quotes.”
★★★★★
“Called on a Tuesday after finding water under the house, and they were crawling the space Thursday morning. Sump pump, perimeter drain, and a Santa Fe dehumidifier were in by Friday afternoon. They came back at 30 days to re-meter everything at no charge. Straight answers, no upsell.”
Questions before we arrive
Frequently Asked Questions About Crawl Space Drainage in McLean
How much does crawl space drainage cost in McLean VA?
Most residential crawl space drainage systems in McLean run $3,200 to $8,500 in 2026, with the average around $5,400. A single sump pump and short perimeter run sits at the low end. Full-perimeter drain, battery backup, and a 20-mil encapsulation liner push toward the top. Tight crawls under 24 inches add labor because everything is hand-dug.
What is the best drainage solution for my crawl space in McLean?
For most McLean homes on clay soil, the best answer is a perimeter French drain in washed gravel tied to a sump basin with battery backup, capped by a sealed 20-mil vapor barrier and a Santa Fe dehumidifier set to 50% RH. Homes with a single low corner sometimes do fine with a localized drain and pump. We tell you which one you need after the inspection, not before.
How long does crawl space drainage installation take in McLean VA?
Plan on two to four working days for a typical 1,200 to 1,800 square foot crawl space. Day one covers source fixes and trenching, day two is pipe, gravel, and sump, and day three handles the vapor barrier and dehumidifier. Larger homes in Langley Forest or Evermay with multiple low points can run five days.
Can I install crawl space drainage myself in McLean VA?
You can, but the failure rate is high. The two mistakes we see most are skipping the exterior grading fix and laying pipe flat instead of on a 1% pitch. Both leave you with a flooded crawl within a season. If you do it yourself, rent a laser level, use washed 3/4-inch stone, and wrap the pipe in filter fabric.
Related services
Related Services We Pair With Drainage Work
Crawl Space Mold Removal
Once the water is gone, mold colonies on joists and subfloor need physical removal with HEPA vacuuming and antimicrobial coating. We handle both in one mobilization so you're not paying two setup fees.
Crawl Space Mold Remediation
Full remediation with air scrubbers, containment, and Fiberlock or Concrobium treatment. Drainage comes first so the mold doesn't return within a season, which is the most common reason remediation fails.
Crawl Space Mold Inspection
A boroscope and moisture meter inspection that maps where mold is growing and traces it back to the water source. We do this before quoting drainage so the scope matches the actual problem.Ready when you are
Get Crawl Space Drainage Solutions McLean VA This Week
We inspect, meter, and quote the same day, and we don't leave until the pump test passes twice. Licensed, insured, and working Fairfax County crawl spaces every week. Call (571) 773-0698 and tell us what your floor is doing.
Talk with the local team
Request Crawl Space Drainage Solutions
Call us at (571) 773-0698 or send an email and we'll get back to you the same business day. We schedule inspections Monday through Friday, 8 a.m. to 6 p.m., and we can usually be in your crawl space within 24 hours. If you've got water, mold, or a smell you can't place, we'll find it.