Basement Waterproofing Case Studies

In 2025 our engineers personally inspected 250 homes across the DMV. The problems repeated. Different neighborhoods, different decades, different foundations — but the same handful of failures, over and over. We completed 79 projects that year, and most of them were variations on those same patterns.

So rather than publish 79 write-ups that say the same thing six different ways, we picked 25 jobs that cover every pattern we found. This page is where they live, and all twenty-five are now written up.

New to the series? Start with our open letter to DMV homeowners, then what your DMV foundation is actually made of — Post #1 in this series.

Every basement fails for a specific, findable reason. The diagnosis came first in each case below, and the system installed followed from what that diagnosis found, not the other way around. Want the same process on your home? Call 1-833-888-2533 for a free inspection. A trained technician walks the property, not a salesperson.

How to Read These Case Studies

Every job below follows the same sequence our engineers use on every basement waterproofing job. First: a wet carpet, a musty smell, a crack that kept reopening, whatever the homeowner actually noticed. Second: the real water source once we opened the wall or slab, often not what the homeowner assumed (see how water actually gets into a DMV basement). Third: why that foundation type and water source called for the system installed. Fourth: what made the job hard, if anything did.

Names, house numbers and contact details are never published. Each case gives the neighborhood and county, nothing more.

Exterior Waterproofing: When the Wall Itself Lets Water Through

These cases share one fix. The water source hit the wall from outside, the wall could be reached, so we sealed it from outside.

Ashburn, VA: Freeze-Thaw Cracks in a CMU Wall

An Ashburn family in Loudoun County kept finding the carpet wet in a finished basement bedroom, with a new baby in the home. The water table was ruled out. Excavating to the footer showed the cause: cracks and a cold joint in the CMU wall, widened over successive winters by freeze-thaw. We sealed the cold joint and cracks, then built a full exterior system: parge coat, primer, bituminous membrane, protection board, and a dimple drain board, backfilled in lifts and graded away from the house. No water has reached that bedroom since. Read the full Ashburn case study.

Northwest DC: A 90-Year-Old Brick Foundation With Failing Mortar

A 1930s brick foundation on Connecticut Avenue NW had water on the floor and mold along the wall. The slab showed no cracks, so the water was not rising from below: it came through ninety years of deteriorated mortar joints, on a wall taking heavy surface water. We excavated to the footer, cleaned the brick, and applied a cementitious coat, a liquid layer, and a bituminous sheet membrane, protected by drain board and drain tile. The wall that had been wicking water for years now stays dry, under a written 25-year exterior warranty. Read the full Connecticut Avenue case study.

Bethesda, MD: Three Wall Sections, Two Different Water Sources

A 1940s CMU home on Massachusetts Avenue was taking on water through three wall sections. High ground ruled out a water table. Two sides were below-grade seepage through the block, sealed with the same exterior system, drain tile raised near grade since the excavation had nowhere lower to fall. The third side was not the foundation at all: a gutter with no downspout was sheeting roof water down the block, so that side got a downspout, not a membrane. Three sides, three causes, three matched fixes. Read the full Bethesda case study.

Interior French Drain: When Water Arrives Faster Than a Coating Can Stop It

These could not be solved from the outside, either because the water table itself was the source or because the property gave us no way to excavate. Each one was drained from the inside instead.

Manassas, VA: A High Water Table Under a Large CMU Basement

A very large CMU basement near Manassas was taking on water and mold across three corners, with a step crack in one. The cause was a high water table pushing against the block from the side and up through the footing at once, not a single leak. We installed an interior French drain with dual sump pumps and a wall vapor barrier, replacing mold-damaged framing along the way. The slab could not open all at once: crews left two feet uncut every six feet so it would not settle while trenching, then doweled rebar into it with epoxy before pouring new concrete. Read the full Manassas case study.

Silver Spring, MD: Mold and Groundwater With No Exterior Access

A Silver Spring townhouse basement had a heavy, musty mold odor, water on the floor, and cracks in a corner wall. Exterior excavation was not an option here, so an outside fix was never on the table. The cause was a high water table pushing groundwater against both walls and slab under hydrostatic pressure. We remediated the mold first, four days before any waterproofing began, then opened the slab at footing depth, set drain tile in clean stone, installed a sump pump at the entry point, and restored the slab. Nine days start to finish, and the basement went from mold-heavy air to dry. Read the full Silver Spring case study.

Olney, MD: When New Downspouts Point Water at the Foundation

An Olney homeowner kept finding mold in the same three spots along the basement walls, no matter how often it was cleaned. The CMU block itself was the reservoir: hollow and porous, holding water like a sponge where oversized downspouts discharged roof water at the foundation corners. Stepped cracks through the mortar joints and a cracked slab at the corners showed the pressure that had built up. We buried and extended the downspouts, removed the mold, installed a vapor barrier, and ran 124 feet of interior French drain to a dual-pump sump with battery backup. Eight days later it was dry, and stayed dry through the storms that followed. Read the full Olney case study.

Yard Drainage: When the Water Never Should Have Reached the House

Not every water problem is a basement problem. Sometimes the fix is in the yard, before the water ever touches the foundation.

North Potomac, MD: The Street Drained Into the Front Yard

A North Potomac home in Montgomery County sat below road grade, and every storm turned the front yard into standing water — wide enough that the owners called it a lake, lingering for hours after the rain stopped, killing the grass and sitting against the foundation. Nothing was wrong with the foundation wall. The problem was that runoff had nowhere to go but toward the house. We cut a graded and compacted trench, wrapped it in geotextile, set a 6-inch perforated pipe in #57 stone, tied in a catch basin, and discharged by gravity to the rear yard. The front yard now sheds a storm instead of holding it. Read the full North Potomac case study.

Gaithersburg, MD: The Pipe Is the Cheapest Part

About 100 feet of yard drain and two catch basins, broken down by where the money actually went. The perforated pipe was under a tenth of the cost. Excavation and hauling, gravel placed and compacted, and restoring the lawn over the whole run accounted for more than eighty percent of it. If a drainage quote looks cheap, check whether restoration is in it. Read the full Gaithersburg case study.

Rockville, MD: Two Downspouts and a Pop-Up

The smallest job in the series, and the last of the twenty-five. Two downspouts were emptying at the foundation, so we took each underground at a fall and ended the run in a pop-up emitter out in the lawn. A little over $1,200, a fraction of a day, and the cause of the problem rather than its consequences. Read the full Rockville case study.

Crawl Spaces: When the Problem Is Under the Floor, Not Behind a Wall

Seven crawl space jobs, and seven different complaints that turned out to describe the same kind of space. A crawl space is not a small basement — it fails differently, and it is diagnosed differently.

Bethesda, MD: The Crawl Space That Was Cooling the Whole House

Cold floors and a house that never heated evenly. The crawl space was vented, the walls were bare and the rim joist band was open, so the floor was losing heat straight down while outside air carried moisture in. We sealed and insulated the whole space: a 20 mil barrier on the floor and up the walls to an insulated liner, insulation cut into every rim joist pocket, two condensate pumps and a dehumidifier sized with room to spare. Three days. Read the full Bethesda case study.

Gaithersburg, MD: The Smell Was the Symptom

A musty smell that cleaning never fixed. The smell was not in the house — it was being delivered to it, from mold growing on the framing of an open, humid crawl space. We treated and physically removed the mold first, then sealed the penetrations, lined and taped the ground, re-hung the fallen insulation and installed a dehumidifier with a real drain line. Then we left a humidity gauge, so the homeowner could check our work without calling us. Read the full Gaithersburg case study.

Southwest DC: We Took the Insulation Out

This crawl space had insulation and ventilation, and both were making it worse. Four open foundation vents were feeding humid summer air into a space that could not dry, and the old fiberglass was holding that moisture against the wood. The first two line items were removals: about 720 square feet of insulation out, all four vents sealed shut. Then mold treatment, and the ground, walls and piers wrapped. Read the full Southwest DC case study.

Burke, VA: The Plastic Would Have Made It Worse

Water was arriving as water, not humidity — running in and standing on the floor. Sealing a barrier over that would have built a lid on a puddle. A dimple board went down first to give the water a drainage path, and the encapsulation went on top of it. A small crawl space, about 210 square feet, that still needed two days and a layer most quotes leave out. Read the full Burke case study.

Germantown, MD: The Draft Was Coming From Underneath

Drafts and uneven temperatures in a house whose crawl space never stabilised. Insulation alone was not the answer: air was physically moving from the crawl space into the living space, carrying temperature, humidity and smell with it, and no amount of insulation in its path changes that. We air-sealed the walls with spray foam, plugged both vents, sealed the floor and walls into one surface and insulated the rim joists. One day. Read the full Germantown case study.

Accokeek, MD: Enough Water to Need a Drain First

The largest crawl space in this series, just under 1,000 square feet, and the only one where water was arriving persistently enough that sealing it alone would have built a lid on a puddle. About 120 feet of perimeter drain pipe went into the dirt floor first, five columns were wrapped and sealed to code, and only then were the floor and walls encapsulated. Four days, most of them on hands and knees. Read the full Accokeek case study.

Leesburg, VA: The Crawl Space We Did Not Encapsulate

The counter-example in this group. Both vents sealed, the rim joists insulated, a dehumidifier and a condensate pump — and deliberately no floor or wall barrier, because the conditions did not call for one. Four line items, because the space had four problems. Read the full Leesburg case study.

Crack Injection: When the Water Comes Through One Line in the Wall

Five jobs on poured concrete foundations where the problem genuinely was a crack and the wall around it was sound. Polyurethane grout, injected under low pressure, travels the whole path of a crack through the thickness of the wall and sets where it meets water. It is also the system most often sold to houses that do not have that problem.

Foggy Bottom, DC: Two Cracks, Sealed From the Inside

Two separate cracks in one foundation wall, both leaking. A crack is not a flat line — it wanders through the wall and connects to voids nobody can see, which is why patching the face of one rarely holds. Both were drilled, packed and injected at low pressure, then the packers cut off flush and the wall patched back with cementitious mortar. Read the full Foggy Bottom case study.

Kensington, MD: Why the Crew Came Back a Month Later

The same job, on two appointments about a month apart. Injection is a two-visit system: inject, let the grout cure with the packers still in the wall, then return to cut them off, remove the excess and finish the surface. The second visit sits inside the original price, which is exactly why it should be named in the quote. Read the full Kensington case study.

Gaithersburg, MD: A Second Crack, Seven Weeks Later

One crack sealed in early summer, and a different crack about seven weeks later. What injection promises is the crack you inject — not the wall and not the house. This file draws the honest line between a sealed crack reopening, which is a warranty matter, and a new crack appearing, which is a new problem. Read the full Gaithersburg case study.

Rockville, MD: Seal the Wall, Then Move the Water

Three jobs at one address, in order: the crack injected, then about 40 feet of exterior French drain along the same wall, then a buried downspout run two months later. Sealing a crack stops the leak. It does not stop the water arriving, and a wall that is permanently wet on the outside keeps finding new places to fail. Read the full Rockville case study.

Silver Spring, MD: Fifteen Feet of Drain

A long crack injected, and then an exterior drain fifteen feet long. Not a perimeter — fifteen feet, dug exactly where the inspection said water was arriving, leaving the rest of the yard, the walkway and the plantings untouched. Most people have never been quoted a fifteen-foot drain, because most people are quoted a perimeter. Read the full Silver Spring case study.

Exterior French Drain: Taking the Water Away Before It Reaches the Wall

Four jobs where the wall did not need sealing — the ground beside it needed draining. They run from about 25 feet to 110 feet, and the differences between them are the whole point: length, discharge, drain board, and whether gravity was available at all.

Montgomery County, MD: 110 Feet Along a School Building

The longest single run in this series, and the only one carrying drain board and a termination bar across its full length. A trench with a pipe in it handles water already in the soil; drain board handles water running down the face of the wall. They are different problems, and a board without a bar sealing its top edge is a funnel pointed the wrong way. Read the full Montgomery County case study.

Alexandria, VA: The Drain That Had Nowhere to Fall

Every French drain quote contains a silent assumption: that there is a downhill. This property did not have one. About 35 feet of trench and a catch basin, discharging to a sump pump with battery backup on its own dedicated electrical line — because a pump on a shared circuit stops working during exactly the storm that needs it. Read the full Alexandria case study.

Montgomery Village, MD: Twenty-Five Feet to Collect It, Fifteen to Carry It

There are two entirely different pipes in a working drain. Perforated pipe collects; solid pipe carries. This job has about 25 feet of the first and 15 feet of the second, and the length of the second is what decides whether the water leaves or walks back. A drain that discharges too close to the house is the most common reason somebody else’s system “never worked.” Read the full Montgomery Village case study.

Silver Spring, MD: The Ordinary Job

Included precisely because nothing went wrong. About 40 feet of textbook exterior drain, layer by layer: trench cut to a fall, non-woven geotextile, perforated pipe, gravel, compaction to grade, and a buried downspout. The fabric is the cheapest material on the job and the one that decides whether the drain is still draining in ten years. Read the full Silver Spring case study.

What These Jobs Have in Common

Twenty-five jobs, six systems, and one pattern that holds across all of them: what the homeowner called a leak was almost never a hole through the wall. It was groundwater pressure, a misrouted downspout, decades of mortar wear, air moving up through a vented crawl space, or water arriving from off the property entirely. An exterior source, far more often than a simple crack.

The roof turns up more than anything else. A buried downspout appears in nearly every drainage job here, and the smallest job in the whole series — a little over $1,200 — was two downspouts and a pop-up emitter. Before you price a system, go outside during a real storm and watch where your own roof water lands.

Older DMV housing stock shows up throughout, CMU and 1930s brick among the worst of it, and no two walls failed the same way. A high water table drove several of the basement jobs, consistent with the clay soils and shallow groundwater our engineers see across this region — while Bethesda and Ashburn both ruled the water table out and still had real intrusion, one from a gutter and one from freeze-thaw cracking.

Mold appeared wherever water sat long enough, in basements and crawl spaces alike. As the EPA puts it in its guide to mold and moisture in the home, the key to mold control is moisture control: clean up the mold and fix the water problem, or it returns.

And the range runs further in both directions than most people expect. The largest jobs here are multi-day excavations and four-day crawl space builds. The smallest is half a day and a four-figure invoice. The same inspection process produced both, which is the entire argument of this series: the diagnosis is the product, and the system is only ever what the diagnosis required.

The Systems Behind These Repairs

Exterior waterproofing seals the wall itself, used where the water source hits the wall from outside, as in Ashburn, DC and Bethesda. Interior French drain systems belong where water arrives from below or excavation is not possible, as in Manassas, Silver Spring and Olney.

Exterior French drains take water out of the ground alongside the foundation before it ever reaches the wall — anywhere from a targeted fifteen-foot run to 110 feet along an institutional building. Yard drainage belongs where the water never should have reached the house at all, as in North Potomac, Gaithersburg and Rockville.

Crack repair by polyurethane injection is for poured concrete walls where the problem really is one line in an otherwise sound wall. It seals that crack through the full thickness of the wall, and it is the wrong answer for every other kind of intrusion.

Crawl space work uses a different set of systems entirely — sealed vapor barriers, insulated liners, drainage layers, air sealing and dehumidification — because there the water is under the floor rather than behind a wall.

Manassas also called on foundation repair to reinforce the slab, and where mold appeared we treat mold removal as part of a waterproofing scope, not a separate service. Where downspouts or grading turned out to be the actual source, correcting those came first.

Where We Work

These cases span our service area, from Northwest DC through Montgomery County to Northern Virginia. We work from four branches: Rockville, MD (our main office, also serving North Bethesda), Kensington, MD, Ashburn, VA, and Manassas, VA.

Schedule a Free Inspection

If any of these case studies sound like your basement, the next step is what every homeowner above started with: a free inspection and a written diagnostic report, photos included, before anything is recommended. A trained technician walks the property, not a salesperson. Call 1-833-888-2533 or email info@dmvwp.com to schedule. Qualified projects can use 0% APR financing through Wisetack, and every system carries our warranty, lifetime and transferable on interior systems, 25 years on exterior.