Case file — Massachusetts Avenue, Bethesda (right on the DC line). One of 79 projects we completed across the DMV in 2025. New here? Start with our open letter.

At a glance

• Location: Massachusetts Ave, Bethesda, MD (on the DC line)
• Home: A charming 1940s two-story
• Foundation: CMU (concrete block)
• The problem: Water entering through the basement walls — on three different sides
• Real cause: Below-grade seepage on two buried walls; gutter overflow + a missing downspout on the third
• The fix: Exterior waterproofing (WallShield™) on the two buried sides; gutter repair + new downspout on the third
• Warranty: Written 25-year exterior warranty

What the homeowner saw

Water was getting into the basement of this pretty little 1940s home — and not in one tidy spot. It was showing up on three different sides of the house. That’s usually the moment a homeowner assumes the whole basement has to be torn up from the inside. It didn’t.

What we found

The first thing we ruled out was the water table. This house sits on relatively high ground, and the water table wasn’t the driver. So the water wasn’t rising up from below — it was coming straight in through the below-grade walls.

But reading the house carefully, the three sides didn’t share one cause:

• Two sides are buried in soil. Here the block wall was taking on water directly from the ground — classic below-grade seepage.
• The third side is different. One back wall is the garage; the other has a stairwell descending toward it. There was no real groundwater problem there — the culprit was a gutter overflowing with no downspout, so two stories of roof water were sheeting straight down the wall face every storm.

Same symptom — a wet basement — but two different problems around one house. That distinction is the whole job.

What we did

We matched each side to its actual cause instead of selling one blanket “system.”

The third side (surface water): we repaired the gutter and added a downspout to carry roof water away from the wall — the cheapest, highest-impact fix for that side.

The two buried sides (exterior waterproofing — WallShield™):

1. Excavated along each wall down to the footing and cleaned the wall so every crack was visible.
2. Layer 1 — cementitious waterproofing, dampened and properly cured.
3. Layer 2 — a bituminous sheet membrane (GCP Bituthene) over primer.
4. Drainage placed where it actually drains. A drain tile at the footing had nowhere to fall here, so we set a grading tile up at grade level — catching water before it descends to the foundation.
5. XPS protection board over the membrane so backfill can’t damage it.
6. Backfill compacted in lifts. For the final foot we shaped the grade with soil and water-tested the slope — water ran away from the house. Then we set the drain board against the wall, laid perforated pipe in a clean-stone channel, and backfilled with gravel.
7. Tested again — water drained away from the foundation. Done.

Every step was done by our own crews — no subcontractors.

The result

We water-tested the grade and the drain before closing up, and the water moved away from the house exactly as it should. Three sides, three correct fixes, one dry basement.

The takeaway

One wet basement can have more than one cause. Two of these walls needed sealing and draining from the outside; the third just needed the roof water managed. The skill isn’t picking a product — it’s reading each side of the house and matching the fix to what’s actually happening there.

Seeing water on more than one wall of your Bethesda or DC-line basement? Schedule a free inspection — we’ll find what’s really happening on each side. Learn more about our exterior waterproofing.

FAQ

Do I always need an interior drainage system to stop basement water?
No. When the water table isn’t the cause and water is coming through the walls, sealing and draining from the outside is often the better fix — and different sides of the same house can need different solutions.

Written by Selcuk Altan Atasoy — civil engineer (University of the District of Columbia) and licensed waterproofing inspector (DC, MD & VA), in the field since 2005.