Hydrostatic pressure is quiet until it isn’t: saturated clay loads an eight-foot wall at 60–80 pounds per square foot — a parked car on every tyre-width of footing. Duty line seven to seven: (555) 021-4436.
Interior vs exterior
Two waterproofings. One of them is yours.
The industry sells one answer per company. The water does not care which company you called. Below is the whole decision — the three routes out of a wet basement, who each one suits, and what each one costs downstream. The diagnostic tells you which column of this table your house is standing in.
Interior — drain, sump, relief
A channel cut inside the footing collecting water at every cold joint, daylit into a sealed basin with a battery-backed pump. Relieves the pressure under your floor instead of fighting all of it. No excavation, no deck torn up, no flowerbed lost — the honest choice when the walls are sound and the water arrives from below.
Exterior — dig, membrane, backfill
The wall opened to the footing, a dimple membrane bonded to it, clean stone backfilled behind. Stops water before it ever touches the wall, which no interior system can promise. Costs more and disturbs the grade — the honest choice for historic stone, free outside access, or water coming through the wall itself.
The hybrid — both, staged
Exterior seal on the one elevation the rain punishes, interior drain and redundant sump under everything else. Most Millrace houses end here: the 1962 additions leak at cold joints an exterior dig cannot reach without removing the porch. We stage the two so the cheap half proves itself before the expensive half is booked.
Priced from readings
The rate card, both columns of it
Last quarter’s closed jobs in Lantern Hill and along the Millrace. The $340 diagnostic comes off any work booked within a year, every line includes cleanup and the instrument log, and the quote is a ceiling — it moves for steel prices between printings, never mid-job.
The diagnostic$340 flat
Laser datum, moisture map, crack gauges — verdict in writing
Interior perimeter drain$58 / lin ft
Channel at the footing, sealed basin, battery pump, alarm
Redundant sump system$2,150 set
Primary + battery secondary on separate floats, texts you
Exterior membrane & dig$96 / lin ft
Open to footing, dimple board, stone backfill, grade restored
Epoxy or urethane injection$98 / lin ft
Structural epoxy; flexible urethane on moving cracks
Carbon-fiber staples$150 / staple
Slots stitched across a bowing wall, skimmed flush
Instruments, then opinions
How a diagnostic runs
Two hours on site, one document in your hands, and no repair sold on the same visit — the cooling-off period is on purpose and it is ours, not yours.
Instrument the water
Moisture map of every wall, tide lines photographed, downspout discharge traced, and the sump — if there is one — scoped and cycle-timed through a bucket test.
Instrument the structure
Laser datum of the slab to the half-millimetre, crack gauges at every fracture wider than a hair, deflection strings slab-to-joist on anything that leans.
Model both fixes
The interior route and the exterior route drawn against your actual readings — what each would do, what each would cost, and which failure each one cannot touch.
Cool off, then choose
You keep the document and the numbers for as long as you like. One household in five chooses nothing, and a diagnostic that ends there is a diagnostic that worked.
Verify after the work
Six weeks on, the moisture map is re-run beside the original. Two maps, same instruments, one expected answer — that is what a warranty is made of.
The group, in figures
2025 — 2026, the book
Basements after the instruments
Six jobs from the last two quarters, photographed at the six-week re-run with the before map still taped to the wall.
Two companies before them sold me an interior drain from the doorway. Halden’s moisture map showed the water arriving through the north wall, not under the floor — so the exterior membrane was the honest fix, and it cost less than the drain quote I almost signed. They talked me out of their own cheaper product and I will never call anybody else.
The diagnostic document is a work of art — readings, photographs, both fixes priced, and a page that says which one they would pick if it were their basement. We picked the other one anyway, they installed it without a word of argument, and the six-week re-run matched their prediction line for line.
Our 1911 stone foundation terrified every contractor who looked at it. Halden gauged it, found the walls sound and the joints tired, injected what wept and drained what rose. The dehumidifier has been in the garage — unplugged — for two full Millrace springs now.
Before the diagnostic
Fair questions
The five the booking line hears most. Anything else, the duty line below runs seven to seven, Millrace-wide. dry@haldenbasements.example
Interior or exterior — which one lasts?
Both, installed right, outlive the mortgage — they answer different questions. The interior system manages water that has arrived; the exterior membrane stops it touching the wall at all. What fails early is the mismatch: a drain fighting water coming through the wall, or a membrane wrapped around a floor that floods from below. The moisture map decides which failure you actually have.
What does hydrostatic pressure actually mean?
That the ground around your house has turned into a reservoir pressing on the walls and floor. Saturated clay pushes 60–80 pounds per square foot at the base of an eight-foot wall, and it is what bulges walls, cracks floors and lifts water through cold joints on the low side. You can seal against it, drain to relieve it, or regrade to starve it — but you cannot paint over it.
Will the exterior dig destroy the garden?
It takes a four-foot working strip along the elevation and it is not gentle on what sits inside it. We sheet, hand-dig around plantings worth keeping, and reinstate the grade and the topsoil — but a rosebush in the strip does not survive, and pretending otherwise would be a lie we would have to garden past. The interior route touches nothing outside, which is half of why it gets chosen.
What does the redundant sump buy me?
The storm that floods a finished basement is almost never a capacity problem — it is the night the power quits, the pump jams or the float sticks. A primary on mains, a secondary on its own battery and float, an alarm that texts you, and check valves each side: the failure of any one part is a log entry, not a claim.
How long before I get the document?
Two hours on site, the written diagnostic within three days — moisture map, datum, both fixes priced, one recommendation, nobody phoning to upsell it. If the verdict is that nothing needs doing, that is the whole verdict, and you paid $340 for peace of mind with readings attached.
Diagnostics booked within the week · one in five chooses no repair at all · (555) 021-4436 · dry@haldenbasements.example
Put the basement on instruments
Tell us what the floor, the walls or the dehumidifier have been doing. The $340 diagnostic comes off any work booked within a year, and the readings are yours whatever you decide. dry@haldenbasements.example