Underpinning · Party walls · Restricted access
Underpinning two party walls in a hilltop rowhouse, by hand
A builder is lowering the back of the cellar in a c. 1840 brick rowhouse to make a family room. The house shares both side walls with its neighbors, the street is steep and narrow, and there is no way in for a machine. The ground is dense glacial till: good for short pits, slow to dig.
Illustrative example — composite site, not a completed ESC project.
- Building
- c. 1840 brick rowhouse, four storeys, mid-row
- Lot
- 22 ft × 70 ft
- Neighbors
- Party walls on both sides
- Lowering
- About 3.5 ft, over the rear 30 ft of the cellar
- Ground
- Dense glacial till with cobbles (typical for a drumlin; confirm by test pit)
- Access
- Through the house only
The situation
The house sits high on a drumlin, one of the rounded glacial hills the oldest parts of Boston were built on. The till there is dense and stands up well in a short, narrow pit, but it carries cobbles and the odd boulder that has to be broken out by hand.
Only the back of the cellar comes down, by about three and a half feet. That stretch of each party wall, about thirty feet a side, loses the ground in front of its footing and has to be underpinned. The front of the cellar stays at today's level.
The street is steep, parking is scarce and the sidewalk is narrow. Materials, spoils and concrete all move through the front door.
What drives the design
Two neighbors on the same walls
Each party wall carries this house and the one next door, and on a hill the neighbors' cellars rarely sit at our level. The first test pits find out how they sit, and surveys of both houses come before the first bay.
The step between old and new floor
Where the lowered back meets the front of the cellar, each wall's footing is exposed at the step. The underpinning turns that corner with a short return so the step holds.
Hand work through a front door
Nothing larger than a wheelbarrow gets in. Spoils go out in bags and buckets, and concrete comes in by line pump or in small batches.
Cobbles in the till
The till stands well, which keeps pit shoring light, but a boulder in a bay can stop the day. Breaking it out by hand is what slows the work, so the schedule allows for it from the start.
Hand-dug pit-and-pour under the lowered length of each party wall, with a return at the step and both neighbors surveyed first.
- Four-foot bays taken about four and a half feet below the old footing, in two alternating passes, so neither wall is ever undermined over more than one bay.
- Each bay shored as the ground needs, cast in concrete and dry-packed tight to the old footing before the bays beside it open.
- A short return of underpinning at the step, where the lowered floor meets the front of the cellar.
- Crack gauges and survey points on both party walls, read at every pour.
- Spoils bagged out and concrete brought in by line pump, within the hours the street allows.
Illustrative example — composite site, not a completed ESC project.
- Note 1: Party wall: brick on a stone footing
- Note 2: The neighbor's cellar floor, often higher or lower on a hill; the test pit tells
- Note 3: Underpinning: concrete in a four-foot bay, about 4.5 ft below the old footing
- Note 4: Dry-pack joint rammed tight under the old footing
- Note 5: Lowered floor, about 3.5 ft down, at the back of the cellar only
- Note 6: Dense till with cobbles: it stands well in a short, narrow pit
Illustrative example — composite site, not a completed ESC project.
- Ground not yet dug
- Open bay, shored
- Cast, with the dry-pack joint (gold) under the old footing
- Numbers under the bays give each bay’s pass.
Illustrative example — composite site, not a completed ESC project.
- Lot line
- Neighboring building
- Building worked on
- Area lowered or excavated
- Yard or open ground
- Underpinning in sequenced bays
- Gap that decides the design (measured on the drawing)
- Synthetic lot for illustration: 22 × 70 ft, attached on both sides, front wall on the sidewalk.
- Underpinning along the rear 30 ft of each party wall, with a 4 ft return at the step: about 68 LF at the low end.
- The rear wall's footing may already step down with the hill; the high end of the budget adds it (22 LF) in case the test pit says otherwise.
- Everything moves through the front door. Nothing on or under the neighbors' lots.
The order of work
- 01Day 0. A test pit at each party wall: footing depth, what it bears on, and how the neighbor's cellar sits.
- 02Week 1. Condition surveys of both neighbors; gauges and survey points on both walls.
- 03Weeks 1–4. Alternating passes along each wall, then the returns at the step.
- 04Then. A level bearing surface at the back of the cellar for the builder's slab.
Who carries what
ESC
the earth-support subcontractor
- Test pits at both party walls and the rear wall
- Underpinning bays: dig, shore, cast, dry-pack
- Returns at the step
- Gauges and readings during the bays
General contractor
or the builder
- Digging the cellar floor and getting spoils out
- New slab, waterproofing and finishes
- Street permits and the pump truck
- Neighbor agreements
Excavator
often the GC's own crew
- No machine: the floor is dug by hand, often by the builder's crew
Engineer of record
designs and signs
- Underpinning details and pass sequence
- Checks for the neighbors' loads
- New floor and bearing levels
Others
- Surveyor: condition surveys and survey points
- Neighbors: access to their cellars for the surveys
Budget range
Budget range · budget, not a quote
$90,000–$270,000
Computed from ESC’s published unit prices, book rev 1 issued September 14, 2026 and valid through December 13, 2026: the low quantities at the book’s low rates to the high quantities at its high rates, rounded out to the nearest $5,000. It is a budget for this composite site, not a quote for yours.
The basis, line by line
Underpinning bays along the lowered length
$90,525–267,030
25.5–41.4 CY × $3,550–6,450 per CY
17 bays on the party walls and returns (about 68 LF) at 1.5 CY each, up to 23 bays with the rear wall at 1.8 CY each.
Book row UP-PIT-POUR †
Budget figure. Depends strongly on ground and configuration; confirm with a firm quote.
Not in this range
- Digging the cellar floor and spoils out of the house (builder)
- New slab, waterproofing and the finished step (builder)
- Underpinning design and pass sequence (engineer of record)
- Condition surveys and readings (surveyor), unless added
- Street permits for the concrete pump (builder)
Where a real job lands
Whether the rear wall needs underpinning, and how wide the old footings turn out to be, decide where in the range a real job lands.
Low end: open site, repetitive work, good ground, larger quantities. High end: tight access, obstructions, variable ground, small quantities. Book rates carry prevailing wage.
Every rate in the published bookWhat we’d need to firm it up
- Structural drawings: the extent of the lowered area and the new levels
- Test pits at each party wall and at the rear wall
- The neighbors' cellar levels, and their agreement to surveys
- Where a pump truck can stand, and when
- Target start
More on the techniques
Send us the address and drawings
We'll send back how we'd approach yours: the support we'd use, the order of work, and a budget range from our published prices. We work for builders, GCs and developers.
Or email plans to bids@earthsupportcorp.com