Mini excavator breaking out the old concrete floor slab inside the stripped rear addition

Wandsworth, southwest London

Wandsworth House

Basement, rear extension and whole-house refurbishment, in progress

Wandsworth House is a detached Victorian house in southwest London: a large new basement under the footprint of the house, a rear extension and a whole-house refurbishment, designed by The Vawdrey House and built by Omniform. It is on site now. This page follows the build month by month.

The ground is the point. A large basement is being formed under the footprint of the house, running out beneath the new rear extension. There is no open-cut shortcut beneath a standing Victorian house: it is underpinned sequentially, in lettered and numbered pins, dug by hand under the house and by machine along the retaining walls beyond it, each one steel fixed, shuttered, poured and cured before the next is opened. In situ concrete retaining walls and reinforced slabs form the shell, lined with a drained cavity waterproofing system to BS 8102 with sumps and pumps, designed by our waterproofing specialist and covered by an insurance backed guarantee. Where the dig runs close to the garden’s mature trees it is staged to the arboriculturist’s method statement, so their roots stay in the ground they grew in.

Above ground the house is stripped back, kept and mended: lattice plaster ceilings and fireplaces protected, doors and radiators set aside for re-use, the roof re-tiled in matching clay over new membrane and battens with the leadwork renewed. A rear extension in reclaimed yellow London stock brick with limestone courses follows the basement out of the ground. And all the temporary works, the propping and shoring and formwork that hold a house up while the ground is taken out from under it, are ours to design as well as to build.

Design: The Vawdrey House

Before

The house as found

Reception room before works with lattice plaster ceiling, ceiling rose and marble fire surround — The reception room’s lattice plaster ceiling and marble fire surround. The scope lists this fabric to be protected and kept: the refurbishment works around the original rooms, not through them.

March 2026

Strip out begins

The tiered deck stripped back to its joist grid along the rear of the house, rotten joist ends exposed — Day one, 30 March. The tiered deck comes up first, stripped back to its joist grid along the full width of the house, the rot in the buried timbers plain to see once the boards are off. Everything about this garden changes; the basement dig starts here.

April 2026

Back to brick

Structural steel sections laid out on the rear lawn, the deck removed and its brick sub-structure exposed at the house — Steel on the lawn for the needles and the temporary works: the sections that will carry the house while the ground is opened beneath it, every one scheduled from the engineer’s design before a spade goes in.

The old rear addition stripped to brick and exposed roof joists — The old rear addition stripped to brick and joists before it comes down. Doors, radiators and fireplaces are set aside for re-use across the scheme; the roof and rear walls go, as the demolition drawings say.

Tree protection fencing around the excavation area in the rear garden — Tree protection fencing goes up before the ground is touched. The new rear extension will sit here, with the basement running out below it, and the dig alongside the trees is staged to the arboriculturist’s method statement so their roots stay undisturbed.

May 2026

The dig, pin by pin

Hand-dug underpinning pit beneath the original brick footing — An underpinning pit part way through its dig, worked by hand beneath the original footing. The house is held up in sections: each pin is excavated, poured and cured before the next is opened. Slow on purpose.

Ground floor reception room mid strip-out, painted panelling retained on one wall, ceiling joists exposed, cast iron fire surround set aside — While the ground opens up below, the strip out moves through the house above. The painted panelling stays on the wall, the cast iron fire surround is lifted and set aside for re-use, and the ceiling comes back to its joists.

June 2026

Holding the house, opening the ground

The rear of the house propped on shores while the basement is dug beneath, new flat roof structure above — The rear of the house stands on props while the basement opens up beneath it, the new flat roof structure already framed above. All the temporary works on this scheme are ours to design as well as to build; the contract says so, and the house depends on it.

Excavation for the basement retaining wall at the rear, starter bars up and reinforcement mesh staged at the edge — The retaining wall forming the rear edge of the basement, starter bars up and mesh staged at the edge. The new extension will be built above this, and in this corner a staircase will rise from basement level into the garden.

Retaining wall reinforcement fixed against plywood shutters at the garden boundary, damp proof membrane behind — The same corner up close: retaining wall reinforcement fixed against the shutters, membrane dressed behind, where the garden stair will eventually land. The walls are cast in situ against the ground, in the sequence the engineer drew.

July 2026

Pins poured, roof stripped back

Reinforcement cage for underpinning pin K4 with damp proof membrane behind and the pin letter sprayed on the board above — Pin K4: cage fixed, membrane behind, ready to shutter and pour, its name sprayed on the board above. Every pin on the scheme has a letter and a number, and none is opened until its neighbour has cured. That is what sequential underpinning means.

Underpinning pin E1 shuttered and braced with adjustable steel shores inside the old cellar — Pin E1 shuttered and shored from inside the old cellar, props braced against the pour to come. Formwork carries real load here; it is engineered, not improvised.

Old cellar wall with underpinning pins A2 and A5 marked in spray paint, shutters and props in the dig below — Pins A2 and A5 marked on the old cellar wall, shutters and props in below. The brickwork reads like a map of the sequence: every pin lettered, dug, poured and struck before its neighbour is opened.

Main roof slopes stripped back to their original battens and underlay beside the chimney stack — Up top in the same month: the roof stripped back to its original battens and underlay. All of it is renewed from here, new membrane, new battens, clay tiles to match the originals, and the leadwork replaced.

The build continues. New months are added as the work moves on; the next update follows the basement slab pours, the waterproofing going in, and the rear extension rising in reclaimed London stock.

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