The Victorian terrace

Solid walls, lime mortar, shallow footings

External walls are usually one brick thick at the upper levels and one-and-a-half at the base, laid in lime mortar with no cavity and no damp-proof course, or a slate one that has been bridged. Footings are shallow — often two or three courses of corbelled brick straight onto London Clay. That is the single most important fact governing basements, underpinning and rear extensions, because any new load or any excavation near those footings has to be considered against a foundation that was never designed for it.

Internally the ground floor is generally suspended timber on sleeper walls, the upper floors span front to back onto the party walls, and the spine wall carrying the stair is frequently loadbearing even where it looks like a partition. Chimney breasts do structural work: they stiffen the party wall and, in many houses, carry a corner of the floor above.

The side return, the loft, and opening up the ground floor

Three moves account for most Victorian terrace projects. A rear or side-return extension filling the L-shape beside the closet wing; a loft conversion into the rear roof slope with a dormer, or a hip-to-gable where the house is at the end of a run; and opening up the ground floor by removing the spine wall and the chimney breast on a new steel frame.

All three are usually achievable. What determines cost is not the floor area but the structural consequence: how the new steels land, whether the party wall needs padstones, whether the neighbour's flank is being excavated against, and how the existing drainage runs under the new floor.

Party walls, movement and moisture

Terraced houses are physically joined to their neighbours, so most of the risk is shared. Notifiable work under the Party Wall etc. Act 1996 includes cutting into the party wall for beams, underpinning, and excavation within three or six metres of an adjoining structure depending on depth. Awards fix the working hours, the schedule of condition and the monitoring regime, and they take time to obtain — six to ten weeks is common where a surveyor has to be appointed on the neighbour's behalf.

Movement is the second risk. Shallow footings on clay respond to nearby trees, leaking drains and seasonal shrinkage. Existing cracking should be recorded and understood before it is decorated over, because a crack that reopens after completion is a dispute nobody wins.

Moisture is the third. Solid lime-built walls are designed to absorb and release water. Sealing them with cement render, impermeable paint or the wrong insulation traps moisture in the fabric and pushes it somewhere else. Where internal insulation is added to a solid wall it needs to be designed as a system, with an understanding of the interstitial condensation risk, not chosen from a merchant's shelf.

What a whole-house project on one of these involves

A full refurbishment of a Victorian terrace typically means: a new steel frame at ground floor, underpinning or a lowered slab where headroom is short, a rear extension with a flat or glazed roof, a loft conversion with a compliant escape route and fire-rated construction, a full rewire and replumb, MVHR or extract to the wet rooms, underfloor heating to the new floors, restored or replaced sash windows, repaired lath-and-plaster or new plasterboard with traditional cornice reinstated, and a landscaped rear garden.

Eternal builds these as a single contract with the trades managed directly, because on a terrace the sequence between the structure, the roof and the services is where the programme is won or lost.

Shepherd's Bush · Brook Green · West Hampstead · Queen's Park · Battersea · Wandsworth

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