Extension pulling away repairs in Greater London

Area: Greater London
Pricing region: London
Ground: Shrinkable clay widespread
Towns listed: 32

How do local ground conditions affect extension pulling away repairs in Greater London?

Ground movement here is more often linked to soils, drains and trees than to mining. Typical buildings in Greater London: Victorian and Edwardian terraces with shallow footings, inter-war semis in the outer boroughs, and converted flats and mansion blocks.

What to expect when we carry out extension pulling away repairs

Show us the junction
Send photos of the crack outside, the internal corner and any flashing above, with a measure for scale. We give a free initial assessment and an initial view on whether the gap is likely old or still opening.
Repair the junction
Drains are repaired first if they are leaking. The joint is then tied, formed as a movement joint or rebuilt after underpinning, with roof flashings reset so the junction stays watertight. Building control is handled where needed.
Finish and hand over
Internal corners are replastered, skirtings and coving refixed, and doors or windows in the extension eased where the movement affected them. Records of the repair and any approvals are passed to you.

Is it time for extension pulling away repairs? Common signs

Mastic or render at the joint repeatedly splitting open
Patio doors or windows in the extension starting to bind
Extension roof flashing lifting off the original wall
Floor level dropping where the extension and house floors meet

What should you budget for extension pulling away repairs in Greater London?

Prices in Greater London are worked out on London rates. They include VAT and are a starting point: access, the extent of the damage and whether an engineer or building control is involved all move the figure.

Guide prices inc VAT on London rates. Items marked est. are our estimates.
Item	Guide price	Per
Junction crack repair with stainless tiesest.	£750 – £2,500	per junction
Movement joint and making goodest.	£500 – £1,500	per junction
Underpinning the extension where needed	£1,250 – £3,100	per metre of wall

Repair options we may recommend

Movement joint and making good

Where some seasonal movement is expected to continue, the junction is formed into a proper flexible movement joint with a compressible filler and sealant, so the two parts can move without cracking. Flashings and internal finishes are detailed to suit.

Best for: Minor ongoing movement that does not threaten the structure

Underpinning the extension

If the extension is still dropping because its footings are too shallow or on poor ground, they are taken deeper by mass concrete, beam-and-base or mini-piles. The engineer designs the scheme, and the junction is repaired once the new foundation is in.

Best for: Active movement from shallow footings, roots or soft ground

Junction crack repair with stainless ties

The open joint is cut out, stainless ties or helical bars are fixed across it into both the old and new masonry, and the joint is repointed or rendered to match. Inside, the corner is replastered. This suits extensions that moved once and have since stopped.

Best for: Settled extensions with a stable gap at the junction

Extension pulling away: tapered gap at the junction tied in with stainless bars. Indicative drawing, not to scale.

Do you need approval for extension pulling away repairs in England?

In England, underpinning and other work that alters or strengthens a wall or foundation is building work under the Building Regulations (Part A, structure), so building control approves and inspects it. Like-for-like repairs often are not, and we tell you which applies before a price is agreed. Work to a party wall, or excavation close to a neighbour’s foundations, can also need a notice under the Party Wall etc. Act 1996.

Towns in Greater London we cover for extension pulling away repairs

Your extension pulling away repairs questions

Is the ground in Greater London prone to subsidence?

Most of Greater London sits on London Clay, among the most shrinkage-prone ground in the UK, with river gravels along the Thames. Subsidence claims here are among the most frequent in the country, especially after dry summers and near street and garden trees. Ground movement here is more often linked to soils, drains and trees than to mining. Only an investigation on site can say why a particular building has moved.

How much will extension pulling away repairs cost in Greater London?

On London rates, extension pulling away repairs starts from about £750 per junction, including VAT. The written price depends on the extent of the damage, access and whether an engineer or building control is needed.

Is it normal for an extension to crack at the join?

A fine crack at the junction is fairly common, especially in the first few years as a new extension settles. It becomes a concern when the gap is widening, tapering, letting in water or matched by sticking doors and sloping floors. Those signs point to continuing movement.

Can a drain under my extension cause it to move?

Yes, a cracked or displaced drain beneath or beside an extension can soften clay or wash away fine soil. A CCTV drain survey usually finds it. Repairing the drain is often the first and most important step before any repair to the walls.

Who is responsible if a recent extension is moving?

If the extension is recent, the original builder, the designer or building control records may be relevant, and you may have rights against the builder. Gather the plans, completion certificate and contract. Insurance often excludes defects in new construction, so check your policy.