Bay window subsidence repairs in Greater London

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

How do local ground conditions affect bay window subsidence repairs in Greater London?

Ground movement here is more often linked to soils, drains and trees than to mining. What you mostly find across 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 bay window subsidence repairs

Photos and first view
Send photos of the outside junction, the inside corners and the window, with a scale. We give a free initial assessment and tell you whether the crack looks old and stable or whether an engineer should inspect first.
Engineer and checks
Where the cause is unclear, an independent chartered structural engineer inspects, sometimes with a trial pit at the bay and a drain survey. We can arrange the engineer. Monitoring may be suggested if the movement could be seasonal.
Make good inside
Plaster around the bay and along the junction is renewed, the window board is refixed and the room is ready for decoration. Building control paperwork, where it applies, is passed to you for your records.

Is it time for bay window subsidence repairs? Common signs

Bay roof or lead flashing pulling away from the main wall
A vertical crack where the bay meets the front wall
Gaps opening around the internal bay window board
Bay window sash or casement sticking or binding

What should you budget for bay window subsidence repairs in Greater London?

These are guide prices for Greater London, using London rates and including VAT. Your written quote follows photos or a survey, and is fixed once the repair is specified.

Guide prices inc VAT on London rates. Items marked est. are our estimates.
Item	Guide price	Per
Bay junction crack repair and tie-inest.	£750 – £2,250	per bay
Traditional underpinning of a bay	£3,750 – £8,750	per bay
Mini-piled bay underpinning	£6,250 – £15,000	per bay

Repair options we may recommend

Junction crack repair and tie-in

Where movement has stopped, the open joint between bay and house is raked out, stainless ties or helical bars are fixed across it, and the joint is repointed to match. Internal plaster along the crack is cut back and renewed before redecoration.

Best for: Old, stable cracks where the bay is no longer moving

Traditional underpinning of the bay

The bay footing is excavated in short sections and new mass concrete is placed down to firmer ground below the zone affected by roots and seasons. Because a bay is a short length of wall, the work is compact, but it needs building control approval.

Best for: Active bay movement on firm ground at moderate depth

Mini-piled bay underpinning

Small piles are installed to depth around or beneath the bay and linked by a reinforced beam or needles that pick up its weight. It suits deeper soft ground and heavy root activity, and the compact rigs fit into a front garden.

Best for: Deep clay, nearby trees, or poor ground below the bay

Bay window subsidence: bay footing strengthened and junction cracks tied in (plan). Indicative drawing, not to scale.

Do you need approval for bay window subsidence 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.

Find bay window subsidence repairs in your Greater London town

Your bay window subsidence repairs questions

Why do houses in Greater London crack?

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 bay window subsidence repairs cost in Greater London?

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

Does a bay window always need underpinning?

No, many bays are fixed by tying the junction and repointing, once any cause such as a leaking gully is put right. Underpinning is for bays still dropping after the cause has been dealt with, or with footings too shallow for the ground they sit on.

Can I just fill the crack myself?

Filling it hides the evidence without dealing with the cause, and if the bay is still moving the crack will reopen. Photograph it with a scale and date first. If you plan to claim on insurance, tell your insurer before any repair, including filling.

Will the bay window need replacing?

Usually not. Most windows can be eased, packed or resealed once the bay is stable. If the frame has twisted badly or the glass has cracked, replacement may be worth considering. Under a claim, upgrades beyond like-for-like are normally priced separately.