Structural Alterations and Knock-Through Costs in Cambridge and Cambridgeshire

Removing a load-bearing wall in Cambridgeshire generally costs around £1,250 to £3,000 for the structural work itself, meaning the engineer’s beam supplied and installed and the wall taken down, before making good and before VAT. A finished kitchen-diner knock-through, with the floor levelled, plaster, radiators and sockets moved and the room decorated, is usually a good deal more, and that gap is what most online estimates miss.

This guide covers 2026 benchmarks for load-bearing wall removal, steel beams, engineer’s calculations and Building Regulations, chimney breast removal, new openings for bifold doors and garage knock-throughs, what moves the price and how long the work takes.

The figures are published guide ranges and budgeting illustrations, not offers. A written, itemised quotation against the engineer’s drawings supersedes any general figure.

Structural alteration costs at a glance

Sources: Checkatrade load-bearing wall removal (March 2026), structural engineer (June 2026), chimney removal (April 2026), bifold door (July 2026) and garage conversion (May 2026) cost guides; MyJobQuote load-bearing wall (30 July 2026) and chimney breast (27 August 2026) guides. Checkatrade’s wall removal, chimney, bifold and garage tables are headed “cost + VAT”, so those figures exclude VAT; the other sources do not state a VAT position and are treated as excluding VAT.

A simple way to form an early knock-through budget

Build the budget in lines: the engineer’s fee, the structural work (beam, padstones, temporary props, demolition, waste), then the making good (floor, plaster, services, decoration), then Building Control, then 20 per cent VAT. The making good is usually the largest line and the one most estimates leave out.

Worked example: opening up a kitchen and dining room

A 4m opening through a load-bearing wall is published at £2,400 to £3,000 for the structural work. Add an engineer at £200 to £400 for the calculations and around £300 for a site visit, and Building Control at £250 to £450. That is £3,150 to £4,150 before anything is made good.

Now the rest. Levelling two floors that were never the same height is published at £10 to £25 per m². Moving a radiator is £150 to £400 and a socket around £150. Plasterboarding and skimming the new reveals is a modest line on its own. A decorator is around £250 a day. A realistic finished room is therefore more likely £5,000 to £7,500 before VAT, or £6,000 to £9,000 with VAT. A new kitchen at the same time is its own budget.

Worked example: removing a chimney breast in a semi

Removing the breast on the ground floor only, with the first-floor breast and the stack supported on a steel or gallows brackets, is published at £1,500 to £1,750. Add the engineer at £250 to £600 and Building Control at £200 to £400, and making good at around £1,000. Roughly £3,000 to £3,750 before VAT. If the breast is on the party wall, the Party Wall Act applies and the neighbour must be served notice.

Why the published figures disagree

Checkatrade’s average for removing a load-bearing wall is £1,250 to £1,750, and both Checkatrade and MyJobQuote put a large open-plan opening at £2,400 to £3,000 before the steel and the making good, which is how the same job can cost two or three times the headline average. The lower figure is the beam and the demolition on a straightforward internal wall in a two-storey house. The higher covers a long span, a second beam or a new pier, a wall carrying the roof as well as the floor, and all the making good. Two quotes for “removing a wall” can describe very different work. Compare the itemised scope, not the total.

Steel beams and the engineer

Almost every load-bearing alteration needs a structural engineer to confirm which walls carry load, size the beam, specify the padstones and bearing, and produce the calculations Building Control will ask for. Published fees are £200 to £400 for a single beam calculation and around £300 for a site visit.

Steel is priced by section and length: £140 to £325 per metre supplied, or £300 to £1,200 per beam for a domestic opening. Getting it in matters as much as buying it. A 4m beam needs several people or a lift, an upstairs beam may have to come through a window, and every beam has to be fire-protected, boxed and plastered afterwards.

The engineer is appointed by you, as with planning and Building Regulations. We work to the engineer’s drawings and coordinate with them on site.

Building Regulations, planning and the Party Wall Act

Removing a load-bearing wall or chimney breast and forming a new external opening are all controlled work under the Building Regulations (the Planning Portal confirms this for load-bearing walls and chimney breasts). You apply, Building Control inspect the beam before it is covered, and you receive a completion certificate your solicitor will ask for when you sell. Our Building Regulations guide explains the routes.

Internal alterations do not normally need planning permission, and nor does a new rear opening, unless the house is listed or in a conservation area with an Article 4 direction, which covers parts of Cambridge. See the planning permission guide.

If a beam bears on a party wall, or a chimney breast on a party wall is removed, the Party Wall etc. Act 1996 applies and the adjoining owner must be given at least two months’ notice. Surveyor fees are published at around £1,000 and an agreement at £1,250 to £1,525 where the neighbour does not consent.

New openings for bifold and sliding doors

Forming a wide opening in a rear wall for bifold or sliding doors is a structural alteration whatever the doors cost. A new lintel is published at £650 to £1,000; a longer span under a heavy roof may need a steel and an engineer. The doors themselves are £3,000 to £7,500 supplied and fitted for aluminium in three to five panels, with uPVC less and timber more. Add the threshold and drainage detail, making good inside and out, and matching brickwork at the reveals, which on a gault brick house means sourcing gault rather than a near colour. Our brickwork page explains why.

Garage knock-throughs

Converting an integral garage into a room is published at £10,000 to £14,000 for a single garage, or £10,000 to £20,000 for an attached one, around £625 to £1,250 per m². That covers the door infill, an insulated floor, insulated walls and ceiling, a window, electrics and heating. The knock-through into the house is a load-bearing opening at the rates above; bathrooms and kitchens are extra. Building Regulations apply to the whole conversion; planning usually does not unless the garage is detached or the house is in a conservation area.

What affects the price

Span and load. A 2m opening in a wall carrying a floor is a different job from a 5m opening under a floor and a roof, and a three-storey house means bigger steel and more propping.

Bearing. A padstone on a sound pier is simple; a new pier, a post or a second beam is not.

Services. Cables, pipes, gas and a soil stack in the wall have to be diverted before it comes down.

Floors. Two rooms rarely share a floor level, so the junction has to be levelled or a threshold accepted.

Making good. Plaster, skirting, coving, flooring and decoration on both sides of the opening.

Access and occupation. Getting a steel into a terraced house, protecting a lived-in home from dust, and working around a family.

Timescales

The structural element of a wall removal usually takes two to three days: prop, cut out, install the beam, remove props. Chimney breast removal is published at five to eight days including making good. A finished kitchen-diner knock-through, with floor, plaster, services and decoration, is more often two to three weeks on site, after the engineer’s calculations and Building Control. We provide a programme with the quotation rather than a general figure.

Costs to allow for outside the builder's price

• Structural engineer’s calculations and visits
• Building Control application and inspections
• Party Wall surveyor where the Act applies
• Planning or listed-building consent where needed
• Kitchen, flooring and other selections beyond making good
• Skip hire, if not included
• VAT at 20 per cent
• Contingency of 10 to 15 per cent, because what is inside a wall is not fully known until it is opened

How to get a useful alterations quotation

Send the engineer’s drawings and calculations if you have them, or say whether an engineer has been appointed, plus photographs of both sides of the wall and the property address. Ask every builder to price the same drawings and to itemise the structural work, the making good and the exclusions separately, and to say what happens if the wall contains something unexpected. The what a builder’s quotation should include guide has the full checklist.

Structural alterations are often part of a bigger job. The Herons Close and Almoners Avenue projects in Cambridge both combined openings into the existing house with extension and renovation work. Our structural alterations page outlines how we scope and run this work.

Structural alteration cost questions

How much does it cost to remove a load-bearing wall?

Published UK guides put the structural work at around £1,000 to £1,500 for a doorway and £2,400 to £3,000 for a 4m open-plan opening, plus the engineer, Building Control and making good, before VAT. A finished room is usually £5,000 to £7,500 or more.

Do I need a structural engineer?

For any load-bearing wall, chimney breast or new external opening, yes. Building Control will ask for the calculations and we work to the engineer’s drawings.

Do I need planning permission for a knock-through?

Usually not for internal work. Listed buildings and some conservation-area properties are the exception. Building Regulations approval is always needed.

How much does it cost to remove a chimney breast?

Published figures are £1,500 to £2,000 for one floor, £2,200 to £2,500 for both floors with the stack left, and £3,000 to £3,500 with the stack, plus engineer, Building Control and making good, before VAT.

Is there VAT on structural alterations?

Yes, at 20 per cent, because it is work to an existing dwelling. Quotations are priced excluding VAT with VAT added on top.

How this guide was prepared

Wall removal, steel, engineer, Building Control and Party Wall benchmarks are from the Checkatrade load-bearing wall removal cost guide (March 2026), the Checkatrade structural engineer cost guide (June 2026) and the MyJobQuote load-bearing wall guide (30 July 2026). Chimney breast figures are from the MyJobQuote chimney breast removal guide (27 August 2026) and the Checkatrade chimney removal guide (April 2026). Bifold and garage conversion figures are from the Checkatrade bifold door (July 2026) and garage conversion (May 2026) guides. Plastering rates are Prestige’s own estimating rates. Building Regulations and Party Wall positions are general guidance drawn from GOV.UK and the Party Wall etc. Act 1996 explanatory booklet. Worked figures are transparent additions of published benchmarks and are conversation starting points rather than quotations.

Get a clear next step for your alteration

Tell us what you want the space to do, send photographs of both sides of the wall and any drawings or engineer’s information you have. We aim to respond to every enquiry within one working day with the most useful next step, whether that is an early figure or a site visit.

Related guides and services

• Structural alterations
• Refurbishment
• Extensions
• Building Regulations for house extensions
• Planning permission guide
• House extension costs
• House refurbishment costs
• What should a builder’s quotation include?
• Building guides
• Building project finance

Last reviewed: 20 September 2026. This guide applies to England. Costs, planning rules, fees and building regulations change; check current official guidance and obtain appropriate professional advice for your property and project.