Structural Alterations Barnet

From new openings to replacement joists and underpinning, GS Renovation carries out structural alterations across Barnet's interwar housing, from the semis of Edgware and Mill Hill to the larger homes near Hadley Common. We build supported openings to the engineer's design that meet the Building Regulations.

In Barnet, a simple new opening starts from £1,500, and underpinning a single elevation typically costs £6,000 to £21,000 (indicative London ranges, MyBuilder and Checkatrade, 2026). GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Barnet.

How the job runs

1. Free site survey at your Barnet address and an itemised quote.
2. The engineer we appoint designs the work, and it is registered with Barnet Council building control or an approved inspector. On a shared wall you serve the party wall notice as building owner; we supply the drawings.
3. Props and any trial holes first, then the opening, joists or underpinning in the engineer's sequence.
4. Building control inspects each stage before it is covered, then issues the completion certificate.

Supported openings and joists in Barnet homes

Interwar Barnet houses were built with timber floor joists spanning between the external and spine walls, and after decades of altered layouts and past extensions those joists are not always where you would expect. When we form a new opening or widen an existing one, the engineer checks the floor above, specifies any replacement or doubled-up joists, and sizes the beam that will carry the wall and floor loads across the new span.

Every supported opening follows the same discipline: temporary props take the load, the masonry is removed in stages, and a steel beam is set onto padstones at each end before the props come out. Whether it is a wider doorway between two reception rooms in a Finchley semi or a structural opening for a rear extension in NW7, the bearings are designed to spread the load safely into the walls that remain.

Housing in Barnet

Barnet's housing, as the Council Tax list records it, is about 160,480 homes: 50% houses, 50% flats, with 20% pre-1919, 34% interwar and 46% built since 1945. Since many homes here are flats, structural repair to a block in Barnet usually falls to the freeholder.

Roof structure changes under Barnet's Mill Hill and Totteridge controls

Structural work that shows on the outside of a house meets planning controls in parts of Barnet that internal steel never does. The Mill Hill Conservation Area covers approximately 152 hectares towards the northwest corner of the borough, and Barnet Council introduced an Article 4 Direction for parts of it shortly after designation in December 1968. Separately, the Mill Hill Conservation Area Article 4(2) direction covers alterations to a roof slope which fronts a relevant location. On a house that direction covers, adding a rooflight to a front slope or rebuilding that slope to a different pitch needs a planning decision before the structural engineer we appoint finalises the rafters, purlins and any new steel.

Totteridge adds a further layer. Its Article 4 Direction allows Barnet Council to control minor works, and roofing materials are on that list. That matters structurally when a roof is re-covered: a heavier tile than the original can overload rafters sized for a lighter covering, and a change to a significantly heavier material is itself a Building Regulations matter. Ask the engineer to check the rafters and purlins against the weight of the proposed tile, and settle the material with the council before scaffold and tiles are ordered. One decision then covers both the appearance and the load on the Totteridge roof.

Underpinning and building control in Barnet

Some Barnet homes on the borough's heavier clay soils show movement at the corners, and where an engineer confirms inadequate foundations we underpin in sequenced bays, excavating and filling one short section at a time so the wall is never left unsupported. This is structural work notifiable under the Building Regulations, and Barnet Council's building control inspects each stage rather than any planning department signing it off.

Because internal structural alterations are a building-control matter, not a planning one, there is usually no planning application unless you are altering the exterior, particularly in a conservation area such as Hampstead Garden Suburb. A listed home also needs listed building consent for internal structural work. Where an alteration affects a party wall shared with a neighbour, the Party Wall Act applies and you serve the notices first, as building owner, with the drawings we supply. We coordinate the engineer and the inspections in one programme.

• New door and window openings in solid masonry
• Party wall process explained, and work built to the award
• Steel beam and RSJ installation

VOA Council Tax stock of properties, March 2025, for all 42 statistical areas in Barnet. Counts rounded by the VOA.

Once you know the scope of the structural alterations in Barnet, it helps to read home renovation in Barnet, our Barnet area guide, builders in Barnet, underpinning in London, structural alterations anywhere in London and Chimney Breast Removal.

Why Barnet Homeowners Choose GS Renovation

GS Renovation is a single accountable team for structural alterations in Barnet: the engineer designs the openings, joists or underpinning, we coordinate the work around the party wall award and Barnet Council building control, and our own trades carry out the work. Expect proper propping, correctly sized steel on padstones, tidy working in your home, and our founder's 30+ years on the tools.

Reviewed jobs near Barnet

2 MyBuilder reviews from Barnet, with each customer's own job title:

• Install new kitchen, Barnet, 15 Apr 2022 (5 out of 5)
• Bathroom Refurbishment, Barnet, 14 Oct 2021 (5 out of 5)

Read all 31 on our reviews page.

Checked by Abdelaaziz Saaid, founder and director of GS Renovation Ltd (Companies House no. 14611254). Structural design is by the consulting engineer appointed to your project.