Structural Alterations Lewisham

GS Renovation carries out structural alterations throughout Lewisham, from new openings in Brockley's SE4 terraces to replacement joists and underpinning in Catford and Forest Hill. We build supported openings to the engineer's design, propped safely and signed off by building control.

In Lewisham, 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 Lewisham.

How the job runs

1. Free site survey at your Lewisham address and an itemised quote.
2. The engineer we appoint designs the work, and it is registered with Lewisham 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.

Structural alterations for Lewisham period homes

The bay-fronted terraces around SE6, SE23 and SE26 present a familiar set of structural jobs: forming a wide opening into a rear closet wing, cutting a new doorway through a solid brick wall, replacing tired or overloaded floor joists, and occasionally underpinning where old foundations have moved on the clay ground around Forest Hill and Sydenham.

Every one of these begins with a structural engineer's design. New and enlarged openings are formed with a steel beam or lintel bearing onto padstones, joists are specified to the correct span and grade, and underpinning is carried out in controlled sequenced bays. We prop, then work, then load, so the SE8 or SE13 home is never left unsupported at any stage.

Housing in Lewisham

Roughly 133,910 dwellings sit on the valuation list for Lewisham. 40% are houses and 60% flats, and by age 34% predate 1919, 18% are interwar and 45% post-war. Since most homes here are flats, structural repair to a block in Lewisham usually falls to the freeholder under the lease, so it is agreed with them before anything is opened up.

Cellars, basements and Policy QD9 in Lewisham

Lewisham Local Plan Policy QD9 requires proposals for basement development to include a Basement Impact Assessment. Under the same policy, basement development must not adversely impact on the structural stability of the host building, neighbouring properties, infrastructure and the public realm, taking into account local geology. For a Lewisham owner thinking of enlarging an old coal cellar or digging beneath a period house, that sets the order of work. The assessment goes in with the planning application, its findings shape the underpinning and retaining walls the structural engineer we appoint designs, and only then can a builder price the dig with any accuracy.

The Lewisham Local Plan also says the assessment must be carried out by a suitably qualified and recognised independent assessor and paid for by the applicant. It is not something a builder writes up. On a Lewisham basement scheme we bring the assessor in early, share the trial pits and the survey of the neighbouring structures, and hold our own programme until their report is in. In a terrace the walls either side of the dig are party walls, so the building owner's party wall notices run alongside the assessment, not after it, and the surveyors see the same ground information the assessor does.

Getting it signed off in Lewisham

Structural alterations inside your home fall under the Building Regulations, so Lewisham Council's building control inspects the propping, the beam bearings and the finished work rather than any planning department. Internal structural work does not need planning permission, even in a conservation area such as Brockley, Blackheath or Telegraph Hill. External changes may need it, depending on permitted development, conservation area and Article 4 rules, and a listed building needs listed building consent for internal work as well as external. Brockley also has an Article 4 direction on its houses, and we flag clearly whether any of this affects your property.

Where an opening or underpinning affects a wall shared with the neighbouring terrace, the Party Wall Act applies and you serve notice on the adjoining owner first, as building owner or through your surveyor, using the drawings we give you. We coordinate the engineer and the building control inspections as one package, keeping the paperwork straight so your alteration is signed off by building control and ready to build on.

Strengthening a floor for a heavy load

Not every structural alteration involves a wall. A stone worktop on a large island, a cast iron or freestanding bath full of water, or a wall of bookshelves all put far more weight on one small area of floor than a Victorian joist was ever sized to take. In a Lewisham terrace with original timbers spanning the full width of the room, the result is a floor that feels lively underfoot or slowly dips.

The fixes are straightforward when they are designed. Doubling up joists under a specific load, adding a new bearer, sistering a new timber alongside a sagging one, or installing a steel below where the span is too great for timber at all. Any of these needs the engineer to confirm the span and the section rather than a guess. We open the floor, record what is there, and price the work with the sizes already established.

• New door and window openings in solid masonry
• Lintel replacement and repair over failed openings
• Reinstatement, plastering and finishing after structural works

VOA Council Tax stock of properties, March 2025, for all 37 statistical areas in Lewisham. Counts rounded by the VOA.

Alongside structural alterations in Lewisham, the pages that usually help next are home renovation in Lewisham, our Lewisham area guide, design and build contracting, underpinning in London, structural alterations anywhere in London and Cracks in Walls: When to Worry.

Why Choose GS Renovation in Lewisham

For structural alterations in Lewisham, GS Renovation gives you a single team that manages the engineer, Lewisham building control and the build itself. New openings, replacement joists and underpinning are designed, propped and inspected properly. We work cleanly in occupied homes and stand behind the result with our founder's 30+ years of structural experience.

Reviewed jobs near Lewisham

1 MyBuilder review from Crofton Park, with each customer's own job title:

• Replace small section of wooden worktop, sink, tap and gas hob, Crofton Park, 17 Apr 2024 (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.