House Extensions Clerkenwell
Single storey rear and double storey extensions in Clerkenwell, planning, structure and build under one contract.
- Rated 4.9 from 31 reviews on MyBuilder
- Single-storey rear extension from £40,000
- Free site survey, itemised quote
GS Renovation builds extensions across Clerkenwell, working with the post-war blocks, warehouse conversions and new-build apartments of this EC1 corner of Islington. We have learned that space here is won cleverly rather than easily, whether that means a rear addition to a period workshop or a considered reconfiguration within a leasehold shell.
In Clerkenwell, a single-storey rear extension typically starts from £40,000, or £2,000 to £2,800 per m² (indicative London ranges, Architecture for London, Resi, MyBuilder and Checkatrade, 2026). GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Clerkenwell: the structural engineer we appoint designs the structure, we build it, and building control signs it off.
Price guide
| Work | Indicative London range |
|---|---|
| Single-storey rear extension | from £40,000 |
| Rear extension, per m² | £2,000 to £2,800 |
| Side return, per m² | £2,400 to £3,200 |
| Wraparound, per m² | £2,400 to £3,200 |
| Double storey, per m² | £1,800 to £2,600 |
| Basement extension | see the basement page |
Indicative London ranges (Architecture for London, Resi, MyBuilder and Checkatrade, 2026), not a quotation. Prices checked September 2026. Full breakdown: Extension Costs & Planning.
Quick estimate for Clerkenwell
Clerkenwell range: choose above
Extension options for Clerkenwell EC1 properties
Clerkenwell is an area of flats rather than generous rear gardens, so extensions here take different forms to the classic side-return you see further into Islington. Where a converted workshop retains a yard or lightwell, a single-storey rear addition can open up a cramped ground floor. We handle the groundworks, foundations, steel beams and roof works, then the full fit-out, all sequenced so you keep as much of the building usable as possible.
Flats have no householder permitted development rights at all, so any extension to a flat needs a full planning application to Islington Council. A house may have them, but much of Clerkenwell is conservation area, where side extensions, two-storey extensions and roof extensions need permission, and Islington has used Article 4 directions in 40 of its 42 conservation areas to bring minor external changes under control too. We assess your title and the council's position before committing to a route.
Housing in Clerkenwell
Clerkenwell counts roughly 7,790 homes for Council Tax; 26% are older than 1919, 6% interwar and 65% post-war, with 96% flats and 4% houses. Since most homes here are flats, a flat in Clerkenwell has no householder permitted development rights, so extending one needs planning permission and the freeholder's consent.
Extending in Clerkenwell starts with whether you own a house
96% of homes in Clerkenwell are flats and 4% are houses, and the planning route for an extension splits along that line. Islington Council says you need to apply for full planning permission to add an extension or conservatory to a flat. A Clerkenwell flat with a yard, a lower ground floor or a flat roof to its rear therefore starts with a full application. It also needs the freeholder's consent, since the outside walls and the ground around them are often held by the freeholder rather than by one flat.
A house keeps permitted development rights, but a conservation area takes some of them away. In the Clerkenwell Green conservation area (CA1), as in any conservation area, side extensions, rear extensions of more than one storey, roof extensions and external cladding need planning permission. A single-storey rear extension within the size limits can remain permitted development unless an Article 4 direction removes it. Islington has used article 4 directions in 40 of its 42 conservation areas to prevent some minor alterations, so the doors and windows of the new work are checked as well.
Party walls and leasehold rules in Clerkenwell
Building against or near a shared structure in Clerkenwell almost always brings the Party Wall Act into play. The dense EC1 street pattern means your extension or new opening frequently touches a wall held in common with the unit next door, so you serve the right notices as building owner, with drawings we supply, before excavation begins. Getting this settled early keeps neighbours onside and stops the programme stalling.
For flats within a warehouse conversion or a new-build block, structural change is limited by the lease. You will need the freeholder's licence to alter, and the managing agent will set conditions on working hours, access and protecting common parts. We coordinate that paperwork alongside the building control applications, and we detail the acoustic and fire separation that regulations demand between one Islington home and the next.
Kitchen extensions in Clerkenwell
96% of homes in Clerkenwell are flats, and a flat has no householder permitted development, so a ground-floor flat's kitchen extension needs planning permission from Islington Council and the freeholder's consent. With so few houses here, the realistic kitchen gain in most Clerkenwell homes is a better layout inside the flat rather than an extension. The fit-out is priced on its own page, kitchen renovation in Clerkenwell; the build figures are in the table above. Double storey extensions belong to the few houses here.
- First fix and second fix plumbing and electrics throughout
- Flat and pitched roofs with rooflights or lanterns
- Roof works and structural alterations at roof level
VOA Council Tax stock of properties, March 2025, for Clerkenwell. Counts rounded by the VOA.
The GS Renovation Difference in Clerkenwell
Extensions in Clerkenwell reward a builder who understands leasehold reality and tight EC1 plots, not just bricks and mortar. GS Renovation manages the planning or permitted development question, the freeholder's licence and the full build under one roof, backed by our founder's 30+ years on the tools.
- Insulation and thermal detailing to current regulations
- Permitted development checked before you pay for a planning application
- One point of contact on the phone, not a call centre
Built a new extension at rear of property. Laid foundations, drainage, raised floor, new roof and completed all fixtures and interior decoration…
George always kept to commitments and arrived on time. He offered helpful suggestions during his initial visit and promptly provided a reasonably…
Saaid is the best craftsman I have worked with. He knows what he is doing from the very beginning. He has a great knowledge of construction…
FAQ
Frequently Asked Questions about House Extensions Clerkenwell
What is the going rate for house extensions around Clerkenwell?
Three Islington builders will give three different numbers for house extensions in Clerkenwell, usually because they have scoped three different jobs within £2,000 to £2,800 per m² for a rear extension (indicative). GS Renovation prices the EC1 property after a survey and sets out labour, materials, approvals and making good in the order they happen: the steel into the house is designed before the rear wall comes down.
Will my Clerkenwell extension need planning permission or is it permitted development?
Flats have no householder permitted development rights at all, so any extension to a flat needs a full planning application to Islington Council. A house may have them, but much of Clerkenwell is conservation area, where side extensions, two-storey extensions and roof extensions need permission, and Islington has used Article 4 directions in 40 of its 42 conservation areas to bring minor external changes under control too. Leasehold terms can restrict change further. We check your title and the council's position first, then handle whichever route applies alongside building regulations and party wall matters.
Can a yard behind a Clerkenwell workshop building be built over?
Sometimes, but what is under the yard matters first. Old workshop yards often carry the drains for the whole building, and where a public sewer runs beneath, building over or near it needs the water company's consent. A camera survey shows the route and depth. The findings can move the footprint, require a diversion or shape the foundation design, so this comes before any drawings.
How will light reach the room behind a Clerkenwell rear addition?
Mostly through the roof. Once an extension covers the old back window, the room behind depends on rooflights or a glazed lantern placed close to the original wall. Glazing has to work alongside Part L insulation standards, so the balance between glass area and the rest of the envelope is worked out at design stage. A glazed link between old and new often gives the best result.
Which notices apply when digging foundations beside neighbouring Clerkenwell buildings?
The Party Wall Act excavation rule. Within 3 metres of a neighbour's building and deeper than its foundations, one month's written notice is required. On tightly packed EC1 plots that captures most extensions. The adjoining owner may consent, or dissent, which leads to a surveyor's award. Serving early lets the period run in parallel with building control approval.
Does a small Clerkenwell rear addition still need building regulations approval?
Yes, every extension does, however modest and whatever its planning route. The inspector sees the foundation trenches before concrete, the drainage before backfilling, steel bearings before boxing and insulation before it is covered. A completion certificate follows the final inspection. Keep it with the freeholder's consent and the planning decision, as a buyer's solicitor will ask for all three.
Which Islington building control charge band covers a small Clerkenwell rear extension?
Islington's Table 1 domestic charges set a band for an extension up to 40 sq m, so the floor area on the drawings decides the fee. A house with no common areas can use a building notice, and that charge is the same total as under full plans, where it is split into a plan charge and an inspection charge. We measure the floor area from the drawings before applying, so the right band is paid at the start.
Can trees be pruned for an extension in a Clerkenwell conservation area without telling Islington?
No. In an Islington conservation area you must give the Council six weeks notice in writing before any work is carried out to prune or fell a tree. A tree whose roots or crown sit close to the line of a rear extension may need work before foundations can be dug, so the notice goes in early. We identify trees near the footprint at the first visit and add those six weeks to the programme before a start date is fixed.
Should a Clerkenwell house owner ask Islington for pre-application advice before extending?
For an extension that needs planning permission, it is often worth it. Islington offers householder pre-application written advice with a site visit, and follow-up advice after that. An officer standing in the garden sees the neighbouring windows, the boundary walls and the conservation area setting the application will be judged against. Planning pre-application fees in Islington increased on 2 January 2025, so we check the current charge when the visit is booked.
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