House Extensions St Albans 2026: Costs, Planning and a Real LCCL Project

By Anderson & the LCCL Construction Team | Finchley N3

St Albans is where a lot of our Hertfordshire work starts: Victorian and Edwardian terraces around the city centre and Fleetville, 1930s semis in Marshalswick and Jersey Farm, and detached houses on the edge of Chiswell Green and Bricket Wood. Most of them have the same brief — a bigger kitchen-diner opening onto the garden, sometimes with a loft on the same programme. This guide gives our 2026 design and build costs for St Albans, how St Albans City and District Council treats extensions, and what one of our own St Albans projects involved.

House extension costs in St Albans in 2026

These are LCCL's 2026 design and build ranges — survey, architectural design, structural calculations, planning or Lawful Development Certificate, building regulations, party wall notices and the build itself, through to the completion certificate. Every home is surveyed and costed individually and you receive a detailed itemised estimate.

Rear extension: £42,000 – £90,000 inc. VAT (£35,000 – £75,000 + VAT) (10–14 weeks on site)

Side return extension: £42,000 – £93,600 inc. VAT (£35,000 – £78,000 + VAT) (10–14 weeks)

Wraparound extension: £72,000 – £153,600 inc. VAT (£60,000 – £128,000 + VAT) (14–18 weeks)

Kitchen extension: £42,000 – £153,600 inc. VAT (£35,000 – £128,000 + VAT) for the build, plus £9,000 – £87,360 inc. VAT (£7,500 – £72,800 + VAT) for the kitchen itself, supplied and fitted, depending on size and specification (economy, mid-range or high-end)

Two storey extension: £90,000 – £198,000 inc. VAT (£75,000 – £165,000 + VAT) (16–24 weeks)

Hertfordshire is about 5% less than the London figures above. Kitchen units, worktops and appliances, flooring, bespoke joinery, landscaping, council planning fees and party wall surveyor fees (if a neighbour dissents) sit on top. The instant estimate gives you a range for your postcode in thirty seconds.

Planning permission in St Albans

St Albans City and District Council is one of the busier planning authorities in Hertfordshire, and a large part of the city sits inside conservation areas — the city centre, Fishpool Street, St Michael's, Fleetville and several others. Inside a conservation area the permitted development limits still apply to a single-storey rear extension, but the larger-home-extension route (6 m on a terrace or semi, 8 m on a detached house) is not available and side extensions need a full application.

Outside conservation areas most single-storey rear and side return extensions are permitted development: 3 m deep on a terrace or semi, 4 m on a detached house, up to 4 m high with a flat roof no higher than 3 m at the eaves. We obtain a Lawful Development Certificate on every permitted-development project — it costs half the householder fee, takes up to eight weeks, and it is the document your buyer's solicitor will ask for when you sell. Wraparounds and two storey extensions go through a full householder application with an eight-week decision. See our house extension planning permission guide for the limits in full.

A real LCCL project in St Albans

Our St Albans design commission was a house on a sloping site where the garden sits well below the ground floor. A standard rear extension would have breached the permitted development height limits, so we designed a sunken rear extension stepping down to garden level, with a loft conversion using a dormer on each side of the roof. St Albans City and District Council granted full planning permission for both the extension and the loft. You can see the existing and proposed drawings in our St Albans loft conversion and rear extension project write-up.

Just over the Hertfordshire border, our Bohun Grove, East Barnet EN4 project— a full-width rear extension, hip-to-gable loft conversion and whole-house renovation of a 1930s semi — won the LABC Building Excellence Award 2024 for Best Residential Extension in London. It is the closest completed example of the extension-plus-loft programme most St Albans families ask us for.

Anderson's Advice: budget for the steel, not just the kitchen

Twenty years of opening up ground floors have taught us one thing about kitchen extensions: clients budget for the units and worktops but forget the structural steelwork that lets the old back wall come out. On a Victorian or Edwardian terrace in St Albans the load-bearing opening through the old back wall — steel, padstones and making good — runs £4,800 – £19,200 inc. VAT (£4,000 – £16,000 + VAT) depending on its width and whether the loft is being converted at the same time — if it is, we design both sets of steel together and crane them in on one day. Ask for the steel as a separate line on any estimate you are comparing; if it is not there, it will appear later as a variation.

Why St Albans homeowners choose LCCL Construction

As LABC Building Excellence Award winners in 2024 (Best Residential Extension in London — Bohun Grove, East Barnet EN4: rear extension, hip-to-gable loft conversion and whole-house renovation) and 2026 (London Regional Winner, Best Conversion or Alteration to an Existing Home — Weech Road, Hampstead NW6: penthouse loft conversion and full renovation), we design and build under one contract: our architects, structural engineer and project manager work with the construction team from the first sketch to the completion certificate, and one person is your point of contact throughout. We are an LABC Registered Partner and a member of the National Federation of Builders, and we have worked across St Albans, Harpenden, Hatfield, Welwyn Garden City, Borehamwood and Potters Bar for over twenty years from our office in Finchley N3.

What our clients say

"We used LCCL for our rear extension and were so impressed that we came back for a loft conversion. The quality of work and communication throughout was excellent."

— Mia M, Google Reviews

Frequently asked questions

Do I need planning permission for a rear extension in St Albans?

Usually not outside a conservation area — a single-storey rear extension up to 3 m (4 m on a detached house) is permitted development and we obtain a Lawful Development Certificate. Inside a conservation area the smaller limits still apply but the 6 m / 8 m prior-approval route does not, and side extensions need a full application. We check your address before the first drawing.

How long does a house extension take in St Albans?

Typically 8–16 weeks of design and approvals, then 10–14 weeks on site for a rear or side return extension and 16–24 weeks for a two storey extension. Adding a loft to the same programme usually adds 4–8 weeks rather than the full loft duration, because the scaffold and steel are shared.

What guarantee do I get?

A 12-month workmanship guarantee from LCCL on every project, and a 10-year LABC structural warranty is available — issued by LABC Warranty in your name, so it does not depend on the builder. Building control sign-off is through LABC.

Get an estimate for your St Albans extension

Use the instant estimate for a range in thirty seconds, or call 020 8037 7332 to book a free consultation call with our team. We cover St Albans and the whole of Hertfordshire from Finchley N3.

One team, one contract, one point of contact — from first sketch to handover.