House Extensions Hertford 2026: Costs, Planning and What to Expect

By Anderson & the LCCL Construction Team | Finchley N3

Hertford's housing runs from Georgian and Victorian terraces in the town centre and Bengeo to 1930s semis in Sele Farm and Hertford Heath, and 1960s–90s family houses in Foxholes and Pinehurst. The brief we hear most from Hertford homeowners is a full-width kitchen-diner opening onto the garden, often with a side return filled in on the older terraces. Here are our 2026 costs, how East Herts Council treats extensions, and what to expect from a design and build programme.

House extension costs in Hertford in 2026

LCCL's 2026 design and build ranges, inclusive of survey, architectural design, structural calculations, planning or Lawful Development Certificate, building regulations, party wall notices and the build to completion certificate:

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 London. Kitchen units and appliances, flooring, bespoke joinery, landscaping, council fees and party wall surveyor fees (only if a neighbour dissents) are on top. Every home is surveyed and costed individually — the instant estimate gives a range for your postcode in thirty seconds.

Planning permission in Hertford

East Herts Council is the planning authority. Hertford has three conservation areas — the town centre, Bengeo and Hertford Heath — where side extensions and anything visible from the street need a full householder application, and the larger-home-extension (6 m / 8 m) route is not available. Outside them, single-storey rear extensions of 3 m on a terrace or semi and 4 m on a detached house are permitted development, and we obtain a Lawful Development Certificate so the work is documented as lawful when you sell. Two storey and wraparound extensions go through a full application with an eight-week decision; East Herts is generally receptive to well-designed rear additions on 1930s and post-war houses, and stricter on the Georgian terraces. Building control is through LABC Hertfordshire — we are an LABC Registered Partner and use LABC on every project.

A real LCCL project: the extension-plus-loft programme

The programme most Hertford families ask us for — kitchen extension and loft on one contract — is exactly what we built at Bohun Grove, East Barnet EN4: a full-width rear extension with an open-plan kitchen-diner, a hip-to-gable loft conversion with a master bedroom and en-suite, two Lusso Stone bathrooms, new windows and landscaping on a 1930s semi. It won the LABC Building Excellence Award 2024 for Best Residential Extension in London. In Hertfordshire we have designed and built lofts and extensions in St Albans, Borehamwood, Welwyn Garden City, Bushey and Potters Bar.

Anderson's Advice: the party wall timeline

Most clients underestimate the party wall timeline. On a Hertford terrace or semi, a rear extension nearly always means building on the boundary or excavating within 3 m of the neighbour's foundations, which is notifiable under the Party Wall Act. Notices go out two months before work starts (one month for excavation); most neighbours consent, and a surveyor is only needed if one dissents — but a dissent can add up to three months. We serve the notices as part of the design stage so the build date does not move. Talk to your neighbours before the drawings are finished; we will show them the plans with you.

Why Hertford 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: architects, structural engineer and project manager working with the construction team from the first sketch to the completion certificate, with one point of contact throughout. We are an LABC Registered Partner and a member of the National Federation of Builders, based in Finchley N3 and working across Hertfordshire.

What our clients say

"I highly recommend LCCL Construction. They completed our loft conversion to a very high standard, and the quality of workmanship throughout was excellent. The team was professional, reliable, and completed everything within a very reasonable timeframe. They were also fairly priced, which made the whole experience even better. We’re really pleased with the finished result and would definitely use them again."

— Alina A, Google Reviews

Frequently asked questions

Do I need planning permission for an extension in Hertford?

Not for most single-storey rear extensions outside the conservation areas — they are permitted development and we obtain a Lawful Development Certificate. Side, two storey and wraparound extensions, and anything in the town centre, Bengeo or Hertford Heath conservation areas, need a full householder application to East Herts Council.

How long does a house extension take?

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.

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 Hertford extension

Use the instant estimate for a range in thirty seconds, or call 020 8037 7332 to book a free consultation call. We cover Hertford, Ware, Hertford Heath and the whole of Hertfordshire from Finchley N3.

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