Best Extension Architects in York

Adding an extension is one of the biggest changes you can make to a home – and in York, where Georgian townhouses, Victorian terraces and converted city-centre properties sit side by side, the design matters as much as the build. The right extension brings in light, reworks how you live and feels like it was always part of the house. Getting there usually starts with one decision: who designs it. This guide looks at five firms worth considering for a house extension in York, what each does best, and how to work out which suits your project.

How we put this together. This is an editorial selection based on each firm’s published work, services and credentials – a starting point for your own research, not a hands-on test. Always ask to see relevant local projects and get a clear written proposal before appointing anyone.

Extension architects in York at a glance

1. WaxWing Design & Build Ltd

WaxWing is the one firm on this list that both designs and builds. Rather than producing drawings and handing them to a separate contractor, it is one of the few extension architects in York to take a project from first concept through to the finished room with a single team – which can simplify accountability and keep the design intent intact through construction.

Its house-extension work spans single-storey rear and kitchen-dining extensions, side returns for terraced homes, double-storey extensions, garden rooms and the structural reconfiguration that often comes with them. Because the practice also runs an in-house joinery service, interior details such as fitted cabinetry, panelling and integrated storage are crafted as part of the same project rather than bought in. The process runs through six stages, from consultation and spatial planning to planning and structural coordination, construction and final interior detailing, with a stated emphasis on respecting York’s period and historic architecture.

WaxWing is a member of the Federation of Master Builders, is TrustMark-registered and an FSB member, and works on cost-plus contracts.

Best for: homeowners who want one team to both design and build the extension.

2. CK Architectural York

CK Architectural York is an award-winning architectural design firm covering York and Harrogate, marking ten years in business in 2025. Its team of designers, technicians and architects specialises in house extensions – single- and double-storey – alongside loft, garage and barn conversions and new builds, with open-plan kitchen extensions a particular focus.

The practice handles the full design journey: site survey, concept design, planning applications, building-regulations drawings, structural engineering and project management, so the paperwork and approvals are managed for you. That end-to-end design support, paired with an emphasis on affordability, makes it a practical first call for a typical home extension.

Best for: an extension-focused design service that carries you through planning and building regulations.

3. Brierley Groom Architects

Brierley Groom is an award-winning RIBA chartered practice based in York, run by brothers Greg and Matt Groom since 2000 and drawing on a long York architectural lineage. It works across residential and commercial projects, with extensions, refurbishments and remodelling sitting alongside new-build developments.

Its track record on extensions specifically is well established – the practice has been a regional LABC award winner for Best Extension to an Existing Home, and has handled domestic projects on heritage and listed buildings as well as larger residential schemes. For homeowners who want the assurance of a chartered, awards-recognised studio that can also handle a more ambitious or sensitive project, it is a strong option.

Best for: a long-established chartered practice comfortable with both everyday extensions and larger or heritage projects.

4. Mass Architecture

Mass Architecture is a RIBA award-winning chartered practice in the City of York with a clear design identity: contemporary architecture handled sensitively within historic settings. The studio specialises in the careful extension, refurbishment and adaptation of period and listed buildings, introducing modern interventions that sit comfortably against the original fabric.

That focus shows in its recognition, including RIBA Yorkshire awards and repeated York Design Awards. Its portfolio features projects such as a rear extension to a Victorian townhouse that reworked the ground floor while contrasting new materials with the existing house. For owners of an older or character property who want a confidently modern extension rather than a like-for-like match, Mass is well worth considering.

Best for: contemporary extensions to period, conservation-area or listed homes.

5. Finn and Finn Architect

Finn and Finn is a father-and-daughter RIBA chartered practice offering a deliberately personal, affordable service. Chris has worked in domestic architecture in York for more than three decades, and the practice focuses on smaller residential extensions, loft conversions, garden annexes and internal alterations rather than large schemes.

A real strength here is local planning knowledge: the practice has an established working relationship with City of York planning officers and detailed familiarity with the city’s residential planning policies, from Green Belt sites to homes within the Walls. For a more modest extension where cost and a close working relationship matter most, it is a natural fit.

Best for: smaller domestic extensions where affordability and a personal service come first.

How to choose someone to design your extension in York

Start with the type of firm you need, because “extension architect” covers several different routes. A RIBA chartered architect (such as Brierley Groom, Mass or Finn and Finn) offers fully qualified design expertise and is ideal for sensitive, complex or design-led projects. An architectural design firm (such as CK Architectural) provides design and technical drawings through planning and building regulations, often at a lower fee. A design-and-build firm (such as WaxWing) both designs and constructs the extension, which can simplify the process by keeping everything with one team. None is automatically “better” – the right choice depends on your project, budget and how much you want to manage yourself.

From there, a few checks help. Look at a portfolio of comparable local projects, ideally on a property similar to yours – period homes in particular bring their own demands. Ask how fees are structured and what each stage includes, and clarify who manages the build and who is responsible if something goes wrong. For chartered architects, you can confirm registration through the Architects Registration Board (ARB) and RIBA. And because almost every extension touches planning and building regulations – with extra restrictions in York’s conservation areas and on listed buildings – it is worth confirming early how those approvals will be handled, and checking the specifics with City of York Council. As ever, more than one proposal makes it easier to compare like with like.

Frequently asked questions

Do I need planning permission for a house extension in York? Many single-storey extensions fall under permitted development and don’t need a full planning application, but this isn’t guaranteed – flats, listed buildings and homes in conservation areas (much of central York) often have tighter rules, and building regulations apply either way. Always check with City of York Council before you start.

What is the 50% rule for a house extension? Under permitted development rights, no more than 50% of the land around the “original house” (as it stood at a set reference date) may be covered by extensions and outbuildings. Exceed that and you’ll generally need planning permission. It’s one of several limits, so treat it as a starting point rather than the whole picture.

What’s the difference between an architect and an architectural designer? “Architect” is a protected title for someone registered with the ARB, usually with RIBA membership; an “architectural designer” or “architectural technician” may have equivalent practical skill in producing designs and drawings but isn’t on the register. Both can design a successful extension – the difference matters most on complex, heritage or design-led schemes.

How much does an architect cost for an extension? Fees vary widely with the size and complexity of the project and how much of the work you ask the firm to handle – some charge a percentage of build cost, others a fixed fee or by stage. The only reliable figure is a written proposal for your specific extension, so it’s worth getting a couple to compare.

Do I need an architect, or is there a cheaper route? You don’t always need a chartered architect. Architectural designers and design-and-build firms can be more cost-effective for straightforward extensions, while a chartered architect tends to add the most value on unusual, sensitive or ambitious projects. Match the route to the job.

The bottom line

There’s no single best extension architect for every project in York. For a sensitive or design-led scheme, a chartered practice such as Brierley Groom or Mass may be ideal; for a smaller budget, Finn and Finn; for full design support through approvals, CK Architectural. WaxWing Design & Build is the one that both designs and builds under a single roof, which suits homeowners who’d rather keep the whole project with one team. Whichever route you take, look at comparable local work and get a clear written proposal first.

The information in this article is intended as a general guide only. House extensions and architectural work can be subject to planning permission, building regulations, party-wall requirements and other statutory obligations that vary by property, location and circumstance – particularly for period, listed or conservation-area homes. Homeowners remain responsible for their own compliance and should carry out their own due diligence and seek advice from qualified architects, structural engineers, building-control or other relevant professionals before commissioning work.