Frequently Asked Questions

Planning permission typically takes 8-12 weeks for standard applications. Complex applications or those in conservation areas may take longer. With our 95% planning success rate including complex sites, we have extensive experience navigating the planning process and keep clients informed throughout.

Related: planning permission · if it's refused, an appeal

Also asked: How long does a planning application take in London? · How long does planning permission take for an extension?

Permitted Development is the set of works the government lets you carry out without a full planning application, under the General Permitted Development Order. For houses it typically covers single-storey rear extensions — up to 4m deep for a detached house, 3m for a semi or terrace, and roughly double that under the 'larger home extension' prior-approval route — plus many loft conversions and outbuildings within set limits. The catch in our part of London is that these rights are often cut back: flats and maisonettes have none at all, conservation areas — which cover large parts of Wandsworth and Richmond — restrict or remove several of them, and an Article 4 direction can take them away entirely. Permitted Development is also no free pass on paperwork: you'll usually still need building regulations approval, sometimes a party wall award, and we'd often advise a Lawful Development Certificate to prove the work was lawful when you sell. We check what your specific address allows before you rely on it.

Related: our Permitted Development guide · a project that maximised it

Also asked: What size extension is allowed without planning permission? · Do Permitted Development rights apply in conservation areas? · What can I build under Permitted Development?

Often you won't — but it depends on the size, the type of property and where it sits. Many single-storey rear extensions fall under Permitted Development (up to 4m for a detached house, 3m for a semi or terrace), so no application is needed. Two exceptions matter in Southwest London: flats and maisonettes have no permitted development rights at all, and houses in conservation areas or under an Article 4 direction lose some or all of theirs — so a project that's permitted on one street needs full permission on the next. And even when you don't need planning permission, you'll usually still need building regulations approval. We check what applies to your address at the outset rather than assume, and apply for a Lawful Development Certificate where it's worth having the proof in writing.

Related: planning permission · making a successful application

Also asked: Do I need planning permission for a rear extension? · Can I build an extension without planning permission? · Do I need planning permission for a single-storey extension?

Yes, subject to planning permission and building regulations. Garden rooms and extensions must comply with height restrictions, boundary setbacks, and overall plot coverage limits. We'll assess your garden's potential and design solutions that provide the best use of available garden space.

Related: a rear extension that opens to the garden

Also asked: Do I need planning permission for a garden room?

Building regulations ensure your project meets safety, energy efficiency, and accessibility standards. Even if you don't need planning permission, you'll usually still need building regulations approval — often for quite small works too. We handle this process and ensure compliance with all requirements.

Also asked: Do I need building regs for an extension? · What's the difference between planning permission and building regulations?

It varies more than almost anything else we're asked, and anyone quoting a firm figure before seeing your house is guessing. Cost is driven by size, level of finish, ground conditions, how easily materials get in and out, and the type of work — a single-storey rear extension sits at one end, a dug-out basement at the other. London adds its own pressures: restricted access and parking, party wall agreements with close neighbours, and high water tables for basements all push costs up. It's worth separating two budgets people tend to merge — the build cost, much the largest, and the professional fees, usually a percentage of it. Every project should carry a contingency for what the building hides until work starts, though we often manage not to spend it. We'll help you put a realistic cost plan together early, before the design commits you to choices you can't afford.

Related: our residential extensions

Also asked: What does a kitchen extension cost in London? · How much per square metre for an extension?

There's no single answer, and it helps to know how fees are structured rather than chase a number. Architects usually charge in one of three ways: a percentage of the final construction cost, a fixed fee for a defined scope, or an hourly or stage-by-stage rate — and many projects mix them, for instance a fixed fee to win planning permission, then a percentage through construction. The fee reflects how much of the work we handle, from design and planning only through to overseeing the build on site. It's a smaller share of the budget than most people expect — the construction cost is much the larger figure — and considered design tends to protect that larger figure from waste. We set out our fee in writing against a clear scope at the start, so you know exactly what's included before you commit.

Related: do I need an architect?

Also asked: What are architects' fees for an extension? · Do architects charge a percentage or a fixed fee?

Single-storey rear extensions are typically the most cost-effective, offering good value for money. Loft conversions also provide excellent value, creating additional living space without extending the building footprint. We'll assess your property and recommend the most cost-effective approach.

Related: residential extensions · loft conversions

Also asked: What's the cheapest way to extend a house? · Is a loft conversion cheaper than an extension?

We're transparent about all costs from the start. Additional costs may include planning fees, building regulations fees, party wall agreements, and unexpected structural issues. We identify potential additional costs early and keep you informed throughout the process. But most buildings hide something you won't find until work starts. Every project should have a contingency — though we often manage not to spend it.

Yes, well-designed extensions typically add significant value to your property. A quality extension often increases property value beyond the construction cost. We design with both lifestyle and investment value in mind, ensuring your extension is a sound financial decision that enhances your home and your quality of life. Refitting adds little to the sale price, but you'll get the value of using it for years to come.

Related: a small extension, big change

Also asked: How much value does an extension add? · Do loft conversions add value?

We work closely with clients to understand their budget from the start. With over 1,200 completed projects and 150+ repeat clients, we've developed expertise in designing within budget parameters and suggesting cost-effective alternatives without compromising quality. We provide detailed cost estimates and help manage costs throughout the project.

The Party Wall etc. Act 1996 is a legal framework for preventing and resolving disputes with neighbours over shared walls, boundary walls and excavations near their building. It applies when you build on or at the boundary with a neighbouring property, carry out work to an existing party wall or structure, or excavate close to a neighbour's building.

Related: our party wall guide

Often, yes — and in Southwest London, more often than not. So much of the housing here is Victorian and Edwardian terraces and semis built off shared walls that the Party Wall etc. Act 1996 catches a high proportion of local extensions, lofts and basements. Common triggers include side extensions built up to or on the boundary, loft conversions involving a shared party wall, basements (because of the excavation), inserting beams into a party wall for open-plan layouts, and removing a chimney breast attached to one. One thing worth clearing up: serving notice doesn't hand your neighbour a veto — if they dissent, surveyors simply agree how the work proceeds. We identify whether the Act applies early in the design, so it's planned for rather than sprung on you.

Related: when you need a party wall agreement · 5 party wall mistakes to avoid

You serve formal notice on the affected neighbour(s) before work begins. They can either consent or dissent. If they dissent — or do not respond — the parties appoint Party Wall Surveyor(s) who prepare an 'Award'. The Award records the existing condition of the neighbouring property and sets out exactly how and when the work should be carried out.

Notices need to be served well in advance of starting on site, and if surveyors are required the process adds time while the Award is prepared. If your neighbours simply consent in writing, it is much quicker. Because it can be surprisingly time-consuming, we aim to get your initial notices out as early as possible so it does not hold up your build.

The building owner — the person carrying out the work — usually pays the costs, including the neighbour's surveyor's fees. We flag any party wall implications early so it is part of your budget from the start, rather than a surprise later.

A dissent does not stop your project. It simply means surveyors are appointed to prepare an Award that sets out how and when the work proceeds — putting a clear, agreed framework in place that protects both you and your neighbour.

Possibly. The Act can still apply to work entirely within your home if it affects a shared structure — for example inserting beams into a party wall, removing a chimney breast attached to one, or excavating close to a neighbour's building. We check this for you during design so nothing is missed.

Yes — Andrew and Melissa have years of experience as Party Wall Surveyors. We identify party wall implications early in the design process, advise on minimising the impact on your neighbours, prepare the notices, recommend experienced surveyors where needed, and coordinate between the surveyors and contractors during construction.

Project timelines vary depending on complexity, size, and planning requirements. The process typically includes design development, planning and building regulations approval, and construction phases. We provide realistic timelines during our initial consultation and keep you informed throughout the process. If you want that kitchen for Christmas, hire us before Easter. New building takes longer, but the biggest delays come from changing your mind part way.

Also asked: What is the typical timeline for a house extension project? · How long does an extension take to build? · How long from design to finished extension?

Yes. We can run the whole construction stage — helping select the contractor, inspecting the work on site, keeping an eye on quality and progress, and valuing the work as it's carried out so payments stay fair. We act as your representative throughout, so the project stays on track and on brief.

Related: why you may need a principal designer

We have a network of trusted, vetted contractors with proven track records built up over 25+ years in practice. We select contractors based on their experience with similar projects, quality of work, reliability, and competitive pricing. With over 1,200 completed projects, we've established strong relationships that ensure quality delivery. Or we can work with contractors you've already selected.

We're on-site regularly to identify and resolve issues early. We have established relationships with contractors and can quickly address any problems. Detailed documentation and regular communication are key to resolving issues efficiently, with minimal disruption.

Yes, we can work with your existing contractors or builders. We'll assess their capabilities and ensure they understand the project requirements. We can provide detailed drawings and specifications to help them deliver the project to our design standards.

We build realistic timelines into our project planning and maintain regular communication with contractors. If delays occur, we identify the cause and work with contractors to minimize impact. We keep clients informed and adjust schedules as needed.

Yes, we have extensive experience working in conservation areas and listed buildings. With our 95% planning success rate including complex sites, we understand the specific requirements and restrictions, ensuring our designs respect the character and heritage of these protected areas while meeting modern living needs.

Related: conservation & heritage projects · our conservation areas guide

Also asked: Can I extend a house in a conservation area? · What can I change in a conservation area?

Conservation areas have additional planning restrictions to preserve architectural character. This may affect materials, design details, and even the overall form of your extension. We have extensive experience working within these constraints and can design solutions that respect heritage while meeting modern needs.

Yes, we have experience working with listed buildings and understand the additional requirements and restrictions. Listed building consent is required for any alterations, and we work closely with conservation officers to identify and ensure our designs preserve the building's historic character.

We cover the full range of architectural work — house extensions, loft conversions and basements, refurbishments, and the occasional one-off new house — together with the planning applications, building regulations, party wall matters, interior design, tendering and project management that go with them. We can take a project from the first sketch through to handover, or simply pick up the stages where you need us.

Related: our architectural services

Not legally — you can use a builder, a draughtsman or an architectural technologist, and 'architect' is itself a protected title, used only by those registered with the ARB. The real question is what your project needs. For a straightforward extension that clearly falls under Permitted Development, you may need little design input. But the moment you're applying for planning permission — particularly in a conservation area — making structural changes, or dealing with a party wall, considered design tends to pay for itself: in approvals won, in space that genuinely works, and in fewer expensive surprises on site. A fair rule of thumb is that the harder the site or the planning context, the more an architect earns their fee. If you're weighing it up, our guide on when you need an architect goes through it in more detail.

Related: when you need an architect · our services

Also asked: Do I need an architect or can I just use a builder? · Do I need an architect for a loft conversion? · Is it worth hiring an architect for a small extension?

Yes. We can take you through every stage — developing the brief, testing what's feasible, the planning application, building regulations and technical drawings, tendering the work, and overseeing the build on site through to completion. Equally, if you only need us for part of the journey — say, to win planning permission — that's fine. Most clients use us end to end, but it's your call.

We do, and gladly. The discipline of cost control on commercial and development work feeds straight back into our home projects — and what homeowners tell us, in turn, shapes the kind of developments people actually want to live in.

Related: our commercial work

Sites for these are rare, but we do — see Lytton Grove or Weybridge, for example. Where there's already a building on the land, we'll often look at adapting or extending it rather than starting from scratch, which tends to give the finished house more character.

Related: 36 Lytton Grove

Yes, we offer comprehensive interior design services including space planning, material selection, bathrooms and kitchens, lighting design, and furniture specification. We ensure the interior design works seamlessly with the architectural design for a cohesive result.

Yes, we can help with furniture selection, decoration, and styling to complete your project. We work with trusted suppliers and can coordinate the entire project from concept to final decoration including finding space for your treasured pieces.

Our design process follows RIBA stages: 1) Brief development and site analysis, 2) Concept design and feasibility, 3) Developed design and planning application, 4) Technical design and building regulations, 5) Construction and handover. We involve clients at every stage. The brief is key, and your input here is the most important part of the project.

Related: every journey begins with the first step

We carefully analyse your existing property's architectural style, materials, proportions, and character. Our designs complement and enhance your home while maintaining visual harmony. We use materials and details that respect the original design language.

We recommend materials that are durable, sustainable, and appropriate for your property type. This includes high-quality bricks, natural stone, sustainable timber, and modern insulation systems. We select materials based on your budget, design preferences, and local character requirements.

We consider acoustics in our designs, especially for extensions near busy roads or for music rooms. We can specify soundproofing materials and design solutions that minimize noise transmission and create comfortable living environments. Unlike in the recent past, modern flat conversions require effective soundproofing between flats.

We work with structural engineers to ensure all designs meet structural requirements. This includes foundation design, structural calculations, and ensuring compliance with building regulations. We never compromise on structural safety.

We assess existing drainage and utilities during the design process and ensure our designs work with or improve these systems. This may include upgrading drainage, repositioning utilities, or installing new systems as required.

Absolutely. We're members of both the Green Register and the AECB, and committed to sustainable design. We can specify eco-friendly materials, energy-efficient systems and low-impact construction methods — natural materials, high-performance insulation and renewable energy where it makes sense.

Related: our approach to sustainability

We design for energy efficiency from the start, including high-performance insulation, energy-efficient glazing, and sustainable heating systems. We can achieve high energy performance standards and help you to qualify for energy efficiency grants or incentives.

Putney and Wandsworth have specific planning requirements including conservation area restrictions, flood risk considerations, and local character preservation. We understand these requirements and design solutions that comply while making the most of your property's potential within local constraints. Most planning policies are very similar wherever you are, but we'll point out any local quirks.

Related: Putney architects · choosing a local architect

Common challenges include Victorian/Edwardian construction methods, party wall issues, basement water tables, and limited garden space. We're experienced in addressing these challenges and can design solutions that work with your property's specific characteristics.

Related: basement conversions · daylight in a basement

Also asked: What are common issues with Victorian houses in London?

Local authorities have specific requirements for parking and access, especially for larger extensions. We ensure our designs comply with these requirements and can suggest solutions that maintain or improve parking and access arrangements. Most London councils now expect new buildings and conversions to be 'car-free'.

We serve South, Southwest, West and sometimes Central London, with particular expertise in Wandsworth, Richmond, Merton and surrounding boroughs including conservation areas.

Also asked: What areas do Andrew Catto Architects serve? · Are you architects in Southwest London? · Do you work in Wandsworth, Richmond or Putney?

Andrew Catto Architects has been serving Londoners since 1999, with over 25 years of architectural expertise. We've successfully completed over 1,200 projects, from small extensions to major renovations, establishing ourselves as trusted experts in these areas.

Our directors Andrew Catto and Melissa Lawrence da Cunha bring extensive experience to every project. Andrew has 35+ years of architectural expertise, qualifying in 1976 and founding the practice in 1999. Melissa has 25+ years of international experience, joining as director in 2017. Together with our experienced team, we've built over 150 trusted client relationships.

You can reach us at our Putney office: Office 11 Apsley House, 176 Upper Richmond Road, London SW15 2SH. Call us on 020 8785 0077 or email [email protected]. We're open Monday to Friday, 9:00 AM to 5:30 PM, and we're always happy to discuss your project requirements.

We maintain regular communication throughout the project. We typically meet weekly during design phases and bi-weekly during construction. We're also available by phone and email for urgent questions and provide regular progress updates. Change at the initial design stage is simple, but changes late, particularly when on site, can cause delay, wasted work and extra cost. Most of the projects we hear about that run over time and over budget are the result of late changes.

We understand that requirements can evolve. We can accommodate design changes, though major changes may affect timeline and cost. We discuss the implications of any changes and ensure you're fully informed before proceeding.

Yes, we provide ongoing support after project completion. This includes addressing any issues that arise, providing maintenance guidance, and being available for future projects. We maintain long-term relationships with our clients.

Client satisfaction is our priority. We work closely with you throughout the project to ensure the result meets your expectations. If you have concerns, we address them immediately and work to resolve any issues to your satisfaction. We can't guarantee consent so if we suggest changes, it's for good reason.