Find out what your house extension is likely to cost, before you pay for drawings

The free guide is a written resource for anyone buying a home in the UK that needs work — a property in the right location but too small, poorly laid out, or in need of renovation. It is not a guide to the legal or financial buying process. It is a guide to the architectural questions you should be asking before you commit to a property. It covers how to research a property for free before you offer, how to choose the right type of building survey, and eleven practical things every buyer planning to alter or extend their home should know.

More than most buyers realise. Four free searches — checking the listing status, checking whether the property is in a conservation area, reading the planning history, and using the Google Street View time travel feature — can tell you what the seller and previous owners have tried to do with the property, what the local authority has approved or refused, and what the building has visibly been through over the past decade. Together they take about two hours and require no professional involvement. The guide explains exactly how to carry out each search.

Each UK nation has its own database. In Scotland, search the Historic Environment Scotland Designations portal at portal.historicenvironment.scot. In England, use the National Heritage List for England at historicengland.org.uk. In Wales, use Cadw's Cof Cymru database at cadw.gov.wales. In Northern Ireland, use the Department for Communities Buildings Database. Search by address and also by street name — many Victorian and Georgian terraces are listed as a group entry rather than by individual house number.

A Level 2 RICS HomeBuyer Report covers the visible parts of a property and is suitable for modern homes where only cosmetic work is planned. A Level 3 RICS Building Survey is the most comprehensive level: the surveyor inspects all accessible parts of the property in detail, identifies defects, explains their causes, and advises on remedial work and likely costs. If you are planning to extend, alter, or renovate a property — or if it is older or in poor condition — always commission a Level 3. It is the only level that examines the structure in enough depth to inform your future plans.

The guide covers everything you can find out yourself before consulting a professional. The next step is a 30-minute online consultation, which takes the research you have done and gives you a specific professional assessment of whether your plans are realistic for the property you are considering. A consultation before buying a house costs £150. The more research you have done before the call, the more useful those 30 minutes will be.​The guide says a mortgage valuation is not a survey — what should I commission instead?Commission your own independent Level 3 Building Survey directly, separately from anything your mortgage lender arranges. A mortgage valuation is done for the lender's benefit and will not assess structural defects, damp, drainage, or the suitability of the property for the work you plan. The fee for a Level 3 Building Survey — typically several hundred pounds for a basic survey, more than a thousand for a comprehensive one — is the cheapest insurance you will buy in the entire purchase process. Always have the survey in hand before you exchange contracts.

The House Extension Guide is a detailed written guide to house extensions, internal alterations and refurbishment projects in the UK. It is divided into three parts: how to find the right architect for your project, how the design and construction process works from feasibility study through to post-construction, and practical things you need to know before starting any building work. It is written for anyone who has never hired an architect or carried out significant building work before.

Yes. The guide covers the design and construction process for domestic projects across the UK. Where procedures differ between Scotland and the rest of the UK — for example, Building Warrant versus Building Regulations Approval, or specifics of the planning application process — these differences are noted in the text. The core content on finding an architect, the design stages, construction contracts, contingency planning, and practical advice applies to projects in England, Wales, Northern Ireland and Scotland.

The guide includes a full fee scale showing the fees charged in Níall's own practice, broken down by construction budget and project stage — from feasibility study through to post-construction snagging. This is published as a guide to help you understand how architectural fees are structured and as a benchmark when comparing quotes. The guide is clear that architects set their own fees independently and these figures should not be used to negotiate with an architect in another location.

Yes — in detail. The guide walks through all six stages: feasibility study, planning application, building regulations application, pre-construction (costing and tendering), construction, and post-construction. For each stage it explains what happens, what decisions you need to make, what other professionals are involved, how long the stage typically takes, and what the common pitfalls are. There is also a process flow chart showing how all the stages connect from initial contact with an architect to a completed building.

The guide is a PDF document. After purchasing, you receive an automated download link by email. It can be read on any device — phone, tablet or desktop. It is the same guide that has been provided to clients of the Real Life Architecture online consultation service and is updated periodically.

The guide gives you the general knowledge to understand the process and ask the right questions of the people you hire. For specific advice on your specific project — your property, your budget, your planning situation — an online consultation is the logical next step. A consultation before altering an existing home costs £130. The guide is good preparation for that call: the better informed you are, the more useful 30 minutes with an architect will be.

The first step is establishing whether full planning permission is required and what that application will need to address. If your plot already has outline permission, you will need to submit a detailed application agreeing the design. If there is no permission, a full application is required from the outset. Before any of that, you need to be clear on your budget and whether it is realistic for the size and type of house you want to build. A 30-minute consultation maps out the approvals required, flags any obvious site risks, and gives you a realistic picture of likely costs before you spend money on drawings or professional fees.

A full planning application is required for a new house in virtually all circumstances. The application must demonstrate that the proposed dwelling is appropriate for the site in terms of design, scale, access, impact on neighbours, and compliance with the local authority's planning policies. In conservation areas or near listed buildings, additional consents may be required. In Scotland the process differs slightly from England and Wales — but the fundamental requirement for planning permission before building a new house is the same across all parts of the UK.

They are entirely separate. Planning permission is about whether you can build. Building regulations are about how you build — covering structural safety, fire safety, thermal performance, drainage, ventilation, and a range of other technical requirements. You must have both planning permission and building regulations approval (called a Building Warrant in Scotland) before construction begins. A structural engineer will be required on any new-build project, and an energy consultant is usually needed to demonstrate compliance with current insulation and energy efficiency standards.

As a broad benchmark, construction costs for a one-off new house in the UK in 2026 start at around £2,300 per square metre, plus VAT where applicable. High-specification finishes, complex sites, remote locations, or difficult ground conditions push costs considerably higher. This figure covers construction only and does not include architect's fees, structural engineering, planning and building regulations fees, or site-specific costs such as ground remediation, a new access road, or connecting to services. Allow a contingency of at least 15% on top of your construction budget for unexpected costs, particularly on sites where the ground conditions are unknown.

You are not legally required to hire an architect, but you must use an ARB-registered architect if you wish to use that title. A design-and-build company combines the design and construction under one contract, which can simplify the process but means the person designing your house also has a financial interest in keeping costs low. An independent architect works solely in your interest, produces drawings that meet planning and building regulations requirements, and can manage the construction process on your behalf. For a new house, independent architectural input at the design stage almost always adds value.

From initial design work to moving in, the full process typically takes two to four years. A planning application for a new house takes three to twelve months from submission to decision — the eight-week statutory target is rarely met, and applications for new houses are more complex than extensions. If neighbours object in sufficient numbers, the decision passes from the planning officer to the local elected committee, which can add months to the process. Building regulations approval takes several weeks to several months. Finding and appointing a builder and agreeing a contract typically takes a further three to six months after approvals are in place. Construction itself usually takes 6 to 12 months, depending on the size and complexity of the build but could take years if you self-build in stages.

In most cases, yes. Converting a non-domestic building to residential use is a change of use under the planning system, and in Scotland, Wales and Northern Ireland this almost always requires a formal planning application. In England, permitted development rights for certain conversions — such as some office-to-residential changes — exist but are subject to a prior approval process and numerous exceptions. The position varies depending on the building type, its location, and any planning designations that apply. A 45-minute consultation will clarify exactly what approvals your specific building and situation require.

The most common types include former commercial units, agricultural buildings such as barns and steadings, redundant offices, and other non-residential structures. Feasibility depends on the building's structural condition, its location, its planning history, and whether the local planning authority supports residential conversion in that area. Some buildings — particularly agricultural ones in rural areas — may face specific policy restrictions. The consultation covers a high-level assessment of whether your specific building is a realistic candidate for conversion.

A full building regulations application (Building Warrant in Scotland) is required for any change-of-use conversion. The regulations that apply include structural adequacy, fire safety, thermal performance and energy efficiency, ventilation, sound insulation, and accessibility. Non-domestic buildings typically need significant upgrades to meet the residential standard — particularly in terms of insulation and fire compartmentation. A structural engineer will almost certainly be required, and depending on the project an energy consultant may also be needed.

A planning application for change of use typically takes between two and four months from submission to decision. This varies by local authority and depends on the complexity of the proposal and whether objections are received. If the building is listed, a Listed Building Consent application runs alongside the planning application. The building regulations application runs independently and typically takes several weeks to several months depending on the local council's workload. Both approvals are required before construction can begin.

The structural condition of a non-domestic building is often less predictable than a residential property, as these buildings were not designed or maintained to domestic standards. Hidden damp, asbestos, inadequate foundations, and the complete absence of insulation are common. The planning position can also be more complex — some local authorities have specific policies restricting residential conversion in certain building types or locations. The 45-minute consultation is designed to identify these risks before you commit, so you understand what the project realistically involves.

Class Q is a permitted development right in England that allows certain agricultural buildings to be converted to residential use without a full planning application. Instead, you submit a prior approval application to the local authority, which assesses a limited set of issues: transport and highways impact, noise, contamination, flooding risk, and whether the building is genuinely capable of conversion. Class Q does not apply in Scotland, Wales or Northern Ireland, which require full planning permission for barn conversions. Class Q also has significant limitations — the building must have been in agricultural use, there are floor area limits, and the local authority can refuse if the structure is not capable of conversion without substantial rebuilding. The 45-minute consultation covers whether Class Q is likely to apply to your specific building and what the prior approval process involves.

Before the call I review the information you send on both properties — addresses, photos, planning history, listing or conservation area status, and your intended plans for each. On the call we work through each property systematically: planning feasibility, likely constraints, estimated cost of the work you want to do, and any red flags that might affect one over the other. 45 minutes is enough to give you a clear professional view on which property is better suited to your plans, and why.

That is not a problem. Planning policies and designations vary across England, Scotland, Wales and Northern Ireland, but the principles are consistent and I can assess planning feasibility for any residential property in the UK. The key information is the listing status, conservation area status, and planning history of each. I will explain how the local planning context differs between the two and what that means for your specific plans.

This is the most common scenario in a choosing consultation. A lower asking price often has constraints that are not immediately visible — a listed status, a previous planning refusal, drainage issues, or structural complications that inflate the true cost of the work. I give you a realistic picture of what each property is likely to cost to achieve your goals, so you can compare them on a like-for-like basis rather than on asking price alone. A cheaper property regularly turns out to be the more expensive option once the full cost of work is factored in.

Yes, and it is particularly useful in that situation. A listed property imposes additional consent requirements and cost premiums on any alteration work. I can explain what Listed Building Consent is likely to require for the specific work you want to do, and compare that directly with what a full planning application on the unlisted property would involve. Many buyers either dismiss listed properties too quickly or underestimate the cost and complexity. The consultation gives you an honest assessment of both.

Yes — please do. Estate agent particulars, floor plans, photos, and rightmove or Zoopla links are all useful. Any research you have already done on listing status or planning history is also helpful. You do not need professional drawings. The more detail I have before the call, the more useful the 45 minutes will be.

Often especially so. Many people come in with a clear preference and leave having confirmed it was the right choice. Others discover a constraint they had not considered that changes the picture entirely. A 45-minute call with an architect is considerably cheaper than discovering after exchange that the property you preferred cannot be altered the way you planned. If it confirms your instinct, that confidence alone has value.

Yes — significantly. Every planning application ever submitted on a property is a public record, including approvals, refusals, and enforcement notices. A previous refusal tells you what the planners have already objected to. An enforcement notice tells you something was built without permission and the council may still require its removal — a liability you would inherit on completion. Reading the planning history before you offer costs nothing and takes about an hour. A consultation before you commit takes 30 minutes and covers exactly what that history means for the plans you have in mind.

A surveyor tells you what is wrong with a building. An architect tells you what you can do with it. These are different skills. Before you offer on a house you intend to alter or extend, a 30-minute call can tell you whether your plans are likely to get planning permission, whether the property type and location present any particular obstacles, and whether your budget is realistic for the work you have in mind. It helps you decide whether to offer, what to offer, and what conditions to set.

Not necessarily. Permitted development rights can be removed or restricted in several ways: if the property is listed, if it is in a conservation area covered by an Article 4 Direction, if previous extensions have already used up the permitted volume, or if the local authority has applied a specific policy. Always verify the position with the local planning authority before relying on what an estate agent tells you about permitted development. This is one of the most common mistakes buyers make.

A conservation area means additional planning controls apply. Some alterations that would normally be permitted development — small extensions, replacing windows, painting brickwork — require formal planning permission. Conservation areas also often have an Article 4 Direction in place, which removes permitted development rights entirely. The local authority will have published design guidance for the area that sets out what is and is not acceptable. During a consultation I can tell you what those constraints are likely to mean for the specific alterations you have in mind.

Ideally before you offer — so you know whether the property is suitable for your plans before spending money on a survey. Many buyers do both in sequence: an architectural consultation first to assess feasibility, then a Level 3 Building Survey to confirm the structural condition. The two serve different purposes. The consultation tells you whether your project is possible. The survey tells you whether the building is sound enough to carry it out. Share a copy of the survey with your architect when you eventually instruct one for the work.

In England and Wales, yes — the Party Wall etc. Act 1996 requires you to serve written notice on adjoining owners before carrying out certain works. This includes building on or near the boundary, excavating within three or six metres of a neighbouring structure, and work directly on a shared wall. Your neighbour then has the right to appoint a surveyor and agree a Party Wall Award before work begins. In Scotland the Act does not apply, but you should still discuss boundary proximity with your architect as it affects design, access, and the structural approach. A consultation can flag whether the extension you are considering on a specific property is likely to trigger party wall obligations.

In most cases, no. Internal alterations — removing walls, relocating a staircase, changing room layouts — do not require planning permission in the UK, as planning controls relate to external appearance and land use rather than internal arrangement. However, there are exceptions: if the property is listed, any alteration including internal changes requires Listed Building Consent before work begins. If you are converting part of a house into a separate self-contained flat, that is a change of use and does require planning permission. A 30-minute consultation will confirm whether your specific project needs any planning approval before you instruct a builder or architect.

Most loft conversions in the UK fall under permitted development and do not require a planning application — provided they meet specific volume and design limits. In England, the permitted development allowance for a loft addition is 40 cubic metres for terraced houses and 50 cubic metres for detached and semi-detached houses. The addition must not exceed the height of the existing roof ridge, and any dormer facing a highway is not permitted. These allowances do not apply if the property is listed, if it is in a conservation area where an Article 4 Direction removes permitted development rights, or if previous alterations have already used up the permitted volume. Even where planning permission is not required, a building regulations application is always needed for a loft conversion — the structural alterations, stair access, fire escape, and insulation all require formal approval.​

Removing a structural wall always requires building regulations approval, regardless of whether planning permission is needed. The regulations require that a structural engineer calculates the load being carried by the wall and specifies the correct beam size and bearing pad to replace it. A building control officer will inspect the work at key stages — before the beam goes in and after the wall is removed — and issue a completion certificate when the work is signed off. That certificate matters: it is required evidence when you sell the property that the work was carried out to the approved standard. Never remove a structural wall based on a builder's estimate of the beam size alone — if the calculation is wrong, the consequences are serious and the liability falls on you as the homeowner.

Extension costs vary considerably depending on size, specification, location, and the complexity of connecting the new structure to the existing building. As a general benchmark, a basic single-storey rear extension in the UK in 2026 starts at around £2,500 to £3,500 per square metre of internal floor area, including a standard specification finish. A larger or more complex extension — two storeys, side returns, a heavily glazed structure — will cost more. These figures are for construction only and do not include architect's fees, structural engineering, planning and building regulations applications, or VAT. VAT at 20% applies to most extension work on existing homes, although reduced rates apply in certain circumstances such as work on listed buildings. Allow a contingency of at least 15% on top of your build cost for unexpected items — particularly in older properties where what is behind walls and floors is often unknown until work begins.

For a straightforward house extension, allow twelve to eighteen months from the first conversation with an architect to completion of construction. The stages are: feasibility and design (four to eight weeks), planning application if required (eight weeks statutory target, though two to four months in practice is more realistic for extensions), building regulations application (four to eight weeks), finding and appointing a builder and agreeing a contract (two to four months), and construction (three to six months for a typical single-storey extension). Projects that do not require planning permission — permitted development extensions, internal alterations — can move faster, but building regulations approval and contractor procurement still take several months. A consultation at the outset gives you a realistic programme for your specific project so you can plan around it rather than being surprised by the timescales later.

Every consultation is with me, Níall Hedderman, directly. I am an ARB-registered architect and have been running my own practice since 2009. You will not be passed to an assistant — you get my direct professional opinion on your specific situation.

Consultations start at £130 for advice on altering your home. A consultation before buying a house is £150, choosing between two properties is £200, buying land or building a house is £170 each, and a property conversion consultation is £190. All fees are shown in the price list above.

Most consultations are 30 minutes on Zoom. The Choosing Between Two Properties consultation and the Consultation Before Converting a Property are 45 minutes. The length of time specified when booking is the duration of the call. If more time is needed, that is at my discretion.

Book a slot using the calendar on this page. You will receive an automated confirmation email asking you to reply with the property address, your budget, photos, and any other relevant information. I read everything before the call, so we can spend the time discussing your specific situation rather than introductions. The more detail you send, the more useful the call will be.

I review your property details and budget in advance, then give you my honest professional assessment on the call: whether your plans are realistic, what planning permission and building regulations issues are likely to arise, and what to do next. After the call I send a written summary email covering the main points discussed, the statutory approvals your project will require, and guidance on how to find and approach the right local architect for the work.

No. Consultations do not include drawings, design work, specifications, or detailed cost estimates. Any costs mentioned during the call are broad estimates and are exclusive of VAT. The written summary email is a record of the discussion and next steps — it is not a formal report or specification. If your project requires design services, the summary will advise you on how to find the right local architect.

I offer consultations on buying a house, choosing between two properties, house extensions and internal alterations, loft conversions, building a new house, buying land, and converting a non-domestic building into a single dwelling. Consultations are for UK residential properties only, and are only available where no other architect is already engaged on the project. I do not advise on HMOs, mixed-use projects, subdivisions, multiple homes on one site, or basement structural alterations, conversions, or waterproofing.

Yes — that is exactly what a consultation is for. Most people book before they have committed to anything. The call helps you decide whether to proceed, understand what a realistic budget looks like, and identify any planning or structural issues before you spend money on drawings or a builder. It is the most useful thing you can do at the very start of a property project.

No. Every question is in plain English, and most come with a drawing or photograph.If you're not sure of a measurement, you can choose a range.

Each part of the build is given as a low to high range, based on the costs of realcompleted projects and adjusted for your area. It is an estimate made from youranswers, not a quotation.

No. It helps you decide whether your project is affordable before you pay fordrawings. A builder's quote comes later, once your project is designed.

The Homeowner version is £40 for one property. A free version and a Professionalversion are coming soon

Yes. Your answers save as you go, and your personal link is emailed to you.

Yes. You can come back once within 7 days of your report, at no extra cost, changeyour answers and get a revised estimate.

The free Before You Start guide lists every measurement, so you can have themready before you buy

No. It is a pricing tool. It prices the choices you make, and the design is for you andyour architect.

No. It looks at cost only. You must get professional advice on planning permission andbuilding regulations before going further.

Yes. During your calculation you can change your answers as often as you like, forexample one or two storeys, or a flat or pitched roof, and see what each change doesto the cost.

Your report is emailed to you as a PDF, with a price range for each part of the build, atotal, and the choices that add most to the cost.

Enter your postcode before you buy, and the page tells you straight away.