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  • How Long Does a Planning Application Take UK

    Architectural drawings and planning documents on a desk

    How Long Does a Planning Application Take in the UK?

    One of the first questions homeowners ask when planning a project is: how long will the planning process take? The honest answer is that it depends on the type of application, the quality of the submission, and how busy your local planning authority is. This guide from Crown Architecture explains the statutory timescales, the step-by-step process, and how to give your application the best chance of a swift approval.

    Statutory Planning Timescales at a Glance

    Application Type Statutory Timescale Typical Real-World Time
    Householder (extensions, lofts, outbuildings) 8 weeks 8–16 weeks
    Full Planning Permission 8 weeks 8–16 weeks
    Major Applications (10+ dwellings) 13 weeks 13–26 weeks
    Prior Approval (larger extensions) 42 days 42 days
    Lawful Development Certificate 8 weeks 8–12 weeks
    Listed Building Consent 8 weeks 8–20 weeks

    The statutory timescale is the period within which the local planning authority (LPA) is supposed to determine the application. In practice, many LPAs are under-resourced and regularly exceed these timescales. In London particularly, it is not uncommon for householder applications to take 12–16 weeks, even with a well-prepared submission.

    The Step-by-Step Planning Application Process

    Step 1: Pre-Application (2–8 weeks)

    Before submitting a planning application, it is often worthwhile to arrange a pre-application meeting with your local planning authority. This is a paid service (typically £100–£500) where a planning officer reviews your proposals informally and provides feedback. It can significantly reduce the risk of refusal and identify any issues before the formal submission.

    Crown Architecture will also carry out our own assessment of your proposal against the relevant planning policies before submission.

    Step 2: Preparation of Drawings and Documents (2–4 weeks)

    A well-prepared application requires professionally drawn plans, elevations, and sections showing the existing and proposed works. It may also require a Design and Access Statement, Heritage Statement (for conservation areas or listed buildings), or a Planning Statement. Crown Architecture prepares all of these as part of our planning service.

    Step 3: Submission and Validation (1–2 weeks)

    The application is submitted online through the Planning Portal, along with the appropriate fee. The LPA then validates the application — checking that all required documents are included and the fee has been paid. If the application is invalid, it is returned and the clock does not start until it is resubmitted correctly.

    Step 4: Consultation Period (21 days)

    Once validated, the LPA notifies neighbours and other consultees (such as the highways authority or conservation officer) and places a site notice. The statutory consultation period is 21 days, during which anyone can submit comments. The case officer cannot determine the application until this period has elapsed.

    Step 5: Assessment and Decision (3–8 weeks after consultation)

    The case officer assesses the application against relevant planning policies — the National Planning Policy Framework (NPPF), the Local Plan, and any neighbourhood plans. For householder applications decided under delegated powers (i.e., by an officer rather than a planning committee), a decision is typically issued within 8 weeks of validation. Applications referred to the planning committee take longer, as they must be scheduled for a committee meeting.

    Step 6: After the Decision

    If permission is granted, it will be subject to conditions. Standard conditions include the commencement period (typically 3 years), materials approval, and sometimes pre-commencement conditions that must be discharged before work starts. Discharging conditions typically takes 8 weeks and should not be overlooked — commencing work without discharging pre-commencement conditions can invalidate your permission.

    Why Planning Applications Take Longer Than Expected

    Several factors routinely delay planning decisions beyond the statutory timescale:

    • Invalid applications: Missing documents, incorrect fee, or insufficient drawings will cause the application to be returned and the clock to restart.
    • Third-party objections: Significant neighbour objections can require the case officer to seek additional information or refer the application to a planning committee.
    • Conservation area or heritage issues: Applications affecting listed buildings or conservation areas require consultation with the conservation officer, which can extend timescales considerably.
    • LPA resourcing: Many local planning authorities in London are under significant resource pressure, with high case loads and staff vacancies. This is the single most common cause of delay.
    • Pre-commencement conditions: Even after a decision, you may need to discharge conditions before starting work, adding several more weeks.

    How to Speed Up Your Planning Application

    There are several steps you can take to maximise the chances of a quick, successful decision:

    1. Use a qualified architect: A well-prepared application from a professional architect is far less likely to be returned as invalid or to generate unnecessary queries from the case officer.
    2. Carry out pre-application engagement: Discussing your proposals with the LPA before submission can identify potential issues early and smooth the formal process.
    3. Engage with neighbours early: Informally discussing your proposals with neighbours before submission can reduce the risk of objections that cause delay.
    4. Avoid peak periods: Some LPAs have seasonal peaks and troughs in workload. Submitting in early January or late summer can sometimes yield quicker decisions.
    5. Respond promptly to queries: If the case officer requests additional information, responding quickly will prevent unnecessary delay.

    What Happens After Planning Approval

    Planning permission is just the first approval you need. Before work starts, you will also need building regulations approval. For most domestic extensions and loft conversions, this involves submitting a full plans application to your LPA’s building control department (or an approved inspector). See our guide on house extensions in London for more detail on the full process from planning to completion.

    Crown Architecture handles the full journey — from initial design through planning permission and building regulations to construction stage inspections.

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    Frequently Asked Questions

    What is the statutory timescale for a householder planning application?

    The statutory timescale for a householder planning application (for works such as extensions, loft conversions, or outbuildings) is 8 weeks from the date of validation. However, many local planning authorities, particularly in London, regularly exceed this timescale due to high workloads, and real-world timescales of 12–16 weeks are common.

    Can I start building before planning permission is granted?

    No. You must not start works that require planning permission until permission has been formally granted. Commencing without permission is a breach of planning control and can result in an enforcement notice requiring you to demolish the works at your own expense. The only exception is works that are genuinely permitted development, which do not require a planning application at all.

    How long does planning permission last once granted?

    Planning permission for most residential developments lasts 3 years from the date of the decision notice. You must commence the development within this period. Commencement is generally defined as a material operation on site, such as breaking ground or laying foundations. If you have not started within 3 years, the permission expires and you would need to reapply.

    What is the planning application fee for a householder extension?

    As of 2025, the planning application fee for a householder application in England is £258. For a Lawful Development Certificate application, the fee is £129 (half the householder fee). Fees for other application types vary — contact Crown Architecture for a full breakdown of all likely costs for your project.

    What happens if my planning application is refused?

    If your application is refused, you have several options. You can revise the design to address the reasons for refusal and resubmit (the first resubmission within 12 months is free). Alternatively, you can appeal to the Planning Inspectorate — the appeal process typically takes 6–12 months. Crown Architecture will advise on the best strategy following a refusal.

  • How Much Does a House Extension Cost UK 2025

    Modern kitchen extension on a UK house

    How Much Does a House Extension Cost in the UK? 2025 Guide

    A house extension is one of the most significant investments you can make in your home. Whether you are creating an open-plan kitchen-diner, adding a bedroom, or building a full wrap-around extension, understanding the costs involved is essential for planning your project. This guide from Crown Architecture & Structural Engineering provides a comprehensive cost breakdown for all types of house extensions in 2025.

    House Extension Cost Guide by Type

    Extension costs are typically quoted per square metre of new floor space created. The ranges below reflect the full build cost, inclusive of all building work but exclusive of architect and engineer fees, planning fees, and furnishings.

    Extension Type Basic Spec (per m²) High Spec (per m²)
    Single-Storey Rear Extension £2,000 – £2,500 £2,500 – £3,500
    Double-Storey Extension £1,800 – £2,200 £2,200 – £2,500
    Wrap-Around Extension £2,000 – £2,500 £2,500 – £3,000
    Side Return Extension £2,200 – £2,800 £2,800 – £3,200
    Basement Extension £3,500 – £4,000 £4,000 – £5,000
    Over-Structure Extension (above garage) £2,000 – £2,500 £2,500 – £3,000

    Single-Storey Rear Extension Costs

    A single-storey rear extension is the most popular type in the UK. For a typical 20m² extension in London, you would expect to pay £40,000–£70,000 for a standard specification, rising to £70,000–£100,000 for a high-spec finish with aluminium bifold doors, underfloor heating, and a lantern roof.

    The cost per square metre is higher for smaller extensions because fixed costs (foundations, structural openings, weatherproofing) are spread over a smaller area. A 10m² extension will have a higher per-m² cost than a 25m² extension.

    Double-Storey Extension Costs

    A double-storey extension costs less per square metre than a single-storey because you are adding two floors for only marginally more foundation and roof cost. For a typical 30m² double-storey extension (15m² per floor), expect to pay £54,000–£75,000 at standard specification in London.

    Double-storey extensions almost always require full planning permission, unless they fall within the (rarely applicable) PD limits. They are excellent value when you need both a ground floor and first floor addition.

    Wrap-Around Extension Costs

    A wrap-around extension combines a side return infill and a rear extension into a single L-shaped structure. It is particularly popular on terraced and semi-detached Victorian and Edwardian houses in London, where the side return (the narrow passage beside the house) can be enclosed to create a dramatic, wide-open kitchen-diner.

    A typical 25m² wrap-around extension in London costs £50,000–£80,000 for standard specification. The configuration and the need to open up the rear and side walls of the house increases complexity and cost compared to a simple rear extension.

    Side Return Extension Costs

    A side return extension infills the narrow passage alongside a Victorian terrace, typically creating additional width to the kitchen. These are smaller by area but higher in per-m² cost because they involve complex junctions, oversailing the party wall, and often require significant structural work to open up the existing ground floor. A typical 8–12m² side return costs £20,000–£40,000 in London.

    Basement Extension Costs

    Basement extensions are the most expensive type because of the excavation required, the need for waterproofing (tanking), and the complexity of underpinning the existing foundations. Costs start at around £3,500 per m² and can reach £5,000+ per m² for a high-spec finish. A 30m² basement extension in London would typically cost £105,000–£150,000 or more.

    Hidden Costs to Budget For

    When budgeting for a house extension, many homeowners underestimate the additional costs beyond the main build contract. Key items to budget for include:

    • Architect and structural engineer fees: Typically £3,000–£8,000 depending on project complexity, covering design, planning, and building regulations drawings.
    • Planning application fee: Currently £258 for a householder application in England.
    • Building regulations fees: Typically £800–£1,500 depending on the size and nature of the works.
    • Party Wall surveyor: If works affect a shared party wall, a Party Wall Award will be required. Costs £700–£3,000+ depending on whether you agree a surveyor or appoint separately.
    • Contingency: Always allow at least 10–15% of the build cost as a contingency for unforeseen work (buried drains, poorly maintained existing structure, etc.).
    • Interior fit-out: Kitchen, bathroom, flooring, decoration, and furniture are not included in standard build contracts.
    • VAT: Extension works are subject to 20% VAT. This is the biggest hidden cost that catches homeowners off guard.

    Return on Investment

    House extensions in London typically offer strong returns. A well-executed single-storey rear extension can add 10–15% to the value of a property, and a double-storey or side return extension can add 15–25%. In London, where property values are high, this translates to significant absolute value uplift. For a £600,000 property, a 15% uplift represents £90,000 — often exceeding the cost of the extension itself.

    How to Get the Best Value

    The best way to ensure value for money on an extension project is to appoint a qualified architect early. A good architect will design for buildability and cost efficiency, obtain competitive contractor tenders, and manage the project to avoid costly variations. Crown Architecture offers a fixed-fee service for all stages of the project — contact us for a quote tailored to your property. See our house extension London page for more details.

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    Frequently Asked Questions

    Is VAT charged on house extension costs?

    Yes. Extension works are subject to 20% VAT. This is one of the most significant hidden costs on an extension project. The only exceptions are new build dwellings and some conversions of existing non-residential buildings to residential use, which qualify for a reduced or zero VAT rate. For a standard extension, always add 20% to any quoted build cost to determine the total cost inclusive of VAT.

    How long does a single-storey rear extension take to build?

    A typical single-storey rear extension takes 8–14 weeks on site, depending on size, complexity, and specification. This does not include the design and planning period, which typically takes 3–6 months prior to the start of construction. A double-storey extension typically takes 14–20 weeks on site.

    Do I need an architect for a house extension?

    While you are not legally required to use an architect, it is very strongly recommended. An architect will ensure your extension makes the most of the available space and light, complies with planning and building regulations requirements, is designed to a professional standard that adds value to your home, and is built in accordance with a detailed specification that protects you from cost overruns. Crown Architecture provides a complete design-to-completion service.

    What is a side return extension?

    A side return extension fills in the narrow passage (typically 1–1.5 metres wide) that runs alongside a Victorian or Edwardian terraced or semi-detached house. By infilling this space, the kitchen is widened significantly. This type of extension is very popular in London and can transform a dark, narrow kitchen into a wide, light-filled kitchen-diner. They typically cost £20,000–£40,000 in London.

    How do I find a reliable builder for my extension?

    The most reliable way to find a good builder is through recommendation from friends, family, or neighbours who have had similar work done. Crown Architecture can also recommend trusted local contractors from our established network. Always obtain at least three competitive quotes from contractors who have tendered on the same detailed drawings and specification — this ensures you are comparing like for like.

  • Do I Need Planning Permission for a Rear Extension UK

    Modern rear extension on a UK semi-detached house

    Do I Need Planning Permission for a Rear Extension in the UK?

    One of the most common questions we receive at Crown Architecture is whether a rear extension needs planning permission. The answer depends on your property type, the size of the extension, and where you live. In many cases, a rear extension can be built under permitted development rights without the need for a planning application. This guide explains everything you need to know.

    What Is Permitted Development?

    Permitted development (PD) rights are a set of nationally defined planning permissions granted to homeowners in England by Parliament. They allow certain types of work — including rear extensions — to be carried out without the need to submit a planning application to your local council, provided the works fall within defined limits and conditions.

    Permitted development rights apply to houses (not flats, maisonettes, or commercial properties). They were introduced to speed up minor domestic works and reduce the administrative burden on local planning authorities. You can learn more in our guide on planning permission in London.

    Rear Extension Size Limits Under Permitted Development

    For single-storey rear extensions in England, the standard permitted development limits are:

    • Terraced and semi-detached houses: Up to 3 metres beyond the rear wall of the original house
    • Detached houses: Up to 4 metres beyond the rear wall of the original house

    The Neighbour Consultation Scheme (Larger Home Extension Scheme)

    Under the Neighbour Consultation Scheme (sometimes called the larger home extension scheme), larger rear extensions are permitted development subject to a prior approval process. The limits are:

    • Terraced and semi-detached houses: Up to 6 metres beyond the rear wall
    • Detached houses: Up to 8 metres beyond the rear wall

    Under this scheme, you must notify the local planning authority, who will consult with adjoining neighbours. If no objections are received within 21 days, the extension can proceed. If objections are received, the local planning authority decides whether to grant prior approval based on the impact on the amenity of adjoining properties.

    Conditions Required for Permitted Development

    Even where the size limits are met, a rear extension must also comply with these conditions to be permitted development:

    • Maximum height of 4 metres for a pitched roof, or 3 metres for any other roof type
    • Where within 2 metres of the boundary, the eaves height must not exceed 3 metres
    • No verandas, raised platforms, or balconies
    • Materials must be of a similar appearance to the existing house
    • The extension must not extend beyond the side elevation of the original house
    • The extension, together with any other extensions, must not exceed 50% of the total area of land around the original house

    When Will You Need Planning Permission for a Rear Extension?

    You will need to apply for full planning permission if:

    • The extension exceeds the size limits above (even under the larger scheme)
    • Your property is a flat or maisonette (PD rights do not apply)
    • The extension is two-storey (separate rules apply — see below)
    • The works do not comply with the conditions listed above
    • Your home’s PD rights have been removed by an Article 4 Direction
    • You live in a conservation area, AONB, National Park, or World Heritage Site and the extension would be visible from a highway
    • You live in a listed building (listed building consent is required in addition to any planning permission)

    Two-Storey Rear Extensions

    Two-storey rear extensions are permitted development up to 3 metres beyond the rear wall of the original house, provided the roof pitch matches the existing house, and there are no windows on the side elevation or any balconies. However, if the extension is within 7 metres of the rear boundary, you will need planning permission.

    Conservation Areas and Article 4 Directions

    If your property is in a conservation area, permitted development rights are more restricted. Any rear extension that is visible from a public road or footpath will require planning permission, even if it would otherwise be permitted development.

    An Article 4 Direction is a local planning authority order that withdraws some or all permitted development rights in a defined area. They are commonly used in conservation areas, but can also apply to individual streets or properties. To find out if your property is affected, check with your local planning authority or use the planning portal.

    At Crown Architecture, we work extensively in conservation areas across Hackney, Islington, and other London boroughs where Article 4 Directions are common.

    Lawful Development Certificate

    Even if your rear extension is permitted development, it is strongly advisable to apply for a Lawful Development Certificate (LDC) from your local planning authority. An LDC is a formal, legally binding document confirming that your works are lawful.

    Without an LDC, you may encounter difficulties when selling your property, as solicitors and buyers will want evidence that any works were lawfully carried out. An LDC application costs around £120 (half the planning fee) and typically takes 8 weeks to process.

    How Crown Architecture Can Help

    Crown Architecture & Structural Engineering provides a comprehensive service for rear extensions, from initial feasibility through to planning and building regulations approval. We will assess your property, advise on the most appropriate route, and prepare all the drawings and documentation needed to get your project approved and built.

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    Frequently Asked Questions

    Can I build a 4-metre rear extension without planning permission?

    On a detached house, a single-storey rear extension up to 4 metres deep is standard permitted development. On a terraced or semi-detached house, the standard PD limit is 3 metres. However, under the Neighbour Consultation Scheme, you may be able to build up to 8 metres (detached) or 6 metres (semi/terraced) subject to a prior approval process.

    Do I need planning permission for a rear extension on a flat?

    Yes. Permitted development rights apply to houses only, not flats or maisonettes. If you live in a flat and wish to extend, you will need to apply for full planning permission regardless of the size of the works.

    How close to my neighbour’s boundary can I build a rear extension?

    There is no minimum distance from a rear boundary set by permitted development rules for single-storey rear extensions, provided the total depth limit is not exceeded. However, where the extension is within 2 metres of a side boundary, the eaves height must not exceed 3 metres. You may also need to serve a Party Wall Notice on your neighbour if the works are within 3 metres of their property.

    What is the maximum height for a rear extension under permitted development?

    The maximum permitted development height for a single-storey rear extension is 4 metres for a pitched roof, or 3 metres for a flat or other roof type. Where the extension is within 2 metres of a boundary, the eaves must not exceed 3 metres regardless of the total height.

    What is a Lawful Development Certificate and do I need one?

    A Lawful Development Certificate (LDC) is a formal document from the local planning authority confirming that your works are lawful under permitted development. While not strictly required before building, it is strongly recommended as it provides legal certainty, protects you when selling the property, and confirms compliance. Crown Architecture can apply for an LDC on your behalf as part of our service.

  • Building Regulations vs Planning Permission — What’s the Difference

    Architect reviewing building regulations documents

    Building Regulations vs Planning Permission — What is the Difference?

    Homeowners planning an extension, loft conversion, or other building project frequently confuse planning permission and building regulations. They are two entirely separate approval systems, administered by different parts of your local council, covering different aspects of your project. Understanding the difference is essential before you start any project. This guide from Crown Architecture & Structural Engineering explains both systems clearly.

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    The Key Difference

    In simple terms:

    • Planning permission controls whether you are allowed to build something — it is about the principle of the development, its size, appearance, and impact on the surrounding area.
    • Building regulations control how you build it — they are technical standards covering structural integrity, fire safety, thermal performance, drainage, and the health and safety of the people who will use the building.

    You may need one, the other, or both, depending on what you are doing. Some projects require planning permission but not building regulations (rare). Most require building regulations but not planning permission. Major works usually require both.

    What Does Planning Permission Cover?

    Planning permission considers the visual impact and amenity of proposed development. When assessing an application, a planning officer will consider:

    • The size, scale, and massing of the proposed development
    • Its appearance and materials, and whether it is appropriate in the context of the street and neighbourhood
    • The impact on the privacy and amenity of neighbouring properties (overlooking, overshadowing, loss of outlook)
    • Impact on protected trees, ecology, or heritage assets
    • Car parking, access, and highway safety
    • Compliance with the National Planning Policy Framework, Local Plan, and any neighbourhood plan policies

    Planning permission is administered by the local planning authority (LPA), which is typically your district or borough council. It is a democratic process — applications are publicly advertised, neighbours can comment, and decisions can be made by an elected planning committee.

    What Do Building Regulations Cover?

    Building regulations are technical minimum standards that apply to most building work in England and Wales. They are set out in the Building Regulations 2010 and the Approved Documents that support them. The key Parts are:

    PartWhat It Covers
    Part AStructure — loads, foundations, walls, floors, roofs
    Part BFire Safety — means of escape, fire spread, access for fire services
    Part CResistance to Contaminants and Moisture — damp-proofing, ground contamination
    Part EResistance to Sound — sound insulation between dwellings
    Part FVentilation — natural and mechanical ventilation
    Part LConservation of Fuel and Power — insulation, energy efficiency, U-values
    Part MAccess to and Use of Buildings — accessibility requirements
    Part PElectrical Safety — notifiable electrical work

    Building regulations are enforced by building control, which is either the local authority building control service or an approved inspector (a private sector body). Building control is a technical process, not a democratic one — there are no public consultations or committees.

    When Do You Need Each?

    Type of WorkPlanning Permission?Building Regs?
    Rear extension (within PD limits)No (permitted development)Yes
    Rear extension (exceeds PD limits)YesYes
    Loft conversionOften no (PD)Yes
    Internal structural alterationNoYes
    Change of use (e.g. office to flat)Usually yes (or prior approval)Yes
    New fence (under 2m)NoNo
    Garage conversionUsually no (PD)Yes

    Full Plans vs Building Notice

    There are two main ways to obtain building regulations approval:

    Full Plans Application: You submit detailed drawings and specifications to building control before work starts. Building control reviews and approves the plans before construction begins. This is the recommended approach for most projects, especially complex ones, because it identifies any compliance issues before work starts rather than after.

    Building Notice: You notify building control that work is starting but do not submit detailed drawings for prior approval. Building control inspects the work as it progresses. This is quicker to start but carries the risk that non-compliant work may need to be undone and rebuilt.

    Crown Architecture prepares full plans applications as standard, ensuring your project is properly documented and building control approval is obtained before work begins.

    Inspections and the Completion Certificate

    Throughout the construction process, the building control officer will carry out inspections at key stages — typically: commencement, foundations, damp-proof course, structural steels, insulation, drainage, and final completion. It is the contractor’s responsibility to notify building control at each stage.

    Once all work is satisfactorily completed, building control issues a Completion Certificate. This is a crucial document — it confirms that the building work has been inspected and complies with the building regulations. Without it, you may encounter difficulties when selling the property.

    Consequences of Non-Compliance

    Carrying out building work that requires building regulations approval without obtaining it is a criminal offence. The local authority can issue an enforcement notice requiring you to open up or demolish non-compliant work. When you come to sell your property, a solicitor will ask for evidence of building regulations compliance for any notifiable work. If you cannot provide it, you may need to obtain indemnity insurance or retrospective regularisation, which is costly and uncertain.

    Crown Architecture manages the building regulations process on every project we undertake, ensuring you receive your completion certificate. For more information on the end-to-end process, see our guides on loft conversions and house extensions in London.

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    Frequently Asked Questions

    Can I get building regulations approval without planning permission?

    Yes. Many projects require building regulations approval but not planning permission — for example, a rear extension carried out under permitted development rights still needs building regulations approval. Building control and planning are entirely separate systems. Building control will not check whether you have obtained planning permission, and the planning authority will not check whether you have building regulations approval. It is your responsibility to ensure you have all the necessary approvals for your project.

    What happens if I sell my house without a building regulations completion certificate?

    If you cannot provide a completion certificate for notifiable building works, your solicitor will flag this as a potential issue in the conveyancing process. The buyer’s solicitor may require you to obtain indemnity insurance to cover the risk of enforcement action. Alternatively, you can apply for a regularisation certificate from the local authority, which involves an inspection of the completed work. Neither option is ideal — the best approach is to ensure all work is properly signed off at the time of construction.

    Do I need building regulations for a kitchen renovation?

    A like-for-like kitchen renovation (replacing units and appliances in the same positions) does not typically require building regulations approval. However, if you are moving a gas supply, adding new electrical circuits, or relocating drainage, individual elements may be notifiable. Gas work must be carried out by a Gas Safe registered engineer, and certain electrical work must be carried out by or notified to building control by a Part P registered electrician.

    How much do building regulations applications cost?

    Building regulations fees are set by each local authority or approved inspector and vary depending on the type and scale of work. For a typical single-storey rear extension, the full plans fee is typically £800–£1,200. For a loft conversion, expect to pay £1,000–£1,500. Fees for larger or more complex projects are higher. Crown Architecture includes the building regulations drawings in our fee — you pay the application fee directly to building control.

    What is an approved inspector and should I use one?

    An approved inspector is a private sector body (or individual) registered with the Construction Industry Council (CIC) to carry out building control work. They provide an alternative to local authority building control. Approved inspectors can sometimes offer a more responsive service and are often preferred for commercial and larger residential projects. For straightforward domestic projects, local authority building control is perfectly adequate and is the most commonly used route.

  • How Much Does a Loft Conversion Cost in London 2025?

    loft conversion cost London 2025 - Crown Architecture

    How Much Does a Loft Conversion Cost in London 2025?

    Loft Conversion Costs in London 2025

    A loft conversion in London typically costs between £35,000 and £80,000 depending on the type, size and specification. Here is a breakdown of the main loft conversion types and their typical costs in 2025.

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    Dormer Loft Conversion Cost

    A dormer loft conversion is the most popular type in London, typically costing £40,000–£60,000. A rear dormer adds a box-shaped extension to the back of your roof, creating a full-height room with vertical walls and a flat or pitched roof.

    Mansard Loft Conversion Cost

    A mansard conversion is more extensive, typically costing £50,000–£80,000. It involves altering the roof structure to create a near-vertical rear wall, maximising headroom and floor space. Mansard conversions usually require planning permission.

    Hip-to-Gable Loft Conversion Cost

    A hip-to-gable conversion suits semi-detached and detached houses with a hipped roof. Costs range from £45,000–£70,000. This type extends the gable end wall to create more floor space.

    What Affects the Cost?

    • Type of conversion (dormer, mansard, hip-to-gable, Velux)
    • Size of the loft space
    • Specification of finishes
    • Structural work required
    • Planning permission fees (if required)
    • Building regulations fees
    • Location within London

    Frequently Asked Questions

    Do I need planning permission for a loft conversion?

    Most loft conversions in London fall under permitted development rights and do not require planning permission, as long as they meet certain limits and conditions. Mansard conversions typically do require planning permission. Crown Architecture will advise you on whether your project needs permission.

    How long does a loft conversion take?

    A typical loft conversion takes 8–12 weeks to complete once the planning and building regulations approvals are in place. The design and planning phase typically takes 6–12 weeks before work can begin on site.

    Does a loft conversion add value to my home?

    Yes — a loft conversion typically adds 15–25% to the value of your home in London. It is one of the most cost-effective ways to add space and value.

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