Crown Architecture & Structural Engineering
House Extension Plans in Harrow
Extending a home in Harrow requires plans that work within the constraints of the existing building, neighbouring properties, and Harrow's local planning policies. Crown Architecture prepares house extension plans — from single-storey kitchen extensions to multi-storey side or rear projects — tailored to your specific property and the requirements of London Borough of Harrow.
Project imagery
House Extension Plans in Harrow — project examples
Residential project, drawing-package, and planning context imagery relevant to this service and borough.
Local planning context
Planning in Harrow
Harrow homeowners who engage with the local planning framework early — understanding conservation area boundaries, permitted development limits, and local design guides — consistently achieve better outcomes than those who treat planning as an afterthought.
Permitted development rights allow many extensions and loft conversions in Harrow to proceed without a planning application, but the limits on height, depth, and materials are specific. A Lawful Development Certificate is the safest way to confirm the position, particularly for properties in conservation areas or affected by Article 4 directions.
Where a Harrow project falls within permitted development limits, a Lawful Development Certificate from London Borough of Harrow provides formal confirmation that no planning permission is required. This is particularly valuable in Harrow where conservation area boundaries and Article 4 zones can affect rights that would otherwise apply, and where mortgage lenders and future buyers often require documentary evidence.
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Conservation Areas in Harrow
Conservation areas are one of the most significant planning considerations in Harrow. With 27 designated conservation areas across the borough — including Little Common Conservation Area, Stanmore, The Grimsdyke Estate and Brookshill Conservation A, West Drive Conservation Area, Pinnerwood Farm Conservation Area Pinner — a large proportion of residential properties fall within a setting where the character and appearance of development is scrutinised more carefully.
Conservation areas affect what is permitted under the General Permitted Development Order, often restricting changes to windows, doors, cladding, satellite dishes, and side extensions without a planning application. In some parts of Harrow, works that would be automatic elsewhere require full permission and design justification.
Conservation areas affect what is permitted under the General Permitted Development Order, often restricting changes to windows, doors, cladding, satellite dishes, and side extensions without a planning application. In some parts of Harrow, works that would be automatic elsewhere require full permission and design justification.
- Little Common Conservation Area, Stanmore
- The Grimsdyke Estate and Brookshill Conservation A
- West Drive Conservation Area
- Pinnerwood Farm Conservation Area Pinner
- Waxwell Close Conservation Area Pinner
- East End Farm Conservation Area Pinner
- RAYNERS LANE
- Waxwell Lane Conservation Area Pinner
- Pinner Hill Estate Conservation Area
- Pinnerwood Park Estate Conservation Area PART 1
- West Towers Conservation Area Pinner
- Pinner High Street Conservation Area Pinner
Service information
House Extension Plans
Our extension plans service for Harrow homeowners begins with a site appraisal that confirms the planning route, the permitted development envelope, and the likely constraints for the specific proposal. We present design options before fixing on the approach, so you can make an informed decision.
House extension plans for Harrow properties need to address the specific constraints of the site: plot depth, proximity to neighbouring windows, the character of the street, and any conservation area or Article 4 designation that changes what is achievable.
Once the design is agreed, we take the extension plans through planning permission (or permitted development confirmation), building regulation approval, and the construction-issue stage, providing a coordinated set of information for each phase.
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Our Process for Harrow Projects
Submissions to London Borough of Harrow are made via the Planning Portal using the householder application form, accompanied by the full drawing set and any required supporting documents. We monitor the application throughout the assessment period, responding to requests for information and liaising with the case officer as required.
All projects in Harrow begin with a free consultation call where we discuss the brief, the property, and the likely planning route. We then issue a detailed fixed-fee proposal before any survey or design work begins, so there are no surprises on costs.
- Free initial consultation and brief assessment
- Fixed-fee proposal covering all agreed services
- Measured survey of the existing property
- Design options and client review
- Planning drawing preparation
- Submission to London Borough of Harrow
- Officer liaison and application management
- Post-consent building regulation package
Service information
Why Choose Crown Architecture in Harrow
Crown Architecture & Structural Engineering Ltd has worked across all 32 London boroughs including Harrow. Our experience with London Borough of Harrow's planning requirements, validation standards, and officer expectations means we can prepare applications that progress efficiently and with a high first-time approval rate.
We are a full-service practice — architecture, structural engineering, and planning consultancy under one roof. For Harrow projects, this means the planning drawings, structural calculations, and building regulation package are all coordinated by the same team rather than produced by separate consultants whose information does not align.
Our registered office is at 71–75 Shelton Street, London WC2H 9JQ (company number 16297850). We are contactable at +44 7950 114633 and cover all projects across London and the home counties, including all areas of Harrow.
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Housing Stock and Local Character in Harrow
Harrow is a north-west London suburb characterised by inter-war residential development, with Harrow on the Hill providing a historic core and significant conservation area coverage. This character shapes what planning applications are likely to succeed and how they need to be presented to London Borough of Harrow.
The residential stock in Harrow consists principally of inter-war semi-detached and detached houses dominate, with Victorian and Edwardian terraces in the older Harrow areas and some new-build on former commercial sites. Understanding how the existing building type responds to extension or alteration is the starting point for any design brief — it defines the structural approach, the planning sensitivities, and the opportunities for the project.
Key areas within Harrow where we regularly work include Harrow on the Hill, Wealdstone, Pinner, Stanmore. Each of these areas has its own micro-character, planning history, and in some cases specific conservation area or Article 4 designations that affect what is achievable on any given street.
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House Extension Plans — Further Information
Extension plans for Harrow homes are most effective when they address both the planning question and the construction question simultaneously. A plan that wins planning permission but requires significant redesign for building regulation compliance wastes time and can cause costs to escalate. Our integrated approach coordinates both from the first design stage.
For Harrow homeowners who are also considering loft conversion or basement work alongside an extension, we can prepare a masterplan that shows how all the works relate to each other — a useful planning tool both for staging the works and for showing London Borough of Harrow the overall intention if the planning applications are to be submitted simultaneously or in sequence.
Service information
Building Regulations in Harrow
Building regulations apply to most construction works in Harrow regardless of planning permission status. Extensions, loft conversions, structural alterations, and changes to drainage or electrics all require compliance with the relevant Parts of the Building Regulations, verified by London Borough of Harrow building control or a registered building control approver.
Building regulation approval in Harrow runs in parallel to planning consent — they are two separate legal processes. We manage both for clients who wish to use Crown Architecture for the full project, or we can work alongside a client's own building contractor or structural engineer where preferred.
Common questions
House Extension Plans in Harrow — frequently asked questions
Answers to the planning, design, and regulatory questions we are most often asked about House Extension Plans in Harrow.
What is an under-build extension and does it need planning permission in Harrow?
An under-build or basement extension involves excavating below ground level to create a new habitable space. In Harrow, basement extensions almost always require planning permission and are subject to additional assessment around structural stability, flood risk, and impact on neighbouring properties. London Borough of Harrow has specific policies on basement development and the drawings must address these comprehensively.
How do I know how big an extension I can build before planning permission is needed in Harrow?
The permitted development limits for extensions in Harrow depend on the property type, existing extensions, plot constraints, and whether any designations apply. We confirm the exact limits as part of our initial assessment — which is included in our design service. We will also tell you when a Lawful Development Certificate is advisable to formally confirm the position before or after works.
Can I build a two-storey extension in Harrow?
Yes. Two-storey rear extensions in Harrow require planning permission in most cases (only the rarest circumstances fall within permitted development for two storeys). London Borough of Harrow assesses two-storey extensions against their relationship to the rear boundary, impact on neighbouring light, and the scale and design relative to the host building and street. We prepare the full planning application including a design justification where required.
Do I need party wall agreements for an extension in Harrow?
If your Harrow extension involves building on or near the boundary with a neighbouring property, excavating within three or six metres of a neighbour's foundations, or carrying out works to a shared wall, the Party Wall etc. Act 1996 applies. You must serve notice on adjoining owners before works start. We can introduce a party wall surveyor from our network to manage the process.
What is an orangery or extension and what planning applies in Harrow?
Orangeries and conservatories attached to houses in Harrow are generally treated the same as extensions for planning purposes. The key distinction for building regulations is whether the space is heated and thermally separated from the house — fully integrated heated extensions have full building regulation compliance requirements, while traditional glazed structures meeting specific criteria may have exemptions.
How long does it take to get planning permission for an extension in Harrow?
From starting the drawings to receiving a planning decision in Harrow, a typical householder application takes twelve to twenty weeks. This includes two to four weeks for drawings, one to two weeks for submission and validation by London Borough of Harrow, and eight weeks for the application to be determined. Our programme is discussed and agreed at the start of each project.
How far back can I extend my house in Harrow without planning permission?
Under current permitted development rights, a detached house in Harrow can extend up to eight metres to the rear (single storey) or three metres (two storey) without planning permission, subject to the prior approval notification scheme for larger extensions. Semi-detached and terraced houses can extend up to six metres (single storey) or three metres (two storey) via the same scheme. These limits assume no conservation area or Article 4 direction applies.
What is the prior approval notification scheme for large extensions in Harrow?
Under the neighbour consultation scheme, extensions between four and eight metres for detached houses, or three and six metres for other house types, can proceed as permitted development in Harrow subject to a prior approval notification to London Borough of Harrow. Neighbours are consulted and the council assesses the impact on amenity. Most applications are approved, but the process takes up to eight weeks from notification.
Can I extend my house in Harrow if it is in a conservation area?
Yes, but permitted development rights are often restricted or removed in conservation areas in Harrow. Rear extensions in conservation areas typically cannot exceed one storey and must use materials that match or complement the host building. In some conservation areas, even single-storey rear extensions require a planning application rather than being automatically permitted. We confirm the specific restrictions for your property as part of the initial assessment.
What is a side return extension and does it need planning permission in Harrow?
A side return extension fills in the narrow strip of land at the side of a Victorian or Edwardian terraced house, typically extending the ground floor outwards. In most parts of Harrow, side return extensions of a single storey can be built under permitted development, but in conservation areas they often require planning permission. The extension typically needs to be set back from the front elevation and use matching materials.
Who is the planning authority for Harrow?
The planning authority for Harrow is London Borough of Harrow. All planning applications for residential and commercial developments in Harrow are submitted to and determined by London Borough of Harrow, which also provides pre-application advice and manages the planning enforcement function for the borough.
What types of development need planning permission in Harrow?
In Harrow, planning permission is required for: new buildings; extensions that exceed the permitted development limits; changes of use (e.g. from residential to commercial); demolition of protected structures; and any works that affect a listed building or its curtilage. Smaller extensions, loft conversions within volume limits, and outbuildings within the curtilage may fall within permitted development, but constraints apply in conservation areas and Article 4 zones.
Is Crown Architecture registered with Companies House?
Yes. Crown Architecture & Structural Engineering Ltd is registered at Companies House under company number 16297850. Our registered address is 71–75 Shelton Street, London WC2H 9JQ. We carry professional indemnity and public liability insurance appropriate to the scale of residential and small commercial projects we undertake.
What are the core contact details for Crown Architecture?
Crown Architecture & Structural Engineering Ltd can be reached by telephone at +44 7950 114633 or via our website contact form. Our address is 71–75 Shelton Street, London WC2H 9JQ. We cover all projects in Harrow and across London and the home counties.
How does Crown Architecture price house extension plans services in Harrow?
Our fees for house extension plans in Harrow are fixed-price, agreed before any work begins. The fee depends on the scale and complexity of the project, whether conservation area or listed building constraints apply, and the scope of services required (planning only, building regulations, or combined). We provide a detailed fee proposal after a free initial consultation.
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