Harrow · London · North West London

House Extension & Loft Conversion
Architects in London & Harrow

Firstly, we are a Harrow-based architecture studio specialising in house extensions, loft conversions, and planning permission. Additionally, our team provides full principal designer support across London and North West London.

  • RIBA-trained architects
  • Fixed-fee proposals
  • Free consultation

What We Do

Four services,
one seamless journey.

Firstly, every project runs under one roof — with one point of contact and one fixed fee. Additionally, we handle everything from the first measured survey to the final building-control sign-off. No handoffs, no surprises.

Rear Extensions

For example, our house extension architects design light-filled kitchens, garden rooms and open-plan living spaces. Consequently, every extension respects both your home's character and Harrow Council's planning policies.

  • Planning drawings
  • Building Regs
  • Structural coordination
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Loft Conversions

Furthermore, whether you need a dormer, hip-to-gable, mansard or rooflight conversion, we turn unused roof space into a bedroom, study or master suite — without losing head height.

  • Feasibility first
  • Party wall advice
  • Full design package
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Planning Permission

Moreover, we prepare drawings, forms, council liaison and appeals. As a result, we know exactly what Harrow Council expects — and how to secure planning permission without wasted months.

  • Householder apps
  • Lawful development
  • Pre-app advice
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Principal Designer

Ultimately, our CDM 2015 compliance, risk management and construction-phase oversight keep your project safe, legal and on programme. In other words, we look after every detail from start to finish.

  • CDM 2015
  • Risk register
  • Site oversight
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However, if you're not sure which service you need, simply tell us about the house — we'll tell you what's possible.

Book a Free Consultation
extension architect London
Est. 2016 Based in Harrow, London

The Studio

A Harrow studio,
built on local knowledge.

We are a Harrow-based architecture studio offering four core services — rear extensions, loft conversions, planning permission and Principal Designer support. Every project begins with listening: how do you want to live, and what is the site telling us?

From there we handle everything — measured surveys, planning drawings, structural coordination and construction oversight. RIBA-trained, deeply familiar with Harrow Council's planning policies, and trusted by homeowners across London and North West London.

  • RIBA-trained architects
  • Local planning expertise
  • Fixed-fee proposals
  • End-to-end support
Extendopedia Studio Harrow · Greater London

How We Work

Five steps,
one clear journey.

From the first phone call to the final sign-off, you always know exactly where your project stands — what's happening now, what's next, and what it costs. However, there is no jargon, no black boxes, and no surprises.

Typical timeline 6–10 months, end to end

Discovery & Feasibility

First, we hold a free consultation — either by phone or on site. We listen to how you want to live, review your property's constraints, and give you an honest view of what's achievable.

Week 1

Measured Survey

Next, we visit your home and record every dimension, level and boundary. This is the foundation every drawing is built on — accuracy now saves weeks later.

Week 2

Concept Design

Meanwhile, we prepare sketch layouts, 3D visuals and material palettes. We present two or three options, then refine the one you love — until it feels exactly right.

Weeks 3–6

Planning & Approvals

Subsequently, we handle the full planning application, including drawings, forms and council liaison. We manage the submission and respond to any queries through to approval.

Weeks 7–18

Technical Design & Build

Finally, we manage building regulations, structural coordination and construction oversight. We stay involved on site until the last snag is closed — and the keys are yours.

Weeks 19–40

Ready to start step one? The first conversation is free — and there's no obligation.

Book a Free Consultation
180+ Projects delivered
4.9 Average client rating
9 Years in Harrow
92% Referred or repeat clients

What Clients Say

Trusted by homeowners
across North West London.

Most of our work comes from people who heard about us from a neighbour, a friend, or a builder we've worked with for years. As a result, we've built a reputation for honest advice across Harrow and North West London. Here's what a few of them had to say.

They understood our house before we did. The planning application went through first time — and the finished rear extension is the room we spend every evening in.

Sarah M. Rear extension · Harrow HA2

Fixed fee, clear timeline, no chasing. Additionally, the Principal Designer role meant the whole build ran smoothly — every contractor on site knew exactly what was expected.

Daniel K. Loft conversion · Pinner

We interviewed three studios. However, Extendopedia was the only one who told us what we couldn't do — and why. That honesty is exactly what we needed.

Priya R. Kitchen extension · Stanmore

We'd been putting off the loft for years. They made the whole thing feel simple — survey in week two, drawings in week five, approval by spring.

James T. Loft conversion · Harrow HA1

Every question got a straight answer. No upselling, no vague fees. When the build started, the site was tidy, on schedule and genuinely well run.

Anita N. Side-return · Northwood

We came to them with a half-formed idea. For example, they took it seriously, drew two versions, and helped us land on something better than we'd imagined.

Rachel C. Double-storey · Kenton

The drawings were ready before our builder even asked for them. Anything the council queried had already been answered — that's why the build never stalled.

Michael B. Wrap-around extension · Hatch End

We wanted somewhere for my mother to stay that still felt like part of the house. They got it right on the first drawing — we changed almost nothing.

Fatima A. Garage conversion · Wealdstone

Two years on, the garden room is still the best money we've spent. They were honest about the budget from day one, and it landed exactly where they said it would.

Tom & Ellie W. Garden room · Ruislip
Rated 4.9 out of 5 from 87 verified reviews on Google and Houzz

Questions, Answered

The things homeowners
ask us first.

Straight answers to the questions we hear most — planning, cost, timelines and everything in between. However, if yours isn't here, the team is one call away.

Do I need planning permission for a rear extension?

Many rear extensions fall under Permitted Development — meaning no formal planning application is needed, provided they meet the rules on depth, height, materials and proximity to boundaries. Generally, single-storey rear extensions can go up to 3–6 metres depending on your property type.

However, if your plans exceed those limits, or your property is in a conservation area, listed, or has had previous extensions, you'll need a full householder application. We check this during the free consultation and tell you honestly which route applies.

How long does planning permission take?

Harrow Council's statutory determination period is 8 weeks for householder applications. In practice, most of ours are decided within 6–10 weeks from submission.

Before submission, allow 3–5 weeks for us to prepare the drawings, forms and supporting documents. Additionally, if a pre-application enquiry is worthwhile — usually for more complex or borderline schemes — add another 4–6 weeks for the council's response.

How much does a rear extension or loft conversion cost?

Our design fees are fixed and quoted upfront — typically £2,500–£5,500 depending on scope. This covers measured survey, concept design, planning drawings and the planning submission.

Build costs are separate and paid directly to your contractor. As a rough London guide, expect £2,400–£3,200 per m² for a rear extension and £45,000–£75,000 for a typical loft conversion. Subsequently, we'll give you a realistic range once we've seen the property.

What's the difference between planning permission and building regulations?

Planning permission is about whether you're allowed to build it — how it affects neighbours, the street scene and the local area. It's granted by the council's planning department.

Building Regulations are about how it's built — structural safety, fire resistance, insulation, drainage, ventilation. These are separate approvals, checked by a Building Control body. Furthermore, they are required regardless of whether planning permission is needed.

Do you manage the build, or just provide the drawings?

Our core service is design and planning — measured survey, drawings, planning submission and building regulations. Most clients then appoint a contractor directly.

If you'd like us to stay involved through construction, we offer Principal Designer support under CDM 2015 — reviewing the site, coordinating risk and checking the work matches the drawings. It's optional, but recommended for larger or more complex projects.

Which areas do you cover?

We're based in Harrow and work across North West London — including Pinner, Stanmore, Northwood, Kenton, Wealdstone, Ruislip, Wembley and Edgware.

Meanwhile, we also take on selected projects in surrounding boroughs. If you're outside our usual radius, get in touch — for the right project we'll travel.

Do I need a Principal Designer under CDM 2015?

CDM 2015 applies to any project with more than one contractor — which includes almost every domestic extension and loft conversion. The role of Principal Designer was introduced to make sure design-stage risks are identified, managed and handed over cleanly to the builder.

For a domestic client, the duties usually fall to the principal contractor if you don't appoint a Principal Designer in writing. Consequently, we offer this role directly and can take it on from the first conversation.

How do I get started?

Book a free consultation — by phone or on site. We'll ask a few questions about the property, what you're hoping to do, and roughly what budget you have in mind. Ultimately, you'll leave the call with a clear view of what's achievable and what it's likely to cost.

If you'd like to proceed, we'll send a fixed-fee proposal in writing within 2 working days. Nothing is billable until you approve it.