Harrow · HA1 · HA2 · HA3
House Extensions in Harrow
Suburban borough with 1930s semis — hip-to-gable lofts and rear extensions common. Single and double-storey extensions delivered as a fixed-scope design and build package.
Postcodes covered
Quick answer
Builderr delivers house extensions across Harrow — HA1, HA2, HA5, HA7 and HA8. Typical Harrow extension cost £42,000–£100,000 over 11–22 weeks. Side returns, single and double-storey rears on interwar semis dominate. Generous rear gardens enable 6m PD Larger Home Extension across most non-CA postcodes.
Harrow
House Extensions specialists across Harrow.
We deliver house extensions projects across the full Harrow postcode set — HA1, HA2, HA3, HA5, HA7, HA8. Suburban borough with 1930s semis — hip-to-gable lofts and rear extensions common.
Every Harrow project includes a free desk-based planning assessment before we quote, so you know upfront whether permitted development, prior approval, or full planning applies to your specific address. Our local project manager for Harrow has detailed knowledge of the planning department's preferences, the conservation area boundaries, and the common construction details for the prevailing housing stock here.
Quotes for Harrow house extensions are fixed-scope after a site survey, valid for 60 days, and never carry provisional sums or open-ended day rates. Every project includes our 10-year structural warranty and 12-month defects period.
Planning in Harrow
Local planning rules for house extensions in Harrow.
Harrow's conservation areas include Pinner Village, Stanmore Hill, Hatch End Village, Harrow on the Hill, Headstone Manor and parts of Wealdstone. Harrow on the Hill is the borough's most protected zone with listed building density and strict design rules. Outside heritage zones, Harrow retains strong PD rights with prior approval commonly used for 6m rear extensions and hip-to-gable lofts. Two-storey side extensions are routinely approved on the prevailing semi stock.
Our planning team handles the full submission for Harrow addresses including drawings, Design and Access Statements where required, and pre-application consultation with the council. We tell you whether your house extension is permitted development, prior approval, or full planning before you sign anything.
Builderr vs other London builders.
The construction industry has a wide distribution of operators. Here's what changes between a directly-employed, fixed-scope outfit and the alternatives.
| Criterion | Builderr | Typical London builder | Cowboy outfit |
|---|---|---|---|
| Labour model | Directly employed team (PAYE) | Mixed subcontract gangs | Day-rate cash labour |
| Pricing | Fixed-scope itemised quote | Estimate + provisional sums | Verbal price + variations |
| Design & engineering | In-house architect + SE | Outsourced, separate billing | Builder draws on the back of an envelope |
| Planning + LDC handled | Yes — included in price | Often charged extra | Builder asks you to apply |
| Party wall surveyors | Instructed by us | Your responsibility | Skipped (illegal) |
| Building control | Plans + site inspections booked by us | Building Notice route | Not registered |
| Project management | Dedicated PM, weekly photo updates | Foreman doubles up | Owner-manager juggles 5 jobs |
| Payment schedule | Stage payments against signed-off milestones | Weekly invoices | Cash up front |
| Insurance | £10M PL + 10yr structural warranty | £2–5M PL only | No documented cover |
| Snags at handover | <3 typical | 20–30 typical | Walk-off mid-job common |
| Variation creep | 0% — fixed scope | +15–25% over original quote | +40%+ regularly |
Save £27,000–£60,750 on a house extension in Harrow.
Industry data (FMB, RICS, Which? Trusted Trader 2024) shows the average London construction project overruns by 18–22% on cost and 25–35% on time. Fixed-scope contracts with a single accountable team eliminate that variance. The savings above assume a typical project at £135,000.
FAQ
House Extensions in Harrow.
How much does a house extension cost in Harrow?
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Most house extensions projects in Harrow cost £50,000–£220,000 depending on size, spec and structural complexity. Inner London postcodes typically sit toward the upper end; outer borough projects trend mid-range. All Builderr Harrow quotes are fixed-price with no provisional sums.
Do I need planning permission for a house extension in Harrow?
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Planning rules vary across Harrow. We check permitted development eligibility, conservation area status and any Article 4 directions affecting your specific postcode before quoting. Many house extensions fall under permitted development, but conservation areas and listed buildings need full planning.
How long does a house extension take in Harrow?
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Typical timeline is 10–20 weeks on site, plus 4–8 weeks for design, structural engineering and approvals. If full planning is required (conservation areas, mansards, larger extensions), add 8–12 weeks for the planning decision before site start.
Do you have house extension references in Harrow?
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Yes — we maintain a live reference list for Harrow and can connect you with two or three completed clients within the borough. We've delivered projects across nearly every Harrow postcode since 2022, so most prospective clients can visit a completed project nearby.
What's included in a Builderr house extension quote in Harrow?
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Every Harrow quote covers structural design, party wall notices and surveyor coordination, planning or prior approval submission where required, building control, full build, snagging and a 10-year structural warranty. Kitchen units, sanitaryware and bespoke finishes are itemised separately so you can flex spec without losing fixed-price certainty on the build.
Other services in Harrow
Get a Harrow house extension quote.
Senior consultant call within one business hour. Free desk-based planning assessment for HA1, HA2, HA3 and surrounding postcodes. Fixed-scope price — no provisional sums.
