House Extension
in Harrow
Compare quotes from vetted Harrow extension builders for single-storey, double-storey and rear extensions. Transparent pricing from £21,500. Free, no-obligation quotes — results in 24 hours.
- Local house extension specialists in Harrow
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How Much Do House Extension Cost in Harrow?
Real prices from completed projects in Harrow and the surrounding area. Costs vary by size, specification and access — use these as a starting guide, then get 3 free quotes for your specific project.
The most popular choice for UK terraces and semis. Adds a kitchen-diner or extra living space at ground level. Typically 3–5m deep, completed in 10–14 weeks.
Get quotes for this →Maximum space gain in a single build — adds a ground-floor room and a bedroom above. Strong ROI in most UK property markets. Requires full planning permission.
Get quotes for this →Ideal for terraced homes with a narrow side alley. Transforms a cramped kitchen into a full-width open-plan space. Often combined with a rear extension.
Get quotes for this →Costs depend on size, spec and access. The best way to know your exact price is to compare 3 quotes from local specialists.
Get free quotes →Harrow pricing note: Building costs in London are typically 30–40% above the national average, driven by higher labour rates, congestion charges, stricter planning requirements and premium material delivery costs. Inner London boroughs (Zones 1–2) command the highest rates. Prices shown are indicative ranges for Harrow and London. Always get at least 3 written quotes before committing to any builder.
House Extension Specialists Who Know Harrow
Tell us about your house extension project once and up to three local specialists who cover Harrow get in touch with quotes — free, with no obligation, and you choose who to hire.
Trades covering Harrow normally work across the surrounding area as well — including Bromley, Lambeth and Greenwich — so your shortlist is drawn from the wider London pool rather than a single postcode.
It helps to know the regional picture before you budget: Building costs in London are typically 30–40% above the national average, driven by higher labour rates, congestion charges, stricter planning requirements and premium material delivery costs. Inner London boroughs (Zones 1–2) command the highest rates. Three like-for-like quotes will show where your Harrow project lands.
Local facts: Harrow
- Local planning authority: Harrow Council
- Region: London
- Town-centre postcode district: HA1
- Average house price (Harrow local authority, June 2026): £524,160 (-1.4% year on year) — detached £1,194,985, semi-detached £659,603, terraced £532,719, flats £318,212
- BestBuilders house extension members covering Harrow: BHM Extensions Ltd (14 miles)
Planning-authority, region and postcode data: ONS Postcode Directory (Open Government Licence). House prices: HM Land Registry UK House Price Index for the local authority (OGL). Member coverage is each member's own registered base and travel radius.
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House Extension in Harrow — FAQs
Plan Your house extension Project in Harrow
Whether you're researching costs, checking planning rules, or comparing approaches before you commit, our editorial team has produced these guides to help Harrow homeowners make informed decisions about their house extension project.
House Extension Cost Guide
Detailed UK price ranges, regional adjustments and worked examples for house extension projects.
Read House Extension Cost Guide →All House Extension Specialists
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Browse House Extension Specialists →All Cost Guides
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View All Cost Guides →Planning your house extension project? Read these guides:
Planning Your House Extension in Harrow
Before you compare quotes, it's worth understanding the full UK price picture for house extension and how Harrow sits within it. The guides below cover average costs, what affects your quote, and how to choose a builder you can trust.
UK House Extension Cost Guide
Full price ranges, worked examples and the factors that move your quote — drawn from real project data across 519 UK towns.
Read the house extension cost guide →House Extension Across the UK
Browse house extension services nationwide, see what's typical in your region, and request quotes from any UK location.
Visit the UK house extension hub →Planning Permission for House Extension in Harrow
Find out whether your house extension needs planning permission in Harrow, what Permitted Development limits apply, and how rules differ in conservation areas, Article 4 zones, and listed-building settings.
Read the house extension planning rules →More homeowner resources: all UK building guides, cost guides, planning permission, comparisons, how-to guides and industry insights.