💡 Don't move, Improve (AL it)
Find out what your extension is really worth
AL it — free. Know your numbers in 60 seconds.
Real build costs. Real ROI. Real property value uplift for your home, your postcode, your project.
Powered by BCIS 2026 data. Upload your photos and get free AI 3D concept renders delivered to your inbox within 48 hours. No email required to get started.
Seven steps. Sixty seconds. Your free AL it estimate.
Work through each step at your own pace — the calculator builds your personalised estimate as you go. No commitment needed at any stage.
Step 1: Your Property Start with your postcode and property basics. This calibrates your estimate to your specific area, build costs in London are very different to Milton Keynes, and the calculator accounts for that automatically.
Step 2: Your Strategy Choose what you want to build — rear extension, loft, garage conversion, garden annex, or combine multiple. Not sure yet? Pick the option you're most drawn to and adjust as you go. There are no wrong answers at this stage.
Step 3: Your Budget & Finishes Enter your current property value and choose your finish level — standard, premium, or luxury. This is what drives the accuracy of your ROI and value-added figures. Use the Advanced Settings to toggle professional fees, contingency, and VAT on or off.
Step 4: Your Rooms & Eco Choose your kitchen fit-out level, bathrooms, dedicated rooms (home office, cinema, gym), and green energy upgrades like solar PV or air source heat pumps.
Step 5: Design Your Dream Extension Upload a photo of your home — exterior and interior — then choose your design preferences: finish material, roof type, windows, doors, flooring, lighting, and more. Our studio takes these choices and generates free bespoke AI 3D concept renders showing what your extension will actually look like. Delivered to your inbox within 48 hours.
Step 6: Your Instant Results Your results appear instantly — build cost range, projected property value uplift, ROI, and rental income potential. Compare your figures against your budget. Share your result directly via WhatsApp to your partner, builder, or estate agent in one tap.
Step 7: Download & Receive Your AI Concepts Enter your details to download your comprehensive PDF dossier featuring a full financial breakdown, phase cost plan, and all your design selections. Our studio then reviews your uploaded photos and delivers your bespoke AI 3D exterior and interior concepts to your inbox within 48 hours.
Why homeowners across the UK trust this calculation?
Live BCIS-Backed Data Our algorithm is powered by the Building Cost Information Service (BCIS) and HM Land Registry, ensuring your estimates reflect current real world UK market rates not outdated guesswork. Regional multipliers adjust costs for your specific postcode.
Upload Your Photos, Get AI 3D Concepts Free This is what sets us apart. Upload a photo of your property, choose your preferred design options, and our studio generates bespoke AI 3D exterior and interior concept images delivered to your inbox within 48 hours, completely free.
100% Secure & Private Your photos are securely uploaded via Cloudinary (an enterprise-grade cloud platform) and processed solely for generating your bespoke concepts. We never share your details or images with third parties without your explicit permission.
Architect-Led Precision This is not just an app it is engineered by the architectural experts at AL-Haitham Ltd with 15+ years of UK industry experience. When you are ready to build, our team is here to take your AI concept through planning permission, structural calculations, and building regulations.
Transparent Pricing, No Hidden Costs The calculator shows you everything: build costs, professional fees, contingency, VAT, and even party wall costs. Toggle each line item on or off to see exactly how your total is calculated.
Popular Exterior Finishes:
- Crisp Modern Render: Clean, sleek, and perfect for contemporary extensions. Pairs beautifully with anthracite grey windows and flat roofs.
- Traditional Matching Brick: Warm, sustainable cedar or larch for an architectural edge. Perfect for garden annexes and rear extensions.
- Natural Timber Cladding: Seamlessly blends your new space with UK heritage masonry. Ideal for semi-detached and terraced homes.
- Dark Zinc / Metal: Striking standing-seam cladding for ultimate modern luxury. A bold statement that adds significant kerb appeal.
- Mixed Heritage & Modern: Combines traditional materials with contemporary elements for a unique transitional aesthetic.
Design Your Dream Extension
Not sure which options will look best on your property? Browse our most popular design choices below. Every option you see here is available inside the calculator — select your favourites and we will apply them to your property using AI.
Door Styles That Transform Your Space:
- Bi-fold Doors: The UK's most popular choice. Open up an entire wall to create a seamless indoor-outdoor flow between your kitchen and garden.
- Sliding Patio Doors: Sleek, minimal frames with maximum glass area. Ideal for contemporary extensions where you want uninterrupted views.
- French Doors: Classic, elegant, and timeless. Perfect for traditional homes and Conservation Areas where planning sensitivity matters.
- Pivot Door (Luxury): An oversized single door that rotates on a central axis. The ultimate architectural statement for high-end extensions.
Window Frames & Glazing:
- Anthracite Grey Aluminium: The industry standard for modern extensions. Slim sightlines, excellent thermal performance, and a sleek, contemporary look.
- White uPVC: Cost-effective and low-maintenance. Works well on traditional properties where matching the existing windows matters.
- Black Crittall-Style: Industrial-chic steel-look frames that add character to both modern and period properties. Increasingly popular in high-end UK renovations.
- Timber Frame: Natural warmth and heritage appeal. Often required in Conservation Areas and Listed Building extensions.
Roof Types:
- Flat Roof (Modern): Clean lines, often paired with a roof lantern for natural light. The go-to choice for single-storey rear and wraparound extensions.
- Pitched Tiles: Matches most existing UK rooflines. Essential for double-storey extensions where planning officers expect visual harmony.
- Pitched Slate: Premium look, especially on period properties. Natural Welsh or Spanish slate adds real character and longevity.
- Mansard: Maximises loft headroom by creating a near-vertical roof wall. Common in London terrace loft conversions.
- Zinc Standing Seam: Architectural-grade metal roofing for a distinctive contemporary finish. Low maintenance and extremely durable.
Bespoke Interior Vibes:
- Minimalist & Bright (Scandi): Natural light floods through large glazing onto light woods and clean white walls. Perfect for open-plan kitchen-diners.
- Modern Industrial: Exposed brick, Crittall-style doors, polished concrete floors, and dark accents. Bold and characterful.
- Warm Modern Farmhouse: Shaker cabinets, earthy tones, engineered oak floors, and rustic textures. Cosy yet contemporary.
- Contemporary Luxury: Marble finishes, quartz worktops, sleek handleless cabinetry, and statement pendant lighting.
- Biophilic (Nature-Inspired): Indoor greenery, natural materials, large rooflights, and an organic connection to your garden.
✅ BCIS-backed 2026 data 🏛️ 15+ years experience 📍 MK · London · Nationwide ⭐ 50+ verified 5-star reviews
Got your estimate? Here's what to do next.
💬 Message us on WhatsApp
📞 Book a free 15-min call
📄 Save & share your PDF
Send Haitham your result directly, get a straight answer from a practising architect within hours, not days.
Want to talk through your numbers? Book a quick call — no obligation, no sales pressure. Just honest answers.
Your downloadable PDF dossier has the full breakdown — save it, share it with your partner, or hand it to a builder to get quotes.
No pressure. No hidden fees. Just straight answers from an architect with 15+ years of UK experience.
How much does a house extension cost in the UK in 2026?
A typical house extension in the UK in 2026 costs between £2,750 and £3,050 per square metre for a standard finish. Most single-storey rear extensions range from £40,000 to £60,000 depending on your postcode, site access, and material choices. Double-storey extensions typically cost £80,000 to £150,000, while loft conversions range from £45,000 to £75,000. Use our calculator above for a personalised estimate based on your exact property and design preferences.
FAQ (Frequently Asked Questions)
Q: How do the free AI 3D concepts work?
A: In Step 5 of the calculator, you upload a photo of your property (exterior and/or interior) and select your preferred design options — finish material, roof type, windows, doors, flooring, worktop, lighting, and more. After you submit your details, our studio uses these selections along with your photos to generate bespoke AI 3D concept renders. You receive these by email within 48 hours, completely free.
Q: What photos should I upload?
A: For the exterior, take a clear photo of the side of your property where the extension will be built — ideally from across the road or garden, showing the full elevation. For the interior, photograph the room you want to transform (e.g. your existing kitchen before the open-plan redesign). Daylight photos work best. Mobile phone quality is fine.
Q: How accurate is this calculator?
A: Our estimates are based on BCIS Q1 2026 construction cost data, adjusted for your region, property type, finish quality, and site access. The final output shows a range (typically ±20%) to account for site-specific variables that can only be confirmed after a professional survey. For an exact quote, book a Free 3D Feasibility Study with our team.
Q: Do I need planning permission for a rear extension in Milton Keynes or London?
A: Many single-storey rear extensions up to 3m (or up to 6m under Permitted Development rights) do not require full planning permission. However, Conservation Areas in London or specific estates in Milton Keynes may have stricter rules. Our calculator flags potential planning requirements based on your inputs, and if you select "Conservation Area," we will highlight the additional considerations.
Q: Are architectural fees included in the estimate?
A: Yes. By default, the calculator includes approximately 8% for architectural and planning fees, 3% for structural engineering, and 2% for building control and party wall costs. You can toggle each of these on or off in the Advanced Cost Settings to see their impact on your total.
Q: What happens after I download my report?
A: You will receive a comprehensive PDF dossier featuring your full financial breakdown, phase cost plan, and all your design selections. Within 48 hours, our studio will email you with your bespoke AI 3D concept images. If you are ready to proceed, we will contact you to discuss a detailed Feasibility Study, site survey, and planning strategy.
Q: Can I use this report to get builder quotes?
A: Absolutely. Your PDF dossier includes a detailed cost breakdown by phase (groundworks, superstructure, roofing, first fix, second fix) which gives builders a clear framework for quoting. Many of our clients use the dossier as a tendering document when approaching contractors.
Q: Is my data safe?
A: Yes. Your personal details are submitted securely via Formspree (an encrypted form-handling service). Uploaded photos are stored on Cloudinary (an enterprise-grade cloud platform used by major brands worldwide). We never sell, share, or distribute your data. Full details in our Privacy Policy.