AL-Haitham LTD for Architectural services
The UK House Extension & ROI Calculator 2026
Property Profit Portal: AI-Powered UK Feasibility Estimator
Welcome to the AL-Haitham Property Profit Portal. Whether you are a homeowner planning a dream rear extension, or a property developer calculating Gross Development Value (GDV) for an HMO or flat conversion, our tool gives you instant clarity.
Use the calculator below to generate a highly accurate estimate based on your exact UK postcode. Powered by live 2026 construction benchmarks from BCIS and official market indices from HM Land Registry and the ONS, you can find out your build costs, required professional fees, and your estimated Return on Investment (ROI) in less than 60 seconds.
How much does a house extension cost in the UK in 2026?
A standard house extension in the UK currently costs between £2,750 and £3,050 per square metre. Most single-storey rear projects range from £40,000 to £60,000 depending on the postcode, site access, and finish quality. Use our AL-Haitham Property Profit Portal below to calculate an exact, location-adjusted estimate and ROI for your specific property.
How to Use the Feasibility Calculator
1. Select Your Profile: Choose your role (Homeowner, Investor, Developer, or Estate Agent). The calculator will dynamically adjust to show the specific financial metrics that matter most to your goals.
2. Enter Existing Details: Input your project postcode and current property value. Our algorithm uses localized data to automatically adjust construction pricing and property values to your specific region, ensuring maximum accuracy.
3. Choose Your Strategy: Select one or multiple build types—from standard rear extensions and staggered double-storey additions to loft conversions and garden annexes.
4. Customise Your Finish: Add premium interior design styling, luxury bathrooms, or modern eco-upgrades like Solar Panels and Air Source Heat Pumps.
5. Generate Your Brief: Click "Generate" to instantly view your estimated costs and ROI on screen. Enter your details to download your comprehensive, phase-by-phase Architectural Brief.
What Are the Expected Results?
By using this tool, you bypass weeks of waiting for initial contractor quotes. When you generate your report, you will instantly receive:
A Phase-by-Phase Breakdown: Clear cost estimates split across Architectural Design, Structural Engineering, and actual Construction.
New Build vs. Renovation Costing: Clear distinctions between the cost of building brand-new square meterage and the discounted cost of renovating existing spaces where your new extension meets the house.
Financial Viability Metrics: Live calculations of your Estimated Added Value, Gross Yield %, and Break-Even Payback timeline.
Planning Permission Guidance: A smart indicator telling you if your project likely falls under Permitted Development or requires Full Planning Permission.
Exclusive Developer Data: Investors and Developers will receive a secondary CSV spreadsheet detailing the exact Labour vs. Materials split for their financial modelling.
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.
FAQ Section
Are architectural fees included in the estimate?
Yes, you can toggle our ~8% fee inclusion
Does this include VAT?
Is this a final quote?
Yes, you can toggle our ~8% fee inclusion
No, this is an algorithmic feasibility estimate. Book a Free 3D Feasibility Study for an exact, site-specific quote