House Extension Added Value Calculator
Thinking about extending your home? Whether you’re planning a single-storey extension, double-storey addition, or loft conversion, it’s important to understand how much value these improvements can add. Below, we’ve answered the most common questions about home extension value, ROI, and property market impact to help you make an informed decision.
Using the calculator
Our Home Extension Value Calculator helps you estimate how much value your new space could add to your property. Simply enter:
- The size of your extension or conversion (in metres)
- The type of project (single storey, double storey, or loft conversion)
- The number of storeys
- Your location
The calculator then estimates both the build cost and the potential increase in property value, based on average regional prices and the typical uplift each project type provides.
Single & double storey extensions
When entering your extension size, use external dimensions. The calculator automatically adjusts for wall thickness to ensure the correct floor area is used in the calculation giving you a more accurate valuation.
Loft conversions
For loft conversions, enter the usable floor space only. This means the total loft area minus:
- The space taken by the stairwell, and
- Any areas where the height from floor to eaves is under 1.2 metres.
This ensures your valuation is based on the actual liveable space your loft will add.
Estimate costs and returns
You can use our extension cost calculator and loft conversion cost calculator to estimate the build cost. Then, combine that figure with your estimated added value (from the valuation calculator above) to work out your return on investment below.
Return on Investment (ROI)
Input your build cost and estimated value increase to calculate your ROI. A strong return is typically around 70%, but this can vary depending on:
- Property type
- Local market conditions
- Quality of finish
For example, if your double-storey extension costs £80,000 and adds £120,000 to your property’s value, your ROI would be 50% meaning you gain £40,000 in added value.
How much value can a single storey extension add to my home?
A single-storey extension can typically add 5 to 10% to your property’s market value. The exact figure depends on factors such as size, design quality, and how well it enhances your living space. For example, creating an open-plan kitchen diner usually delivers a higher uplift than adding a small study or utility room.
Use our Home Extension Value Calculator to estimate your property’s potential increase.
What is the potential value addition from a double storey extension?
A double-storey extension may boost your home’s value by 10 to 20%, as it often adds both living space and extra bedrooms or bathrooms. These are often key selling points for buyers. Because the additional floor shares the same foundations and roof, it’s also a cost-efficient way to increase property value per square metre.
Do loft conversions significantly increase property value?
Yes, a loft conversion can increase your property’s value by up to 20%, especially for three-bedroom homes in built-up areas where outdoor space is limited. Loft conversions are popular because they add usable living space without extending the property’s footprint, making them one of the best value-for-money home improvements.
How does the quality of an extension affect my home’s value?
The quality of construction and finish plays a crucial role. A well-designed, professionally built extension with high-quality materials and finishes can maximise your return on investment and appeal to buyers. However, a poorly built extension can reduce your home’s value and create costly issues later.
Are there other factors that influence the value added by an extension?
Several factors affect how much value an extension adds, including:
- Your location and local property market
- The type and style of extension
- How well it integrates with your existing home
For the most accurate insights, use our calculator and consult a local estate agent or architect to understand your potential resale value uplift.
Is it more cost-effective to build an extension or move to a larger home?
In many cases, extending your home is more cost-effective than moving. You’ll avoid stamp duty, legal fees, and moving costs, while gaining a home tailored to your lifestyle. Plus, the added value from an extension can make it a smart long-term investment.
Does location affect how much value an extension adds?
Yes, property values vary significantly by region, which directly impacts how much value an extension can add. For example, extensions in London and the Southeast often yield higher uplifts than in lower-priced areas. Our calculator adjusts for regional price per square metre to give a realistic estimate based on your postcode.
Do I need planning permission for an extension?
Many smaller extensions fall under Permitted Development Rights, meaning you may not need full planning permission. However, larger or double-storey extensions often do. Always check with your local planning authority or speak to your architect before starting work.
Ready to find out how much value your home extension could add?
Use our Extension Value Calculator for an instant estimate, or explore our Extension Cost Calculator to compare build prices and ROI before you start planning.
Sources
https://www.gov.uk/guidance/about-the-price-paid-data
https://epc.opendatacommunities.org/
