How much value does an extension add?

Home renovations in London can be a worthy investment, particularly if they are completed in an effective way. If you are undertaking an extension purely for investment purposes, there are lots of ways you can tick those all-important boxes that perspective buyers love. Estate agents have loads of advice when it comes to home modifications, so it’s well worth speaking to a local agent and understanding the must-haves. The majority of our clients here at Home Tales are undertaking a home extension or home improvements works for their own personal use. That doesn’t mean it won’t be a financially savvy investment, and our designers have loads of effective advice to ensure that our clients get the most out of their project.   

We thought we would run the different types of extensions and associated cost benefits with each one. We’ve also included some top tips on how to add value to your property, as well as a case study project with actual before and after values given by a local agent. 

Ground floor extension 

Ground floor extensions typically add functional floorspace. This means floorspace that is dedicated to your kitchen, living or dining area (not a bedroom). Ground floor extensions don’t always add a huge amount in terms of SQM area. In fact, sometimes the amount is fairly small in comparison to what you can gain from a loft conversion, as local council guidelines generally want the extension to remain subservient to the original building. That being said, a small amount of space makes a huge impact when it’s added to a room. Take a look at the before and after of this project below. The actual SQM rate added was only 11SQM, but the finished room size is a massive 30SQM. This is enough room for a large kitchen including a kitchen island as well as a 6-seater dining table. 

Due to this capacity for additional space, when it comes to adding value to a property, the finish of the room is the larger draw factor rather than the literal SQM added to the property. Once you have that large envelope to work with, you can add loads of cool features. Full width glass doors are very popular and give a wonderful inside outside feel. This is very appealing to prospective and current homeowners. Velux windows also help to catapult light into the home which is another appealing feature for prospect buyers. 

Ground floor extensions in a flat 

Ground floor extensions in flats typically add a second bedroom, as well as increase the living, dining and kitchen area. We frequently work with clients who want to completely reconfigure their flat and extend to the rear. In this case we generally recommend considering a courtyard. This enables natural light penetration and ventilation to the middle of the flat, enabling that formation of a second bedroom. 

Loft conversion 

Loft conversions typically add bedrooms to a property. In some cases, particularly in first floor flats, extending into the loft can add valuable space for a larger kitchen or living area. Nationwide conducted some research earlier this year and suggested that adding a double bedroom and an en-suite to an average sized 3-bedroom house adds 23% onto the property value. Loft conversions in London can almost always enable the creation of a new bedroom with en-suite. In many cases you can undertake a l-shaped dormer extension which can add two bedrooms and an en-suite. 

Case Study – Ground Floor Extension and Loft Conversion in SW18

This property was bought for £825k in 2018. It was a 3-bed, 1-bathroom property on the Southfields grid in Wandsworth, and it did require modernisation throughout. The internal floor area was 100 SQM which is about 1100SQFT. We undertook a side return extension, an l-shaped dormer loft conversion and modernised the property throughout. We undertook additional structural works, including the removal of 3 full chimney stacks and a load bearing wall on the ground floor. We added a ground floor WC and removed a stud wall on the first floor which separated the bathroom and WC, creating one large family bathroom. The side return extension added 11SQM onto the property, and the loft conversion added two bedrooms and a bathroom, adding a massive 35SQM onto the property. This meant the added space was 46SQM, leaving the final SQFT at 1614 SQFT. The valuation taken after the works were complete valued the property at £1.15m. The homeowner added £325k of value onto this property. So how much did the work cost? Good question. The build was £140k with project management included that cost. Design fees were £5k and party wall and building control added another £4k. The kitchen was £20k and the window replacement was £20k. That brings a total of £189k, leaving a profit of £136k. 

If you are considering a home extension, get in touch with our team today. We would love to learn more about your project. Call us on 0207 043 2378 or email us at You can also book a slot online via our online booking page

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