Ground Floor Extension vs Loft Conversion: Which is Better?

House extensions in London are popular. Homeowners need more space and let’s face it – moving is inconvenient and expensive. Extending also might also be a more cost-effective solution in the long run, as you can make back the investment by increasing the value of the property. Traditional style properties in London are also very good at being extended. There are many ways you can extend your home, be it via a ground floor extension, first floor extension, second floor extension or a loft conversion. We are often asked what the ‘best’ kind of extension is. The truth is – there isn’t one blanket answer that will apply for everyone. It depends on your existing property layout and also what you are seeking from the project. Do you need more space in the kitchen to cook, entertain and seat your family around the dinner table? Or are you after more bedrooms or perhaps a quiet office, tucked away in the loft? Whatever the answer – we would be delighted to advise on design, practicality, budget estimate costs, and anything else you might need answered.   

What is the main difference?

A ground floor extension in London generally adds liveable space. Liveable space is your day-to-day space and generally includes your living area, dining area and kitchen. If you have a house, the ground floor is most typically dedicated to these functions. In a typical Victorian terrace, the front room with the bay window is the living area, the middle room is the dining area and the rear outrigger (usually not full width, as there is a side return into the garden), is the kitchen. This layout is very typical of the properties we work with and in this case, the most common type of extension is either a side return extension or a wraparound extension. A wraparound extension extends into the side return and to the rear. We recently published a blog on wraparounds in London and the expected cost associated with them which you can read here. Another type of extension we frequently work with is a rear extension. If your property is flat to the rear, you can simply extend to back into the garden. Regardless of the type of extension, the additional space can be used for whatever you want – but typically, homeowners will use it to have a larger kitchen. There is often additional space left over for a spacious dining area too. 

A loft conversion tends to add bedrooms and bathrooms to a property. Most loft conversions will install a new staircase leading up to the new floor of the property. If you have an existing outrigger you can opt for a l-shape dormer extension. This involves having a main dormer over the width of the main property and a second dormer over the outrigger to the rear. We often add two bedrooms and bathroom with this style of loft conversion. If you don’t have an outrigger, you can have a single dormer extension which typically adds a sizable bedroom and a small bathroom or en-suite. Bedrooms needs to have a window and sufficient head height to be identified as a ‘bedroom’ by building control. For this reason, lofts are perfectly designed to add bedrooms. Bedrooms can be used for whatever you wish – an office, a gym, a library, a playroom – the options are endless! Lofts are also convenient for storage as you gain eaves storage. 

Cost – which is more expensive? 

Ground floor extensions tend to be more expensive, and they don’t always add as much SQM to the property. With a loft conversion, you are adding an entire new floor to your property. All of the space is counted as ‘new SQM’ and adds onto the overall SQM size. With a ground floor extension, you are typically adding less, and encompassing it into an existing area. For example, we recently completed a ground floor side return extension on our Wandsworth project. The side return was about 1.5m x 6m in size, so we added about 10SQM of additional space to the property. With that said, the additional floor area was encompassed into a room which now spans an impressive 4.5m x 6m. This size of room offers way more opportunity and possibility, so it has completely transformed the room. The cost of this extension was approx. £70k + VAT.

In comparison, we also completed a loft conversion to the same property, which added 2 double bedrooms and a bathroom to the second floor, adding 35SQM of additional space. The cost of this extension was £45k + VAT. If you are looking at the cost per SQM, lofts are far more efficient. With that said, both add a significant amount of value onto a property. 

Is one more risky than the other?

It’s important to understand that building sites can be unpredictable, and, in some circumstances, things might be uncovered that weren’t accounted for in the original scope of works. As a result, it’s important to have contingency budget set aside, just in case. Ground floor extensions involve digging down into the ground. Most of the properties we work on are period style properties and as a result, they were built over a century ago. This means items might be uncovered that are unexpected, which might eat into that contingency budget. Loft conversions are a bit less risky because you are adding on top of an existing building, rather than digging down to uncover unknown items. A contingency budget should be accounted for, but it’s far less likely to be needed with a loft conversion. 

If you are thinking of extending, but aren’t sure what option is best for you, call our team on 0207 043 2378 or email us at We would be delighted to talk you through the different options and how they would apply to your specific project. You can also book a telephone consultation directly via our website here. We look forward to hearing from you! 

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