Why you should extend your house!

Wrap around house extension in Hertfordshire with facing brickwork

Maybe you have considered adding extra space to your London home but thought it was perhaps a bit too expensive. While the average price of a house in Greater London is currently around £5,000 per square metre, a house extension will cost between £1,500 - £4,000 per square metre depending on the type of the project, the materials used, and the quality of the finish. For example, a Velux loft conversion will be cheaper than a one or two storey house extension, as it requires a lot less structural changes. Traditional masonry (An outer brick wall tied to an inner concrete leaf with an insulated cavity in between the two) will cost more than a modular timber structure but should last much longer. You might be happy with a kitchen from Ikea, or you might choose custom-made hand painted solid wood units, adding to the cost.

If you don't need more space, you could consider renting the extra room. A Dormer Loft conversion could turn your unused attic into a double bedroom. A single-storey house extension could accommodate a small studio. And a two-storey extension might be enough to create a one-bedroom flat, earning you up to £1000 a month.

To give you an idea of how much money you will need to complete your project, we have listed different types of extension and conversion projects sorted from the cheapest to the most expensive:

  • Garage conversion
  • Roof light loft conversion
  • Dormer loft conversion
  • Single storey extension
  • Double storey extension
  • Basement conversion
  • Double bedroom in a Velux roof light loft conversion

    A garage conversion is an easy way to add an extra room such as an office or a gym to your house. If your garage has double-skin brickwork, you might be able to convert it for as little as £20,000. If the brickwork is single-skin, more advanced insulation will be required, adding to the cost.


    A roof light conversion, often called Velux as these are the windows commonly used in this type of project, is an affordable way of adding an extra bedroom to your home. You will need to build a staircase, reinforce the floor, and add a couple of skylight windows. The cost starts from £25,000.

    Single storey rear house extension in London Barnet

    Dormer loft conversions are around forty per cent more expensive than Velux. With this type of project, the back (or sometimes the front) of the roof will be replaced with a flat roof dormer, creating a box-like extension with vertical windows, giving you more headspace.


    A single-storey extension can connect your home with the garden. There are three types of one storey extensions available: a rear home extension, side return, and a wrap-around extension. You could use your extra space to create a large kitchen with a kitchen island or a cosy family lounge. The cost of this type of project will start from £40,000.

    Basement extension in Hampstead, North West London

    The cost of a double-storey house extension will be about fifty per cent more than a single-storey. However, you will be getting twice as much space, making it a better value. A two-storey extension can be added onto the back or the side of the property.


    Building a basement is the most expensive type of extension project, with the price starting at around £5,000 per square metre. This is mainly due to the cost of excavation and underpinning the foundations of the existing house. For this reason, basements are most commonly added to homes in popular London locations such as Kensington and Hampstead, where house prices can reach up to £20,000 per square metre. If you live in a prime location and have limited garden space and existing loft conversion already in place, expanding your home below the ground is definitely worth the cost.

    House Extension Ideas

    To provide you with some inspiration of what you could do with your new space, we have put together this guide:

  • Sliding Glass Doors
  • Open-Plan Kitchen with a Kitchen Island
  • Exposed Interior Brick Wall
  • Lounging Area with a Fireplace
  • Extra Bedroom
  • Personal Gym
  • Sliding glass doors corner system

    Sliding glass doors are a popular choice amongst homeowners in London, and it is easy to see why. With only the glass panels separating the indoors and outdoors, the garden visually becomes part of the home extension and vice versa. Made of quality materials, fully insulated sliding glass doors will bring natural light into your home without wasting energy. 

    There are three types of sliding glass doors from which to choose: Stacking Sliding Glass Doors are low maintenance and easy to use. The glass panels simply slide along a track when pushed, and stack behind one other at the end of the frame. With Pocket System, the panels disappear from view when fully open, as they tuck into the wall itself. This needs a bit of planning, as the wall will need to fit all the sliding panels. Corner System will bring light into your home regardless of the position of your house. For even more seamless transition between the indoors and out, you can find a design that does not require a supporting column.

    Sliding glass door frames come in two different materials. Aluminium will give your home a modern contemporary look while the slim frames will maximise your view. Aluminium is a super durable material, which makes it the perfect choice for a new house extension door. Cheaper than aluminium but just as weather-resistant, sliding glass doors with uPVC frames are a great solution for replacement patio doors.

    Large shaker kitchen in a home extension in London

    An open-plan kitchen will give you more space to prepare food, and it has several other advantages. Perhaps the most important one being the fact that your family will gravitate to such a bright, open space. And, of course, the heart of the kitchen has always been a ‘gathering area'.

    Open-plan kitchens work really well with the current hot interior trend - Kitchen Islands with large worktops that can be used not only for preparing meals but also for completing homework or arts and crafts projects. And, there is enough space to store all your dinner sets and kitchen gadgets. The seating area allows you to entertain your family or friends during a party or a get-together. Relaxed, open-plan kitchens with sitting area such as the one pictured have been incredibly popular for several years now – and the desire by just about every homeowner in London to get one doesn’t seem likely to go away anytime soon.

    Exposed brick wall in a house extension

    An interior exposed brick wall can add a touch of elegance to your extension while beautifully contrasting with your furniture or kitchen units.

    We offer our clients a choice of two patterns: Stretcher bond – where all the bricks are laid sideways exposing just the long side of each brick (the stretcher), and Flemish bond – which is created by arranging the stretcher side and the short side (the header) alternately.

    There are many colours and types of bricks available, some of the most popular being the London stock brick, which is yellow in colour and reclaimed multi stock bricks (pictured).

    wood burning fireplace in a house extension

    A house extension provides you with the perfect opportunity to get a fireplace or a stove fitted. With room-sealed wood-burning fireplaces which are connected to an internal air source to prevent draughts, you can enjoy the warmth of a real fire even if your extension does not have a chimney.

    Modern stoves are highly energy-efficient, so nothing can stop you and your family or friend from spending hours sitting in front of the fire in cold winter months. And with so many different design options available on the market, you should be able to find a solution regardless of your budget, whether you prefer a classic-looking fireplace or a contemporary hole-in-the-wall design.

    double bedroom in a loft conversion

    A loft conversion or the second level of a two-storey extension can easily be turned into an extra bedroom. This spacious bedroom in a dormer loft conversion we have built for our client in Mill Hill is a great example. The combination of white and brown colours gives the interiors a luxurious feel. The made-to-measure wardrobe fitted by our carpenter ensures maximum use of the space.

    To keep the bedroom bright and airy, we fitted large Schuco windows. The brown and beige tiles help the bathroom match with the rest of the interior. For our clients' comfort, our team of electricians fitted the conversion with state of the art electronic smart home system that operates the curtains, lights, heating, air conditioning, TV and more. 

    home gym in a house extension

    If you tend to work out several times a week, turning your new room into a home gym could save you money as well as time by not having to travel back and forth to your local fitness centre. And it has plenty of other advantages too, such as being fully customizable. You can select from different equipment such as treadmills, cycles, rowing machines, boxing gear, free weights and other fitness accessories.

    A lot of gym-goers like to work out to the sound of music. With a home gym, you can listen to your favourite songs while you exercise, save in the knowledge that you will never again have to endure James Blunt blurting out 'You are beautiful!' while you are kicking the punch bag.

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    183 Edgware Road
    London
    NW9 6LP


    CONTACT US

    0208 205 8173  
    office@marriottconstruction.co.uk

    We operate across all of North London and North West London including Hampstead, Mill Hill, Finchley, Edgware and Barnet. We also cover parts of Hertfordshire including Bushey, Elstree, Potters Bar, and St. Albans.