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Adding a Room onto a House

An extension doesn’t always have to be a complex remodel of a large section of the house – it might be that you’re completely happy with the way your home is laid out, or maybe you don’t have the funds to remodel your home at this time but you just need an extra room.

There are four basic types of additions that you can make when you’re thinking about adding another room to your house:

  • Converting a room, such as a loft or garage
  • Ground addition: A single storey room added to the ground floor of your house
  • Second-floor addition: A room added to the second floor of your house (usually above a garage)
  • Detached addition: A room added separately from your house, such as a conservatory or summer house

If you need extra space but don’t necessarily need it attached to the main home, a cheap extension option is a summer house/hobby room.

Costs of Adding a New Room

Converting a Loft

The easiest type of loft conversion is a ‘Room Loft Conversion’. This is where you board out the loft and add a staircase. Maybe add a few skylight windows in the slope of the roof. You would require a good sized loft with good head height. The best roof type for the loft extension is a gabled roof (2 sides slope) rather than a hipped roof (all 4 sides slope). Always remember, you may lose a bit of space on the floor below when installing the staircase. Loft conversions are great for creating an extra bedroom, maybe with an ensuite.

Prices start from £15,000


Dormer Loft Extension

A dormer loft extension is where a big box is typically added to the rear of the roof. This gives lots more space. Typically created via permitted development.

Prices start from £20,000 or from £35,000 with the inclusion of an en suite


Converting a Garage/Basement

Turning an existing basement/garage into a usable living space costs from £700 per square meter for the build costs

Other cost factors that you may need to consider include:

  • Will you need to move your boiler/consumer unit/gas meter?
  • Will you need to underpin (reinforce existing foundations)?
  • Will you need to lower the floor to increase ceiling height?
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Ground Addition

For a single storey, ground floor addition, if you worked out a square meter at £1500, that’s a good base price for basic quality; £1900 per square meter for good quality and £2200 per square meter for excellent quality. For an average single storey extension of 20 square metres, the build cost would be from £30,000 for a basic quality room addition.


Second-floor Addition

If the ground floor’s existing foundations can take the load, then you may have the option to build a second-floor addition on top of an existing room. This is much more cost-effective than building a new extension but will need planning permission if the addition is at the front of the property (i.e. above a garage)

Prices start from £15,000


Detached Addition

Build a Conservatory

Conservatories can usually extend by a maximum of 3 meters from the rear of the property and also have a height restriction of 3 meters without needing planning permission.

A conservatory could be a great dining area/child’s play area/pet room etc, freeing up space for a larger kitchen/lounge area in your home.

DIY, ready-to-install conservatories can cost as little as £3,000 or a mid-priced design that will be comfortable even on hot and cold days can cost from £15,000.


Build a Summer House

If you need extra space but don’t necessarily need it attached to the main home, a cheap extension option is a summer house/hobby room. A quite generous size can be easily achieved under permitted development unless the unit will contain a toilet and kitchen (then the building will be considered a self-contained unit and may need planning permission).

Costs vary depending on the size, quality, level of insulation, type of interior and exterior finishes etc of the summer house/hobby room but a cheap, modular kit can cost as little as £2,000

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Adding an extra room will generally come under permitted development unless the addition is at the front of the property.

Additional costs that you may need to consider include:

  • Professional fees (if you need an architect/structural engineer/project management)
  • Reports about your property (Tree/Flood Risk/Ecology etc)
  • Building Regulations Approval
  • Party Wall Agreement
    (Covers shared walls/structures and protects both yourself and your neighbours whilst work is being carried out)
  • Build Over Agreement
    (If you’ve got a shared drain running across the back of your garden and you’re going to build over it or within three meters proximity)
  • Insurance


Total Cost

To calculate the cost of your project, Yoop Architects take a measured survey of your property, which captures all the information. Then we draw it all up in 3D and create sketches to show sometimes five or six options if it’s not entirely clear how you want to achieve your brief.

A lot of the times there are different ways of achieving your desired result and the more you work with the building, the cheaper, easier and faster your build will be. Once you’ve got a favorite scheme or a couple of favorite schemes, we have a phase called ‘Meet the Builders’. That’s when we can introduce you to a couple of builders, they visit the property and they give you a ballpark figure.


Thinking of your dream home improvement or how to start your project? 
Need your planning questions answered? Talk to an expert today.
Book a FREE 20 Minute Call with one of our home improvement Architects.

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Post Author: yoopadmin