Basement Conversion Costs

There are plenty of aspects that can affect the eventual cost of a basement conversion. Here we’re going to list the most usual parameters that can add to the cost, and also take a quick look at the general costs for an ‘average project’ according to size and the specification demanded.

  • Will external access need to be accommodated for?
  • Lighting is very important and needs to be carefully thought through. How many light wells will be needed to provide satisfactory illumination appropriate to the room’s purpose? What size and softness must these lights be able to offer?
  • Headroom generally ranges between 2.2 and 3.5 meters – what can the basement accommodate and how will light fittings and suchlike affect the ceiling space?
  • Plumbing – what needs to be fitted and what is the standard of drainage facilities? Will they need upgrading?
  • Waterproofing is very important, as basements will obviously be at risk from any leaks elsewhere in the property. Also we need to consider how external water might flow and secure against erosion by seepage.
  • Access to the site – where can spoil be removed to and where can equipment/materials be stored?
  • Is the basement below the water level?

Some of these issues may/may not be a concern in many projects but they are among the main questions that need to be asked when considering a basement conversion. Average prices for certain buildings now follow – remember these are strictly guideline prices:

General Basement Conversion

Lowering the floor in a two-room space, fitting and arranging light wells and underpinning the walls: Generally £80-120K.

Excavation Expansions

Excavating 2/3 rooms worth of space where no basement currently exists. Light wells and underpinning the walls. Plus a shower room. Generally £100-150K.

Excavation & Casting

New build property: £150K +.

Excavating & Casting Plus Facilities

Swimming pool and gym: £400K +.


We treat all projects as unique cases and these figures are very approximate, so please contact us to discuss the nature of the property and we shall determine a much more precise fee.