Basements – A Look at Costs and Options

Basements are a great way to increase the value of your home and add extra living space.

While basements aren’t cheap, when you consider the cost of moving home and rising house prices, this type of extension looks more and more attractive.

There are dozens of ways to add extra floor space to a home, garage conversions are often the cheapest with loft extensions only slightly more expensive.

We’ve already explored house extension costs and on this page, we’ll look at basements and how much they cost.

How Much Do You Think a Basement Extension Will Cost?

We like to ask our visitors how much they think home improvement projects will cost.

The question below is entirely optional, you can skip it if you wish.

How much do you think a 25 square metre basement extension will cost?

Factors That Will Affect The Price

Every basement extension is different and no two projects are ever the same.

The price for one extension could work out quite different to a similar one in your neighbour’s home.

Here are the key points to consider:

  • Converting an existing cellar will cost around half as much as digging out an entirely new basement. If you have an existing cellar, you could get extra usable floor space at a great price.
  • Basements underneath the garden are cheaper than those directly under the house.
  • Creating external access to the basement will add around £6000 – £8000.
  • The home’s proximity to the water table is a key pricing factor.
  • Diverting sewers and drains can be costly.
  • General access issues and problematic soil types can also bump up the price.

Our Basement Extension Cost Guide

We got in touch with six basement extension companies based in the south-east of the UK and asked them for an estimate to create a basement beneath our 3-bed property.

We didn’t want a swimming pool, jacuzzi or anything like that, just a room that we could use as a second lounge with a small bar.

The figures below are average of the prices given to us.

The average price for a basement shell; that’s the dig out, underpinning and creation of the concrete structure, will cost around £2600 per square metre +VAT

The fitting out of the basement, that’s the electrics, plumbing, staircase, plasterboard walls and flooring etc will depend on the desired specification but we were told to budget from £900 per square metre +VAT for a basic fit out.

For a 25 square metre basement, the build cost came to £87,500 +VAT

What’s Not Included in These Figures

Architect and structural engineer’s fees, survey fees, party wall fees, planning application and building regulation application fees are not included in the cost.

These can add up to a considerable amount so we suggest you budget for:

Architect fees are usually between 9% and 15% of the overall build cost.

Structural engineer fees vary from project to project but around £1100 appears to be the going rate for a basement of this size.

A planning application isn’t always needed but will cost upward of £175 if you need one.

Building Regulations approval will cost from £700.

Party wall agreements can cost up to £750 per neighbour.

Survey fees for drains, water table, trees and general geology will vary but often cost several hundred each.

Compare Basement Prices to Extensions and Loft or Garage Conversions

We know from experience that garage conversions are the cheapest and easiest way to create additional usable floor space in the home. This is because the structure is already built and just requires an upgrade and fitting out. Explore our garage conversion prices here.

The price for a loft conversion will vary and depends on the size of the build and also whether roof windows or dormers will be used. While prices start at around £25,000 we think you’ll pay closer to £35,000 for a fully fitted loft conversion with a dormer, add a bathroom and the price goes up further. Explore our loft conversion guide here.

For single and double storey extensions, check out our house extension cost guide.

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