The Cost to Convert a Basement

All you need to know about to renovating a basement including costs of materials, labour and time frames.

Cost to Convert a Basement

What the job entails

One of the main reasons for deciding on a basement or cellar conversion is a straightforward lack of living space. In London and other crowded cities with sky high house prices, a basement conversion, while far from cheap, can be cheaper than the cost of moving to a larger property, once you take into account stamp duty, removals costs plus the additional cost of purchasing a larger property. A basement conversion is also a good way to maximise the potential of your property, perhaps creating leisure space on a completely new floor level. This additional space can be used in many different ways, but popular options are a media room, playroom, games room, gym, sauna, extra bedrooms, nanny or granny flat, swimming pool, artists studio or just an extra bathroom. The possibilities are endless and whatever you decide to use the extra space for, it will likely increase the value of your house too!

A basement conversion project will always work out cheaper than moving if there is no excavation required to create the underground space required. The excavation to create this space is the most expensive and difficult part of the project. Especially if difficulties are encountered such as concrete slabs, sewer and drains, or awkward access for removing the excavated materials. Without major excavation, the job really just entails waterproofing the space and making it habitable with safe access and light. So converting an existing space that doe snot need extra headroom can cost half as much as having to excavate a new space from scratch.

During a basement conversion project, the builders will typically use the front garden for access and to create an external entrance/exit to the new level. Expect whatever garden you have to be pretty much destroyed! Landscaping the garden after the basement conversion maybe part of the quote you received, but often it is not. So budget for some extensive gardening work after the basement project, or if doing it yourself expect many hours of backbreaking work!

The UK currently builds the smallest new homes in Europe, this is thought to be mainly because of the high cost of land with permission to build, which in turn is caused by a lack of space. But basement conversions can add another whole storey to every new home without requiring any more land, or even add multiple storeys if required. Adding a basement is a simple solution and hardly a new idea, basements and cellars were common in most town houses built in the 19th century, so what we are really seeing is a surge in popularity for a traditional idea. Space is highly prized in inner cities and in London new basements several storeys deep are being excavated beneath existing homes. It is of course much easier to build a lower ground floor at the same time as the house construction, adding a basement retrospectively is a much more expensive option. But if you need the extra space, it can often be the best option.

In the large part, these new basements are driven by the need to get more built volume out of an expensive site, restricted either by physical size, or planning policies on footprint area or ridge height. This, in turn, is leading to great improvements in design and build quality and helping to bring down costs. A basement beneath your new home is a realistic prospect and well worth pursuing. Designed well, it can provide considerable extra space at a cost comparable with that above ground.

The cheapest basement option is a simple utility basement with no windows, fine for a workshop, utility room, wine cellar, or just for extra storage. With a little more money, space can be upgraded to make a gym, sauna or games room. But to use as living space (a family room, kitchen, office, extra bedrooms or bathrooms, then considerably more money will have to be spent in addition to complying with building regulations.

Light is crucial for creating quality extra space and living space should get priority of daylight and any space near the centre of the floor-plan with no light-wells should be utilised for cloakrooms, storage space and utility rooms. Light can be maximised by incorporating multiple light-wells, using a large open plan stairwell with glass balustrades and open tread steps, glass partition walls, glazed or partially glazed doors, flat roof-lights where the basement extends underneath the garden, and a good lighting scheme.

The Cost to Convert a Basement

To provide accurate pricing information we have contacted local and national companies, plus have used various online quotation tools. The figures provided should give a good rough idea of the costs involved if you are considering renovating your basement, but of course you will need to gather detailed quotes from tradespeople to get an exact price for your requirements.

The average material cost to convert a basement will firstly depend on the size and the quality of materials which are used. Material costs will include underpinning, any changes to current plumbing, new windows and electrics. Material cost will also vary when decorating the renovated space, such as flooring, light fixtures and paint.

The average specialist will usually charge around £150-£200 per day. Basement conversion specialists will often work in pairs to ensure the job is done as smoothly as possible. The overall labour price will be factored into the overall price quoted by the trade, which can be anywhere from £2000-£10,000 depending on location but will be mostly affected by the duration of the project.

Below are some estimated costs of hiring a specialist to renovate a basement

Job Description Avg. Cost Duration
Convert an existing basement £1000-£1800 / sq. m 2-4 weeks
Dig & underpin new basement £2000-£3000 / sq. m 2-6 months
Lower floor level & underpin existing basement £1500-£2500 / sq. m 1-2 months


Cost Breakdown

Individual costs to dig & underpin a new basement of 20 sq. metres - Total Cost: £50,000

45%

Materials
£22500

50%

Tradesmen
£25000

5%

Waste Removal
£2500

FAQ's

This is a popular but difficult question! There are many factors associated with this type of project and they all impact the overall costs. For example, the cost will depend on the type of property, size of the basement, intended usage, proposed plumbing and electrical services, current floor to ceiling height, access routes and the type of ground. Expect the total cost to be anywhere up to £1000-£3000 per square metre.
No, in most cases a basement can be constructed from scratch where there is no existing cellar.
It really all depends on the size of the area and the extent of the works, but typically a few months.
Tanking is just a specific form of waterproofing using a barrier product on a structure.
The majority of our people do remain in their homes during the conversion, but do expect some major inconvenience!
Yes, this is common and the basement can be extended below front or rear gardens, ground conditions permitting.