Builders Job Costs

Basement Conversion Cost


A basement conversion is an excellent way to get more living space without needing to build a new extension or make any changes to your home’s external looks. Basement conversions have become increasingly popular over the last decade, especially in big cities like London.

If you’re considering getting a basement conversion done, but you’re not sure what the work will cost or what building regulations need to be considered, then you’ve come to the right place. Let’s get onto the important questions.

Do Basement Conversions Add Value to a Home?

Empty basement room

It makes sense to think that the increase in space that you’ll get from a basement conversion will add to the value of your home. But it’s not necessarily true.

Firstly, you need to factor in the cost of the basement work, as this can add up, so even if the value of your home rises, then it needs to go up more than the cost of the work for it to be financially worthwhile.

It’s best to contact an estate agent to discuss what you’ve got in mind and for them to suggest if your home will become more valuable after the new basement has been put in your home.

You should also remember that simply adding more space to your home through a new basement won’t add value because you have more space. It’s important to consider what that space is. For example, a gloomy basement won’t appeal to homebuyers in the same way that a well-lit, new basement will.

How Much Does a Basement Conversion Cost?

House basement

The cost of converting a cellar or basement will usually be calculated per square metre. But the cost that you encounter will vary dramatically depending on what kind of work needs to be done.

A simple conversion of your existing basement or existing cellar is the cheapest option available. You can expect to pay approximately between £1,150 and £1,450 per square metre to convert your existing cellar or basement into a new one.

Costs will rise if you need more complicated work to be done. For example, if the floor level in your existing cellar or basement needs to be lowered and the floor needs to be underpinned, then you’ll have to pay between £1,500 and £2,000 per square metre to get this done.

If there needs to be digging done, then you can expect the cost of the basement conversion to rise again. For example, if a new basement needs to be dug under your home, the cost will be between £2,000 and £3,000 per square metre.

If you get the basement dug underneath your garden, then this work is a little cheaper, with the average cost being between £1,750 and £2,250 per square metre.

Another job that can end up being quite expensive but is recommended for a lot of converted cellars and basements is the installation of a new lightwell. Similarly, building a new access point for the basement can be expensive too. Either of these jobs will be priced between £5,500 and £9,000. This is not calculated per square metre but simply for the whole job.

If you need a party wall survey done, then that will come to £700 for each of your neighbours. Then, in some cases, planning permission will be required too, and that’ll come to £172 for the application. If you need to get a building regulations application done, then this will be £750.

Do You Need Planning Permission to Convert a Basement?

Client Signs Document

It depends on the basement conversion that you get done. Planning permission isn’t required if you’re simply turning your existing space into something else without altering the floor level or ceiling height.

If, however, you are doing this, then you’ll need to put in a planning permission application. It’s unlikely that the council will reject your application if it doesn’t alter the looks of your home.

Of course, if you’re planning on creating a multi-floor basement as it has become common for the ultra-rich to do so in London, then you may come up against more obstacles. But for an average basement conversion, planning permission is usually granted.

Do You Need to Inform Your Neighbours that You’re Converting Your Basement?

Two men shaking hands

Yes, if the work affects party wall agreements. If you have an adjoining wall with your neighbours and converting the basement will mean that the walls will be worked on, then it could affect party wall agreements. It’s best to ask your contractor about this, as they’ll be able to inform you of all the relevant information.

How Long Does a Basement Conversion Take?

House basement

Once again, it depends on the space and exactly what’s being done to it. Let’s say it’s a simple job, where you’re just converting an existing space without any need to dig or alter the level of the flooring; then, this can be done in a matter of weeks.

If, however, you’re creating a whole new space under your home, then this will take much longer – perhaps a few months or more. If you do get this type of conversion done, then it’s also likely that you’ll have to move out of your house while it’s being done. That means you’ll have to factor in the price of finding alternative accommodation to the price of the basement conversion.

What Could Add to the Cost of a Cellar Conversion?

New home basement

There are a few different factors that can increase the price of a basement conversion. One big issue that you could run into is the ground conditions underneath your home. If you want to dig a basement to create a whole new living space, then the quality of the ground conditions will be extremely important.

For example, clay or marsh or sand will create more problems for a builder, and this could push up the price of the conversion. The same goes for the water table. If it’s high, then you’ll need special machinery to pump out the water at all times until the job is finished.