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Updated: Jun 17, 2022

I’ve had a keen interest in basement conversion for many years and have prepared basement conversion plans for loads of clients even though I thought they were nuts to spend so much money digging out the earth under their homes to create more living space.

It used to be that doing a basement conversion rarely made financial sense unless you happened to live in central London or a very affluent suburb but the rise in house prices over the past decade has now tipped the scales to the point that doing a basement conversion anywhere in London may not be such a bad idea.


I’m sure that there are many reasons why homeowners choose to do a basement conversion but speaking to people over the years the primary reason seems to be the challenge and whilst quite a few of us seem to find the idea of having a whole new world under our house very appealing we tend to go with the flow and build upwards and outwards.

There is also the psychological aspect of having a subterranean retreat under your home which brings out the boy in most men; afterall, who wouldn’t want a secret den, or a hideout stuffed under our house.

There is also the question as to why some of us would have a preference to dig down rather than build up and I think that is also another big part of the puzzle as to why people do a basement conversion.


The big turn off for me was always that the cost of a basement conversion was really high compared to other ways of adding more living space. In fact, recent figures I have seen indicate that the build costs per square foot for a basement conversion are not far off double the cost of building an extension which reinforces my old argument.

Of course, what I didn’t know was that had I taken a more long-term view of the financial rewards of doing a basement conversion then my outlook would have been far more favourable.

To make my argument as to why a basement conversion can make financial sense we need to look at house prices over the past decade. From 2010 to 2020 house prices nationally went up by an average of 33%. Of course, those are the national statistics and the figures vary significantly depending on which part of the country you live.

This is how house prices changed regionally over the period 2010 / 2020:

  • London 66%

  • Outer Metropolitan Areas 54%

  • Outer South East 43%

  • East Anglia 43%

  • South West 38%

  • East Midlands 36%

  • West Midlands 33%

  • Wales 17%

  • North West 17%

  • Yorkshire & Humberside 17%

  • North 11%

  • Scotland 8%

  • Northern Ireland 2%

  • UK 33%

If you break down the house price rises yet again in London, you will find that some London boroughs have skyrocketed with price increases of 200% / 300% over the decade.

If you took a longer look, say from 2000 / 2020 you will find that Hackney had the highest rise of 427% and was closely followed by Waltham Forest which had a price rise of 415%.

My point of course is that had you invested £125k ten years ago in a basement conversion in the right part of London you could have had a return on your investment of 100% / 300%.

Of course, you will get a better return on your investment by building a house extension or converting your loft but if building up or out is not an option then a basement conversion may be a great long-term investment.

Just remember, for the best return on investment the key is still location when it comes to basement conversions.


Q: How Much Does a Basement Conversion Cost?

A: The cost of a basement conversion varies significently depending on various factors such as: size of conversion, depth of excavation and number of floors above.

Q: How Long Does It Take to Do a Basement Conversion?

A: It varies but 6 to 9 months is realistic from concept to handover.

Q: Can I get Planning Approval for a Basement Conversion?

A: Oddly enough, if you know the rules, getting planning approval is not that difficult.

Q: Can I Add a Basement Conversion to My Flat?

A: A great idea if you need the space or if you plan on holding the flat for a considerable period. In addition to planning you will need freeholder consent and you may be charged a premium by the freeholder.

Q: What Size are Basement Conversions?

A: Many basement conversions take a similar foorprint to the property above. However you can make them smaller if you wish.

Q: Will I Need a Party Wall Agreemeent?

A: Absolutely YES. The party wall agreement is an essential part of any basement conversion are you will be excavating directly under the party wall foundations.


If you are thinking about a basement conversion for your property then get in touch with Draw Plans for an informal chat. Draw Plans are Architecural Technicians and can create design plans and building regulations drawings for any type of conversion.

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