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Going Underground: Top Ten Tips for Converting Your Basement in SW London

Last Updated on : 28th May 2015

By Zoe Dare Hall

Another week, another basement war.


Top Ten Tips for Converting Your Basement in SW London


Whether it’s Zipporah Lisle-Mainwaring painting her £15m Kensington house with red and white stripes in response to neighbours’ objections to her double basement plans, or Robbie Williams and his neighbour, Lep Zeppelin’s Jimmy Page, locked in verbal fisticuffs over Robbie’s desire to dig down, expansionist plans of the subterranean kind are guaranteed to get local residents hot under the collar.

Since the Royal Borough of Kensington & Chelsea tightened up on their basement rules in late 2014, other boroughs – including Wandsworth – have signalled their intention to follow suit and make it harder and costlier to get planning permission for basement digs.

Currently, a planning application in Wandsworth borough can be submitted for less than £2,000, according to Balham-based planning consultancy Revive Renovations, but that figure is likely to be at least £17,000 if stricter measures are introduced, which will require many more supporting documentation from specialist firms, including borehole investigations, tree reports, traffic management plans and dust, noise and vibration assessments. “All this takes time and costs money that could otherwise be spent at the other end on that cinema screen, wine store or sofa,” comments Rosie Caley from basement experts The Oxford & London Building Company (OLBC).

Wandsworth basement - OLBC

So, if you are thinking of digging down, there is no better time than now. Planning consent will typically last for three years – that’s the time you must have started work by – so best get it now before the rules change and costs go up. “Most of the cost is in preparing the plans, so even if you decide to ‘refresh’ the application in a couple of years to extend the life of your consent, now is the time to act,” says Caley. “And if you sell, the consent alone will be an incentive for any buyer.”

Here are the experts’ top tips:


1. Prepare for a basement to take up a year of your life, from planning to patching up the cracks: The dig itself will take about 3-4 months, the fit-out the same again – then you’ll need to patch some things up and wait for the building to settle. “It’s a very strange feeling knowing there is a big hole under your house and, more importantly, we totally lost the light in our living room for a few months as we had a big plywood box outside our house blocking our front window. We got some serious uplighters to see us through and it felt wonderful when the box was removed and we had natural light again,” says Jonathan Dyson from Hamptons International.


2. Family life can continue more or less as usual, however… “Believe it or not, doing a basement is less intrusive than converting a loft,” comments Richard Peel from Estbury Basements. “We are completely self-contained and don’t need to enter the house. We construct everything, and gain access from, outside. You won’t be connected internally to the basement until around halfway through the fit-out stage when the stairs go in – and by that point, you’ll want to be connected so you can see it evolve.”

Top Ten Tips for Converting Your Basement in SW London

Maya Brown, studio manager for build and design company Ashville Inc., adds that there is an unavoidable level of noise that comes with any major construction work, “but once the project is underway and site access has been created, clients have a level of normality when leaving and returning home”. That’s a big plus compared to the ‘move out or lose your sanity’ impact of a side return!”

3. Make sure your builders/basement company are adequately insured: One London couple recently saw their building crack in half and collapse due to basement builders who failed to support the structure correctly. The builders weren’t just incompetent – they were also insolvent, so the couple are unlikely to ever see the £300,000 in damages they were awarded. “It stands as a warning to others who reckon they can get by with the cheapest job on offer and close their eyes to due diligence,” says OLBC’s Rosie Caley.

Estbury’s Richard Peel adds that it’s neither easy nor cheap to get insurance to undertake basements “and there are only a handful of insurers out there who offer the correct cover – at a VERY high premium. There is no regulated organisation overseeing basement construction, meaning anyone can do it, so do your homework.”

4. Take time choosing the right people for the job: “We got six companies to come and quote. Two never came back and quotes from the other four ranged from £300,000-£400,000. One company took us around houses they had worked on and it was like meeting their fan club. Everyone was very complimentary, nothing was too much trouble, so we went with them,” says one NappyValleyNetter.

5. As prices for the work will be relatively comparable, OLBC’s Rosie Caley advises making your decision based on who you get on with best and how you want to approach the project. “Either hire an architect to draw up plans and get your consents then look for the contractor, or put the whole project from the outset into the hands of a specialist design and build company who have achieved the consents time and again,” she says. “The advantage of the latter is that we can reliably estimate the build cost before it is even drawn up, saving both time and money,” says Caley.

6. Think about what you’ll really need and use: most people build basements to create extra space for their kids, whether they’re toddlers or teenagers, and digging a half-house basement beneath the front of the house gives them the space they need and it costs about £200,000, which is about 60% of the price of digging a whole-house basement. But Tamzin Incledon from Douglas & Gordon would recommend going for the full front to back basement where possible – and is seeing more people digging beneath the garden too. “Although it’s a lot more expensive, it has the wow factor and the additional space. The best use of space is a TV room at the front, utility in the middle with an additional shower room/WC, then a bedroom/playroom at the back.”

2-Hillier-road, HamptonsAshville Inc’s Maya Brown adds that the primary focus of all of their clients is to create more living space. “Every project varies, but ordinarily clients will request a family living area, utility room and bathroom. The meticulous planning and detailed design that goes into each basement ensure they are rewarding spaces for families to use.”

EXAMPLE FOR SALE: Four-bed end-of-terrace in Hillier Road, SW11, with large converted basement that provides a store room and additional reception or even bedroom space under the whole front section of the house. “By far the most useful conversions for a family, as they create vast amounts of additional children’s space without having to interrupt the tranquillity of the formal sitting room above,” says Jonathan Dyson from Hamptons International. £1.85m. (click here).

EXAMPLE FOR SALE: Five-bed house in Bramfield Rd, SW11, extended into the side return, loft and basement.  The basement has been converted into a large reception room – an ideal playroom – with a utilities area. £1.775m, Marsh & Parsons. (click here)

bramfield road

7. Look at the payback: Jonathan Dyson reckons a half-house basement costing £200,000 is likely to add about £300,000 to the value to your house, while a whole-house basement will cost about £350,000-400,000 and see you break even. Why? Because £1.5m is the comfort zone for family houses in Battersea, says Dyson. Above that, the numbers of potential buyers drop off dramatically. So if you add a £400,000 basement to your house, there will be a small pool of buyers prepared to pay £1.9m for a big house with the same size garden as it had before. “For £2m, they could move to Tooting and get a stonking great house with a huge garden,” says Dyson.

OLBC’s Rosie Caley is more black and white about the pay-back of basements. “As long as you create GOOD space, you can’t fail to make a profit. It’s expensive to upgrade to a house with an extra bedroom, there’s the extra stamp duty and hassle to consider, so financially it can make a lot of sense to dig a basement.”

Other people’s reluctance to endure “the upheaval of a 10-month project” is also what will make your basement a valuable asset to buyers. “You’ll certainly get your money back on your spend immediately,” adds Tamzin Incledon.

8. It’s hard to go wrong if you live around Northcote Road: That’s where Marsh & Parsons’ Tom Crabtree sees most basement digs. “There are a lot of high value properties here with a relatively small footprint and owners have expanded every way but down. If you want a bigger house but want to stay in the area, it’s the only option. And buyers around here have deep pockets. The price per sq ft is getting to the point where a £250,000 dig down is still worth it.”

9. It’s all about seeing the light: Not every basement will add value – and those that don’t are invariably because they feel too dark and uninviting. “A basement needs to look like it’s always been there and that it belongs,” says Douglas & Gordon’s Tamzin Incledon. “Some estate agents have been less enthusiastic about the value-add to properties of creating basement space, but they have witnessed the good, bad and downright ugly over the years,” adds OLBC’s Rosie Caley, who says that a fully-fitted basement costs around £500/psf with average values across the whole area of £700-£800/psf. “Cramped ‘half footprint’ basements with poorly designed light wells could not be described as prime living space and were used mainly for utilities and storage or kids’ ‘play dens’. But basements have reached a new level of sophistication in terms of membrane waterproofing systems that eliminate damp and good quality design that maximises light and space.” Getting the light right is crucial. “You should have light wells at the front and back,” says Tamzin Incledon. “Connecting the light well so that it opens up onto the garden is a must,” says Marsh & Parsons’ Tom Crabtree.

Chatham Rd, Hamptons

EXAMPLE: For an example of expertly-done basements, Jonathan Dyson at Hamptons International rates a new development of four mews-style houses with large basements on Chatham Road, SW11. There are two types of property – two six-bed houses and two five-bed houses, some with media/family/play rooms in the basement, some with media room/bedrooms and studies. They are priced at £2.95m, Hamptons International.


EXAMPLE: A new-build seven-bedroom detached house in Patten Road, SW18, finished to an extremely high standard, with a huge lower ground floor which includes two bedrooms leading onto a patio, a wine room and media room. £4.75m, Rampton Baseley. (click here)

10. Keep the space open-plan: A cinema room can work well, as can a kitchen/family room. But it would make me nervous if someone says they’re turning their basement into a bedroom,” says Crabtree. Also keep the space flexible “so that the current owners have their needs met but the space can easily be adapted for the next person,” suggests Charlotte Martin from Rampton Baseley. “The use of the rooms is a personal choice and requirement, whether it’s for bedrooms and family space or a cinema room and gym.”

Nicosia Road_mandP11. Add lots of storage: If you are developing an existing basement space, then you will be losing vital storage space. Make sure your new basement design incorporates plenty of large cupboards to keep it hidden away.

EXAMPLE: A rental with plenty of basement storage: Five-bed semi-detached Victorian house on Nicosia Road with a basement that includes a guest cloakroom, large utility room and a huge amount of space for storage. Available to rent for £2,100/pw. (click here).

12 Dig deep:  “Digging dirt is expensive – it’s not like building a loft – but it’s worth the extra cost to dig down that extra foot as you will get it back. The aim is to make the space feel as non-basement as possible,” says Tom Crabtree. The legal minimum for basement ceilings is 2.3m, but go for 3m to avoid a dark, dingy feeling.

EXAMPLE FOR SALE: Six-bed house in Nicosia Road, SW18, completely refurbished by the current owners including a light, spacious basement with three-metre high ceilings in the main family room and masses of built-in storage. The basement also includes a well-equipped utility room/second kitchen, shower room, bedroom, two storage rooms and a gym (which could otherwise make an ideal media room or office). £3.75m, Rampton Baseley. (click here).

Nicosia Road

13.  Don’t stint on the fit-out: “What we’ve done is great, but if we’d had double the amount to spend, it would have been amazing,” says Jonathan Dyson, who spent £180,000-£200,000 on the dig and £60,000-£70,000 (minus VAT) on the fit-out of his basement in his Mallinson Road home.

Robert Ditcham, MD of Ayrton Bespoke, says homeowners tend to focus on the dig and the internal build “and the externals often get a back seat”. It’s worth paying extra on “value products”, he says, such as windows and doors that have to protect against the external elements. “Cheaper timber products cost less because they have inferior wood, glazing, paintwork, workmanship and ironmongery so they won’t last as long whereas a quality product can last generations. Upvc is also sourced in budget cases and it detracts from the original features of a Victorian property. It also won’t last as long as timber.”

14. Set aside money for redecoration: After the work is done, the house will take some time to get used to its new dimensions – and that will invariably lead to a few (hopefully manageable) cracks. “Our front door moved, which cracked the floor tiles in the bathroom above. Our neighbour also had some cracks as a result, so we set aside £10,000 to cover repairs. Legally, you only have to redecorate your neighbour’s house once, but if you want to stay friends…” says Jonathan Dyson.

Keeping your neighbours onside should be a key part of your basement planning. “A basement dig absolutely affects neighbours with the noise and dust, but we live in London and there has to be an element of live and let live,” says Tamzin Incledon. “However, if you make life unbearable for your neighbour who’s doing a basement, feel very sure the favour will be returned when you want to do it.”

15. Look out for opportunities with planning permission in place: There aren’t many around, but here are some…

EXAMPLE: Five-bed family house in Canford Road, SW11. It currently has 2,250 sq ft of living space and is wider than most mid-terrace houses in the area – but the next owner can expand it further by digging down as planning permission has already been granted. £1.675m, Rampton Baseley. (click here)

EXAMPLE: Four-bed house in Mallinson Road, SW11: This Victorian house has three floors currently and planning approval for a full basement and mansard extension. £1.5m, Rampton Baselely. (click here).

EXAMPLE: Two-bed flat with basement in Byrne Road, SW12: This large, elegant flat on the raised ground floor of a Victorian building – originally two townhouses converted into three large, lateral flats – also has a disused basement that is being developed. The flat also comes with planning permission to add a third bedroom and second bathroom to the ground floor. £649,000, Marsh & Parsons. (click here).

9-Altenburg-Gardens, Hamptons - opportunity to fit outAnd for those who want to add value but can’t face the hassle of months of digging work, here is an even rarer opportunity – a house whose basement has been dug but not fitted out:

EXAMPLE: Five-bed house on Altenburg Gardens with a basement ready to be customised: The owners of this modern-build house in Victorian style have dug a large (627 sq ft) front basement but, due to an overseas posting, are selling so that the next owner can fit it out to their own layout and finish. £1.795m, Hamptons International. (click here).

16. ‘If you want to do it, do it now for peace of mind: “I have no doubt that Wandsworth will eventually clamp down on basement conversions, but feel this move will be a long way off. If the homeowner is worried, then get the planning permission in place now,” advises Incledon.

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