Services/Construction, structural & civils

Basement conversions in West London

The most technical work we do and the least forgiving. Waterproofing is designed in from the start, not patched on at the end.

WhatsApp a photo

16–28weeks on site, typically
Type Ccavity drain as standard
Party wallprocess handled for you
Engineerdesigned throughout

Listed, vetted and reviewed on

Ogival Ltd, registered in England & Wales no. 15191703 · Public liability insured · NICEIC registered electrical work · Gas Safe registered plumbing and heating

Digging out a London basement is a structural and a water problem at the same time, and the water is the one that comes back to haunt people. We decide the waterproofing strategy before the floor plan, because a basement that leaks in year three is not a snagging item — it's the whole job again.

Why basements go wrong

Waterproofing treated as a finish rather than a design. A membrane installed over a wall that was never detailed for it will fail.
Underpinning sequenced badly. Bays have to go in the right order, with monitoring, or the house above moves.
Access. Most London basements have no vehicle access, which is why the muck away and the plant strategy matter as much as the structure.

Basement conversions by Ogival in West London

Excavation, propping and below-ground construction

What's included in a basement conversion job

Our groundworkers and engineers handle the whole of it, so there's no second company to chase and no gap between trades for something to fall through.

Structural engineering and design
Party wall awards
Excavation and muck away
Underpinning in sequenced bays
Movement monitoring
Cavity drain membrane
Perimeter drainage channel
Sump and pump with backup
Drainage alterations
Insulation and screeds
Lighting design
Full fit-out

Send a photo of the cellar

A photo of each wall and the floor, plus anything that looks damp. We'll tell you whether it's a conversion, a tanking job or neither.

WhatsApp a photo Free site visit and written quote · No obligation

At a glance

ServiceBasement conversions
GroupConstruction, structural & civils
Typically16–28 weeks on site
CoveringWest London
BasedLondon W10

Why Ogival

25 years in London construction
Thirty-one trades under one contractor
Drawings and calculations in-house
A written schedule of works and payments
NICEIC and Gas Safe registered

How we work

Options

Three very different jobs people call a basement

Converting an existing cellar

Already a void, already the right height. Waterproofing, drainage and finishes rather than structural excavation.

Lowering an existing basement

Digging down to gain head height, which means underpinning the existing foundations in sequenced bays.

A new basement dug from scratch

No void to start with. Excavation, structure, waterproofing and fit-out — the largest and most technical version.

Quickest way to get an answer

Send a photo of the cellar.

A photo of each wall and the floor, plus anything that looks damp. We'll tell you whether it's a conversion, a tanking job or neither.

No form, no callback queue, no salesman. Emanuel looks at it himself and tells you what he sees — including the times the answer is that you don't need us.

WhatsApp a photo Call 07428 135100

OOgivalonline

We've got a cellar under the front of the house. Could it become a room? Photos attached.

That's a proper Victorian cellar, so you've got a head start — the question is head height and whether you need to dig down.

The white staining on the wall is salting, so it's taking water. Any conversion needs a cavity drain system designing in from the start.

Worth a visit. I can tell you in twenty minutes whether it's a conversion or a dig.

Message

A typical exchange. Usually answered the same day.

How it runs

How a basement conversion job runs, stage by stage

Four stages, and you'll always know which one you're in.

01
Survey and structural engineering
Ground conditions, the existing foundations and the water table decide what's possible and what it costs.
02
Design, consents and party wall
Structural design, waterproofing strategy, planning where required and the party wall process with every affected neighbour.
03
Schedule of works
Stage payments tied to structural milestones rather than dates.
04
Build the basement
Sequenced underpinning, tanking, services and fit-out, with monitoring throughout.

Excavation, propping and below-ground construction

Recent projects

Basements we've built

Two basements built from the ground up — one residential, one commercial.

Macfarlane Road, W12Read the case study →

Providence Villas, W12Read the case study →

Minotti Kitchens, W1Read the case study →

All our case studies

Permissions

Do I need planning permission for a basement?

In most West London boroughs, yes. Basement policy is tighter here than almost anywhere else in the country, with limits on footprint, depth and the construction method statement you have to submit. Building regulations and party wall awards apply on top.

Rules change and every property is different. We confirm what applies to yours in writing at the survey rather than leaving you to guess.

Most boroughs require full planning for new or extended basements, with a Basement Impact Assessment
A Construction Method Statement is commonly required, prepared by an engineer
Building regulations cover structure, waterproofing, ventilation, escape and head height
Party Wall Awards are needed with every affected neighbour, and take time to agree
Listed buildings need listed building consent as well as planning

Budget

How much does a basement conversion cost in London?

We don't publish prices, because a number without a survey is a guess and you'd be right not to trust it. These are the things that actually move it.

Depth of dig and how much underpinning is needed

Ground conditions and water table

Access for muck away and how spoil leaves the site

Number of party wall neighbours

Waterproofing specification and pump redundancy

Whether you're adding a bathroom or a kitchen below

How long does a basement conversion job take?

16–28 weeks on site on site for a typical job in West London, though the drawings, permissions and party wall process before it can add longer. We give you a written programme with the quote so you can see both.

A site visit and a written quote cost nothing, and the quote comes with a written schedule of works so you can see what every stage is for.

WhatsApp a photo

Before you appoint anyone

Four questions to ask before you hire anyone for basement conversion work

Ask them of us as well. The answers tell you more than the number at the bottom of the page — and a contractor who can't answer them quickly is telling you something too.

Ask us right now

01
Ask who designs the waterproofing, and whether it's a Type C cavity drain system
02
Ask what the pump redundancy is, and what happens in a power cut
03
Ask to see the underpinning sequence drawing, not just a price
04
Check they have run the party wall process before, because it will decide your start date

What clients say

Word of mouth, written down.

Left by Ogival customers on MyBuilder and TrustATrader

I have used this company for years for many different jobs including painting my whole house, tiling my bathroom, laying flooring, astroturfing my garden and putting up fences. Very knowledgeable, professional and polite. If you want a company that care, I'd stick with Ogival.

★★★★★Repeat client, MyBuilder

Ogival has a friendly and professional team. Our new bathroom looks great and we're very happy with the choice of products used and the quality of their work.
★★★★★New bathroom, MyBuilder

Great communication, polite workers and excellent tidying up afterwards. Definitely recommend.
★★★★★Painting and maintenance, MyBuilder

They were professional, polite, easy to get hold of and easy to deal with. They did a great deal of work for me including building an internal wall, moving a bathroom, carpentry, electrics and plumbing, they re-rendered my balcony, relaid the decking and repainted the whole flat.
★★★★★Full flat refurbishment

I have used this company for years for many different jobs including painting my whole house, tiling my bathroom, laying flooring, astroturfing my garden and putting up fences. Very knowledgeable, professional and polite. If you want a company that care, I'd stick with Ogival.
★★★★★Repeat client, MyBuilder

Ogival has a friendly and professional team. Our new bathroom looks great and we're very happy with the choice of products used and the quality of their work.
★★★★★New bathroom, MyBuilder

Great communication, polite workers and excellent tidying up afterwards. Definitely recommend.
★★★★★Painting and maintenance, MyBuilder

They were professional, polite, easy to get hold of and easy to deal with. They did a great deal of work for me including building an internal wall, moving a bathroom, carpentry, electrics and plumbing, they re-rendered my balcony, relaid the decking and repainted the whole flat.
★★★★★Full flat refurbishment

He replaced eroded bricks and once the wall was dry replastered ready to decorate. Work was delayed because he uncovered wet rot in the ceiling joists. He fixed the cause of those leaks. Throughout this saga Ogival has been professional, reliable, extremely thorough and honest.
★★★★★Exterior leak repairs, MyBuilder

I found them really helpful and honest. They went out of their way to help. They also finished on time and left the place spotless.
★★★★★Renovation, TrustATrader

I decided to go with them as I liked their ideas and Emanuel knew what he was talking about. He made floor to ceiling units, redecorated my room and laid laminate flooring. I have no hesitation in recommending them.
★★★★★Bespoke joinery, TrustATrader

Good finishing.
★★★★★Mohammed D., MyBuilder

He replaced eroded bricks and once the wall was dry replastered ready to decorate. Work was delayed because he uncovered wet rot in the ceiling joists. He fixed the cause of those leaks. Throughout this saga Ogival has been professional, reliable, extremely thorough and honest.
★★★★★Exterior leak repairs, MyBuilder

I found them really helpful and honest. They went out of their way to help. They also finished on time and left the place spotless.
★★★★★Renovation, TrustATrader

I decided to go with them as I liked their ideas and Emanuel knew what he was talking about. He made floor to ceiling units, redecorated my room and laid laminate flooring. I have no hesitation in recommending them.
★★★★★Bespoke joinery, TrustATrader

Good finishing.
★★★★★Mohammed D., MyBuilder

Read them in full on MyBuilder, TrustATrader and Houzz.

Where we work

Basement conversions across West London.

Basement work in Kensington, Chelsea, Notting Hill and Hammersmith, where the boroughs are strict, the neighbours are close and the access is almost always through the house.

Ogival, W10 5DW
Everyday patch, within 10 miles
Regular work, 10 to 20 miles
By arrangement, out to 30 miles

Where we do this most

Outside this? Ask anyway. We'll tell you honestly whether we're the right firm for the journey.

Questions we get asked

What people ask before digging down.

The questions that come up on the phone most often, answered the way we'd answer them on site.

Do I need planning permission for a basement?

In most West London boroughs, yes — basement policy is tight and varies by council. You will also need building regulations approval and, almost certainly, party wall awards with your neighbours.

How disruptive is it for the neighbours?

Honestly: it is the most disruptive work we do. Managing that starts with the party wall process and a realistic programme, and continues with keeping the street clean and the hours agreed.

What waterproofing do you use?

Usually a Type C cavity drain system — a membrane, perimeter channel, sump and pump — because it manages water rather than trying to hold it back. Often combined with cementitious tanking where it's appropriate.

What happens if the pump fails?

That's why the design includes a backup pump and, where we can, a battery or a second circuit. A single pump on a single circuit is not a waterproofing system.

The rest of what we do

Basement conversions, and thirty other things we do

Most jobs pull in more than one of these. Having them all under the same roof is what stops a project stalling for three weeks waiting on somebody else's diary.

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See all thirty-one services

Start here

Tell us what you're planning.

A site visit and a written quote cost nothing. If the job isn't right for us, we'll say so and point you somewhere better.

Free, no-obligation site visit and written quote
You deal with Emanuel, not a sales rep
A written schedule of works and payments before anything starts
Covering Kensington, Chelsea, Hammersmith and Fulham

07428 135100 info@ogival.co.uk

WhatsApp a photo See the case studies

Basement conversions in West London

Why basements go wrong

What's included in a basement conversion job

Three very different jobs people call a basement

Converting an existing cellar

Lowering an existing basement

A new basement dug from scratch

Send a photo of the cellar.

How a basement conversion job runs, stage by stage

Survey and structural engineering

Design, consents and party wall

Schedule of works

Build the basement

Basements we've built

Do I need planning permission for a basement?

How much does a basement conversion cost in London?

How long does a basement conversion job take?

Four questions to ask before you hire anyone for basement conversion work

Word of mouth, written down.

Basement conversions across West London.

What people ask before digging down.

Basement conversions, and thirty other things we do

Tell us what you're planning.

Contractors, trades and suppliers — let’s talk.

Tell us what you do