Basement conversions in Hale and Bowdon: what's involved

When a house in Hale or Bowdon has run out of room to extend outwards, and sometimes out of planning goodwill too, the only direction left is down.

A basement can give you a cinema room, an office, a gym or a playroom without touching the garden. It is also one of the most technically demanding jobs you can do to a house, and the one where the price depends most on things nobody can see from the surface.

What we built in Hale

Our Hale basement was a full conversion beneath an existing house: structural underpinning, tanking and waterproofing, services, and the finished rooms, a cinema room, a home office and a lounge. It is one of several basement projects we've carried out across Hale, Bowdon, Altrincham and Cheshire, and you can see it on our site walkthroughs page.

The finished rooms are what people notice. The work that made them possible is mostly hidden, and it falls into three parts: holding the house up, keeping the water out, and making the space somewhere you'd want to spend time.

Holding the house up

Lowering a floor or forming a new basement means taking the ground away from under the existing walls. Those walls have to be carried down onto new, deeper foundations. That is underpinning.

It is done in short sections, in a sequence set by the structural engineer, so that most of the wall is always sitting on undisturbed ground while each section is dug out and concreted. Temporary propping holds things in place where needed, a new floor slab goes in, and building control inspects as the work goes.

Spoil is the other practical issue. Every bucket of earth has to come out of the house and off the site, often through a single opening and a narrow side passage, and that shapes both the method and the programme.

If the walls being underpinned are shared with a neighbour, or the excavation comes close to their foundations, the Party Wall Act applies. Even detached houses on tighter plots can fall within its excavation rules. There is more on that in the Party Wall Act for homeowners.

Keeping the water out

Waterproofing below ground is designed to a British Standard, BS 8102, which describes three types of protection:

• Type A, barrier protection. A tanking material applied to the walls and floor to hold water back.
• Type B, structurally integral. The concrete structure itself is designed to resist water.
• Type C, drained protection. A cavity membrane lets any water that gets through the structure run to a sump, where a pump removes it.

For living space, designers often combine two types so there is a second line of defence. A pumped system needs regular servicing and a plan for what happens if the power goes off, and that should be in your handover information.

How much water is in the ground, and how high it sits, changes the design considerably. It is one of the main reasons a basement can't be priced properly without a site investigation.

Every basement is priced from a survey, because the most expensive part of it is the part nobody can see yet.

Making it a room you'd want to sit in

A basement used as living space needs building regulations approval, and building control will look closely at a few things.

Means of escape. In a fire, people in a basement room need a safe way out, either through a suitable window or door to the outside or along a protected route. Resolve this early, because it can decide where lightwells and stairs go.

Light and air. Lightwells bring daylight in, and mechanical ventilation keeps the air fresh and the humidity down.

Services. Heating, electrics and data, plus drainage. A WC or shower below the level of the main drains needs a pumped system.

Planning. Converting an existing cellar with no change to the outside often doesn't need planning permission. Digging a new basement, enlarging one, or adding lightwells that change how the house looks may well need it. Much of Bowdon and parts of Hale sit in conservation areas, so check with Trafford Council before you assume anything.

What it costs, and where to start

Our working figure for 2026 is £3,000 to £5,000 per square metre of basement floor area, excluding VAT, fees and abnormals. That makes it the most expensive floor of any house by a long way.

Where a project sits in that range depends on the depth, the water, how much of the house needs underpinning, how easily spoil can be got out, the party wall position and the finish. A cinema room is a different fit-out from a playroom.

Anyone who gives you a single figure for a basement before seeing the site is guessing. The full set of ranges is on our cost guide.

If you're thinking about a basement in Hale, Bowdon, Altrincham or nearby, send us the address, any drawings you have, and photos of the existing cellar if there is one. We'll tell you whether it's realistic, and what needs investigating before anyone can give you a proper number. More on our work locally is on our extension builders in Hale page.