Drawing room with ornate Georgian plasterwork, a marble chimneypiece and tall sash windows.

Basement construction in Marylebone.

Marylebone · W1 · Marylebone listed apartmentCompleted work, photograph

Basements beneath Marylebone terraces, drawn to Westminster’s Policy 50. Engineered, priced and built by one team.

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A Marylebone basement, within the rules.

Policy 50
City Plan, adopted January 2026
1 metre
Of soil over any garden basement
W1
Georgian terraces, many above shops

NU Projects is a design and build company in Fulham SW6, founded in 2010. We handle basement conversion and construction in Marylebone W1, under one contract. A new basement dig typically runs £500k to £900k. Converting an existing basement runs £180k to £300k. Call 020 7731 6841, and a budget estimate typically follows within seven days.

Marylebone is Georgian terraces, many above shops and now split into apartments.

Westminster has a separate rule for short gardens.

A garden of 8 metres or less may take a 4 metre reach.

Above it, a metre of soil and a drainage layer keep the garden planted.

Sewer flooding is designed out with sustainable drainage and a pumped device.

We renovated a listed apartment here, keeping its period fabric. Our basements are in Fulham and Chelsea.

What the council allows in Marylebone.

Council
City of Westminster, whose City Plan was adopted in January 2026.
Storeys
Policy 50 permits a single storey under the lowest original floor.
Short gardens
Gardens of 8 metres or less allow a 4 metre reach.
Soil
A metre minimum, plus a 200mm drainage layer. Up to 1.5 metres for trees.
Sewers
Sustainable drainage and a positive pumped device guard against sewer flooding.
Flood risk
Flood zones 2 and 3 need a site specific flood risk assessment.
Neighbours
Westminster strongly encourages talking to neighbours before the application.

Source: Westminster’s City Plan, January 2026 edition, Policy 50. Read on 16 October 2026. Policies change, so we read them again for your address.

Our work in Marylebone, and below ground.

Drawing room with low sofas beside a tall sash window and panelled walls.

Marylebone·Apartment

Marylebone listed apartment

A listed Marylebone apartment, renovated with its period fabric kept.

See the project
Kitchen in dark figured timber with a dark marble worktop.

Chelsea·Townhouse

Chelsea basement and extension

A new basement and a kitchen extension in Chelsea, built by one team.

See the project

Completed work, photographs

What a basement costs in Marylebone.

£180k to £300kConverting an existing basement. A project total, from our 2026 cost guide.

£500k to £900k+Digging a new basement. A project total, from our 2026 cost guide.

Both guide figures are whole project totals.

A listed Marylebone house can add design and monitoring time. Fees, contingency and VAT are extra.

Open the calculatorThe 2026 cost guideBasement costs in full

How far can a basement reach under a small Marylebone garden?

Gardens of 8 metres or less allow a 4 metre reach.

Larger gardens keep at least half undeveloped.

How much soil must cover a Marylebone garden basement?

At least one metre, plus a 200mm drainage layer.

Up to 1.5 metres may be asked for, so trees can grow.

How is a Marylebone basement protected from sewer flooding?

Sustainable drainage and a positive pumped device, under Policy 50.

We design both alongside the waterproofing.

Does a listed Marylebone house rule out a basement?

Not by itself. Policy 50 protects heritage assets rather than banning basements.

The original hierarchy of rooms must stay in balance.

What does a Marylebone basement cost?

Converting an existing basement runs £180k to £300k as a project total.

A new dig runs £500k to £900k and more in our 2026 cost guide.

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