Basement gyms in Marylebone.

Chelsea · SW3 · Chelsea townhouse, opened up and fitted outCompleted work, photograph

Many Marylebone homes already have a lower ground floor. A gym often fits there, with no new dig.

A Marylebone gym starts below the hall.

Lower ground: Often the gym’s space already
Policy 50: A single storey if you dig new
W1U · W1G: Terraces above shops, and mews

NU Projects is a design and build company in Fulham SW6, founded in 2010. We handle basement gyms and spa rooms 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 terraces usually have a lower ground floor, half below the pavement. For a gym, that floor is often enough. Lowering it a little can win the height a rack needs. A new dig is the second option, not the first.

Weights dropped below a flat travel through the structure. Neighbours above and beside will hear them. So the gym floor floats on an isolating layer. Mirrors and rack fixings avoid the party walls.

For a fresh dig, Policy 50 gives one storey below the lowest original floor. Since July 2016, that needs planning permission across the city. A structural methodology statement goes in with the application.

We renovated a listed Marylebone apartment, keeping its plaster and chimneypieces. In Chelsea we built a lower floor gym between lit pilasters. One team designs, prices and builds yours.

What the council allows in Marylebone.

Council: City of Westminster, under its City Plan of January 2026.
New storey: Policy 50 allows one storey under the lowest original floor.
Permission: Basement permitted development was removed citywide by Article 4, in July 2016.
Engineering: A qualified engineer’s structural methodology statement goes in with the application.
On site: Westminster’s Code of Construction Practice applies to every basement scheme.

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.