Amalgamating Flats in the City

Given the confined footprint of many City apartments, a common strategy for high-net-worth individuals is to purchase the adjacent apartment—either laterally (next door) or vertically (above/below)—and amalgamate them into a single, expansive 'super-flat'.

While physically knocking through concrete walls seems simple, combining properties in the City of London triggers a cascade of severe legal, planning, and structural hurdles.

The 'Loss of a Dwelling' Veto

The City’s primary objection is mathematical, not structural:

• Policy Against Net Dwelling Loss: Like most central London boroughs experiencing intense housing pressure, the City enforces policies that explicitly prohibit development resulting in the net loss of residential units. Combining two flats into one means the City loses a housing ‘unit’. Unless you can prove the original units were exceptionally sub-standard or currently un-lettable, the amalgamation will be refused.
• Lateral Knock-Throughs: To merge lateral flats, you must pierce the dividing structural wall (the 'party wall'). Because City blocks are often massive, multi-tiered concrete structures, cutting even a standard doorway through a load-bearing shear wall creates complex seismic and structural risks, demanding immense temporary propping and heavy steel framing.
• Vertical Mergers and Staircases: Cutting a hole through a concrete floor slab to insert a new feature staircase between flat A and flat B above it physically compromises the acoustic and fire separation of the entire building. The Building Control requirements simply to install a spiral staircase between two stacked flats are extraordinarily punishing.

How We Can Help

If you are considering a major refurbishment, amalgamation or penthouse extension in the City of London, our in-house architectural and construction teams are highly experienced with the specific constraints and policies of this council. Do not leave your planning application to chance—our Planning & Permissions and Architecture services are explicitly designed to handle strict London authorities from initial conceptual design through to final, legal consent.

Once permission is secured, our Refurbishment & Interiors division carefully manages the execution, guaranteeing the design integrity is maintained throughout the build phase.

*Published in the Hampstead Renovations Planning Guide Collection — delivering expert design and build strategies for London's most heavily guarded conservation boroughs.*