Renovating an Apartment in London: What You Need to Know

London's prime residential market is built on apartments — mansion block flats in Mayfair and Belgravia, lateral conversions in Kensington and Chelsea, modern penthouses, and period conversions across the city's most sought-after postcodes. Renovating these properties requires a different approach to renovating a house.

The constraints are real and must be understood before any design work begins.

The lease comes first

If you own a flat in London, you almost certainly own a leasehold interest — a long lease (typically 99 or 125 years) from the freeholder. That lease is a legal document that governs what you can and cannot do with your property.

Most leases require leaseholder consent for:

• —Structural alterations (removing walls, creating new openings)
• —Changes to plumbing or drainage
• —Alterations to the electrical installation
• —Changes to the external appearance of the flat or building
• —Wet rooms or water features that might affect the flat below
• —Changes to floor coverings (many leases require acoustic underlays)

The process of obtaining consent varies from building to building. Some freeholders have streamlined processes; others are slow, expensive, or unreasonably obstructive. Before commissioning any design work, obtain the lease and read the alterations clauses carefully.

Building management and service charges

Most prime London apartments are managed by a managing agent on behalf of the freeholder or residents' management company. Before any renovation work starts, you will typically need to:

• —Notify the managing agent and obtain their written consent (separate from the freeholder's)
• —Agree on working hours (usually 8am–5pm Monday to Friday, with restrictions on noisy work)
• —Agree on delivery and skip arrangements
• —Provide evidence of contractor insurance
• —Pay a deposit against potential damage to common areas
• —Agree on a dust and noise management plan

Failing to obtain proper consent before starting work is one of the most common causes of dispute between leaseholders and their building management. ASAAN manages all consent applications as part of our project pre-construction process.

Structural realities

Unlike a house, you do not own the structure of your apartment — walls, floors, ceiling slabs, and the roof are typically held in the freehold and covered by the building's insurance. Any work affecting structure requires consent from the freeholder and, in many cases, the signature of the building's structural engineer.

In practice, this means:

Removing walls — even non-structural partition walls should be confirmed as non-structural by a structural engineer before removal. In older mansion blocks, what appears to be a partition may be carrying load from the floor above.

Opening up to create an open-plan layout — popular and achievable, but requires formal structural approval and may require temporary propping during construction.

Lowering ceilings or adding mezzanines — floor-to-ceiling heights in prime London apartments are often one of their most prized features. Lowering a ceiling for a concealed plant room can be controversial with the freeholder and should be discussed early.

Acoustic and waterproofing requirements

Two issues come up consistently in apartment renovation projects:

Acoustic separation — most leases require a minimum level of impact sound insulation between floors. Replacing a carpet with a hard floor (stone, timber, or porcelain) almost always requires an acoustic underlay or floating floor construction to meet lease requirements and protect the relationship with the occupant below.

Waterproofing — a wet room, large shower, or bathroom in an upper-floor apartment is a risk to the flat below. Correct tanking and waterproofing is not just good practice — it is essential to protect against the significant financial liability of a water ingress claim. ASAAN uses a full tanking membrane system on all wet areas, applied before any tiling.

Planning considerations

Apartments have no permitted development rights. Any alteration that affects the external appearance of the building — including changes to windows and doors — requires planning permission from the local authority, regardless of the lease position.

In practice, most internal alterations in apartments do not require planning permission. But if your project involves:

• —Changes to the external facade
• —New windows or doors visible from the street
• —Rooftop terraces or extensions
• —Basement works

...then you will need a planning application before work can start.

Cost ranges for apartment renovation in London, 2026

These are all-in costs for the renovation works, excluding professional fees and VAT:

Costs are driven by specification, structural complexity, the extent of services work, and the administrative overhead of lease and building management consent.

Working with ASAAN

ASAAN has extensive experience renovating prime London apartments — from Belgravia mansion blocks to Kensington lateral conversions. We manage the full process: lease review, freeholder and managing agent consent, structural assessment, planning (where required), and the build itself.

Get in touch to discuss your property, or see our Belgravia apartment project for an example of this type of work.