From the team behind Hampstead Renovations · Est. 2009 · Learn more
Process GuidesNW London

House Extension Process — Step-by-Step NW London Guide

Step-by-step guide to building a house extension in NW London. Design, planning, groundworks, structure, and fit-out. What to expect at each stage.

Getting the sequence right is the single most important factor in a successful renovation. In NW London period properties, where layers of previous owners' works often reveal surprises, a structured approach with clear stage milestones is essential. This guide walks through every stage in the order they need to happen.

Stage 1 — Feasibility and brief

Following the correct sequence of works is essential in any renovation project, but particularly in NW London period properties where the interaction between wet trades (plaster, screed), dry trades (joinery, electrics), and finishing trades (tiling, decorating) must be managed precisely. Carrying works out of sequence adds cost and time.

Each stage should be signed off before the next begins. Stage sign-off typically involves an inspection by the project manager or lead contractor, confirmation that any required Building Control inspections have been passed, and agreement that the next trade's work area is prepared and protected. This discipline prevents expensive rework.

Stage 2 — Design and architect appointment

Following the correct sequence of works is essential in any renovation project, but particularly in NW London period properties where the interaction between wet trades (plaster, screed), dry trades (joinery, electrics), and finishing trades (tiling, decorating) must be managed precisely. Carrying works out of sequence adds cost and time.

Each stage should be signed off before the next begins. Stage sign-off typically involves an inspection by the project manager or lead contractor, confirmation that any required Building Control inspections have been passed, and agreement that the next trade's work area is prepared and protected. This discipline prevents expensive rework.

Stage 3 — Planning application

Pre-application advice from Camden or Westminster planning officers is strongly recommended for any substantial project in NW3 or NW8. The service is paid (£200–£600 depending on project scale) but typically saves multiples of that cost by identifying issues before a formal application is submitted and refused.

Conservation area status adds an additional layer of planning constraint. Even if a work is not normally notifiable, if it affects the character or appearance of a conservation area, it requires consent. Camden's conservation area guidance and Westminster's equivalent documents set out what is and is not likely to be approved — reading them before applying is time well spent.

Stage 4 — Building Regulations submission

Each stage should be signed off before the next begins. Stage sign-off typically involves an inspection by the project manager or lead contractor, confirmation that any required Building Control inspections have been passed, and agreement that the next trade's work area is prepared and protected. This discipline prevents expensive rework.

Communication between trades is as important as the sequence itself. The plasterer needs to know where the electrician's first fix is; the tiler needs confirmation that the plumber's pressure test has passed; the decorator needs to know the joinery is complete. In NW London projects where multiple specialist subcontractors are involved, this coordination requires active management.

Stage 5 — Groundworks and foundations

Following the correct sequence of works is essential in any renovation project, but particularly in NW London period properties where the interaction between wet trades (plaster, screed), dry trades (joinery, electrics), and finishing trades (tiling, decorating) must be managed precisely. Carrying works out of sequence adds cost and time.

Each stage should be signed off before the next begins. Stage sign-off typically involves an inspection by the project manager or lead contractor, confirmation that any required Building Control inspections have been passed, and agreement that the next trade's work area is prepared and protected. This discipline prevents expensive rework.

Stage 6 — Structure and weatherproofing

Following the correct sequence of works is essential in any renovation project, but particularly in NW London period properties where the interaction between wet trades (plaster, screed), dry trades (joinery, electrics), and finishing trades (tiling, decorating) must be managed precisely. Carrying works out of sequence adds cost and time.

Each stage should be signed off before the next begins. Stage sign-off typically involves an inspection by the project manager or lead contractor, confirmation that any required Building Control inspections have been passed, and agreement that the next trade's work area is prepared and protected. This discipline prevents expensive rework.

Stage 7 — First fix services

Each stage should be signed off before the next begins. Stage sign-off typically involves an inspection by the project manager or lead contractor, confirmation that any required Building Control inspections have been passed, and agreement that the next trade's work area is prepared and protected. This discipline prevents expensive rework.

Communication between trades is as important as the sequence itself. The plasterer needs to know where the electrician's first fix is; the tiler needs confirmation that the plumber's pressure test has passed; the decorator needs to know the joinery is complete. In NW London projects where multiple specialist subcontractors are involved, this coordination requires active management.

Stage 8 — Plastering and second fix

Each stage should be signed off before the next begins. Stage sign-off typically involves an inspection by the project manager or lead contractor, confirmation that any required Building Control inspections have been passed, and agreement that the next trade's work area is prepared and protected. This discipline prevents expensive rework.

Communication between trades is as important as the sequence itself. The plasterer needs to know where the electrician's first fix is; the tiler needs confirmation that the plumber's pressure test has passed; the decorator needs to know the joinery is complete. In NW London projects where multiple specialist subcontractors are involved, this coordination requires active management.

Stage 9 — Fit-out and finishes

Communication between trades is as important as the sequence itself. The plasterer needs to know where the electrician's first fix is; the tiler needs confirmation that the plumber's pressure test has passed; the decorator needs to know the joinery is complete. In NW London projects where multiple specialist subcontractors are involved, this coordination requires active management.

Following the correct sequence of works is essential in any renovation project, but particularly in NW London period properties where the interaction between wet trades (plaster, screed), dry trades (joinery, electrics), and finishing trades (tiling, decorating) must be managed precisely. Carrying works out of sequence adds cost and time.

Stage 10 — Snagging and sign-off

Following the correct sequence of works is essential in any renovation project, but particularly in NW London period properties where the interaction between wet trades (plaster, screed), dry trades (joinery, electrics), and finishing trades (tiling, decorating) must be managed precisely. Carrying works out of sequence adds cost and time.

Each stage should be signed off before the next begins. Stage sign-off typically involves an inspection by the project manager or lead contractor, confirmation that any required Building Control inspections have been passed, and agreement that the next trade's work area is prepared and protected. This discipline prevents expensive rework.

Ready to discuss your project?

To arrange a site visit or get a fixed-price quote, contact us on +44 20 8054 8756. All our work is fully insured, and we provide certificates for every notifiable piece of work we carry out.