Do you need planning permission for a rear extension and garden room in Wandsworth?

In most cases, yes, particularly once a rear extension and a separate garden room are combined, as they were here. This project went through a householder planning application to Wandsworth Council, with pre-application advice taken first to confirm scale and materials before formal submission.

How long did this project take, from first design to completion?

From initial design through planning approval to building control sign-off, this project took around four months. A householder application with pre-app advice factored in early generally moves faster than a full planning route, which helped keep the programme tight here.

What was the approximate cost of this project?

Combined, the rear extension and garden room came to just over £110,000, split roughly £90,000 for the extension and £22,000 for the outbuilding. Costs like this vary with specification, particularly glazing and roofing detail, both a focus here.

Can Rosace deliver the interior design as well as the architecture?

Yes, interior design is in-house at Rosace, designed alongside the architecture from the first sketch rather than added afterwards.

Rear Extension Architect Putney, SW15

The brief

The client entertains often, and their existing layout could not keep up: not enough room for a proper dining table, and no natural spot to spill outside during a party. The brief was straightforward on paper and precise in practice, more space for living and dining, plus a garden room where the boundary between inside and outside could soften.

Rosace's response was a simple rear extension, with the living area stretched along the back of the house and a dining space to the side generous enough for a table seating eight with room to move around it comfortably. The garden room outbuilding was tucked into a corner of the plot, positioned and detailed so it reads as though it has always belonged there rather than as a later addition.

The idea for the garden room was to tuck it into the corner, as if it had always been part of the building.

Planning context

This project went in as a householder planning application to Wandsworth Council, covering the rear extension and garden room outbuilding together. Rosace began with pre-application advice, using it to confirm the council's expectations on scale, depth and materials before the formal submission, an approach that reduces the risk of delay or refusal on a terrace property where precedent from neighbouring extensions carries real weight. Householder applications of this kind are assessed primarily on their impact on neighbouring light and amenity, which shaped the extension's massing from the outset.

Design & materials

The rear extension is built on steel beam lintels, allowing the kitchen and dining area to open up without interrupting sightlines across the room. Externally, the brickwork is finished in white paint rather than left as standard London stock, a material decision led by Wandsworth's planning requirements, discussed further below. Slimline aluminium sliding doors run the width of the extension, opening the dining space directly onto the garden, and the flat roof is finished in liquid rubber for a durable, low-maintenance seal. Inside, herringbone wood flooring runs through the new living and dining areas, adding texture underfoot without competing with the room's simplicity.