House Extensions in Sutton: Single or Double Storey?

Building advice · Sutton

When comparing house extensions in Sutton, the first question is what your home needs most. A single-storey extension can improve ground-floor living, while a double-storey design can add space upstairs as well. The right choice depends on the property, the plot and how the rooms will work together.

Our Sutton building team serves homeowners in Sutton, Cheam, Belmont, Carshalton and Worcester Park. Here is how to approach the decision before developing detailed plans.

When a single-storey extension may suit your home

A single-storey extension can create a larger kitchen, dining space, living room or utility area. It can be a useful option if the upstairs accommodation already works and the main priority is improving how the ground floor connects to the garden.

Rear, side and wraparound layouts each make different use of the plot. Check circulation through the existing house, remaining garden space and daylight to rooms behind the extension. A more modest addition with a well-planned layout may solve the brief better than a larger footprint.

When to investigate a double-storey extension

If you need another bedroom or bathroom as well as more living space, explore whether a double-storey extension is feasible. The upper-floor layout needs to connect sensibly to the landing, and the ground floor should still work as part of the original house.

Roof design, window positions, neighbouring properties and the scale of the addition all need consideration. Do not assume that adding an upper storey is a simple upgrade to a single-storey plan. Our house extension service covers both approaches.

Compare the finished layout, not just the extra floor area

Draw the proposed furniture and fittings into each option. A new bedroom needs useful wall space and a practical route from the landing. A bigger kitchen needs room for storage, appliances and people moving through it.

Check what happens to the existing rooms. An upstairs extension that creates a long corridor, or a ground-floor addition that leaves a room without a clear purpose, may need more design work. Architectural plans can help you compare the whole-house arrangement.

Check Sutton’s planning guidance for your property

Some extensions can be carried out under permitted development rights when the proposal meets all the relevant conditions. Others need planning permission. The route depends on the design and the property’s circumstances, including previous additions and any restrictions on development rights.

Start with Sutton Council’s guidance on whether planning permission is needed. Do not assume that every single-storey extension is permitted development or that every two-storey proposal follows the same planning route. Check the relevant local authority for your exact address.

Building regulations approval is separate. Extensions also need appropriate structural and technical design. Where work affects a shared wall, boundary or nearby foundations, check whether notices are required under the Party Wall etc. Act.

Investigate the ground, drainage and existing structure

Before agreeing the construction approach, establish what needs checking below ground and where existing drains run. Trees, ground conditions, access and neighbouring structures can influence the design and the work involved.

If you are considering building above an existing extension or garage, its foundations and structure need assessing for the proposed loads. Existing walls should not be assumed suitable simply because the addition would fit above them.

Understand what drives the quotation

The number of storeys is only one part of the cost. Floor area, foundations, steelwork, drainage, roof design, glazing and the level of internal finishes all affect the scope. A new bathroom or a major change to the existing layout adds work beyond the outer shell.

Ask for comparable quotations using the same plans and specification. Confirm what is included for design information, approvals, services, kitchen or bathroom fitting, decoration and external making good. Discuss allowances, VAT and how changes will be agreed.

Could a loft conversion solve the upstairs requirement?

If the main need is an extra bedroom and the garden is important to you, a loft conversion may be another option to investigate. Its suitability depends on the roof, staircase and approvals. Comparing it with an extension at the brief stage can help you decide where investment will make the most practical difference.

Discuss your Sutton house extension

Tell us which rooms you need, what currently feels awkward and whether you have drawings. We can discuss the next steps for a single or double-storey extension shaped around your home.

Published 5 November 2026. General guidance: the design, permissions and technical requirements should be checked for your individual property.