Two storey extensions: Designing the right space

Adding space over two levels will provide the flexibility to transform your layout and will add signifi cant value to your home. Use this guide to fi nd inspiration and expert advice.

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ABOVE: This two storey glazed extension was added create a connection between the living spaces on the first floor and the kitchen below. Find out more…

Experienced renovator Michael Holmes advises on how to design a two-storey extension that enhances the original building.

Roof height

‘The main limitation on two-storey extensions is usually the roof height. Planning policy requires an extension to be sympathetic to the existing house, so the height of its ridge and eaves should not be taller than the existing roof.

‘Where a building has low ceilings, it can be difficult to build an extension tall enough to integrate two full (2.4-metre) storeys. However, there are solutions, such as using lower ceiling heights in the new rooms, especially at first-floor level, partially integrating upstairs rooms into the roof space, or setting the extension down slightly in the ground.

‘A shallow pitched roof can cover a large extension without being too tall, but this is not always acceptable, especially on a period building or in a sensitive location such as a Conservation Area. A flat roof can cover an area of any size, but is not usually considered acceptable for a two-storey extension, unless part of an overall contemporary design scheme of significant architectural merit. Other solutions for covering large extensions without too much height include creating a series of small intersecting traditional pitched roofs (at an angle of between 40 and 55 degrees), or an area of flat roofing “hidden” behind a more traditional pitched roof.’

Footprint and projection

‘Planning rules limit how far a two-storey extension can project, and how close it can be to the boundary, so as to prevent a loss of light to neighbouring properties. It must project no further back than a line set at 45 degrees horizontally from the centre of neighbouring windows – the so-called “sight lines”.’

Location and flow

‘Another major consideration is the position of the extension, as this will affect views, garden access, privacy, and which windows will be obscured. It’s also important to consider where the new space will adjoin the existing room plan. Ideally, any new principal rooms should be accessible from the main hallway and landing area. Often, part of an existing room has to be sacrificed to create the circulation space required.’

Natural light

‘The quality of space will be significantly reduced by the loss of windows, so those areas left without them should either be integrated within the new space or used as a room that will not need natural light. When adding a two-storey extension, it is common for the existing landing to lose its only window. In this instance, consider options to bring light in from above by adding a rooflight or sunpipe.’

Is it worth the cost?

A two-storey extension can offer double the floor space of a single-storey extension without costing twice as much. And since properties are generally valued based on size, it is worth considering an extension to your home. Costs will vary greatly depending on where you live in the UK and how complex your design is, but £1,250 per square metre is a rough guide. If you’ve already obtained a quote for a single-storey extension, double it and deduct 20 per cent to calculate an approximate total. Of course, extending over a garage and re-purposing, for example, will cost less.

Before you decide on your final design, speak to local estate agents to find out whether the cost of the work planned will match your home’s new potential sale price. This will reduce the risk of over-developing and overspending on your project.