Image showing a home extension

Building an extension

Many families outgrow their property – but the costs of moving are so high, many decide to extend and adapt their existing homes. A structural engineer helps ensure your work is safe and cost effective.

Who do I talk to first?

You should ideally consult both an architect and a structural engineer about your extension: you will need a design for planning and building regulations approval that includes both architectural and structural elements.

The design should clearly define the project so that a fixed construction quotation can be obtained.

On a small project the ideal is to find a designer who can supply both elements as a single agreement, if possible.

What sort of work is involved in building an extension?

Building will typically involve creating foundations for the extension; construction of the extension and roof; and linking through to the existing house - usually by removal of a section of the existing external wall. Then, once the shell is ready electrics, plumbing and finishes are added.

The Construction (Design and Management) Regulations 2015 (CDM2015) impose Health & Safety duties on all parties (client, designer and builder) involved in an extension building project.

The Party Wall Act may require a Party Wall Award to be made and if underground drains are nearby a ‘Build Over’ agreement may be needed from the local water company.

Why is a structural engineer necessary when building an extension?

An extension always involves structural engineering of the foundations, walls and roof. Increasingly, the rooms required are large open plan spaces and these require more innovative structural designs. And of course, supporting the first floor, wall and roof above the opening into the extension requires structural design and specification.

Often a designer will tell a client about the need for ‘structural calculations’ late in the process – which almost certainly leads to increased construction costs.

Involving a structural engineer early can help identify minor design changes which make the scheme far easier and cheaper to build.

What can I expect the structural engineer to provide and/or guarantee?

The engineer should provide both construction drawings for the builder and calculations for Building Control approval. Whilst Building Control will inspect during the build phase, you may wish to have your engineer inspect construction to confirm that the structural design has been implemented correctly.

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