Working with a structural engineer will help to prevent long-term, costly problems for your self build or home extension. Here's what you need to know...

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When beginning a self build, extension or major renovation project, it can become confusing as to whom you should consult during the process, and for what purpose.

Of course, there are the obvious ports of call, such as the architect and contractor, who will make your dreams and visions a reality. Less obvious, but in many instances no less important, is the role the structural engineer can play in the journey.

Alan Lace-Evans, Technical Director at independent civil engineering consultancy Perega, explains when, where and why you may need to consult a structural engineer during your project. 

What is a structural engineer?

A structural engineer, in essence, analyses, designs, plans, and researches structural systems and components in order to deliver on the overall design objective and cost constraints. 

Broadly speaking, a structural engineer will be involved with the property’s superstructure, foundations and water drainage systems. However, our primary concern is to deliver structural integrity which ensures the safety of the owner/occupant.

When do you need to hire a structural engineer? 

Typically, a structural engineer would get involved in a project via the architect. On many Grand Design-type projects, the proposed building needs to fulfil so many demands that it wouldn’t be possible to achieve without their input. 

Understanding material performance is a key part of the skillset, enabling engineers to advise on how best to work with everything from steelwork and reinforced concrete to timber, masonry, glass and even carbon fibre. 

Often, structural engineers will have to make the owner’s, and architects, vision a reality within the confines of the possible. This is why it’s so important to work with a trained professional who understands the potential and limitations of specified products, fixtures and fittings. It will avoid major structural issues and huge disappointment at a later stage. It is more cost effective to iron out the issues at the planning stage rather than having to backtrack when issues arise over weeks/months of work.'

Engineering foundations 

This takes care of the superstructure - how the home is constructed and performs above ground. Digging a little deeper is the advice structural engineers provide on the foundations. 

This involves looking carefully at the geology of the area, particularly arranging for a geotechnical investigation of the area, which is hugely important to prevent long-term, costly problems such as subsidence and flooding. 

This could be as small as ‘trial pitting’, which is digging 1.5m into the ground to find out the lie of the land. For more complex projects, boreholes are undertaken, which go a lot deeper and can go down to depths of 30m; typically for a grand design project these would be about 10-15 metres at the most. 

This process identifies the first point at which there is a suitable bearing strata in the ground, after all you do not want the house to be sitting on loose fill or contaminated material. A structural engineer's skillset means it is possible to identify and design a suitable and appropriate foundation scheme at an early stage, saving a huge amount of hassle and remedial work later in the construction journey or further down the line, post-build.

Analysing serious problems

Structural engineers are regularly involved in a substantial amount of remedial work to existing buildings, mostly dealing with subsistence issues or structural failures caused because an expert was not consulted during the original build. 

Fundamentally, an experienced professional can help sidestep such issues, preventing excruciatingly expensive, and highly stressful, problems in the future.

Waste water and rainwater run-off

Structural engineers also provide consultancy advice for rainwater run-off from a building and its safe disposal. If you are living in a region with heavy rainfall (such as the English West Coast), you need to incorporate systems to prevent flooding. This may take the form of attenuation tanks or soakaways.

Regarding waste water from a building, the architect or contractor will want to know, at the earliest possible juncture, how it is to be disposed. This could be to a mains drainage system or an on-site sewage treatment tank were there are not any nearby sewers.

How do I find a structural engineer?

There are many reasons why you would involve a structural engineer in your project and it’s an investment which will pay for itself very quickly. 

However, as with anything, before you commit your strictly budgeted cash, make sure you are working with a quality supplier. There are many contractors who claim to offer a ‘one-stop-shop’, including structural engineering services, however, employing an independent, impartial engineer is preferrable as this enables them to report directly to the architect and yourself on structural options and to certify that works have been completed to the correct standards.

The best way to ensure you’re working with an accredited, skilled professional is to check they are members of the Institution of Structural Engineers. This is an official, globally recognised institution for the profession and certification confirms that you are working with a recognised expert. Furthermore, the organisation holds a categorised database of its chartered members, so you can find the right engineer for your requirements.

For more self build advice and inspiration, read Grand Designs magazine digitally for free now by registering your details. 

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