Do I need a structural engineer for my extension? This is such a common question asked by homeowners building a new addition and yet the answer is not always a straightforward yes or no.
There are many reasons why the services of structural engineers are needed on a project and understanding these as well as what hiring this kind of professional entails is really important in ensuring your extension is a success.
"A structural engineer can investigate problems with your home, provide technical calculations for a home improvement project or give you an independent expert report if you are in a dispute, explains Paula Higgins, chief executive at HomeOwners Alliance.
Here, we explain when you will need a structural engineer for an extension to remove any guesswork from the project.
Do I need a structural engineer for an extension?
In most cases, a structural engineer's expertise will be required when building an extension, although there are certain instances where homeowners try to reduce their overall build costs by doing without.
"If your home improvements affect the building’s stability, you’ll likely need a structural engineer," advises Paula Higgins. "They provide drawings and calculations for builders, architects and Building Control to ensure compliance with regulations."
According to Paula, if any of the following apply to your extension, you will need to call in the help of a structural engineer:
Extensions to a property
Modifying doors/windows
Installing solar panels
Loft or garage conversions
Removing/modifying walls or chimney breasts
Structural inspections
Issues like cracks, movement or sagging ceilings/rooflines,
An Expert Witness Service is required
Disputes over structural matters, where an engineer can provide independent reports and advice
Paula Higgins
After spending 15 years reforming housing policy in government, enough was enough. Homeowners needed a voice and HomeOwners Alliance was born. Their Find a Structural Engineer tool is particularly useful.
Is a structural engineer required to remove a wall?
In the majority of cases, an extension will mean removing load-bearing walls, as well as some non-structural partitions.
"Structural engineers are required when you remove a load-bearing wall inside your home, and you need to replace it with a steel beam," explains architect Graham Ford of Graham Ford Architects. "You will need to know if the wall in question is structural. In other words, is it supporting floor joists or roof rafters, for example?
"This will depend on which way the joists run," continues Graham. "If they span over your wall, then it is probably structural and if you remove it the joists will need a steel support otherwise they will be spanning too far. If the floor joists run in the same direction as the wall, then it may not be structural, but I would always get a structural engineer to check. To work out which way your joists span you need to look at the original floorboards. Normally the joists run in the opposite direction to the floor boards, but the boards have to be the original floor boards not an overlay."
Removing a load-bearing wall will usually need input from a structural engineer(Image credit: Getty Images)
Graham Ford
Graham has been working for over 22 years in residential, academic, institutional and sports projects including the London 2012 Olympic Games and MIST university in Abu Dhabi with Landolt and Brown Architects. Recently completed projects include Leiths School of Food and Wine and West Reading Station. He is currently working on the River Club masterplan which includes a new gym and swimming pool and project managing the renovation of Grade II listed retail spaces above Paddington Station.
Do side extensions require the input of a structural engineer?
Side extensions are a really popular way of adding space to all kinds of properties, including terraced and semi-detached houses – but will you need a structural engineer for this type of project?
"When clients complete side extensions, often openings are made in the existing external brick wall so the area in the proposed side extension is connected with the existing space at the rear of the house," explains Graham Ford. "This opening needs to be supported with a steel beam and new foundations to support any accommodation on the first floor and so will need calculations from a structural engineer. The engineer will also design the concrete slab that the new extension sits on."
Is a structural engineer needed for building regulations?
While there is no legal requirement to use a structural engineer to gain building regulations approval for an extension, a set of calculations will be required either way. This will including calculations for materials, structural works, foundations, beams, load-bearing walls and so on.
Some homeowners do come up with their own calculations, or ask their builder to do this, but unless you are totally confident you can do this, it is best to leave it to the pros.
"The calculations structural engineers do are submitted to building control," adds Graham Ford. "Once the design has been approved and correctly installed then Part A of the building regulations can be approved. This sign off is one of the key parts of gaining your completion certificate along with thermal design, fire design and all other aspects of the building regulations."
FAQs
Do I need a structural engineer for a loft conversion?
Just as with extensions at ground level, the services of a structural engineer will also usually be required for loft conversions.
"When you design a loft extension with a rear dormer with a flat roof – which is very common – a new steel ridge beam is required to support the roof," explains Graham Ford. "There are new ridge rafters and a new floor structure to support the live loads (people) and dead loads (furniture, equipment and so on). Your architect will design the spatial arrangement, and they will work together with a structural engineer to design the structure."
How much does a structural engineer cost?
The number one reason some homeowners try to avoid using a structural engineer is down to worrying about extension costs – yet in many cases, using an engineer could see you making savings in the long run.
"Structural engineers typically charge £100-£200 per hour," says Paula Higgins. "Simple designs may cost a few hundred pounds, while expert witness services can run into thousands.
"It’s important to be clear what services are included in the quote provided by the engineer," continues Paula. "Talk it through carefully and get a breakdown of costs. For example, if you are engaging their help to produce technical drawings to be submitted to your local Building Control department for approval, check whether site inspections are included and be aware that if further changes are made by you or your architect or builder, there are likely to be additional charges to have the technical calculations and drawings altered."
Still unsure of the types of house extension that will give you the additional space you need? Check out our guide.
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Natasha was Homebuilding & Renovating’s Associate Content Editor and was a member of the Homebuilding team for over two decades. In her role on Homebuilding & Renovating she imparted her knowledge on a wide range of renovation topics, from window condensation to renovating bathrooms, to removing walls and adding an extension. She continues to write for Homebuilding on these topics, and more. An experienced journalist and renovation expert, she also writes for a number of other homes titles, including Homes & Gardens and Ideal Homes. Over the years Natasha has renovated and carried out a side extension to a Victorian terrace. She is currently living in the rural Edwardian cottage she renovated and extended on a largely DIY basis, living on site for the duration of the project.
