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What is a structural engineer and why do you need one?

2 min read
Oct '25 • by Heather

Quick summary

A structural engineer is a professional who ensures your building’s strength, safety, and durability through clever calculations. They’re needed for projects involving building regulations, like extensions, loft conversions, or removing load-bearing walls. Costs typically range from £950 to £2500 including VAT for a project around the size of an extension, with higher prices in London, and they usually take a few weeks to deliver the plans and calculations.

Architect. Surveyor. Structural engineers.

When it comes to big home projects, you often find yourself confronted with a list of professionals that leaves you scratching your head. One of the biggest offenders is the structural engineer. Just what exactly do they do, and why do you need one?

Let’s find out…

What is an structural engineer?

Ever wonder why more building don’t just fall down? That’s because structural engineers exist. These professionals specialise in the structure of buildings, determining a project’s strength, durability, and safety - thanks to some very clever calculations.

They’ll tell you what steel beams need to be in place, where to put them, whether or not your structural glass has the strength for your home, and advise on the foundations of your project.

Because structure is so important to so many areas of your home, a structural engineer will often work alongside your architect and contractor, to make sure your home is as safe as it can possibly be.

When do I need a structural engineer?

You’ll likely need a structural engineer if you’re…

  • Building an extension
  • Converting a loft
  • Removing a chimney breast
  • Removing / modifying internal walls, especially load bearing walls
  • Fitting solar panels
  • Underpinning floors
  • Modifying / adding doors and windows

Basically, anything that involves building regulations, you’ll want a structural engineer involved.

What will a structural engineer provide?

The first thing a structural engineer is going to need is an initial brief on your project. For this, you’ll need provide as much background information as you can, including measured surveys already undertaken. They’ll then arrange a home visit, whereby they’ll make sure the measurements they have are up to scratch.

Once this has been taken care of, they’ll then liaise with your architect, if you have one, to put together a set of in detail plans to be submitted to your local building control.

How much does a structural engineer cost?

The price of your structural engineer depends on three things:

  • The size of your project
  • The type of project
  • The location of your engineer - London always sports higher costs

For any project like an extension, you’re likely to be looking at costs ranging from £950-2500 (incl. VAT). This should cover your site visit, production of calculations, and the drawings / plans produced in the end. To make sure you get the best quote, either approach three different companies to compare, or ask for a recommendation from a trusted professional.

At Resi, our Connect service introduces you to vetted contractors in your area to help assist you in choosing the right people for your project.

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