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


Who’s the first person we call when we need a new extension? An architect!

But once your architect has sent you the plans for your dream home, they might mention you need a structural engineer. This comes as a surprise to some people.

Most have heard of the job title but are not always 100% sure what an engineer’s role is. Or what it is they do as part of the project.

Bearing that in mind, we thought it would be helpful to answer some of our most frequently asked questions about structural engineers.

1. What is a structural engineer?

When it comes to renovations and extensions, a structural engineer’s job is to calculate stability, strength and rigidity. They make sure the right materials are used for each project to make sure the extension is safe and secure. 

For example, if you’re planning to build a loft conversion a structural engineer will need to assess the structural condition of your existing house. i.e. can the existing structure support the weight of your new roof?

Not only that, but your engineer will also need to calculate the types, weights and dimensions of any steel needed to support your new loft extension.

2. When do I need a structural engineer?

There are two circumstances where homeowners might need a structural engineer:

2.1. Renovations or extensions

  • Building an extension
  • New loft conversion
  • Removing a chimney breast
  • Removing load-bearing walls
  • Fitting solar panels
  • Modifying/adding doors and windows
  • Building retaining walls in gardens

2.3. House Purchase

When buying a house, it’s important to know the existing structure is safe and in good condition before exchanging. Structural engineers will often carry out a structural survey before a house purchase and the mortgage provider may even insist on it. Common issues they would be looking for include:

  • Signs of subsidence
  • Structural movement
  • Cracking 
  • A sagging ceiling or roof line 

3. How much does a structural engineer cost?

As with all professionals, structural engineer fees can vary. For smaller projects like removing a chimney breast or supporting walls, you might find that engineers who work for themselves as sole traders charge slightly less than smaller or large companies.

But for larger scale projects such as multiple extensions or even a new house. The entire service offered by an engineering practice might be better suited. As they will have the expertise to offer more support.

Here are the average fees you should expect to pay a structural engineer for typical household renovation and extension projects. We have separated them into self-employed structural engineers and small/medium size engineering practices:

Project typeSelf Employed Engineer
Removing a chimney breast£300£500
Removing a load bearing wall£350£600
Single storey rear extension£700 – £800£1,000 – £1,200
Rear extension & loft conversion£1,000 – £1,200£1,500 – £1,700

4. What will a structural engineer provide?

4.1. Renovations and Extensions

Site Visit: Depending on the complexity of the project the first thing an engineer will do is carry out a site visit. They will double check which of the walls are supporting and the condition of your house in general. For example, if you’re carrying out a loft conversion, they will have a very good idea of the existing floor structure by going into your loft. This will inform them how a new floor would be best supported.

Structural drawings and calculations: These will show how your extension or loft conversion will be constructed. The design will go into details such as:

  • What type of timbers to use
  • The thickness of the steel
  • The type of concrete to be used
  • Whether it is a slab or block and beam floor
  • What type of steel connections are to be used and more.

Your builder will then use these drawings as a template for building your extension or loft conversion.

4.2. For structural Inspections

Visual Inspection: A structural inspection will normally involve an initial visual inspection and assessment of the property’s structural integrity. The engineer will look for signs of subsidence, cracking, sagging ceilings or rooflines.

Intrusive Inspection: If the engineer highlights any issues during the visual inspection, they may recommend further surveys to understand the exact extent of any issues. This could include

  • Making trial holes to expose foundations
  • Lifting floorboards to establish the size of joists
  • Cutting holes in the ceiling to establish how walls above are supported.

They will not only identify concerns but will also suggest possible treatments.

5. How can I find the right structural engineer?

Architect: As your architect will spend a huge amount of their time dealing with engineers, they will have a list of those they recommend. Not only will they have a good idea of what fees they charge but they will also have a good working relationship with them, which always helps.

Your builder: When building works start and the floors and ceilings are removed or uncovered, it’s quite common that builders find things that neither the architect nor engineer expected. Your builder will therefore always be in contact with lots of engineers if they work on different sites at once. They will certainly be able to recommend those with whom they have a good working relationship.

Friends and family:  We all know someone who has renovated their house or added an extension. No doubt that person will have worked with an engineer. Why not give them a call to see how the process went? Most importantly, find out whether the engineer delivered their drawings and calculations on time. Also, check if any revisions needed to be made during the construction process.  If so, were they provided quickly?

6. What’s the difference between a structural engineer and an architect?

What is a structural engineer
An engineer will make sure structures are safe and secure. An architect makes sure they look stunning.

This is a question we are often asked:

Architect: An architect’s focus is design, aesthetics and functionality. Their job is to bring all your ideas to life and prepare a set of plans for your dream home.

Structural Engineer: An engineer would take your architect’s designs and make sure they are stable, safe and structurally sound.

7. Anything else I should know?

Professional Indemnity Insurance: Due to the nature of engineering it carries with it a huge amount of responsibility. A small error in the structural design can be very costly to fix once your renovation or extension project is complete. For this reason, we would always advise that you check your engineer is fully insured before starting your project.

Scope of works: It’s also important to be clear about what services are included in your engineer’s quote. To avoid any issues we would always suggest that your architect prepares a clear brief of exactly what they need. For example, it is always worth double checking if an initial site inspection is included in their service. If not, what additional fees would they charge?

Amendments: As discussed above, when work begins it’s common for the existing structure once uncovered to be different to what the engineer or architect expected. If this happens and the structural drawings or calculations need to be changed, double-check if those amendments would be included within the original fee proposal. If they’re not, find out how much the engineer charges for basic changes to their drawings.


At Adara, our team of creative architects have a huge amount of experience with building regulations and the detailed design aspects of all renovation and extension projects.

If you already have planning permission and need any help or advice with the building regulations stage or would like us to suggest engineers who come highly recommended, feel free to call us anytime.

If you have some design ideas for a new project and are just tentatively dipping your toe in the water, you can also book a free 30-min consultation with one of our architects.

We’re always here to help.

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