Do I Need A Structural Engineer? 33 Times You Do

Check this list before starting your planned home improvements.

One of the most common questions about structural engineering on Google is, “Do you really need a structural engineer?” In this article, the BSF Consulting Engineers team share 33 situations in which you need to consult one and why.

How Do I Know If I Need A Structural Engineer?

As a rule of thumb, you need to speak with a structural engineer when you:

• Build a new structure
• Plan to make internal or external changes to an existing building
• Need to make repairs to structural features like the roof
• Install heavy fittings or equipment, such as a hot tub
• Need to prove a building is structurally sound to a bank or buyer
• Your building shows signs of distress, such as uneven floors and cracks
• And in case of fire, impact, storm, or flood damage. 

Why Should You Engage A Structural Engineer?

Seeking the guidance of a structural engineer will save you time, money, and potential headaches.  

Sometimes, they might simply reassure you about a threatening-looking crack in your basement. Other times, by analysing the potential impact of a home improvement project, they can save your house from developing structural damage. You will never regret consulting a structural engineer. 

Here’s how things usually work. The first step is a site visit: the engineer inspects your building and takes measurements. Next, they provide a report - either a structural survey or an appraisal - including calculations, ideas, and recommendations. Finally, they create engineering plans for your project if you request them. 

33 Times You Need A Structural Engineer

1) Knocking Down, Or Removing Part Of, An Internal Wall

A structural engineer must assess whether the walls you want to remove are load-bearing to prevent structural issues, such as cracks, sagging floors, and roof instability. 

If they are load-bearing, the engineer will design structural support to redistribute loads. Our engineers often use steel or timber beams and precast concrete lintels. 

2) When You Notice Cracks

The nature of cracks is often more complicated than it seems. A myriad of factors comes into play: how wide is the crack? How old is it? Where is it? What materials is the wall made of? Have you done any work to your home? Is the wall wet? How stable are the foundations? Is the structure subject to movement?

It’s always worth contacting a structural engineer when you notice a crack in your home. They will diagnose the cause of a crack and advise a suitable solution.

3) Installing Large Windows Or Bi-Fold Doors 

Before installing large windows and doors, ask a structural engineer if the new openings affect structural integrity and could cause deflecting (when a structural element, like a beam or the floor, bends or displaces under a load). 

If you need to remove a large part of a load-bearing wall, you will likely need to install a steel beam and possibly columns. Additionally, large openings might overstress the existing foundations, so changes, such as pad footings, may be required.

4) Loft Conversions

Loft conversions aren’t as easy to achieve as it may seem. 

When people undertake a DIY conversion, they often cut out the roof structure's struts and ties (the key components of the truss system). But these are crucial members - they work together to distribute load and provide stability. Removing them weakens the roof. That’s why you should consult a structural engineer before you start your loft conversion.

They will make sure the existing floor and roof can support the added load and provide a structural design for the new floor, staircase, and openings. 

5) Adding A Mezzanine Floor

Adding a mezzanine floor can add stress to a structure. A structural engineer must first verify the building’s load capacity and condition. 

You can integrate the new floor into the existing structure if there is capacity. If not, you may need to install posts and beams around the perimeter to support the new floor. 

6) Removing A Chimney Breast

Removing a chimney breast can affect load distribution and compromise your home’s structural integrity. Engage a structural engineer to assess whether that’s the case; if so, they will recommend the proper support. 

Say you’re removing a chimney breast in a ground-floor room and retaining it on the first floor. The easiest solution is to run a steel beam between two load-bearing locations, like walls. You can hide this within the floor zone (the structure under the floor) so it’s invisible. 

If the chimney breast you want to remove is in a party wall, the removal might also affect your neighbour’s property. So you will have to speak to them to agree on your approach.

7) Replacing Or Fixing The Roof 

If you need to replace or fix your roof, a structural engineer must confirm that the structure will stay sound once you’ve completed the work. Should it not be able to support the new roof, you will need to reinforce it. 

Our engineers recommend choosing a lighter material than the original roof covering so you don’t affect the structure. Bear in mind that, under new legislation, you might have to add insulation. This isn’t heavy, generally, but it still amounts to additional weight. 

8) Installing Solar Panels

Before installing solar panels, you should check with a structural engineer that the array’s load doesn’t exceed the roof’s capacity. 

If it does, you can either choose lighter panels or reinforce the roof structure with beams.

9) Installing Heavy Fixtures

Adding heavy fixtures, like large aquariums, safes, or stone kitchen islands, increases the load on a building’s structure. Before booking the installation, consult a structural engineer to ensure your home can support the new load.

If it can’t, you will need to add floor support to avoid deflection failure (when a floor bends under load, possibly causing cracking in finishes such as ceiling plaster). When you have no restrictions on ceiling heights, our engineers may recommend adding deeper floor joists.

10) Converting Attic Space For Storage

Most attics are designed for a lower imposed loading (the variable loads a structure must support) than other floors. Usually, the residential load is 1.5 kilonewton (kN) per square metre, while the typical attic load is 0.25 kilonewton (kN) per square metre. So, by using the space in the attic for storing heavy items, you’re increasing its potential for loading by a factor of 6. 

Chat with a structural engineer about turning your attic into storage space. Tell them what sort of things you plan to store up there so they can check if the joists can handle the increased weight. Even light things like clothes can weigh a lot when accumulated.

11) Barn Conversions

Agricultural buildings weren’t designed to be habitable. So, a barn conversion involves much more work than simply upgrading the roof, adding staircases, and creating new openings. 

For example, most barns come with concrete floors, so you’ll likely need to add some form of insulation, heating, and possibly a suspended floor. Upgrading to glazed doors likely means installing supports. Adding new windows can be challenging for steel barns because a steel structure may require bracing for stability; often this is installed at the corners.

Always consult a structural engineer before hiring an architecture firm for your barn conversion.

12) Selling Or Buying A Property That Has Been Previously Altered Or Converted

When selling a property that has been converted or altered in a way that could affect structural stability, you may be liable for future issues - if you don’t obtain proper approvals or provide required warranties. Beware of small projects, like installing solar panels, too.

So, if you don’t have the paperwork to prove the engineering for the work was done, you need to commission a structural survey. Likewise, if you’re buying a property that looks like it’s been converted or altered, you should arrange a structural assessment. 

If the work has put structural integrity at risk, the sale price might be lowered to cover the remedial work.

13) Creating Boundary Or Retaining Walls

When building a boundary or retaining wall, you need to consult a structural engineer to make sure it can handle soil and water pressure loads. 

If it can’t, an engineer may be able to suggest alterations to existing walls or a suitable alternative type, such as a gravity (slightly sloped) wall.

14) Basement Conversions

In the case of a basement conversion, an engineer needs to verify the structural stability. Waterproofing is also crucial for any kind of basement structure because it prevents water infiltration.

Bear in mind that if you plan to reduce the floor level, you may also need to underpin (strengthen or stabilise) the foundations, if they do not extend deep enough.

15) Adding A Wood-Burning Stove

If you live on the ground floor and want to install a stove, you can take the flue straight out through the wall and up the outside of the building - if local regulations allow it. This type of project doesn’t require any structural engineering work. 

If, on the other hand, you need to take the flue up through the building and exhaust it at the roof level, then you must seek the advice of a structural engineer. The flue will likely need to run through the floor joists, so you will need to reinforce the opening to ensure the structure isn’t affected.

16) Garage Conversion

Garages aren’t built for residential purposes. So, a structural engineer needs to check the condition of your garage and advise you on how to install insulation, upgrade the floor zone, add new windows, and change doors.

17) Before Making An Offer On A New Property Or Refinancing Your Property 

You may need to commission a structural survey before placing an offer on a building or refinancing your home. This depends on what the building survey for the building reveals.

A structural survey is a professional assessment of a building’s physical and structural health; it evaluates its stability to confirm it meets safety standards.

18) Adding Home Extensions And Conservatories

A structural engineer doesn’t only calculate the structural support required for the new walls, roof, and openings when extending a house. They also need to assess the foundations and ground conditions to make sure the extension is feasible. 

For example, tree roots might stop you from building deep enough foundations. Incidentally, cutting down the tree in question doesn’t solve the problem because the root system has lasting effects on soil quality. 

19) Creating A New Staircase Opening

When adding a new staircase to your home, you need to hire a structural engineer to assess the impact of the opening on the structure. The building needs to support a load that’s bigger than the opening. For a concrete floor, for example, the load imposed is three times as big. So you might need to add support like posts.

Here’s a tip from our engineers. The opening has less impact if its long dimension is parallel with the floor span. If you can, orientate the opening in this way.

20) Making Changes To Balconies Or Building New Ones 

Altering and building new balconies doesn’t always make economic sense. Hire a structural engineer to establish if it does and provide a solid design. Project feasibility depends on the size of the balcony and how much weight the existing structure is capable of supporting

There are two ways to add a balcony to a property. The easiest one is to suspend it off the building and add some posts on the corners. Alternatively, you can build a cantilevered balcony, which is much more complicated. You’d need to place beams between the floor joists to support the balcony, but cables and pipes are probably between these. So you might have to rewire and replumb your entire home.

21) When You Notice Uneven Or Sloping Floors

If you notice your floors are becoming uneven or sloping, a structural engineer must establish the reason behind it and diagnose potential subsidence, rot, or structural movement. 

There are three solutions to this issue: accept and leave the defect. Relay the floor. Or, if the floor is stable, rebuild the levels and reboard it.

22) Designing Drainage

Any project that involves drainage design, such as new builds, requires a structural or civil engineer. Good drainage design is essential to prevent flooding and preserve the foundations.

Suppose you’d like to install soakaway drainage - an underground system that allows surface water to drain into the ground. In that case, you will need an engineer to visit your property to check feasibility and design the system.

23) Fire, Impact, Storm, And Flood Damage

Fire and impact (for example, when a car is driven through a shop window) damage often cause structural issues. A structural engineer must verify if the building is safe to enter and the extent of the damage. 

If the damage is relatively minor, they will probably recommend temporary works to support what you're retaining and then rebuild. They may recommend demolishing and building from scratch if the damage is significant.

Storm damage is less likely to be structural; it usually involves coverings. A structural engineer often only needs to inspect the building and check the existing structure.

Timber and steel structures can develop rot after a flood. In that case, an engineer needs to design replacement items.

When it comes to fire, impact, storm, and flood damage, insurance companies are involved. So, the engineer’s recommendations will be tailored to the insurance’s coverage, where possible. 

24) Adding Skylights Or Roof Lanterns

If you want to add a skylight, a structural engineer needs to assess how to modify roof trusses or rafters to maintain the solid roof. 

If it's a traditional house with a cut and pitch rafters, you can cut the rafters out and add additional members on either side above and below the opening. That’s called trimming out.

If it’s a modern home, you will likely be unable to cut the trusses. One option is to install light tubes.

25) Securing A Mortgage On An Older Home

Suppose you want to secure a mortgage on an older home, and the building survey flagged potential structural concerns. In that case, you must commission a structural survey, which a structural engineer will conduct.

26) Converting A Bungalow Into A House

If you're adding a storey to a property, you need a structural engineer to assess the existing structure, its foundation’s load capacity, and the ground conditions. That’s because the added weight will transfer a more significant load to the ground. 

Once they’ve done this, they can advise you on the type of structure you can build. If you’re close to capacity, they will likely recommend a timber structure, as it’s lighter.

27) New Build Or Development 

When building a new structure, you need an engineer at every project stage: site visit, foundations design, structural frame design, roof and drainage design, load calculations, structural analysis, material selection, and scaffolding, props, or formwork design. They also need to provide approval to meet Building Regulations. Finally, they carry out site inspections and modifications.

28) Installing A Swimming Pool

You should hire a structural engineer when adding an in-ground swimming pool to your property, especially if it’s close to your home and trees. They will commission and analyse a ground investigation report to advise you on the project's feasibility. 

If the ground is weak, you might need to do ground improvement work or consider more substantial foundation options, such as piled foundations.

29) Converting Two Flats Into One

When joining two flats, you need to engage a structural engineer to assess how to remove or alter shared walls and modify load paths. 

Often, part of the shared walls is load-bearing. You will likely need to reinforce the structure using beams and frames.

30) Underpinning Foundations

If your foundations are no longer stable, you should underpin them. Consult an engineer to conduct a site investigation and interpret soil and tree surveys. 

They will be able to advise you on whether it’s worth underpinning and on the extent and sequencing of the works. The best practice is to work in metre sections, so each section can set before you move on to the next one.

31) Fitting A Hot Tub Indoors Or On A Deck

Did you buy a hot tub? Don’t install it just yet. A structural engineer needs to assess the tub’s weight and construction. For example, installing a hot tub with feet will affect your home differently than one with a flat bottom. 

A structural engineer also needs to check on your home’s condition and investigate drainage.

32) Replacing Timber Floors With Precast Concrete

If your timber floor is rotting and you can’t protect the timbers against moisture ingress, you might need to replace it with a precast concrete floor, which is more resistant to moisture attack. 

However, you are going to massively increase the dead load - the weight of the flooring system. So, you need a structural engineer to check if the foundations can take the new load and design adequate support. 

33) Timber And Steel Frame Repairs

Timber and steel-framed structures can rot at the bottom. You likely need to remove and replace the rotting parts.

A structural engineer will assess rot and the frame’s structural stability and direct the repairs. 

At BSF Engineering, we offer civil, structural, heritage, drainage and building diagnostics, as well as architectural design services through our sister company, James Clague Architects. 

Our expert structural engineers provide solutions for all your structural needs - from design and inspections to alterations and foundation work.

If you need help with any of the projects we discussed above, contact us today for a free exploratory call. 

We have offices in Canterbury and work on both residential and commercial projects in London and throughout the South East.