It’s a common question client’s ask, why do I need a structural engineer? Architects will design the look of a building or structure and a Structural Engineer calculates the various ‘forces’ and ‘loads’ (weights) that might affect a structure and design structural elements that will withstand them, including fundamental elements like foundations.
You might need a structural engineer for a new project, or there might be an issue with an existing structure such as a crack in your wall – a common sign there might be structural issue. Cracks are generally caused by movement within a structure (the building materials are reacting to a water or temperature change) or the foundations are moving because the ground is swelling or contracting because of a change in water levels.
The weight of the building, the potential for movement, and the primary forces that cause may cause movement or add weight are what structural engineers consider and calculate for. Some of the loads and forces they consider include:
- Dead Loads – Static forces that remain constant over time, like the weight of the building components such as beams, walls, floors, and roofs, as well as the permanent fixtures like plumbing, electrical systems, and built-in furniture.
Let’s say for example you want to remove a wall from your home, to open a kitchen dining area or you want to remove an existing door or window and add bi-folding doors. You will need to consult a structural engineer to ensure that the changes your planning are strong enough to support the weight of your home – otherwise you will have real problems. Determining load bearing walls is not always obvious, and a structural engineer will calculate and design the measures you need to take to complete the work safely and get is approved by building control.
If you are planning a loft conversion you will be adding weight, load, to your existing structure. More floor, furniture, plumbing etc.. a structural engineer will come and assess whether your existing building and its foundations will be able to support the weight of the new conversion, and if not they can recommend design changes to make it possible. This is also the case if you are planning to add solar panels to your existing roof.
- Soil and Foundation Loads – The ground and the that sits on it creates soil and foundation loads. These include ‘bearing pressure’ from the weight of the structure and lateral (sideways) pressures from soil, especially for retaining walls (walls ‘dug into the ground to hold back soil) and basements. Engineers must assess soil properties and the ground conditions to ensure they design the right foundations which will support the structure.
If you are planning an extension or loft conversion (as mentioned above) structural engineers will need to asses the ground in which new foundations will be dug or assess your existing foundations to determine whether your foundations need reinforcing for any additional weight. Sometimes a trial pit is needed to assess the ground and/or existing foundations if no building records are available.
As mentioned above changes in ground conditions, excess ground water or the growth of nearby trees for example, might affect the water levels in the soil causing it to expand or contract. This movement can affect your building and cause cracks, or in the worst cases subsidence. A structural engineer will then need to asses the situation and design a long-term solution.
Other loads that might affect your structure and need to be taken into account are:
- Live Loads – Live loads are temporary or movable forces that structure must support like the weight of people, furniture, vehicles, and other movable objects. Live loads vary significantly depending on the building’s use, such as residential or commercial.
- Wind Loads – Wind loads are the forces exerted by wind pressure on the structure’s surfaces. These forces will vary depending on the building’s height, shape, and location. Engineers must design structures to withstand both the positive pressure on windward sides and the negative pressure (suction) on all sides, open and sheltered, and roof overhangs.
- Snow and Ice Loads – In regions with significant snowfall, structures must be designed to handle the weight of accumulated snow and ice. This is particularly important for roofs, which can experience varying loads depending on snow depth, density, and potential ice formation. This may not seem significant for the UK but the last thing you want to happen is your roof collapsing, in the ‘Big Snow’ of 1982 some areas saw 23ft.
- Thermal Loads – Thermal loads result from temperature changes that cause materials to expand or contract, take wood for example. These forces can lead to stresses within the structure, especially if different parts of the building heat up or cool down at different rates. Engineers must account for thermal expansion and contraction as this kind of ‘movement’ is what causes cracking and other damage.
- Hydrostatic and Hydrodynamic Loads – Hydrostatic loads are due to water pressure against a structure, like in a basement or a swimming pool – structures built into the ground. Hydrodynamic loads occur when water is in ‘motion’, like during a time of heavy rainfall or flash floods – the water exerts additional forces on structures. Engineers must design for these loads to prevent water-related damage and ensure stability.
If you are considering a basement or a swimming pool then understanding hydrostatic loads are critical. You don’t want to have a basement that develops cracks and leaks, or a swimming pool that is pushed up from the ground when you empty the water to clean it.
Depending on where you are in the world your structural engineer might also consider seismic loads, earthquakes, or impact loads, the likelihood of a sudden impact from the surrounding area. The list above is not exhaustive but gives you an idea of all the factors that need to be taken into consideration when designing or altering a building in any way.
In conclusion
Structural engineers consider a wide range of forces when analysing and designing not only structures but their foundations and the surrounding area. This comprehensive approach helps to protect both the physical integrity of the building and the well-being of the people using them.
If you have concerns about your home, or a planning an extension, conversion, basement or swimming pool and you live within 25 minutes of Oxford then give SWJ Consulting a call on 01993 225085. We are happy to have an initial chat with you and advice on the next steps. It might be that we need to come and complete a site visit to assess what you’re working with structurally or recommend further investigations so we can understand ground conditions and/or existing foundations.