Common Structural Engineering Mistakes to Avoid on Your Project
Common structural engineering mistakes often start with simple renovation ideas. Removing a wall, converting a loft, or building an extension changes how your property carries load. If you don't track the load path correctly, you risk sagging floors, cracked walls, or even structural failure. This guide explains the errors we see most often on site and how to prevent them.
Why Common Structural Engineering Mistakes Happen
Relying on guesswork
It is dangerous to assume a wall is not load-bearing just because it looks thin. In many UK homes, 100mm brick partitions carry floor joists or roof loads. Guessing is one of the most frequent common structural engineering mistakes.
Builders designing steel beams
There is no "standard RSJ". A beam that worked on another job might fail on yours. Builders construct; engineers design. Relying on a builder for calculations often leads to deflection or overstress.
Ignoring the load path
Your house acts as a complete system. When you remove a support, the load must go somewhere else. If you don't check where that weight ends up, you create weak points in the structure.
Serious Examples of Common Structural Engineering Mistakes
Removing walls without calculations
Knocking through a wall without proving it is safe is the biggest risk. Always verify the structure first. See our guide on removal of load bearing walls.
Undersized steel beams
Beams must be calculated for bending, shear, and deflection. If a beam is too light, it will sag and crack the ceiling. Always get a steel beam calculation.
Inadequate padstones
A strong beam is useless if it sits on weak masonry. You need correct padstones to spread the load into the wall and prevent the bricks from crushing.
Cutting joists incorrectly
Tradespeople often notch floor joists for pipes or cables. If these cuts are too deep or in the wrong place, the floor loses its strength and becomes bouncy.
Poor temporary propping
Structural failure often happens during the work, not after. Acrows and needles must be set up correctly before demolition begins.
Overloading existing foundations
Loft conversions and extensions add weight. The old footings might not cope. See our page on home extension structural design.
The Consequences of Poor Design
- Sagging floors: A clear sign of undersized beams or cut joists.
- Cracked plaster and brickwork: Movement in the structure transferring to the finishes.
- Twisting beams: Lack of lateral restraint allowing the steel to rotate.
- Roof spread: Removing ties allows the roof timbers to push the walls outward.
- Subsidence: Putting new heavy loads onto old, shallow foundations.
How to Avoid These Common Structural Engineering Mistakes
- Get structural calculations: Every alteration needs a specific design to be safe.
- Trace the load path: Understand exactly where the weight goes before you cut anything.
- Check the ground: You may need trial pits to check foundation depth before adding load.
- Prop securely: Ensure your builder uses sufficient temporary support during demolition.
- Submit to Building Control: Provide calculations early to avoid delays. See the Planning Portal for rules.
When You Need a Structural Engineer
- Knocking down internal walls
- Building an extension
- Loft conversions
- Removing chimney breasts
- Investigating cracks or movement
An engineer provides the calculations required for Building Control approval and site safety.
The Correct Process
- Site assessment
- Structural layout review
- Engineering calculations
- Technical drawings
- Building Control submission
- Construction begins
FAQ — Common Structural Engineering Mistakes
Do I really need calculations for one beam?
Yes. Building Control requires them to prove the steel is adequate.
Can my builder size the steel?
No. Builders construct; engineers design. Builders are not insured to calculate structural loads.
What happens if I remove a wall without checking?
You risk immediate collapse or long-term sagging and cracking.
Are Victorian houses harder to work on?
Often, yes. They have older mortar and shallow foundations that need careful checking.