Structural calculations are the engineering proof that a proposed structure will safely carry its loads. Building control will not sign off structural work without them. They are required whenever you remove a load-bearing wall or chimney breast, convert a loft, or form a significant new opening. TM Architectural Designs Ltd provides engineer-signed calculations from £550, delivered within two weeks.
If you've been told you need "structural calcs" and aren't sure what that means or why it costs what it does, this explains what they are and when they're required.
What are structural calculations?
Structural calculations are the mathematical proof that the structure you're proposing will safely carry the loads placed on it. When you remove a wall, the weight it was carrying has to go somewhere else — usually into a beam, and then down through supports into the foundations. Calculations demonstrate that the beam you've specified is strong enough, stiff enough, and properly supported at each end.
Building control won't sign off structural work without them, and no competent builder should start without them either.
Which projects need structural calculations?
You'll need structural calculations for work including:
- Removing a load-bearing wall — the classic kitchen-diner knock-through
- Chimney breast removal — the stack above still needs supporting
- Loft conversions — existing ceiling joists are rarely adequate as floor joists
- Extensions — new openings, beams over bi-folds, and foundation design
- Loft or boiler installations where new point loads are introduced
- New builds — the full structural design
A reasonable rule of thumb: if you're taking something structural away, adding significant weight, or forming a large opening, expect to need calculations.
What is included in a structural calculation set?
A proper set isn't a single number. It works through the structure logically:
| Check | What it confirms | Consequence if omitted |
|---|---|---|
| Load take-down | Total load carried, including self-weight and imposed loads | Undersized members throughout |
| Bending | The member resists bending forces | Structural failure risk |
| Shear | The member resists vertical shearing at supports | Failure at bearing points |
| Deflection | The member does not sag beyond serviceable limits | Cracked plaster, sticking doors, bouncing floors |
| Lateral-torsional buckling | A steel beam will not twist under load | Instability in longer spans |
| Bearing and padstones | Beam ends do not crush supporting masonry | Local crushing and settlement |
- Load take-down — establishing what weight is actually being carried, including the structure's own weight, floors, roof, and imposed loads
- Member sizing — selecting the steel section or timber size that can carry it
- Limit-state checks — bending, shear, deflection and buckling all checked separately, because a beam can be strong enough yet still sag unacceptably
- Bearing and padstones — making sure the ends of the beam don't crush the masonry they sit on
- Connection and support details — how the load continues safely down to the foundations
The output is a signed document set your building control body can check, plus the specification your builder works to.
Why does deflection matter as much as strength?
A beam can pass every strength check and still be the wrong beam. Deflection limits control how much it bends under load. Get this wrong and you don't get a collapse — you get cracked plaster, doors that stick, and a bounce in the floor above. It's one of the more common reasons a "cheap" beam specification proves expensive later.
Who signs off structural calculations?
Calculations should be prepared and signed by a suitably qualified engineer, and presented in a form building control can review. Ours are engineer-signed and building control ready, prepared to Eurocode and British Standard methods with every limit-state check shown in full rather than summarised.
How much do structural calculations cost?
Our structural calculations start at £550 with a two-week turnaround. If your project also needs planning drawings — which most extensions and loft conversions do — the Full Package at £1,650 covers planning, structural and building regulations together, which works out considerably cheaper than commissioning each separately.
Do you provide calculations outside London and Surrey?
Yes. Calculations are prepared remotely and issued as engineer-signed PDFs, so the service is available UK-wide at the same fixed fee, with a concentration of work across Surrey, South London and Suffolk.
Each set is prepared to Eurocode and British Standard methods and presented in a form any building control body — local authority or approved inspector — can check.
Please note: this guide is general information for UK homeowners, not a formal planning determination. Rules vary by local authority and by property — conservation areas, listed buildings and Article 4 directions all change what applies. We confirm exactly what your project needs as part of your free quote.