The short answer
To produce structural calculations an engineer needs a clear picture of what they are designing and what it carries. At a minimum that means measured drawings (a scaled plan and section), the spans of the opening or beam, the wall construction (solid, cavity, brick, block or timber frame), and — most importantly — what sits above the element: a roof, one or more floors, a wall, a water tank or another storey. They also need to know which walls are load-bearing, the property age and type, and the proposed layout change. For anything uncertain, an old building, or where the load path cannot be read from drawings, a site survey is usually required. Giving a complete brief up front is the single biggest factor in getting calculations back quickly, because it removes the queries and return visits that cause most delays.
The quality of the calculations — and how fast they arrive — depends almost entirely on the brief you give. Here is exactly what to provide.
What to send
- DrawingsScaled plan + section
- SpansOpening width, beam length
- Wall typeSolid / cavity / timber frame
- Loads aboveRoof, floors, wall, tank
- SurveyWhere load path is unclear
The core information every job needs
Whatever the project, the engineer is tracing load from where it lands down to the ground. To do that they need a handful of facts that you can usually gather before instructing anyone:
- Measured drawings: a scaled floor plan and at least one section showing the area of work — the more accurate, the fewer queries and the less chance of a chargeable visit.
- Spans and dimensions: the width of the opening or the length the beam must span, plus room dimensions and ceiling heights.
- Wall construction: whether walls are solid masonry, cavity, single-skin block, or timber frame — this changes both the load and what the beam can bear on.
- What is above: the single most important fact. A beam carrying only a single floor is a different design from one carrying a floor, a wall and a roof, or another storey.
- Which walls are load-bearing: if you are unsure, say so — the engineer will confirm it, often on a survey.
None of this needs to be exhaustive or expert. The engineer is not expecting you to know beam sizes or load figures — that is their job. What helps most is honest, accurate description: the dimensions you can measure, photographs of the area, and a plain account of what you want changed and what is above it. Where you genuinely do not know something, saying so is far better than guessing, because a wrong assumption fed into the brief produces a wrong design. A good engineer will tell you quickly whether what you have provided is enough to proceed on drawings alone or whether a visit is needed to fill the gaps.
Information that speeds the calculations up
Beyond the essentials, a few extra details let the engineer work without stopping to ask, which is what turns a week into a few days.
| Information | Why it matters | Where to get it |
|---|---|---|
| Property age / type | Sets likely construction | You / deeds / survey |
| Proposed layout | Defines the new openings | Architect's drawings |
| Floor / roof build-up | Sets the dead load | Drawings or survey |
| Existing foundations | Checks load to ground | Survey / records |
| Finishes (plaster etc.) | Sets deflection limit | You / specification |
Indicative checklist; the engineer will confirm what they need for your job. Sources: IStructE guidance; typical UK practice.
When a site survey is unavoidable
Sometimes drawings are not enough and the engineer must visit. This is normal and not a sign anything is wrong — it is how they confirm what cannot be read from paper.
Putting together a brief that gets it right first time
The difference between calculations that come back in a few days and ones that drag on for weeks is almost always the brief. Engineers spend a surprising amount of time chasing missing dimensions and asking what sits above an opening — every query adds days. A complete brief removes that friction and also lets the engineer quote firmly rather than hedging.
A strong brief to hand over at instruction looks like this:
- A scaled plan and section of the area, with wall thicknesses and the position of the new opening or beam marked clearly.
- A short written description of what you want to do — "remove the wall between kitchen and dining room", "convert the loft to a bedroom", "form a 3.6m opening for bifold doors".
- The loads above stated plainly: what is on the next floor up, whether there is a wall or chimney over the opening, and what the roof does — this is the fact engineers most often have to ask for.
- Photographs of the area, including the wall to be altered and the ceiling/floor above, which help the engineer read the construction before any visit.
- Any existing information you hold: old building records, a previous survey, the architect's drawings, or details of earlier alterations.
It also helps to involve the engineer at the same time as the architect rather than after the design is fixed. When the two work in parallel, the engineer can flag where a beam will be needed and roughly what size, so the layout allows for it and the final calculations confirm a workable design rather than forcing a redraw. If a survey is needed, book it at the point of instruction so it is not the thing everyone waits on. Provide all of this up front and the engineer can usually proceed straight to the design — which is how you get accurate calculations, a firm fee, and a beam your builder can order without a single chased question.
Frequently asked questions
Can a structural engineer work from photos alone?
Photos help an engineer read construction and plan a visit, but they are rarely enough on their own for calculations. The engineer needs accurate dimensions and an understanding of the loads above, which usually means measured drawings or a survey.
What is the most important thing to tell the engineer?
What sits above the element being altered. A beam carrying a single floor is a completely different design from one carrying a floor, a wall and a roof, or another storey. This is the fact engineers most often have to chase, so state it clearly up front.
Do I need an architect's drawings before the engineer?
It helps a great deal. Scaled architect's drawings let the engineer work without remeasuring and reduce the chance of a chargeable site visit. Where there are no drawings, the engineer usually surveys the property to gather the dimensions themselves.
Sources & further reading
- The Institution of Structural Engineers — finding and briefing an engineer
- Planning Portal — Approved Document A (structure)
- LABC — preparing for Building Control
Figures on this page are typical UK ranges drawn from published sources and depend on your specific project. They are guidance, not a quotation.