How we measured a new house from its drawings to within 5 cm

Measuring a house by hand, one window at a time.

Every new home needs an energy calculation before it’s built. Every calculation starts with someone measuring the drawings.

Architects send a pack of PDFs: floor plans, side views (elevations) and cross-sections. An assessor checks the scale, measures every wall, floor, roof slope and window, then types the numbers into the energy software. It’s skilled, careful work, and it’s slow. Our client had a whole team doing little else.

The drawings don’t always help. Specifications go missing, so a coordinator spends 15 hours a week chasing architects for them. Sheets disagree with each other. And every update to the energy rules asks for more measurements, while the fee for each job stays the same.

The director put the brief in one sentence.

Three separate measurements of the same house.

We compared independent readings to find differences that needed checking.

We used a new house the client’s assessor had already measured by hand. We kept their figures back until the end, so they could be used to check the results without influencing them.

Claude read the pack twice and GPT once, each without seeing the other answers, so we could check readings from different models against each other.

We built a measuring tool that zooms into a sheet, finds the exact corners stored inside the drawing file and converts the distance to metres. The reader chooses the line to measure. The tool calculates its length.

Every number names its source sheet and shows how it was worked out. Each value shows whether it was measured, calculated or assumed, or whether it still needs the architect’s confirmation.

The label said 1:100. The drawing didn’t.

The side views were drawn at a different scale from the one printed on the sheet.

The side views were labelled 1:100. They were really drawn at 1:160. All three readings found the error independently by comparing the side views with dimensions printed on the floor plans.

Trust the label and every length on that sheet comes out more than a third short, and every area at well under half its real size. On this house, that would have turned a failed overheating check into a pass. The windows would have looked like 16% of the floor area, safely under the 18% limit. The real figure was 21%.

The system checks the scale of every sheet before measuring it. The assessor can see the scale used alongside the measurements.

Checked against the assessor’s own numbers.

Then we put our figures next to the assessor’s.

After we reconciled the three readings, 10 of the 11 window and door measurements matched the assessor’s figures to within 5 cm. The best single reading differed by 1.9 cm on average, with 10 of 11 within 5 cm. The remaining difference was a door measured to its frame in our reading and to the surrounding cladding by the assessor.

The three readings of the ground floor area came within 0.3 m² of each other, on a floor of 97 m². They also found a window drawn 1.20 m wide on the plan and 1.57 m on the side view, high windows shown on opposite sides on two sheets, and a missing solar panel rating. Each became a question for the architect.

Before the client received the figures, separate checks challenged the results and raised eight more issues. We confirmed, corrected or removed each claim they checked. Our code then recalculated every number.

A spreadsheet for the assessor to check and approve.

We designed the output for the person who has to sign it off.

The result is a spreadsheet in the same order the energy software asks for its figures: the main dimensions, all 18 windows and doors, the walls, floors and roofs, 323 metres of joins where heat can escape, the solar panels and the overheating checks. A separate tab lists everything missing from the pack, ready to send to the architect.

Every value links to a marked-up drawing with a box around the line it came from. The assessor checks those lines, resolves the open questions and signs off the measurements.

We also built a 3D model of the house from the measured values alone. Floors lift apart, every window can be checked against its source drawing, and where two sheets disagree you see the clash on the model itself.

1. Read the pack. Every sheet’s scale is checked before anything is measured.
2. Measure the lines. Every value comes from the exact lines stored in the drawing, in metres.
3. Compare the readings. Three separate readings are compared, then checked again.
4. Hand over. The assessor approves a spreadsheet with every source boxed.