Building Services Design Engineer Interview Questions UK: 8 Real Questions and What Interviewers Want

Most Building Services Design Engineer interviews in the UK follow a pattern, and knowing it beats guessing. Below are eight questions from our bank of 12, each with a note on what the interviewer is really after.

Eight Building Services Design Engineer interview questions, and what the interviewer is thinking

1. How would you carry out heating and cooling load calculations for a new office floor, and which standards and software would you use?

Why they ask: Load calculations underpin every sizing decision, so they test core competence.

2. What does a typical week as a building services design engineer involve, and why did you choose this career?

Why they ask: They want to see you understand the role and that your motivation is realistic.

3. How do you coordinate your mechanical and electrical design with the architect and structural engineer in a BIM environment?

Why they ask: Coordination failures are the main cause of rework on MEP projects.

4. How do Part L of the Building Regulations and Part O affect your design decisions on a new building?

Why they ask: Regulatory compliance is a daily design driver and shows current knowledge.

5. At Stage 4 the architect reduces the ceiling void by 100 millimetres after you have sized the main ductwork. What do you do?

Why they ask: It tests problem solving under design change and how you protect performance.

6. Tell me about a time you value engineered a services design without compromising performance.

Why they ask: Cost pressure is constant and they want evidence you can cut cost sensibly.

7. How would you size the main LV distribution for a commercial building, including applying diversity?

Why they ask: Electrical sizing shows knowledge of BS 7671 and realistic load assessment.

8. The client wants to delete comfort cooling from a design to save money, but your model shows the spaces will overheat. How do you respond?

Why they ask: It tests integrity and the ability to advise a client with evidence.

A sample answer to question 1

How would you carry out heating and cooling load calculations for a new office floor, and which standards and software would you use?

I start by agreeing the design criteria with the client and architect: internal temperatures, occupancy, equipment gains, lighting power and ventilation rates, using CIBSE Guide A and the BCO guide for offices. I then collect fabric U-values, glazing g-values and air permeability from the architect. For peak loads I model in IES VE or Hevacomp, running steady-state heat loss to BS EN 12831 and dynamic simulation for cooling. I check summer performance against CIBSE TM52 so that we avoid overheating rather than just oversizing plant. Results go through a sanity check, comparing W/m2 against benchmarks, typically around 80 to 100 W/m2 for cooling in a modern office, and I query anything outside that range. I record assumptions in a design basis document, and keep it live because glazing and occupancy often change between RIBA Stages 3 and 4. Finally, I add sensible margins rather than stacking safety factors, which drives up cost and carbon.

Common mistake to avoid: Stacking safety factors on every input; Not updating loads when the architect changes glazing

Want the rest?

Full model answers, key points and common mistakes for all 12 questions are on the Building Services Design Engineer interview questions page. The first five are free, no sign-up needed.