Building Services and Thermal Performance
Building Services and Thermal Performance tests how heating, ventilation and insulation work together to keep a building warm, dry and healthy. Expect U-values, airtightness, thermal bridging, condensation and controls.
Core rules
- U-value measures heat loss through a build-up; lower is better. Include surface resistances and all layers.
- Thermal bridging is a localised path of higher heat loss at junctions; continuity of insulation reduces it.
- Airtightness limits uncontrolled air leakage; ventilation must still be provided deliberately.
- Interstitial condensation occurs when vapour reaches a surface below dew point; a vapour control layer and ventilation manage it.
- Controls and zoning match heat delivery to demand.
Worked example
A wall has Rsi = 0.13, Rso = 0.04, 100 mm insulation with λ = 0.022 and 100 mm blockwork with λ = 0.11. Insulation R = 0.100/0.022 = 4.545; blockwork R = 0.100/0.11 = 0.909. Total R = 0.13 + 0.04 + 4.545 + 0.909 = 5.624 m²K/W. U = 1/5.624 = 0.178 W/m²K. The reasoning is: convert thicknesses to metres, add every resistance, then invert.
Traps
- Forgetting surface resistances.
- Ignoring repeating thermal bridges such as studs or wall ties.
- Adding insulation without a vapour control layer where needed.
- Confusing airtightness with ventilation.
State the layer, the resistance and the effect on U.