The full case study of the Woodland Trust (updated February 2015) is available to view here.
Matt Vaudin, Feilden Clegg Bradley
Building type, sector and stage
Non-domestic new build, office in operation, one year into study. East Midlands.
Natural ventilation, Glulam timber, timber frame, thermal mass, airtightness, embodied energy, night cooling, daylighting
This is one of a series of high profile buildings by architects Feilden Clegg Bradley and environmental engineers Max Fordham. It builds on the successes at their earlier building, the National Trust Central Office. It is unusual in being a timber frame building with added thermal mass, achieved by bolting "concrete radiators" to the undersides of the timber roof and floors. These add rigidity and absorb excess heat during the day, removed by ventilation at night in summer.
The designers say 400 tonnes of CO2 were saved by using a timber frame instead of a concrete structure, equivalent to 10 years of CO2 to heat and light the building.
The building provides accommodation for 180 full and part-time staff, plus another 140 people who visit only occasionally. A Building Use Studies survey showed that regular users like most aspects of the building, although they are less satisfied with noise, summer temperature and health.
The building has 15m-wide floors, with 4m floor to floor height. This, combined with light shelves and light walls and ceilings, means there is excellent daylighting. There is also task lighting on each desk, controlled by users, rather than the standard background lighting found in most offices. These strategies should bring significant savings. Early findings suggest that lighting energy is around 19kWh/m2/y, slightly better than ECON 19's Good Practice Benchmark.
Construction costs were modest for a headquarters building: £1,797/m2 (Q2 2010).
Woodland Trust considered IT energy carefully and specified ‘thin client' technology using low power terminals (using just 4 Watts) rather than PCs.
Like the low energy lighting, this both saves energy and reduces internal gains, helping to limit overheating in summer.
The building was handed over in October 2010, although some snags remain – notably problems with cooling in the server room, heating, hot water and window controls, and energy metering. Preliminary findings suggest that energy use for heating, hot water and ventilation is much lower than at the National Trust Central Office, although energy for IT is similar.
Overall CO2 emissions in use are currently about 50% above the ECON19 Good Practice benchmark, largely because of high energy use for the server room and cooling. However, the team has identified a number of opportunities for saving energy and work is in hand to address these.
|Floor area (GIA)||2,728m2|
|Floor area (Treated)||2,650 m2|
|Air permeability||2.44 m3/m2/h@50Pa|
|Building Regs estimate of CO2||16.2 kgCO2/m2/y|
|Measured electricity use||117 kWh/m2/y*|
|Measured gas use||34 kWh/m2/y*|
|Measured CO2 emissions (inc. unregulated energy)||68 kgCO2/m2/y*|
|Total CO2 emissions (inc. unregulated energy)||180 tonnes/y*|
* Estimated from limited data (no early meter readings, and unreliable metering)