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Bartholomew Barn

Bartholomew Barn

The Kings School, Worcester required a new multi-purpose hall for sports, assemblies, drama, music & dance for their Junior School, Kings Hawford. The building was to replace the existing school hall (The Cobb, 141 m2) and would also be used external lettings and events.

The new multi-purpose hall would also have a requirement for a kitchen and servery for after-match catering and other functions and events, plus changing facilities with showers and bathrooms to suit all of the potential users.

The specification of the main external building fabric targeted providing optimum Thermal Comfort and Indoor Air Comfort. The external roof and wall systems used a combination of high-performance Isover Timber Frame Batt insulation and Vario KM Duplex* airtightness membranes, with internal finish linings from British Gypsum that would also ensure durability plus Acoustic Comfort within the Barn. 

Designing to ensure the thermal comfort of the pupils and teachers at Bartholomew Barn required designing the building’s temperature, humidity, airflow and radiant sources to all stay within an acceptable range for the activities within the building.

For the pupils and teachers to be thermally comfortable for the variations in activity likely to take place in the building – from lessons to drama to sport – the thermal design including ventilation needed careful consideration.

The Multi Comfort design for Bartholomew Barn used a well-insulated fabric achieved by a relatively thin overall construction.

The Barn makes use of the sun’s heat to warm the space, includes mechanical ventilation and heat recovery (MVHR) to moderate the air temperature and humidity, and move air when it’s too warm.

For larger events with more people in the Barn, automatic opening rooflights assist to expel air warm air if needed ensuring thermal comfort whatever the use.

Thermal Comfortcan only be achieved if the temperature being controlled by the high levels of insulation isn’t allowed to disappear through unwanted gaps in the building fabric.

A disproportionate amount of heat can be lost through the smallest of gaps.

The Multi Comfort criterion for non-residential new-build, for airtightness, is 0.6 V/h @ 50Pa (N50 standard). That is 0.6 air changes, by volume, per hour when the building is subjected to a pressure of 50 Pascal.

This is roughly equivalent to 1m³/m²h @ 50Pa for the UK Q50 standard.

In order to carry out the test, the building was sealed and blowers attached.

The blowers work in two directions. The blowers push air in (pressurisation) and draw air out (depressurisation) up to a pressure of 50 Pascal.

The amount of energy required to keep the pressure/depressurisation at 50 Pascal is then recorded. From this you can work out how airtight the structure is.

The test result for the King’s School in Worcester was 0.48 V/h @ 50Pa for the fabric airtightness test.

With this level of airtightness uncontrolled air infiltration is minimised and the introduction of mechanical ventilation provides controlled air circulation.

The system extracts stale air from inside the building and replaces it with filtered fresh air.

Seminal research links significant gains in productivity with Indoor Air Comfortfrom delivered fresh air and reduced pollutants.

That’s a difference of just 0.02, from the test undertaken in November 2015 at fabric completion stage with no service renovation – but we could have got a better result!

The opening roof-lights have a two stage seal in order to deliver the required performance requirements. The second seal delivers Passive House levels of airtightness.

When the final airtightness test was carried out, the windows were only sealed to the first stage.

Many potential air tightness pitfalls were designed out early in the project by choosing to mount services to the internal wall surfaces rather than having them penetrate the external structure and airtightness membrane.

Although the project was tendered in the usual way, Speller Metcalfe ensured all trades worked together, Toolbox talks were held and an airtightness champion appointed.

Each trade involved in the project knew of the impact their activity could have on the previous and following trades.

Like any project, changes were made along the way, but by working together the end goal, an airtight building, was achieved ensuring Thermal Comfortfor the occupants.

At the time of the build, VarioKM Duplex was the most advanced airtightness and moisture management solution available. However, due to Isover’s commitment to continual improvement, KM Duplex has since been superseded by the VarioXtraSafe range, which gives the same excellent levels of airtightness as KM Duplex, but greater control of moisture and is much quicker and easier to install.