Bellerbys College Case Study
 |
| Products Used |
Polyfoam Roofboard and Slimline Membrane |
| Project |
Bellerbys College |
| Client |
Pinnacle Group |
| Main Contractor |
Balfour Beatty |
| Architect |
Architecture PLB |
| Knauf Insulation Manager |
Andrew Tichy |
| “The Polyfoam Slimline system is a welcome
innovation in protected membrane flat roofs. The Polyfoam Slimline
system provides more than a 40% reduction in the thickness of
insulation required in comparison to a traditional protected
membrane build-up. This of course provides a significant cost
saving to the client and increased design flexibility for the
specifier.” - Andrew Tichy, Divisional Specification
Manager at Knauf Insulation. |
Challenge
A 3,500m2 protected membrane roof has also
been specified for the soon-to-be-completed extension to Bellerbys
College in Brighton. Its new multi-million pound International
Study Centre will house 62 classrooms, library, exam hall and
lecture theatre, 375 en-suite student bedrooms, cafeteria, internet
cafe and common room.
The roof will have some ballasted areas and some green roof
construction. Green roofs can be flat, pitched or curved and are
generally finished with sedum mats/plug plants (extensive systems)
or trees and shrubs (intensive systems). They deliver a number of
well-established benefits:
- Thermal insulation
- Acoustic insulation
- Rainwater retention/management of surface water run-off
- Reduction of urban temperatures (albedo effect)
- Improvements to air quality
- Provision of extra open space
Solution
By marrying together Polyfoam extruded polystyrene
rigid board insulation with the Slimline membrane, Knauf Insulation
has delivered a straight-forward solution to a problem bugging the
industry – that of water finding its way into protected membrane
and green roofs and having a ‘chilling’ effect within the roof
construction.
Before the 2002 changes to Part L of the Building Regulations,
manufacturers generally counteracted this ‘chilling’ effect by
recommending a thicker insulation, typically 120mm when using
XPS.
However, updates to Part L revised the conventions for calculating
U-values and advised designers to take more account of the chilling
effect, potentially pushing insulation thicknesses up to around
180mm. This increased depth would have created its own problems –
wind uplift calculations and upstand sizes had to be revised and
access to roof spaces became more difficult etc.
Knauf Insulation’s solution was simple – swap the filtration layer
used in this roof construction for its Slimline membrane. The
high-performance, non-woven polyethylene geotextile membrane is
water-resistant but vapour permeable (water vapour molecules are
small enough to diffuse through the fabric, liquid water molecules
are not). This prevents water collecting within the roof build-up,
allowing for reduced insulation thicknesses to to provide high
thermal and structural performance roofs.
