SEN School, Walton on Thames, Surrey

Brief:

Funded by the Department for Education and Surrey County Council’s Special Educational Needs and Disabilities (SEND) Capital Programme, the school was built to a design produced by HNW Architects. The company’s proposals included specialist classrooms and support spaces, a library and a range of other facilities for pupils and staff. Outside, the plan called for new sports pitches, a multi-use games area, and extensive landscaping.

In addition to providing the badly needed free specialist places for pupils, the project sought to achieve a number of other important outcomes:

• To create a building that demonstrates exemplary levels of energy efficiency
• To meet the demands of the new DfE Spec 21 specification, which requires ‘Net Zero in Operation’ sustainability standards
• To provide learning environments that are warm, comfortable, quiet and calming

Given the team’s desire to make the school a beacon of sustainability, the design included a green roof with an extensive covering of solar PV panels, together with air source heat pumps and very effective insulation on the roof, floors and walls.

The main structure of the school comprised a steel frame overlaid with a suitable sheathing board to receive the EWI system. Over these, the installer, Express Group Construction, would install a non-combustible external wall insulation system designed and supplied by Permarock. This would provide the outstanding thermal performance demanded by the brief. In addition, its weatherproof silicone-based finish would help keep the walls protected and airtight, thereby eliminating cold draughts and contributing to a more secure and effective building envelope.

Importantly, the 250 mm mineral fibre boards would also provide effective acoustic insulation, which would help to block out extraneous noise, which could otherwise be distracting or upsetting for some pupils.

Further requirements were that, in accordance with the DfE Schools Output Specification, the chosen system should have a design life of at least 40 years. Additionally, it would meet a key fire safety requirement in the Schools Output Specification Technical Annex 2C: External Fabric, which dictates that “for all special schools, any cladding to external walls shall achieve Class A2–s1,d0 or better.”

Design and Specification:

The design team chose an EWI system by Permarock, which comprised:

• Permarock Mineral Fibre External Wall Insulation System with insulation boards of 250 mm thickness adhesively bonded and mechanically fixed to the substrate;
• Permarock Silicone^Ultra K Finish (textured render).

In this case, the Permarock Silicone^Ultra K finish combined with Permarock Mineral Fibre EWI system to all elevations and heights achieved an A2-s1,d0 reaction to fire classification (to BS EN 13501-1 “Fire classification of construction products and building elements.”) The system can be used on buildings of any height.

The Permarock Mineral Fibre Insulation was supplied in boards measuring 1200 mm x 600 mm were both adhesively bonded and mechanically fixed. They were installed in thicknesses of 250 mm on all external walls at the first-floor level. Other thicknesses were used as necessary to complete the detailed design of the system.

Permarock Silicone^Ultra K Finish is a flexible, vapour-permeable render with an attractive textured finish. It provides effective and long-lasting weather protection and allows very airtight facades to be created. Additionally, the incorporation of special preservatives and nano-quartz technologies helps it to resist the accumulation of dirt and unsightly growths. Consequently, it tends to maintain a clean, bright appearance for much longer than conventional finishes. In turn, this means that building owners can make appreciable savings on the costs of regular cleaning and maintenance.