Using Celotex insulation boards for the first carbon negative Passivhaus commercial office

Products Used:	Celotex GA4000
Sector:	Offices

A new office building at Watermead Business Park in Leicestershire has become the first carbon negative Passivhaus commercial office in England. With thermal efficiency and the creation of an airtight building envelope a priority, the choice of materials was of paramount importance. With this in mind, Celotex' GA4000 PIR insulation was chosen. 

Built by main contractor Interserve Construction in partnership with Raynsway Developments, the project was delivered by a multi-disciplinary design team including CPMG Architects, environmental building consultancy Couch Perry & Wilkes and structural engineers BWB. During the design stage, thermal efficiency was built into the structure's fabric as naturally as possible to help achieve Passivhaus accreditation for air tightness, ten times that of standard UK legislation. In fact, when the building was complete, air tightness tested at an 800% reduction from current building regulation standards.

The creation of an airtight and thermally efficient envelope was a priority for the project. To achieve this, a specification was created that included triple glazed windows and Durisol walling units - pre-insulated with 50mm thick Celotex GA4000. With these elements in place, the wall's U value was reduced to 0.15 W/m²K and ensured the building's total energy use is expected to be only 25% of the UK's current best practice.

Made from PIR (polyisocyanurate) with foil facers for improved emissivity, Celotex GA4000 helped the building to meet strict levels of energy efficiency.

To provide a thermally efficient envelope, an additional layer of Celotex GA4000 insulation was applied to the exterior block works. The exterior was then finished with Thermowood cladding. The internal walls were coated with two layers of plaster, helping the building to achieve a final wall U-value of 0.12W/m²K and air tightness of 0.885m³/hr/m² @ 50pa.

Interserve, now occupants of Watermead Park, has predicted that the new facility will save them approximately £20,000 in energy bills and almost 100 tonnes of CO2 emissions every year, when compared with the company's previous offices.

By using only the very highest standards of design, construction and product selection throughout the build process, the pioneering Passivhaus commercial property demonstrates why Celotex has the range of PIR solutions to help architects, contractors and specifiers set the standard for energy efficiency in commercial properties.

Key considerations

When using Celotex products, you need to satisfy yourself that use of the product meets all relevant national Building Regulations and guidance as well as local, national and other applicable standards relevant for your construction or application, including requirements in relation to fire and applicable height restrictions. In addition to the product datasheet, please refer to the following product documents:

• BBA certificates - where applicable to the application
• Declarations of Performance
• Health and safety datasheets

Celotex products should not be used in the external walls of buildings over 11 metres in height. Recent changes to Building Regulations mean that only non-combustible insulation or insulation of limited combustibility should be used in buildings of that height.

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