A development of 13 homes in the Bedfordshire village of Sharnbrook has been certified to the requirements of the Passivhaus Standard, with a specification combining Kingspan’s premium performance insulation boards and the Kingspan TEK Building System of Structural Insulated Panels (SIPs).
Following a local survey, Hastoe Housing Association identified a need for affordable housing within the Sharnbrook Parish. Together with Parrott Construction and DP Architects, it developed the Lower Furlong estate to provide four homes for affordable rent, along with a further five shared ownership dwellings and four houses for general sale. In addition to creating attractive properties that sit naturally within the rural setting, the project team were also determined to minimise heating bills for owners by constructing the two storey properties to the Passivhaus energy efficiency standard.
The standard sets clear energy performance and space heating targets which must be met post-construction for properties to be certified. Homes must be highly insulated, airtight and virtually thermal bridge free. In order to meet these requirements, a number of Kingspan’s insulation solutions were fitted within the homes.
To insulate the beam and block floor construction of several of the homes, a 225 mm layer of Kingspan Kooltherm K103 Floorboard was installed. The boards provide outstanding insulation performance, with a thermal conductivity of just 0.018 W/mK across all thicknesses. This allowed the project team to reach a ground floor U-value of just 0.08 W/m2K on these properties whilst limiting the depth of groundworks.
Kingspan TEK SIPs were used to form the external walls of the properties and were fabricated and installed by Kingspan Timber Solutions (KTS). The panels feature a high performance insulation core bonded between two layers of OSB/3. Their proprietary jointing system helps to limit air-leakage whilst maintaining insulation continuity throughout the building envelope.
Once the designs were agreed for the homes, KTS cut the panels to the project dimensions including precisely measured entrances for the triple-glaze windows and doors. This accurate offsite manufacturing process limited the need for onsite adjustments and supported accurate detailing around openings to minimise thermal bridging. It also allowed the external walls to be rapidly erected with a small team of site operatives.
To complement the architectural style of nearby properties, brick was chosen for the external façade of the homes. In order to keep the overall construction depth to a minimum whilst achieving the target wall U-value of 0.10 W/m2K, a 120 mm thickness of Kingspan Kooltherm K12 Framing Board was installed on the outer face of the panels. The insulation board is designed for use in timber and steel frame constructions and achieves thermal conductivities as low as 0.020 W/mK. This performance, combined with that of the 142 mm Kingspan TEK SIPs, limited the external wall thickness to 457 mm including the external brickwork and cavity.
An airtight barrier was fitted on the internal face of the panels and airtight tape was applied to all junctions. By paying close attention to these details, the project team were able to keep air-leakage from all completed properties below the Passivhaus limit of 0.6 ACH @ 50 Pa. Mechanical ventilation heat recovery (MVHR) systems were installed in all of the properties to maintain a steady flow of fresh air within the homes. These systems use the heat from exhaust air to warm incoming fresh air – further limiting heating demand.