With growth in the use of modern methods of construction (MMC) in the new homes market, in part fuelled by the ODPM ‘Design for Manufacture’ competition (£60,000 home competition), this article features one particular form of MMC, Structural Insulated Panel Systems (SIPS).
Published by NHBC
SIPS are engineered building panels, manufactured in a controlled environment and shipped to site ready for erection. There are many variations in the type of SIPS available, but typically they comprise an inner rigid insulating core of expanded polystyrene (EPS) or polyurethene sandwiched between two outer skins of board e.g. oriented strand board (OSB) or cement-based board. The board is normally bonded to the insulation with proprietary adhesive using a press to ensure a bond over the entire surface area.
Variations can include the use of different boards or insulation, the addition of strategic timber studs into the insulation core, and alternative methods for fixing the board to the core. The finished panels need to be handled with care after manufacture to prevent damage and possible de-bonding of the materials. SIPS can provide the external load-bearing walls and roof of a building, together with its load-bearing and nonload-bearing internal walls.
SIPS can also be used to form the external infill walls of structural concrete or hot rolled steel framed buildings. Homes with SIPS walls usually have upper floors formed with I-joists, metal web joists or timber joists, and these should be designed in accordance with NHBC Standards Chapter 6.4 ’Timber and concrete upper floors’. Like timber frame construction, the adequacy of connections between the panels, and between the panels and other components, are absolutely vital to the structural performance, durability and weather-tightness of the building. Careful planning of internal services is extremely important to ensure that wherever possible there is no disturbance to the load-bearing wall panels. Where this is unavoidable, consideration must be given on how to overcome the possible adverse effects on structural, thermal and acoustic performance. External cladding to the SIPS structure should be designed in accordance with NHBC Standards Chapter 6.9 ‘Curtain walling and cladding’ and in all circumstances a minimum 15mm drained and ventilated cavity is required between the cladding and the panels. As with timber frame, a breather membrane is needed to provide temporary protection during the construction process.
To satisfy NHBC Technical Requirement R3, SIPS are required to have a design life of at least 60 years, and consistent with our requirements for other proprietary building systems, SIPS will need to achieve satisfactory independent assessment before we can accept their use on homes covered by Buildmark. The independent assessment should be carried out by an appropriate technical approvals authority accepted by NHBC, including BBA (British Board of Agrement), BRE (Building Research Establishment) certification, or BM TRADA (Timber Research and Development Association). We would expect the independent assessment to be thorough and cover a range of issues including structure, fire, thermal and acoustic performance, air tightness, durability and weather resistance (cladding), fabrication, delivery, storage and erection.l Systems
Action
If you are considering using SIPS for any part of a home to be covered by the Buildmark, make sure that the design, fabrication and construction comply with NHBC Standards. Furthermore make sure that the panels have undergone appropriate independent assessment to confirm they will achieve satisfactory in-service performance for a design life of at least 60 years.