Simply SIPS

Tony Millichap, technical manager, Kingspan Insulation Limited discusses the reasons for choosing SIPs.

Many people dream of building their own home and, whether it is to be a futuristic timber clad construction or a traditional looking brick faced house, the one thing that they all share is the desire for shelter and space, comfort and aesthetics, an individual lifestyle under their very own roof. Structural Insulated Panels, or SIPs, offer a versatile and sustainable method of building a highly energy efficient home that can meet all of these requirements, in a matter of weeks.

SIPs have been used for decades in North America, and are becoming increasingly popular in the UK as a proven way of constructing very airtight and thermally efficient buildings, both for housing and non-domestic projects. SIPs can offer a number of clear benefits over more traditional methods of construction, including speed of installation, high levels of energy efficiency, airtightness and reduced waste. Add to that the flexibility to have pretty much any kind of finish to the exterior, and SIPs look like the ideal product for any self-builder to consider.

What exactly are SIPs?
An example of a typical SIP construction would be two 15 mm OSB3 (Oriented Strand Board) facings with a 112 mm rigid urethane insulation core, providing a thermally efficient, structurally strong, rigid panel. The panels are factory cut to the design of the building, ready to slot together like a giant 3D jigsaw puzzle using special jointing systems that provide very high levels of airtightness.

Because the panels are pre-cut ready to assemble there is very little onsite waste, the risk of defects is greatly reduced, and installation is extremely simple. Panels can be 1.22 m wide by up to 7.45 m tall, and the single fix installation format reduces construction time, and is less labour intensive. A quality weatherproof envelope can be constructed in considerably less time than if using some traditional methods of construction such as brick and blockwork, and tasks such as drylining the walls can be carried out at the same time as finishing the roof. Follow on trades also start sooner and can be programmed in without risk of delay, making project completion times more reliable and keeping costs down.

Thermal performance
One of the most important aspects of any home is its thermal performance. SIPs can provide a whole wall U-value no worse than 0.21 W/m².K, and U-values of 0.10 W/m2.K or better can easily be achieved with the addition of an insulated lining.

Finished constructions can produce air-leakage rates as low as 1 m³/hour/m² at 50 Pa, keeping the warm air in and cold air out. SIPs can also help to avoid problems which may be associated with other common construction techniques such as air-leakage through poorly sealed sockets or switches, at floor zones through masonry cavity walls, under skirting boards and through poorly sealed loft hatches and top storey ceiling light fittings.

As well as providing an effective air seal, the jointing arrangements in SIPs mean that the insulation layer is typically interrupted by less repeating studwork than in a timber frame, greatly reducing repeating thermal bridging. For example, in a property constructed with traditional timber frame, the repeating thermal bridges caused by timber studs in the walls and rafters in the roof, means that you could typically expect 15 per cent of the walls and 6 per cent of the roof to be uninsulated. By comparison, in a property constructed with SIPs, as little as 4 per cent of the walls and 1 per cent of the roof may be uninsulated.

These very high levels of performance mean that the size of any heating systems can be greatly reduced, keeping both capital and running costs down. By cutting energy demand with a ‘fabric first approach’ SIPs also greatly reduce dependency on expensive renewable technologies, and lend themselves easily to achieving the levels of performance needed to meet the Passivhaus standard, which requires almost zero heating.

Because the buildings can be so airtight, good, controlled ventilation is an essential part of the design. By introducing MVHR (Mechanical Ventilation with Heat Recovery), the energy savings can be further enhanced, as heat recovered from the old air being expelled is used to warm the incoming airflow.

Space saver
Where space is at a premium, the highly efficient integral insulation helps to make the most of the available footprint, keeping wall constructions much thinner than traditional methods such as brick and block, without loss of strength or thermal performance. Using SIPs for the whole construction also generates an intrinsic warm roof space, which can easily be designed as an additional room, or to provide a safe, dry storage area.

SIPs can provide all of the structure and the performance that could be required for the building envelope. All that remains then is to complete with whatever finish is desired, whether that is brick, render, timber, stone, tile or metal. The design possibilities are wide and varied.

SIPs for self-build
Building your own home can be an exciting prospect. Building with SIPs can help to make sure that projects are kept on track, that the finished building meets the designed performance, and that the ‘dream home’ is realised, with the added bonus of minimal heating bills.