Structural Insulated Panels (SIPs) are another method of timber frame construction but their composition is very different from the other systems and produces some impressive properties.
What Are Structural Insulated Panels?
Whereas normal timber frame panels are constructed based around a softwood stud framework with sheet material fixed on either side with insulation in between, structural insulated panels dispense with the studwork frame and the timber sheet material is bonded directly to each face of the insulation producing an incredibly strong composite sandwich.
Animation from the Structural Insulated Panel Association (US) displays the SIPS system.
Oriented strand board (OSB) is often used as the structural sheet material and is basically made of small strips of wood, graded, orientated and bonded together with adhesive under compression. Although OSB is the norm, other materials including metals can be used depending on the application of the panel. The rigid insulating foam in the centre is usually polyurethane foam (PU) although again, other foam materials can be used.
The materials used and the composite structure of the finished panel removes the need for not only timber studs but also vapour barriers and breather membranes. Their inherent strength means they can be used for walls, floors and roofs. They can also be used in a non-structural capacity acting as infill panels or to produce an insulated shell with other construction methods.
SIPs are another modern method of construction that have actually been around for some time. They are popular in the United States where they have been in use for over 50 years.
The Construction Process
When constructing a home using structural insulated panels, excavation and foundation installation takes place as with masonry construction and footings are normally brought up above ground to damp course level using masonry materials. Due to the lighter structural frame, it is possible to have a lower foundation specification.
Scaffold is erected around the perimeter of the house and again depending on panel sizes and weights it may be necessary to hire a crane or lifting equipment.
Prefabricated SIPs manufactured in accordance with the house design are delivered to site and are erected, interlocking to form a continuous layer of insulation and so forming the inner skin of the house. This is the structural load-bearing element of the house supporting floors, the roof and internal loads. It serves the same function as the block work inner skin in traditional masonry and the panels in normal timber frame construction.
Upper floors are constructed as the framing progresses using solid timber joists or composite I joists and decking.
Roof construction can be traditional, roof trusses or can be constructed using more structural insulated panels which leave an open, usable and fully insulated space.
As with normal timber frame construction, a watertight shell can be achieved within days, allowing external facing and internal trades to progress simultaneously. SIPs can be compatible with any of the usual facing materials including brick, stone or timber.
Site work can be reduced further by pre-cutting window and door openings in the factory cut and incorporating wire chases into the panels. Plasterboard can be fixed to the OSB without the need to locate studs as there aren’t any!
Structural insulated panels boast the same advantages as open and closed panel timber framing but offer a few added extras.
SIPs offer the same advantages as regular timber frame construction including those offered by factory prefabrication. These advantages are listed on our timber framed houses page.
In addition to these there are some extra bonuses:
- Reduced labour times and costs.
- Doors, windows etc. can be factory cut.
- They are fast and simple to build.
- SIPs can be used as walls floors and roofs. Using panels for roof construction creates an open insulated roof space.
- Interlocking connections and the absence of studs means that insulation within the panels is continuous and cold bridging is eliminated.
- A higher level of air tightness can be achieved.
- SIPs achieve superior thermal insulation producing a comfortable living environment and energy savings.
- They use less timber than conventional timber frame construction due to removal of studs.
- Excellent structural performance in both compression and tension. The homogeneous nature of the structure distributes loads effectively.
- The continuous internal OSB face of the SIPs means that services, fixtures and fittings can be fixed anywhere without the need to locate studs.
The Structural Timber Association (STA) is another membership body committed to raising standards and driving innovation in the structural timber industry through research and guidance. There’s lots of useful information on the site.
You’ll also find more good information on the The Timber Research and Development Association (TRADA) website.
As with any timber frame method make sure that timber is sourced from properly managed suppliers who are FSC certified. Visit their site to find out more about their work.
SIPs boast some impressive credentials but make sure to research the options before you decide which method suits your self build needs.
Have a look through the rest of our construction method section to compare structural insulated panels with the alternatives.
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