What are Structural Insulated Panels (SIPs)?
Structural insulated panels (SIPs) are prefabricated building panels that can be used in place of conventional timber framing and insulation for the floors, walls and roof of a building. They combine a structural skin and insulation in one airtight panel.
- SIPs are (generally) 10 – 20cm thick, where rigid foam insulation is sandwiched between two stiff sheathing materials.
- Common sheathing materials are strand board (a reconstituted timber panel as pictured above), or plywood.
- Either expanded polystyrene (EPS), extruded polystyrene (XPS), polyurethane (PUR) or polyisocyanurate (PIR) are used to make the insulation foam.
- SIPs are also known as structural foam panels, foam-core panels, stress-skin panels, and sandwich panels.
The above image, courtesy of NZ SIPS (one of several manufacturers in NZ) illustrates the building process once the panels are in place:
- They are generally lined with internal cavity battens (as shown above in green) to create a void for a service cavity. This is so plumbing, electrical and other services do not interfere with the thermal and structural performance of the panel.
- Interior wall linings (such as GIB plasterboard or ply) can then be fixed to the cavity battens (not the SIPs directly) and plastered and painted as per conventional buildings.
- On the exterior, cavity battens are fixed over an air barrier (such as building paper), to provide the substrate for cladding systems.
What are the benefits of having a home constructed with SIPs?
- Airtightness – an airtight building envelope prevents drafts and air leakage, resulting in significant regulation of interior air temperature.
- Reduced cold bridging – cold (or thermal) bridging occurs when cold air is able to transfer from the outside environment, into the internal environment. Due to the panels having an insulated core and fewer framing members (due to the structural skin), the risk of thermal bridging is reduced.
- Fast track construction – the panels are prefabricated off-site and arrive ready to be slotted together like a giant Lego set, by the main project contractor.
- High performance & energy efficient – due to airtightness and reduced cold bridging, SIPs homes are much easier to heat and maintain a constant internal temperature. This results in reduced energy consumption and lower energy bills.
Considerations to make when choosing SIPs
- Cost saving – there are some notions that building with SIPs can be more economical than traditional timber-frame building. This is due to the speed at which the prefabricated panels can be assembled on site (saving labour costs). However, in our experience, this save in labour cost does not translate to a significant overall lower build cost. SIPs are a premium building material and its price reflects this. However, it is worth keeping in mind the long term savings that a SIPs house provides. You can expect reduced annual power bills and an overall warmer, dryer and more sustainable home.
- Design flexibility – because the panels are rigid and modular, there can be more design constraints compared to using standard building techniques and materials. However, this can be factored in early in the design process, so that it never really becomes a problem. A good designer will liaise with a SIPs manufacturer early in the design process. This ensures the design can be easily constructed with a SIPs system.
- Late stage change of mind issues – due to the above, if there does need to be a change in design during the later stage of the process, this can be a costly time investment. Even something that could be considered a ‘small’ change – say tweaking the dimensions of a room – can mean that the entire panel plan needs to be re-done.