3 Aug 2020
Modern building has seen a move away from brick and blockwork as the market identifies building methods that are quicker, safer, more sustainable, and easier to make energy efficient. Both structural insulated panels and timber frames have these increasingly sought-after qualities, and can achieve fairly similar levels of construction speed and thermal performance. Though both options are timber-based, there are a lot of differences between them.
Structural insulated panels are ideal for self builders wanting to create high-performing, energy-efficient homes. As their name suggests, SIPs come pre-insulated to such high standards that, even without additional insulated liners, they can achieve U-values as low as 0.18 W/m²K. Adding suitable liners can get this number down to as low as 0.09 W/m²K. SIPs support loads by their very nature as composite structural panels, and the external boards are bonded to the insulation they sandwich to prevent buckling. SIPs are prefabricated in a controlled factory environment. The precise cutting processes employed during the fabrication process means that when larger scale construction elements are joined together onsite, the finished construction is more accurate. Where SIPs are slotted together, joining splines can often be used and these significantly reduce thermal bridging when compared to a solid timber post. Buildings constructed using SIP systems can readily achieve levels of airtightness significantly beyond those required by the Building Regulations.
Timber Frame Systems
In general, timber frames are more economical than SIPs. Buildings constructed using SIPs can be around 15% more than timber frames. Timber frames support loads using regularly spaced studs, with insulation filling the gaps between them. Since the timber frame is the load-bearing element of the building, any brickwork will act only decoratively, rather than structurally, and must be tied back to the frame using wall ties. Most of the build components are measured and fabricated in a quality-controlled factory environment, leaving only the final assembly to be completed onsite, normally with the assistance of a crane. This results in less inconsistencies, lower labour costs, and improved health and safety, since the bulk of the assembly is carried out offsite.
The good news is that SIPs and timber frames can be hybridised. This can help manage costs and deliver impressive thermal performance without compromising on creative design features. Timber-frame walls supporting SIP panels on the roof will retain heat efficiently while also giving you the option for loft conversions. The composite load-bearing nature of SIPs can free up more space than other build systems.
So which is best?
There’s no clear answer here. Both build systems perform exceptionally in terms of thermal efficiency and they are both faster and more efficient to erect than masonry systems. They also both have slim profiles that can release additional floor space into the property. SIPs outperform timber-frame systems in terms of airtightness, but they do so at a higher price. Their airtightness levels are so good that a mechanical ventilation and heat recovery (MVHR) system is normally required to ensure air is kept fresh and circulated. So, if you want to build an exceptionally insulated Passivhaus, then SIPs are the method for you. If you want an energy-efficient house that still achieves levels of thermal performance superior to the national standard, then timber frames are the right fit.