STRUCTURAL INSULATED PANELS 43
SIPS VS TIMBER FRAME
Ian Loughnane of Kingspan Timber Solutions weighs up the relative merits of structural insulated panels (SIPs) and timber frame structures.
frame structure. D
A timber frame supports loads via regularly spaced studs, whereas a SIPs panel supports loads via the facing aminate, which is restrained from buckling by its bond to the internal insulation core. So for a SIP, the nature of the insulation in the core, its bond to the external laminate and the type of laminate used all combine to determine the structural characteristics of the panel as opposed to timber frame, where the stud centres and stud size are the key drivers.
SIPs structures do use timber studs, but generally only to support significant point loads generated by purlins, for example. From a buyer’s viewpoint, a timber frame can be bought with or without any thermal properties, but a SIP always has thermal properties built in. Common thermal core types are XPS, PUR or PIR. The XPS versions will be thicker than the PIR/PUR versions for the same thermal performance because XPS doesn’t perform as well as PIR/PUR.
There are two main forms of manufac-
ture: liquid core injection and adhesive bonding. Liquid core injection involves either a static hydraulic press or a rolling
A TIMBER FRAME SUPPORTS LOADS VIA REGULARLY SPACED STUDS, WHEREAS A SIPS PANEL SUPPORTS LOADS VIA THE FACING LAMINATE, WHICH IS RESTRAINED FROM BUCKLING BY ITS BOND TO THE INTERNAL INSULATION CORE
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espite them often being confused, there are quite a lot of differences between a SIPs and a timber
press. In each case the top and bottom laminate is held in place by spacers between and pressure externally. The liquid insulation is injected and expands to fill the gap between the sheets. The liquid core chemically bonds to the sheets. The adhesive method applies structural adhesive to the core and laminates in controlled conditions. The three elements are then assembled and pressed to create the panel. In both methods quality control of the chemicals/adhesives and the factory conditions/processes are important to the quality of the finished panel.
SIPs behave as a composite structure and are surprisingly strong. It is not unusual to have certified performance equivalent to a building four storeys high.
SIPs behaviour in fire is determined by the core and laminate reaction to fire. One
manufacturer, for example, uses a PUR core and 15 mm OSB3 laminates which achieves 60 REI with one layer of 12.5 mm Type F plasterboard. So sourcing a good fire rating isn’t a problem. The other key difference is how the structure is constructed on site. SIPs are usually jointed with a “spline” which fits into a groove around the panel. These splines are usually a thinner version of the main panel and thereby continue the insulation integrity through the joint. This jointing method means that in general SIPs structures have much less thermal bridging than a timber frame. The use of a spline joint also allows the joint to be sealed with foam or silicone resulting in a highly airtight structure.
As overall thermal performance is driven by U-values influenced by core type and bridging fraction, Psi values and airtight- ness, it can be seen that the thermal performance of SIPs panels potentially score well on all three counts. Most systems range from below 0.2 W/m2 down to 0.1 W/m2
K K.
Compared to masonry all this perform- ance is achieved within a relatively slim profile. Indeed, SIPs systems have always been significantly ahead of the game in thermal performance. It’s only now that regulations are becoming tighter that we are seeing larger builders seriously look at SIPs as a possible building method. Developers can gain significant advantage from high performance wall systems like SIPs. Firstly, there is the
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