Structural Insulated Panels: Yay or Nay?

Structural insulated panels (often abbreviated to SIPs) are a modern build system that act as an alternative to more traditional constructions such as brick and block. Now one of the most popular construction methods, they’re an easy and low-hassle approach; and already are estimated to make up to 8% of self builds already. If you’re looking to embark on a self build journey or are considering SIPs for a renovation, read on to make the best possible informed decision.

What exactly are SIPs?

Structural insulated panels are panels made of two boards of OSB (oriented strand board) with insulative foam sandwiched between. They come in various standardised heights but can also be cut to size, timber edged and then installed into the walls being constructed; external and internal loadbearing as well as in roof panels.

What are the different types of SIPs?

SIPs come in two different forms. The first sandwiches polystyrene board between its OSB boards and the other has urethane pumped in between them. Both are wrapped in timber for stability and strength, and come in a series of standard depths of between 195mm and 250mm, although urethane-injected panels can be as slim as 172mm. The urethane has a slightly greater thermal performance. Most manufacturers use a ‘male-to-female’ stud to connect the timber outers together, but timber l-joists (with a vertical web made from OSB combined with a top and bottom flange of solid timber) and post-joists (the same but with a metal vertical web) can also be installed.
Low-energy homes should always use deeper panels as the U values can reach as low as 0.13W/m2K – considered extremely efficient!

What are the benefits of SIPs?

SIPs have many tangible benefits to their installation in homes, including, but not limited to:
Reduced cold-bridging and increased insulation performance
SIPs have larger spacing in walls than most vertical timber studs permit in traditional builds. In a timber framed building, spacing is at 600mm centres and with SIPs, 1200mm. This halves the amount of poorly performing timber within the wall and dramatically reduces cold-bridging (where a gap occurs and condensation and mould are more likely). Factory-made SIPs are more accurately shaped than timber frames cut on-site which increases the inherent insulation airtightness and prevents any unnecessary air leakage. As a result of this great insulative performance, SIPs are often favoured for Passivhaus and other sustainable build projects.
No need for roof trusses
As SIPs are structural there is no need for traditional roof trusses where they’re being used. SIPs can easily span 4.8m from eaves to ridge and can sit on a boxed-in steel beam or a feature glulam beam. This can help extend the top floor of the home from the standard 2.4m up to 3.6m – an impressive increase in floor-in-ceiling height!
Quicker build
The initial creation of SIPs takes place in a safe, dry factory – negating the need for custom work to be done on-site and in accordance with weather restrictions. This can have big impact on the fabrication and build times of the property, particularly in the UK where we can be very much at the mercy of the rain.

Are there any circumstances in which SIPs can’t be used?

As with any building materials, SIPs aren’t suitable for every build. SIPs can encounter issues when exposed to moisture, so may not be appropriate for sites that are situated in a flood zone or anything below ground; in these cases, a masonry build would probably suffice. In these incidences, hybrid builds can be integrated with SIPs in upper storeys and masonry below, which will still benefit from the SIP fitting where it exists.
SIPs are extremely airtight compared to traditional construction methods and so properties with them will need adequate ventilation measures installed to avoid condensation building up.
There are very few circumstances in which SIPs entirely couldn’t be used, but they are not a product every builder is experienced in and so not all tradespeople may offer them.

How long does a build with SIPs take?

Of course, every property build varies but SIPs certainly help expedite the process beyond traditional build timescales. A two-storey 200m² house could be factory fabricated and then fully erected in just 12 days on-site with SIPs, whereas a standard timber frame can take up to 4 weeks for the frame alone. On average, building with SIPs is 55% quicker – saving on costs like plant hire, site insurance and scaffolding. These savings can help reduce the overall cost to that of other build systems; so although the initial investment may be higher, the project altogether should even out.

How much do SIPs cost?

SIPs are often fairly expensive to install as their overall value is higher and they will save on costs elsewhere in a build project. Dependent on specification, anything from £250-£500/m² can be paid – which is a costly initial investment compared to a low-spec timber frame with trussed roof which can reach as low as £150/m². A telescopic handler will be used to manoeuvre the wall panels around and a crane will be needed for the roof panels. This may incur extra expense, especially if access to the property is difficult.
The savings incurred by using SIPs are apparent later in a property build. This means that those working with some self build mortgages may find they’re unable to finance SIPs upfront and instead need to opt for a cheaper option, even where long-term this may not provide the best possible value.

How do I know if SIPs are suitable for my new build or extension?

Speak to the experts! SIPs are a fantastic addition to most property projects but aren’t appropriate for everyone and everything. Consulting with a renovation or development expert will help you appraise and work through all of the available options – and if you contact your local Refresh Renovations team, you should be able to do so totally free of charge and with no obligation to make a purchase or sign a contract.
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