To SIP or Not to SIP? It’s Complicated.

Outdoor view of a small building with solar panels on the roof

Habitech systems

Australian company uses Structural Insulated Panels to build very efficient homes that go up fast.

Structural Insulated Panels are like an OREO cookie with a foam filling and and OSB (oriented strand board) or plywood on the outside. Australian design/builder Habitech Systems uses them to build houses that are really energy efficient; SIPS are extremely airtight and with a solid foam core, there is no thermal bridging at all. Habitech recently completed this addition to a small house in Melbourne, Australia for clients who wanted to get off natural gas and go all-electric. Sanctuary Magazine talks to Chris Barnett, an architect and managing director of Habitech:

Interior view of living room with couch open to a bar area
Habitech Systems
“Joe and Tamsin came to us wanting to renovate and extend, and looking for a highly insulated building fabric that they knew would work,” Chris says. He explains that because SIPs are made in a factory with a high degree of precision and arrive on site as complete wall units already insulated and clad, there’s far less scope for leaks and gaps to creep in and compromise the performance of the finished building shell. “They are quick, too – once the SIPs are up and the joins sealed, the wall’s finished.”

How SIPs Are Made

A woman jumping in the middle of a house construction site
Habitech Systems

Habitech’s SIPs have an exterior panel of what’s called Magnesium Oxide Board. Chris notes: “We use magnesium oxide board for its stability and longevity. It’s made with 50 per cent sawdust, and the manufacturing process actually absorbs carbon dioxide.” They also use plantation grown Australian plywood, far more durable than OSB, for the interior.

That’s a good thing, because a big knock against SIPS is the foam core, in Habitech’s panels made of expanded polystyrene (EPS), but they are so energy efficient that even the anti-foam people at BuildingGreen note:

BuildingGreen does not generally recommend EPS as an insulation material because it is made with several problematic materials, including benzene and the brominated flame retardant HBCD, but we list EPS-core SIPs because they provide a relatively easy way to create walls with superb energy performance.
A unit under construction
Habitech Systems

It is one of those difficult trade-offs that designers and builders often have to make. There are also other issues; In North America, there have been serious problems with SIPs, but usually in cold climates and where they were not installed properly. Malcolm Taylor tells Green Building Advisor:

There are a number of extreme sports, like rock climbing, that are very safe when performed by experienced, well-trained participants," Taylor says. "That doesn't negate the reality that they are inherently more risky that other activities. To me, SIPs are like that. Installed by experienced, diligent, conscientious workers they perform as expected. But the chances of success are so much lower than assemblies that are inherently more robust.

Climate Effects

But in Australia the climate is not so extreme, the moisture control and condensation issues as important, and Habitech Systems is obviously experienced and well-trained. And their SIPS are, as they note, energy efficient, strong, high-quality and cost effective. “Their high R values and low air leakage both contribute to a greater level of thermal performance than traditional framed construction.”

Conditions also are different in Australia, and it's not just the climate. According to a Renew Magazine article on SIPS,

Australian homes are notoriously leaky due to poor construction practices and no compliance requirements. Our national construction code does not require a minimum air leakage rate. Leaky homes result in more uncomfortable indoor conditions and considerable wast of heating and cooling energy. We tested three other homes using SIPs and all houses performed extremely well in air tightness.

Complicated Trade-Off

Materials being delivered on a large commercial truck
Habitech Systems

It’s a green building conundrum. This TreeHugger prefers foam free building with renewable building materials, suggesting that we should be building out of sunshine. On the other hand, SIPS are energy efficient, really airtight, and give you a thin, strong wall that is ready to go. It’s much, much easier to build with than foam-free systems. Habitech is using the least offensive foam and definitely better skins over it than the usual. There are less likely to be problems with the panels than there might be in colder climates, and as GBA’s Peter Yost notes, most SIP problems are in fact design and detailing problems.

To SIP or not to SIP? It’s complicated.