SIPs can deliver ultra-fast build times and airtight, well-insulated homes but there are cons that need to be considered too.

Structurally insulated panels (SIPs) have been used in Scandinavia for around 50 years, but only became popular in the UK in the last decade, with growing recognition of the need for well insulated homes. It's a modern construction method that can be used for home extensions as well as new builds. Here’s our rundown of the pros and cons of SIPs as a building system compared to traditional brick and block or simple timber frame.

What are SIPs

Structurally insulated panels (SIPs) are rigid panels of foam or polystyrene insulation sandwiched between two wood-based sheets, usually orientated strand boards or OSBs, which is a type of engineered wood sheeting, formed by adding adhesives to layers of wood strands and compressing them. Factory-made, they come as prefabricated boards that can simply be slotted together on site to create walls, ceilings, and floors. The strong, composite panels are load-bearing, reducing the need for additional structure and beams. SIPs are usually clad externally with render or brick slip to ensure the insulation remains completely dry.

SIPs construction: the advantages

Maximise energy savings

The most obvious advantage of SIPs is that they’re excellent insulators with a high-quality thermal core.  The weather outside won’t affect the temperature inside your home so much and this reduces your heating and energy costs. They are an ideal choice for homes built to Passivhaus standards, with achievable U-values as low as 0.14W/m2.

Faster construction

SIPs builds are super-speedy, it may only take days to erect the structural shell, not weeks or months. Manufactured off-site, the interlocking panels will go up in entire sections rather than brick by brick. Insulation is pre-fitted and doesn’t need to be added after walls, ceilings and roofs have been built. Manufacture and panel fabrication usually takes about five weeks, with all window and door openings pre-cut in the factory, following preliminary design and structural engineering sign-off, though lead times will vary.

Enhanced overall airtightness

Factory-engineered construction delivers more precision than conventional on-site cut timber framing methods, reducing the risk of small gaps in the construction. This level of precision together with the in-built insulation, helps to limit air leaking in and out of your home.

Environmentally friendly

In addition to delivering airtight, fully insulated buildings, SIPs use less timber and the wood casing is typically made from young, fast-growing trees which are sustainable and renewable. Check the timber used to form the OSB comes from responsibly managed plantations accredited by the Forestry Stewardship Council (FSC) or equivalent. SIPs are manufactured off-site in computer-controlled conditions, minimising waste and loose materials sent to site. The lightweight nature of SIPs, can minimise foundations loadings, requiring smaller quantities of high-energy concrete.

Labour cost savings

Using a pre-built system, reduces the need for a skilled labour force, firstly as it requires less on-site construction and secondly, as it’s relatively easy to build, compared to bricks and mortar. There is also less construction waste to be removed from a SIPs build site which is another cost saving, compared to a traditionally built extension. The super-fast build times reduces time spent on site, so you are less at the mercy of the weather. SIPs can make the construction quicker and easier.

Make the most of available space

SIP roof panels can span from wall to ridge beam, say suppliers, with no need for trusses or further support. This opens up the possibilities for vaulted ceilings, extra rooms and storage space in lofts as well as large, open plan spaces. SIPs can be custom designed for each project. That said, most SIPs panels come in set sizes, so it may make sense to base your design around those if you opt to use them in your project,

SIPs construction: the disadvantages

Cost

A SIPs build is often more expensive per metre square compared to a timber frame or brick and block construction, though the labour costs are likely to be lower. The built-in insulation also needs to be factored into the equation, which means the overall additional cost of SIPs may be less than it first appears. It’s best to get an individual quotation to compare costs.

Requires a specialist crew

As SIPs are relatively new in the UK, finding experienced building supervisors can be tricky. The large SIPs are heavy for even a couple of people to move and usually require a crane or forklift. One small mistake can be disastrous. If a SIP is accidentally damaged, it can reduce its performance considerably. It’s best to hire a specialist crew, which may mean a long wait for a team.

Requires extra ventilation

While airtightness is an advantage of SIPs, it means you will need to have additional ventilation, such as a mechanical ventilation heat recovery (MVHR) system, due to the way warm, humid air is trapped in the house.  Without ventilation, the air can become stale and condensation build up on internal walls, risking damp, mould and rot.

Difficult to modify on site

After the design of your SIP building has been agreed and signed-off it’s difficult to modify. The panels will have been cut and sent to site. Electrical wires are pulled through pre-cut channels inside the core of the panels, according to the electrical design of the project. Adding wiring or plumbing holes can be tricky without damaging the panels. By comparison, a traditional build is easier to modify on site and change in future.  

Uses plastic

The rigid insulation material at the core of SIPs puts a dent in the product’s eco-credentials from a building material point of view, as it’s made from thermosetting plastic. Typically, this will either be polystyrene or polyurethane, both made from petrochemicals obtained from oil and natural gas (fossil fuels with high embodied energy).

Susceptible to moisture damage 

As SIPs are a mostly wood-based construction, a big concern is potential damage from water exposure, mildew and rotting. You may need to install a waterproof surface and it may not be suitable for basement conversions.

Not pest resistant

Like any other timber structure, SIPs are susceptible to insects. To prevent pests many suppliers will offer SIPs with borate-treated foam and/or OSB. However further termite prevention and maintenance may be required.

There are lots of pros to building with SIPs. They are eco-friendly solutions when considering energy-efficiency, that can deliver long-term savings on heating bills but there are significant downsides, too. Before going down this route, investigate further and ask your architect for their advice.