When does a new building method stop being new and become part of the established way of doing things? It’s impossible to say exactly, but public recognition is one of the important factors determining this. An awful lot of what passes as ‘new’ in the construction industry turns out to have been around for 30 years or more: it’s simply never managed to get onto people’s radar.
For a while it seemed that structural insulated panels (or SIPs) would remain in the category of ‘interesting innovations you might like to be aware of but won’t actually use’. But slowly and steadily, SIPs look to be headed for the mainstream, thanks in no small amount to British self-build pioneers, who have always been at the forefront of adopting new build methods. SIPs have indeed been around for a long time – the first SIPs building went up in Madison, Wisconsin in 1937 and is still doing fine – and they now have a proven track record for both energy saving and durability. They have been used in all kinds of climates, in hurricane zones and earthquake belts but, in the relatively tame UK, SIPs were perceived to be just a little bit too expensive to bother with.
Like timber frame, SIPs are a factory-built, panelised building system that arrives on site on a lorry. Instead of using timber studwork for load-bearing purposes, SIPs rely on the structural qualities of glueing insulation between two sheets of a building board, usually oriented strand board (OSB). The resulting benefits are that you create a structure with superb insulation levels, few cold bridges and excellent airtightness — all the things that we are being encouraged to do in this era of carbon consciousness. In addition to this, SIPs advocates reckon that:
- SIPs have the potential for even faster construction speeds than timber frame, as there is less on-site work involved.
- The panelised roof elements lend themselves to building rooms in the roof, in a manner which is much simpler and quicker than traditional methods.
- Having the insulation built into the system ensures a level of quality control. This is particularly true with roofs, where it is difficult to insulate complex roof structures.
- You can build narrower external walls. This is particularly beneficial on small sites where space is at a premium. With a lightweight wall cladding, such as timber board or a rain screen, you can build an external wall, still easily exceeding Building Regulations insulation standards, in a width of around 250mm.
- SIPs offer a relatively simple way of constructing a home which requires very little in the way of space heating. A number of self-builders have now specified homes without conventional central heating systems, relying on the insulation and airtightness of SIPs, combined with a mechanical ventilation system with heat recovery, which is used to distribute the heat of a woodburning stove around the house.
But what about the extra cost? It’s hard to be specific about it because SIPs are not a commodity product which can be easily costed with a spreadsheet — every project is quoted for on an individual basis. What seems to be happening is that each time the energy-efficiency regulations are strengthened (roughly every three years), the cost differential between SIPs and conventional timber frame and/or blockwork narrows. And the experience of one business suggests that there may no longer be anything in it.
In 2006, Custom Homes started offering its customers a SIPs option. Peter Keogh Snr. of Custom Homes comments: “When we started manufacturing and fabricating SIPs, we offered all of our existing customers the option to change from timber frame to SIPs. We expected about 10% of our customers would like to change to the new system, especially as it was costing them a little more. How wrong we were. The 10% belonged to the customers who did not want SIPs. We were caught out in the short term, but quickly realised we were on the right track, and it did not take long for all of our customers to request SIPs frames.”
Custom Homes has now become founder member of the newly formed UK SIPs Association (uksips.org), a trade body formed to promote the use of SIPs to a wider audience, and a first port of call for anyone interested in knowing more about SIPs building and SIPs builders.
SIPs don’t suit every site – they are hardly recommended in flood zones – and they work best with simple-shaped houses where you want to utilise the roof space. Having said that, there are not many self-build homes that couldn’t be constructed from SIPs and, as general awareness continues to grow, the prospects for SIPs look good.
A SIPs Passivhaus
This four bedroom SIPs house, designed by Studio Kap, is situated on a sloping site in Balfron, Scotland. The Avalon™ SIPs by Advanced Housing Systems (020 7193 1461) were fabricated off site. This house is built to PassivHaus standards but the company can increase or decrease the specification dependant upon budget.
ABOVE: 1. Supplied ‘closed’, the panels are ready for decorating with the electrical services pre-installed; 2. The panels arrive on site and are craned off a flat-bed directly into position. The house is weathertight in around two weeks; 3. The cladding, in this case cedar shingles, is fixed on battens on the exterior leaf of the SIPs panel; 4. The windows, all triple-glazed lowe from Sweden, are part of the standard package.
How the Pieces Fit
This diagram (BELOW), based on the Kingspan TEK® Building System (kingspan.com; 0844 967 0455), shows clearly how each panel fits into place. The walls tend to consist of narrower panels, which slot tightly together into grooves, while the roofing panels are of much larger expanses. The panels are all prefabricated off site, so every window and door opening must be planned in at the early design stages. Some manufacturers even fit the windows off site before the panels are erected. Due to the flat, rectangular nature of SIPs, they work best with simple house designs.
Three SIPs Houses:
1 This timber-clad barn-style house was built by package company Custom Homes (01787 377388)
2 A beautiful oak frame/SIPs hybrid cottage by Border Oak (01568 708752; borderoak.com)
3 This brick-clad house by SIPS@Clays (01756 799498; claysllp.co.uk) is so well-insulated it has no central heating.
This article is sponsored by Flight Homes