Source: Housing New Zealand Corporation
A high-tech building product Housing New Zealand is beginning to use in new state houses will not only help them build homes faster, it will have health and wellbeing benefits for the occupants.
Timber is a resource central to the New Zealand economy and one at the heart of Housing New Zealand’s plans to build thousands of warm, healthy, new homes. Housing New Zealand is transforming not only the way we live, but the way we build, by embracing modern methods of construction and materials. One of those high-tech materials is cross-laminated timber (CLT).
The technology behind CLT was developed in Europe in the early 1990s, and since then it has become a hot product in the global construction industry. Formed by glueing together layers of wood with the grain at right angles, it creates a product with the structural strength of concrete and steel. Importantly, it can also be cut into prefabricated panels in a factory and assembled quickly and easily on a building site.
“The CLT wall-panel system is ahead of its time,” says Tim Campbell, Housing New Zealand’s Business Innovation Research and Design Director. “Essentially, the structure of a building that you’d normally see in made in concrete or steel, or with a timber frame, is replaced by CLT panels. It’s faster, safer and the cost structures are more predictable than a traditional build. And from an end-user perspective, there are proven health benefits.”
The surprising benefits of living with wood
One of Housing New Zealand’s key objectives is to replace its old housing stock with modern homes that support the health of tenants. CLT does this by providing better thermal performance than conventional building products and processes. (Occupants are able to keep the home at a steady, comfortable temperature more easily). CLT also offers improved air quality through its natural ability to moderate humidity. On top of these benefits, living with wood improves mental wellbeing.
‘Biophilic design’ – where natural materials are incorporated into building interiors – can lower blood pressure and stress levels and elicit feelings of warmth, comfort and relaxation in occupants similar to the benefits people get from being in nature.
Multiple reports have identified the psychological benefits of wooden interiors. Although CLT is a structural material it can be left exposed, rather than being covered with plasterboard or other wall linings.
“From a tenant’s perspective, there’s really strong data that supports the psychological benefits that come with living in timber,” says Tim. “Exposing the timber in the walls and ceilings of our buildings that use CLT is a target outcome from our current research and development programme.”
Better performance in a fire or earthquake
As well as offering health benefits, CLT improves safety for the occupants and during every stage of the construction process.
Over the past seven years, 37 people have died in workplace accidents on New Zealand building sites. That’s only two less than in the notoriously dangerous forestry industry. As Housing New Zealand’s building programme gains pace, increased use of CLT should significantly reduce workplace risks.
“It is very safe from an assembly perspective. Within two weeks of the panels going up, we have a roof in place and internal stairs dropped in. We can shift materials and people can move up and down the building without having to use ladders and scaffolding, which is always a big safety issue on traditional construction sites, due to falling objects,” says Tim.
“From a fire perspective, CLT burns at a very predictable rate,” says Tim. “When it does burn, it just chars – it’s almost impossible to burn through a wall. It’s extraordinarily safe for residents.”
It’s also resilient in an earthquake, which is especially important here in New Zealand. To further enhance this, Housing New Zealand is researching embedding sensors into the wood so that engineers will be able to tell instantly if a building is still safe to be occupied after an earthquake.
Buildings go up twice as fast
The typical construction process used to build multi-storey buildings out of steel and concrete is a lengthy and labour-intensive process. Prefabricated CLT panels have the ability to cut time frames in half. Everything – including battens, cladding and window joinery – can be assembled in the factory, so once on site the components can be quickly and easily assembled into a building.
“The pre-completed wall panels are produced to a factory-level quality and arrive on site where they are simply craned into place,” says Tim. “Take a typical three-storey building that has three one-bedroom units stacked on top of each other: historically, that would have taken us 12 to 13 months to build, and that’s with a little bit of optimism. Our CLT buildings are being assembled in around five months, so it’s a hundred percent faster.”
Not cheap, but affordable for terraces and apartments
Cross-laminated timber is not a cheap product. Due to our stringent building code requirements concerning timber treatments and their durability, Housing New Zealand is unable to import CLT from overseas manufacturers at this stage.
At present, only one factory in New Zealand makes the panels: XLam in Nelson. CLT is not economically viable for use in individual houses yet, but thanks to the economies of scale, Housing New Zealand is able to utilise the product for multi-unit dwellings.
“We can’t yet get the cost structures to work in standalone homes,” says Tim. “It is a higher quality system, so it comes with a higher price tag, but when you deliver it in medium density you can start to get the numbers to work. The height is an important factor – it can reach three levels quite easily without the need for structural steel. And scaffolding is only needed for a short period of time for the installation of the final touches, which is another cost benefit.”
Better building systems are a key to better futures
Housing New Zealand’s Auckland Housing Programme will deliver thousands of new homes over the next decade. Those homes are being designed to provide a healthy, safe environment for at least as long as the 50-65 year-old state houses they are replacing.
“My role as business innovation research and design director has an over-the-horizon focus,” says Tim. “Housing New Zealand is going to own these buildings for 50 to 100 years, so it’s all about identifying new building systems that can help us build faster and safer, and deliver healthier homes at more predictable costs. Cross-laminated timber is the first of these systems.”
There’s a high level of commitment within Housing New Zealand to CLT because of the difference it can make to people’s lives. Housing New Zealand would like to help facilitate the establishment of more large CLT factories here in New Zealand to remove supply constraints and reduce costs.
“Our tenants spend a huge amount of time in our buildings,” says Tim, “So knowing they’re in a structure that’s made out of a material that is safe and has proven wellbeing characteristics – for us it’s one of the most important features CLT has to offer.”