More thought is needed on how the construction industry, known for its waste, can fit into the circular economy. In New Zealand, timber framing technology is being developed that allows for future reuse.
PLATFORM TIMBER FRAMING that can be designed prescriptively according to NZS 3604:2011 Timber-framed buildings has served New Zealand well by offering a method of construction that is safe, minimises bureaucracy and is highly adaptable.
Remarkably, this method has remained largely unchanged since the 1960s. Yes, we now treat our structural timber to prevent issues of rot and insect attack. And we insulate our buildings a lot better than we did in the 1960s. We even sometimes use light gauge metal instead of timber. Yet basically. platform framing remains unchanged and the backbone of New Zealand’s residential construction.
Is platform framing still the best option?
It’s timely to ask ourselves whether platform framing is the best building technique for the future homes of New Zealand. So much has changed since the 1960s in technology, materials, building science knowledge and sustainability. Is it really the best we can do?
Method leads to waste, not reuse
A key area in which the performance of platform framing fails significantly is end of life.
The materials we use today – for example, boron-treated pine – and how we fix them together – nails, adhesives and screws – mean that material recovery, reuse and recycling is rarely economically viable. As a result, a considerable part of New Zealand’s waste is from the demolition of buildings.
This suggests major changes are needed to make timber-framed buildings 21st century ready.
X-Frame answers waste issues
X-Frame is a response to these concerning waste issues. It is designed to be a modular plywood structural frame for non-loadbearing partition walls, and loadbearing walls and floors in low-density and medium-density construction. Manufactured using computer numerically controlled (CNC) routing technology, it only uses reversible and reusable connections designed specifically for end-of-life material recovery and reuse.
Move to circular economy construction
X-Frame is a shift from buildings that become waste at the end of their lives to buildings that are the resource for new buildings. This is called circular economy construction.
The circular economy refers to an economic model in which material value is retained as much as possible through use. The idea is to separate economic growth from environmental destruction and material consumption. The model goes beyond conventional recycling as it demands that processes for recovery and reuse are designed in from the start – and that those processes make economic sense.
How is X-Frame different?
X-Frame achieves circular economy status by separating traditionally dependent layers of the building envelope.
The classic example of a dependent layer in platform framing is plasterboard and its connection to structural timber members. Plasterboard is not only used as an internal lining but also to brace the timber frame.
The result is hundreds of single-use fixings between the plasterboard and the frame that ensure both layers are damaged during separation. Damage reduces material reuse value and potential, while also ensuring materials have limited recycling potential due to contaminants.
X-Frame aims to counteract these issues by being inherently braced – providing restraint to lateral forces such as earthquakes and wind. A self-braced frame means no sheet materials are required to provide bracing which in turn allows the way internal linings are fixed to also change.
In the case of X-Frame, 590 mm square panels clip on and off the structure using reversible pressure mounted fixings.
The X-Frame concept takes a similar approach for external building layers. A ventilated cavity is created that uses a solid structural timber cavity batten bolted directly on to the nodes of the X-Frame system.
The result is a ventilated cavity that can be disassembled as required and ensures that the main structural frame does not become contaminated with nail and screw fixings. If a profiled timber cavity batten is used, the system can be further detailed to include a clip-on/clip-off cladding system for weatherboards or sheet claddings.
The structural frame itself is made up of 13 distinct components that allow modules of 420 mm or 840 mm to be created as needed. This module size is based on an optimisation of a useful architectural spatial module and the requirement of eliminating waste at the time of fabrication.
The parts have been optimised so they can be arranged onto a standard 12 mm thick plywood sheet, cut using a CNC router and only produce sawdust cutting waste. Most of this comes from forming mortise and tenon joints in the timber components.
These joints are key to the system and mean that components can be assembled and disassembled without additional fixings or expensive equipment. The mortise and tenon connections are supported by bolted plywood straps where larger loads occur – such as where second floor loads are transferred.
Further developments needed
The X-Frame technology is still in its infancy and needs major changes to be market ready. The time it takes to manufacture and assemble the frame needs to be reduced, and the way in which the frame interacts with other existing building technologies needs to be refined.
A treated plywood product also needs to be identified that ensures the frame meets New Zealand Building Code structural durability requirements and circular economy material restrictions.
Not the final solution
X-Frame does not, however, aim to be the ultimate solution to achieve a waste-free circular building industry. The technology and this research project aim to explore potential solutions and bring attention to the problem that is end-of-life building waste.
To further this study, the research team wants to test the commercial viability of the X-Frame technology in the New Zealand industry. With support from KiwiNet, market research is already under way to determine how the cost benefits of material recovery could impact the cost of construction.
KiwiNet is also supporting an investigation of the viability of certifying a reusable structural product under CodeMark.
The X-Frame project illustrated was supported by Plytech International, Fastmount, Jacobsen, Steel & Tube New Zealand, Abodo and Unitec.
For further information on the circular economy and the building industry, and the X-Frame technology, visit tinyurl.com/branz-xframe. The development of X-Frame has been funded by the Building Research Levy.
Articles are correct at the time of publication but may have since become outdated.