It’s not heavy

13 October 2017

A new design of lightweight panel offers the advantages of continuous production with applications that could make it a substitute for OSB. Julian Champkin looks at panel which seems to weigh in just right.

Lightweight panels are a common goal of the engineered wood industry, long sought-after and, nowadays, with increasing urgency and application. Several approaches have been suggested or tried, for specialist applications or with the simple aim of economising on raw material; a honey-comb type panel consisting largely of air spaces clearly consumes less wood.

However, until now, such panels have been labour-intensive to produce, and therefore high in cost. They have been batch-produced rather than by any continuous process. This has meant that they have been low-volume products, therefore again militating against economies of scale. A new design may have overcome these drawbacks to achieve what its devisors claim is a paradigm change in the production, and the potential applications, of light-weight panels.

The LSP, short for Light Structural Panel, offers the advantages of continuous production in a simple add-on to existing production lines for OSB. Hence labour and investment costs for it are low and efficiency of production will be a given. Potential applications for the product itself are myriad.

It is the brainchild of Advanced Structural Engineering GmbH, whose wood technology expert Dr Albrecht Eppel has over 40 years experience in engineered wood.

Most proposed lightweight panels are composites: wood based outer skins cover some kind of less dense core like the filling in a sandwich. The layers are generally glued up and assembled by hand, from cut panels that have already come off the production line – a process that is slow, limiting and expensive.

The LSP is also a composite. Its production, however, is different.

It is based on standard OSB. A rigid, wood based surface of OSB on both sides encloses a polyurethane-foam filling or core (Figure 1). The foam keeps the two sides apart, imparting strength; it adds insulation, making the panel ideal for housing construction as well as being a highly versatile material for other uses. Its key selling point, however, is that it can be produced on a continuous press, giving efficiency, with low labour input, in large volume, and therefore at an attractive cost.

The construction principle is unusual. It has the advantage of needing no amendments to a standard OSB line; the additions, and the filling in the sandwich, come immediately after the board leaves the press as a downline add-on.

Standard OSB, taken in cross-section, is not uniform in density. This is a result of its production process. The heat and steam near the press-belt is greater than in the centre; the fibres therefore are more compressed, and resins cured differently, at the surfaces than in the centre. An OSB panel coming off its production line is less dense, and therefore weaker, along the centre of its cross-section.

The LSP process takes advantage of this. It splits the panel in two, along that plane of weakness, automatically and immediately after it leaves the press, while it is still hot. “The splitting can happen accidentally, if parameters are not exactly right.

Manufacturers usually take care to avoid this,” says Stefan Langguth, spokesman for Advanced Structural Engineering. "We instead take advantage of it.

The separation device is not a knife-edge but a wedge, which does not cut but instead forces apart the top and bottom surfaces of the OSB panel along its centre-line of weakness - see Figure 2.

“This leaves the inner surfaces rough, with fibre strands protruding” says Mr Langguth, "and this roughness is ideal for the polyurethane to grip on”. Figure 3 shows the rough surface well. The liquid polyurethane is injected between the two layers, reacts with water, and solidifies to a foam as it cools. The end result is a panel consisting of a core of polyurethane firmly sandwiched between OSP.

“You will note that its production is a continuous process, not a batch one,” says Mr Langguth. “Production rates of 30m/min, equating to 600,000m3 – 1,500,000m3/year, are achievable. So this can be a high-volume product, with the cost-efficiencies that go with it.”

“The process easily allows for variable LSP products: different panel thicknesses can be produced, with different ratios of wood-fibre and core depths and with different strength and density of the PUR core. And single LSP panels can themselves be layered together to form multi-core LSPs.”

Some obvious advantages follow from the design. One is low weight: an LSP panel it is about 50% lighter than its equivalent strength in OSB. A large-dimension 1 1/8in panel of 8ft x 4ft size weighs about 28kg and can easily be handled by a single person – a clear advantage on a building site.

Another is strength. The polyurethane core is statically loadable in itself; the separation it provides gives the OSB portion of the panel extra resistance to bending moments. While conventional OSB needs timber framing in construction, LSP construction is feasible with reduced framing or even with no framing at all. This, says Stefan, may be the face of much future house-building.

Its insulation value is six times that of OSB. The R-value of a roof or wall system increases six-fold over standard OSB on a 2x4 or 2x6 timber frame, while its wind resistance and its stability is greater. “With it builders can reach North American building code standards with less effort. Installing insulation and external sheathing on a timber frame becomes a single-stage operation instead of a two-stage one.”

In addition, its increased insulation properties mean that using 2x4 framing with LSP can give the same R-value as using more costly 2x6 framing, which has been required for thicker insulation mats.

The economics of producing it look promising. The devisors claim it is 25% more cost effective than an OSB panel with the same dimensions – the LSP panel having superior product characteristics into the bargain.

Existing OSB lines can be adapted or extended to produce LSP, and if necessary for market flexibility can revert to standard OSB without difficulty – which would reduce the risk for potential producers of the new panel while the product is gaining market penetration.

However OSB is already an established product in the construction industry, and LSP can be seen as a variant or an improvement upon it. “This should help LSP gain acceptance, as a modification of a known product rather than a new concept,” says Mr Langguth.

Recent tragic events have thrown fire safely of cladding panels into sharp focus. It is important to note that the core of the LSB is polyurethane foam, not polyethylene.

It is the latter which has been implicated in the Grenfell Tower disaster. Stefan Fox, Head of Application Engineering and Development at PUR systems, the Advanced Engineering Solutions partner company supplying the foam, gave us the following statement concerning the insulation material used for LSP:

“LSP panels have an insulation core made of PIR foam. Like all organic insulation materials standard polyurethane foam is flammable. However flame retarded polyurethane foam or so called polyisocyanurate foam (PIR) is regarded as an excellent insulation material with good fire properties. PIR insulation panels meet the stringent German building codes.

"PIR foams are rated class E according to the European standard EN 13501-1. Sandwich panels with PIR foam core achieve level BS1D0 which stands for low smoke production and no droplets. This kind of insulation panels is widely used especially for cladding of buildings.”

There are on the market products by the name of Structural Insulated Panels, or SIPs. Mr Langguth wanted to emphasise that there is no real comparison. “SIPs are manufactured by coating a foam core with adhesive, and then pressing the wood panels onto it. It is thus a batch process, and highly labour-intensive.

"It is important to understand that SIPs cannot be manufactured economically below a certain thickness because of this labour intensive batch production” he says.

“Consequently a SIP with a thickness below 4.5in does not exist today. LSP on the other hand due to its fully automated process can be manufactured to as low as 1 1/8in thickness. Of course the process is also good for greater thicknesses as well.

“From our experience interested parties often equate LSP with SIPs. That comparison is not correct There is no thin SIP that could be used as OSB substitute in existing building processes. That is only possible with LSP.

“LSP can be a direct substitute for standard OSB but with the advantages of higher insulation properties, continuous insulation for the building envelope and increased airtightness. You can add a massive decrease in labour costs in construction.”

For ease of joining panels in construction LSP can be manufactured with tongue and groove edges. The groove profiles are generated using a peeling tool; the tongues are constructed form the residuals of the peeling process.

Highly-insulated exterior walls, and lightweight, self-supporting interior walls, with no timber frame required, make modular designed prefabricated buildings one obvious application.

“Standard OSB was invented in 1963,” says Mr Langguth, “and has had phenomenal growth over the past 30 years. Nevertheless global warming policies, energy efficiency requirements, the latest North American building codes and the general market situation have brought OSB timber framed based construction to its limits. Ever increasing insulation requirements, the requirement for continuous insulation without thermal bridges, and labour shortages all contribute to this.” LSP, he says, can solve these challenges without i changing existing and established processes.

“LSP and Multi-LSP components can achieve cost savings of more than 50% compared to conventional prefabricated housing systems. Multi-LSP elements are highly suitable for layout-controlled pre-processing modules that are ready-to-assemble on site.”

And he pointed to a future of industry 4.0 controlling CAD pre-fabrication. "The availability of large-dimensional panels – up to 18m long and 2.9m wide – and LSP’s high stability open up a completely new approach to prefabrication. The need for complex and labour-intensive timber frame construction is over. Larger-scale advanced wall, roof and floor components can be manufactured with 100% automation, in less time, and with better performance."

German patents for the product and the process were applied for in 2013 and granted a year later. The US patent was granted in December 2016. Currently the company is seeking partners for commercial production. Mr Langguth points to the paradigm change in construction that LSP can bring about – and to the needs which it can serve.

Highly-automated industrial manufacturing, with modular prefabrication and much accelerated on-site building times, all with Industry 4.0 to bring it about: here is a solution to the demand for affordable housing in lower and middle income groups, which is a challenge in both rich and poor countries worldwide.

“The bottom line it that it is important to understand that LSP opens up a huge untapped market, and the substitution of standard OSB, by delivering superior performance at similar cost and reduced overall labour” he says.

“Nor is it the end. LSP is a substantial starting base for additional waves of innovation.” For the future, watch this space.  

Figure 1: LSP in close-up
Fig 2: The down line manufacturing process foe LSP
Figure 3: The ragged interior surface of split OSB gives ideal purchase for the inner foam