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Story | 09/19/2022 08:51:00 | 4 min Read time

The lightness of WISA spruce plywood makes construction easier

WISA-Spruce is a lightweight yet strong and rigid spruce plywood panel, especially designed for load-bearing structures such as floors, walls and ceilings. Lightness brings many advantages in terms of handling, structural design and transport.

WISA-Spruce plywood has several advantages up its sleeve that make it easier to build with: strong and rigid, it is ideal for load-bearing structures and, being lightweight, it is easy to handle and transport. These characteristics are combined thanks to the raw material and structure used in WISA spruce plywood.  

"The raw material used for WISA-Spruce plywood is Finnish spruce, which is a light-density wood. The strength properties are also affected by the structure of the plywood, where the wood material, or veneer, forms an unbroken, continuous area that extends from edge to edge of the board", says Riku Härkönen, Product Manager at UPM Plywood. 

WISA-spruce plywood is lightweight compared to many other wood materials used in construction. Due to its strength and rigidity, a thinner sheet is often sufficient for the construction of structures than with other materials. For example, the strength of WISA-Spruce plywood in 18mm thickness is usually sufficient to build a load bearing floor, whereas a 22mm thickness OSB (Orientated Strand board) or particleboard would be needed to meet the same strength criteria.  

  WISA-Spruce (18 mm) Particleboard (22 mm) OSB (22 mm)
Weight/m2* 8.1-8.5 kg 15.3-15.7 kg 13.3-13.5 kg

 

*The comparison has been made using the declared product information for flooring building boards. 

The weight of building boards is important when they are moved, handled and installed on site. It is not just about the physical strain on the builder, but also about the manpower required to handle the board - can you carry the board on your own in the middle of the afternoon, or do you need help from a second or third builder? For spruce plywood, the burden is up to almost half that of particleboard and OSB, for example. 

In addition to site work, the lightness of WISA-Spruce plywood also has an impact on transport. According to EN 13986, which defines wood-based panels in construction, plywood must have a minimum density of 400 kg/m3, while particleboard and OSB have a minimum density of 600 kg/m3. Coniferous plywood typically has a density of 460-520 kg/m3, which is significantly lighter than particleboard and OSB. In addition, more 18-millimetre than 22-millimetre thick boards can be accommodated in the same space. With less weight and more boards per vehicle, transport is more economical and less polluting. 

Spruce plywood is a lightweight load-bearing structure 

The light weight and low specific gravity of WISA-spruce plywood is also useful for structural solutions. Especially in cities, the life cycle of buildings can be extended in a cost-effective way, for example by re-installing floors. The mass of the structures can affect the number of additional layers and, consequently, the profitability of the project. The lighter solutions will also not put any strain on the existing old structures of the building. 

"In one renovation project in central Europe, the use of spruce plywood as a structural frame material allowed for two additional layers, while the alternative with CLT (Cross Laminated Timber) elements allowed for so much mass that the additional construction would have been limited to a single layer", Härkönen cites as an example of the importance of lightweight materials.  

WISA-spruce plywood has little bonding material and even half of it is the wood's own lignin 

WISA plywood is one and the same spruce from top to bottom and no other wood species are used as raw material. This ensures consistently high quality and reliable technical performance.  

"In addition, spruce plywood surfaces are easy to handle and have a harmonious appearance when there are no other softwoods in the mix", Härkönen adds. 

WISA-Spruce plywood is produced at the UPM Pellos plywood mill in Finland. All the spruce used for plywood comes from responsibly managed Finnish forests in the vicinity of the mill. The proportion of bonding resin in WISA plywood is less than 3%, resulting in a high proportion of renewable and carbon-storing wood in the board. Typically, the adhesive content of particleboard is close to 10%.  

WISA-Spruce plywood panels use UPM Plywood's proprietary innovation, WISA® BioBond bonding technology. In the bonding material of spruce plywood, at least 50% of the fossil phenol is replaced by the wood's own natural glue, lignin. This will reduce the already low fossil CO2 emissions of the WISA plywood life cycle, helping builders to meet their own sustainability targets. 

Read more about the properties of WISA-Spruce plywood from the product leaflet. 

Text: Janne Suokas

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