Wood Fibre (Rigid)

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We stock a high quality range of rigid natural wood fibre boards from Steico with thermal conductivity ranging from 0.04 to 0.05 W/m2kK and densities from 70 to 270 kg/m3 to meet the insulation needs of your new build or refurbishment project.

Some of our wall boards are impregnated to improve moisture resistance for internal or external applications, behind facades and tiles or as part of an External Wall Insulated (EWI) render system.

We only stock the very best fibre boards for walls and offer fair prices. Shop online below or call us on 01793 847444 for more information on any of our options.

What is a wood fibre board?

Wood fibre board is made of wood fibres, which are connected to each other through the effect of heat and pressure. In terms of its basic properties, a wood fibre board is comparable to wood possessing many of wood’s best features: strength, toughness and warmth.

Rigid natural wood fibre boards range in thermal conductivity from 0.04 to 0.05 W/m2K and densities ranging from 70 to 270 kg/m3.

Benefits of wood fibre boards

Wood fibre boards also offer the following benefits

  • Non-toxic, do not off gas
  • Made from a renewable resource
  • Low or negative embodied carbon
  • Homogeneous, no grain direction
  • Dense but vapour open, acts as a moisture buffer offers high resistance to heat transfer
  • Easy to work with and quick to install
  • Acts as additional thermal insulation
  • Competitively priced
  • T & g profile
  • Aids air and wind tightness
  • Provides robust jointing between rafter spacing
  • Provides weathering protection during construction
  • Negates thermal bridging
  • Adds rigidity to structure (aids racking strength)
  • Key product to improve phase shift (reduces heat transfer)
  • Provides additional insulation layer And. they are environmentally friendly!

Insulation that's naturally better

Wood fibre insulation protects from cold weather, heat and noise, provides a pleasant internal climate and balanced air humidity making the property particularly suitable for allergy sufferers and those with respiratory conditions.

Wood fibre does not off gas, shrink or collapse over time providing long lasting protection and performance. Recycled and recyclable this natural product achieves more than many petrochemical or synthetic insulation materials with none of the potentially harmful side effects or embodied carbon.

Simplicity of construction

The use of mineral wool (vitreous) or PUR foil backed boards requires the use of vapour barriers to prevent air leakage from the interior causing condensation in the structure. Rigid insulation boards must be cut very accurately to fit between timber structures with all of the joints taped and all junctions sealed. The security and durability of the seals and vapour control becomes more important as insulation levels increase levels meaning a corresponding increase in condensation risk.

On a timber frame (wall or roof) synthetic insulation materials require breather membranes, ventilated cavities and either tile battens, cladding battens or render carrier boards to finish. Construction must allow for the timber to be able to shrink and move whilst still staying weather and wind tight. Lastly and due to their inability to buffer moisture, they have to be kept dry on site, a significant challenge in our climate.

Choosing wood fibre insulation simplifies the construction process by allowing a much simpler timber structure to be used. It requires fewer layers and does not require any cavities (except an internal service void or behind a ventilated rain screen such as timber cladding or if using a non-wood fibre ender carrying board). To eliminate the need for a cavity on the external side a wood fibre render carrying board, such as Steico Protect, is directly fixed to the timber frame with render applied to the external face.

Flexible properties

  • Moisture absorbent
  • Provides strength and airtightness
  • Vapour permeable
  • Capillary active

Internal walls can be faced with a rigid wood fibre board, between studs can be full filled with flexible wood fibre batts or blown wood fibre floc. Flexible wood fibre batts are a flexible but dense form of wood fibre which can be friction fitted between studs ensuring a snug fit with no gaps.

It is quite a moisture absorbent material so does get wet if rained on, however it also dries extremely quickly and ensures that any moisture is drawn away from the timber structure. This makes it much safer to use than mineral wool or rigid synthetic PUR boards as it allows the frame to dry quickly once weathertight, preventing mould formation and rot occurring.

Alternatively specifically designed internal racking boards can be used to provide strength, airtightness and as a vapour control layer, for example Durelis VapourBlock. If using an airtight board ensure the joints are taped with an airtight tape such as Pro Clima Tescon Vana, which will ensure very high levels of air tightness, even as the timber frame shrinks.

Most roof applications over 16 degrees do not require an external membrane if using a wood fibre board offering another saving in cash and labour. Steico wood fibre boards can be left exposed for up to 8 weeks on site. Most wood fibre boards use a tongue and groove profile to ensure weather tightness but also wind tightness. They are highly vapour permeable, ensuring that no construction moisture gets trapped in the finished building and that the timber frame remains dry.

Small air leaks in the envelope of the building can transport large amounts of moisture into the fabric of the building during the winter months. Wood fibre insulation is not only vapour permeable but very capillary active, meaning it can transport moisture very quickly down each wood fibre. This ensures that any moisture leaking into the fabric of the building can be quickly dispersed and allowed to evaporate from the exterior of the building.

Increasing simplicity also ensures that the building is built as designed and therefore performs as designed, eliminating the well-known ‘performance gap’.

Wood fibre insulation vs rigid foam boards

  • Improved acoustic insulation
  • Reduced overheating risk

Wood fibre insulation is slightly less of an insulator in the traditional sense than rigid foam boards. However, because of the simpler construction, significantly lower thermal bridging values and lack of cavities the overall thickness is rarely thicker and may even be thinner.

Wood fibre offers two more significant bonuses when used in timber frame construction, in improved acoustic insulation and reducing or eliminating overheating risk. This is valuable as even in traditional block and brick construction a portion of the living space will often be timber frame when creating a warm roof to maximise space.

A standard timber frame wall build-up will typically offer noise reduction of around 50dB, making most common traffic and weather noise inaudible. The most common remark people make when entering buildings with wood fibre insulation is how quiet they are.

Flexible wood fibre insulation stores around 20 times more heat energy than the equivalent volume of glass or mineral wool. Typical wood fibre boards will store around 12 – 15 times more heat energy than foam boards. This ensures that the internal temperature stays very stable all year round and little of the summer sun’s heat passes through the walls to cause overheating.

Common uses of natural wood fibre board

Sarking & Sheathing

Wood fibre boards are usually used on the exterior of studs to create a weather tight shell that keeps the building warm in winter but, as importantly, cool in summer. Wood fibre sarking boards, such as Steico Universal and Steico Special are used to create a weathertight surface on roofs or behind cladding systems. These boards with full tongue and groove profile are quickly and simply fixed with counter battens and instantly form a weathertight surface.

External Wall Insulation (EWI)

Steico Protect boards are fixed to the exterior and rendered directly. Steico Protect can be used on timber frames and masonry. Used in conjunction with high performance lime renders the structure is vapour permeable, flexible and durable, finish should be with vapour open paints with either lime or water glass as the binder.

Internal Wall Insulation (IWI)

On masonry and brick a directly applied wood fibre board such as Steico Therm is ideal, ensure full contact by mechanically fixing and finish with a lime (vapour open) plaster, this ensures breathability and airtightness plus it maintains the required difference of permeability between the wall’s inner surface and outer skin which should be a factor between 7 to 10 times greater on the internal wall. In a fully vapour open structure this will move moisture to the outside of the building where it can be lost through evaporation.

This is one place where a wet-processed board such as Steico Therm can offer improved performance is for internal solid wall insulation as it offers a greater ability to buffer moisture.

For internal timber frame use Steico Protect as it has a full tongue and groove profile to support plaster application without potential cracking should subsequent movement or shrinkage occur.

Wood fibre boards FAQ

What’s the difference between wet and dry process insulation?

Wet-process and dry-process wood fibre boards may look the same on the surface but there are a few differences that should be considered when selecting wood fibre insulation boards. All types of flexible wood fibre boards use the same thermally bonded processes to create the product.

All of Steico’s wood fibre insulation boards are made from fresh, untreated forest thinning and waste wood from sawmills. In line with FSC and PEFC certification all the softwood used comes from regional and sustainability managed forests.

In the wet-process, chipped and waste timber (thinnings) are ground up into small pieces and then boiled up with water and a few other chemicals designed to break down the timber into the fibres. During this process, many of the sugars which could support fungus and mould are removed. This slurry is then poured on to a belt sieve and compressed to remove as much water as possible then re-heated with steam to bond the fibres together.

The steaming process softens the natural lignin around the fibres which bonds the fibres together in the board, the optimum thickness for this process is 20mm. These boards are then laminated using water glass as the bonding agent which creates a mineral - organic reinforced bond to produce boards up to 120mm thick.

The dry-process starts with the same timber source which is dried and ground up into fibres and then mixed with a synthetic glue. The glue, called PMDI (polymeric methylene diphenyl diisocyanate) is a polyurethane based glue which is used in fairly small quantities (3-4% by mass). This is basically the same glue that is used in OSB and MDF boards and is widely regarded to be very stable and inert and does not ‘off gas’.

The mixture is then laid on a conveyor belt and compressed to the correct thickness and density then steam is applied to cure the boards. These boards are made to the desired thickness, typically 20mm to 200mm and are not usually laminated.

The main differences between the two types of boards are density (and consequently thermal conductivity and thermal mass) and ability to transport moisture. Wet-processed boards tend to be better at transporting liquid moisture (capillarity), a property which lends itself to managing moisture very well and so these boards tend to be by far the safest for internal wall insulation situations.

Wet process boards also tend to have a higher density which is often simply because to get the required compressive strength they need more fibre in the board. This higher density makes them better at preventing overheating and also better for sound absorption, two of the big benefits of wood fibre insulation but does mean their thermal conductivity is higher.

Dry process boards are often used for roof and timber-framed wall applications as they are tough and can be made in large single thicknesses, usually up to 200mm. Because they are less dense than wet process boards they are easier to handle when on a roof, making them safer and preferable. Even in saturating conditions, these boards are not going to soak up water additionally, the lower conductivity of the boards means lower U-values can be achieved in a given thickness.

The dry process itself also consumes less energy than the wet process so produces less carbon in manufacture, making the boards carbon negative overall instead of the roughly carbon neutral wet process boards. This reduction in manufacturing energy also makes them a cheaper board to produce.

How sustainable is wood?

This very much depends on the type of wood that is being used. Many hardwoods come from slow old, slow growing forests which are not managed in a sustainable way. This means they are being felled at a rate greater that they are being replenished. This is not only unsustainable but destructive to our natural habitats.

A responsible choice can be made by only sourcing wood from forestry that is monitored by sustainability initiatives such as the FSC or PEFC. If this is done then wood can be truly sustainable and we have the ability to meet global demand in a responsible way.

Can wood-fibre be re-used?

Put simply yes, but it often depends on using systems that allow an easy dismantling process in order to access the insulation at the end of a building's life. Wood fibre does retain its properties over a long period and does not break down. In this way, it can be reused for other purposes.

Is wood fibre insulation easy to dispose of?

If wood fibre can’t be re-used then it can be recycled in the same way as timber. They have the same waste code. Wood fibre can also be composted.

How should wood fibre insulation be stored?

It’s important to store wood fibre away from moisture sources. That means it should always be stored off the ground and on bearers and ideally in its original packaging. If boards are removed then an additional loose cover should be placed over the top to protect from weathering and still allow for airflow.

What additives are there in wet and dry process boards?

Wet-process boards generally contain no additives relying on the natural lignin to bond the boards under heat and pressure, they can have Aluminium sulphate added as a precipitant and/or paraffin wax added as a water repellent.

Dry-process boards contain a glue, called PMDI (polymeric methylene diphenyl diisocyanate) is a polyurethane based glue which is used in fairly small quantities (3-4% by mass). This is basically the same glue that is used in OSB and MDF boards and is widely regarded to be very stable and inert and does not ‘off gas’.

Are wood fibre boards waterproof?

Wood fibre boards can add an element of weathering protection. The external surface ensures that water will run off and provide up to 4 weeks weathering protection. Even if they are exposed for longer periods they can still dry out if given the time and opportunity and will not degrade.

How to install wood fibre boards?

This depends on the different types of boards but generally they are laid in a brick bond format with staggered edges and the tongue of the T & G profile pointing upwards. Specific installation detailing for each board can be found on the STEICO website.

Do I need to use a membrane in the wall?

All wall or roof structures should consider air tightness, breathability and vapour control at the same time. This is generally done by using a vapour control layer on the inside of the structure and a breather membrane of the external side. However, this isn’t always the case.

A 15mm OSB3 or airtight particle board such as Durelis VapourBlock can be used as an internal vapour control layer, rather than a membrane, though it has to be fully taped and sealed at all joints and junctions. External wood fibre boards can be used without a breather membrane as long as the pitch is greater than 16°.

Typically you should always be 10x more vapour tight on the inside face than on the outside. This will ensure zero condensation risk.

Great value wood fibre boards

All our Steico products are priced individually by the board or pack (for Flex). Buying online couldn't be easier, just one click and the goods are on their way, just when you need them and no need to waste or store any surplus if you prefer you can call to place your order, we carry stocks in several locations in the UK including Canterbury serving the south and midlands and in Grangemouth for deliveries to Scotland and the north.

We are happy to offer technical support for your project. Please get in touch and call 01793 847 444 to speak to one of our technical sales team.