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FAQ’s – Wood Fibre Insulation | Pavatex Wood Fibre Boards

Pavatex Wood Fibre Thermal Insulation


FAQ’s – Raw Materials and Manufacture of Pavatex Wood Fibre Insulation

Pavatex wood fibre insulation boards are only manufactured from untreated softwood supplied in the form of sawmill slabs, splinters and chippings which represent a by-product from the manufacture of timber for furniture or construction use. The wood, which comes from fir and spruce trees, is sourced from local, sustainably managed, FSC or PEFC certified forests.


Pavatex uses two manufacturing processes – in the French factory the boards are manufactured using the dry process which manufactures homogenous boards from 20 to 240mm thick. In Switzerland the wet process is used to produce board thicknesses of 4 to 25mm and these thinner boards are then bonded together in layers.


The raw wood material is cut into smaller wood chips, which is then thermo mechanically broken up in a defibrator. In the wet process the pulp fibre is mixed with water and a water suspension is created. This water suspension is heated which releases the natural lignin and hemicellulose glues which occur naturally in the tree and then it is drained, forming a fibre sheet that forms the basis for the new board. The drained boards are then dried out to attain the final moisture content. In the dry process the dry pulp fibres are mixed with a PMDI synthetic resin in order to bond the fibres and then the boards are cured by a steam and air mixture and cut to size.


Yes, they are. The wood used to produce Pavatex wood fibre boards is a natural resource that grows again and again and comes from new timber off-cuts from local sawmills. This timber is sourced from local forests which are farmed sustainably, as certified by FSC and PEFC. Pavatex insulation panels are fully recyclable and they can be composted after their useful life.


Are Pavatex insulation boards safe for a person‘s health?

Pavatex wood fibre insulation boards contain predominately only natural materials which cause no health problems – up to 98% is comprised of wood fibres. Pavatex wood fibre boards are natureplus certified which means that they are toxic-free. Natureplus regularly inspects and certifies Pavatex products to ensure that they remain free from any harmful substances. Wood fibre boards also absorb internal humidity and hinder mould growth so make the internal environment healthier.


To increase the water resistance of boards that are used on the external surface of a building, a natural water resistant ingredient, paraffin, is added to some of the boards (Isolair, Pavatherm-Plus, Diffutherm, Diffuboard and Pavadentro) during production. This is not just a surface treatment – this water resistant ingredient is added when the fibre suspension is being created so that the entire thickness of the board, including both sides, has excellent water resistance.


Under the European harmonised EN 13501-1 Reaction to Fire board standard, Pavatex wood fibre boards are classified as Class E combustible materials. In accordance with the German DIN 4102 standard, wood fibre boards are listed in Flammability Class B2. This fire resistance is the same as other commonly used thermal insulation materials such as polystyrene, polyurethane etc. However the wood fibre board surface chars and slows down the speed of the fire spreading through the structure. This results in an above-standard fire resistance for the entire building structure when used alongside plasterboard. Pavatex wood fibre insulating boards release virtually no harmful emissions in the event of a fire.


FAQ’s – Wood Fibre Insulation | Use and Installation

They are widely used in almost all types of constructions – roofs, external walls, floors and attics and the structure can be masonry, timber frame or solid wood.


Thermal bridges are created in places where a thermal insulation layer is in some way interrupted by materials with poor heat resistance, e.g. above the rafters in a pitched roof. In the roof, these rafters may take up to 20% of the entire roof area, and because these timber rafters are four times worse at resisting heat than the Pavatex insulation panels, a significant heat loss will escape through the roof in these areas. Thermal bridges can be limited by having a complete blanket coverage layer of insulation of adequate thickness, either above or below the rafters.


The most effective wall thermal insulation method is to have it on the outside because the complete building envelope will be thermally insulated, including the junctions between e.g. the ground floor and the first floor. This minimises the risk of thermal leakages. It is also a safer method from the perspective of possible water vapour condensation. External wall insulation also gives a facelift to drab buildings. Internal wall thermal insulation is only recommended in situations where external insulation is not possible e.g. on traditional or historic buildings where modifications to the external façade of the building are not permitted or desired. In this case, Pavadentro or Pavadry panels are recommended due to their integrated mineral functional layer.


There are two options to externally insulate external walls depending on the type of finish that is required. If a direct render finish is desired, the walls must be insulated with Diffutherm or Diffuboard boards. These are suitable for both masonry and timber-frame buildings. They can be rendered directly with diffusion open renders e.g. lime or clay renders. If the wall is to be finished with cladding or a façade, then a ventilated space must be kept between the wood fibre layer and the finished cladding or façade. Isolair or Pavatherm-Plus panels should be used in these situations as they are water resistant and diffusion open. Again, these are suitable for timber-framed or solid walls.


No, because Pavadentro and Pavadry wood fibre boards have an integrated mineral functional layer which controls the passage of moisture. It actively uses the capillary and hygroscopic properties of wood fibres to transport moisture and to reduce the destructive effect of condensation within wall structures.


The tongues of the boards must face upwards towards the roof. There are various insulation fixings available depending on the substrate behind the wood fibre and we will advise on the best option. The number and length of insulation fixings used also depends on the substrate, but as a general rule 6 fixings are required per board on masonry walls and 3 per board per stud on timber studs. On masonry backgrounds the first fixings are into the centre of the board.


The benefit is that it restricts thermal bridging from arising in the area above the rafters. Another advantage of this warm roof insulation method is that the attic space can be used as living accommodation, because there will be a comfortable, healthy internal climate all year round within this space due to the high thermal mass of the wood fibre layer. Inadequately insulated spaces can overheat in summer time and be cold in winter time.


Isolair or Pavatherm-Plus panels are installed above the rafters. The tongues must face upwards towards the apex of the roof. Then battens and counter battens are fitted above this insulation layer to allow air to circulate. The entire system is secured to the rafters using special insulation screw fixings. The roof covering is then fitted to the batten system.


No, it is not necessary to use a vapour control layer (membrane) above the rafters or on the outside of a timber frame structure prior to fitting the Isolair or Pavatherm-Plus wood fibre layer. The Isolair and Pavatherm-Plus panels are open to diffusion so they will allow water vapour to escape but they also have increased water resistance on the surface so rain will not penetrate the boards during construction.  However an airtight membrane or OSB board is required on the inside of the building frame to provide airtightness.


Isolair and Pavatherm-Plus panels have tongue and groove joints at the 4 perimeter edges which firmly join the boards together without having to use glue. However on roofs with a pitch < 18°, the joints are glued together and in addition roofs which have pitches of between 5 and 9° must be totally covered with a breather membrane.  For water tightness, seal all exposed board edges, openings, corners etc with Pavatex Primer and Pavatape. This is to eliminate the risk of water penetration into the joints.


As a temporary decking, they can be exposed to the weather conditions for up to three months. However in the winter months, they must not be loaded down with snow.


Pavaflex is ideal to use between rafters and studs because it is a flexible wood fibre product which can compress slightly and fit snugly in areas where widths are exactly defined so that heat will not escape through any gaps. Due to its high density (40kg/m³) it is also very good at reducing sound through the structure and will help to stabilise internal temperatures.


Yes, they can, but please contact the Acara Concepts sales team for technical support. The boards must be protected with a damp proof membrane before the screed is poured.


The Pavatex wood fibre boards are laid on the dry sub-deck of the concrete or timber floor in a brickwork formation. The next row can begin with the off-cut from the previous row to avoid waste. Leave a 10 mm expansion gap around the perimeter edges and around any fixed objects in the room and seal this gap with a permanently flexible sealant. The laminate and engineered timber floors are also laid as floating floors. The tongue and grooves of the engineered flooring are usually glued with wood adhesive, as per manufacturer’s instructions. If the sub-deck is a new concrete floor, lay a damp proof membrane onto the floor first to prevent rising damp getting into the wood fibre.


Wood fibre insulation boards can be cut using common tools for cutting wood and wood products – an electric circular saw with a dust collector can be used for boards up to 80mm thick. The saw should have a large number of teeth and run at a high cutting speed. An electric reciprocating saw with a wide-toothed blade can be used for all board thicknesses. Jigsaws are very handy for cut-outs and trimming. An insulation or serrated knife is ideal for thin wood fibre boards e.g. Pavastep.  Pavaflex is easiest cut with an insulation knife.


High density Pavatex wood fibre insulation boards have excellent shape retention and, even after many years in place, do not show any signs of degradation. Also because of their excellent hygroscopic properties they will not sag over time like other insulation materials and their insulation capacity is not diminished when they hold water vapour. The CE marked Pavatex wood fibre boards will last as long as the building in which they are installed.


FAQ’s – Technical Information and Definitions for Thermal Insulation

Thermal insulation has to protect the building from heat loss in the winter months (winter heat protection) while also safeguarding the interior against overheating in the summer (summer heat protection). Thermal insulation should also be able to adequately deal with moisture in the air and water vapour in the structure.


Thermal conductivity represents the insulation’s ability to conduct heat and is expressed as a Thermal Conductivity Co-efficient λ or lambda (also known as K-Value) – the lower the value, the more effective the insulation. It is a critical property of thermal insulation as it prevents heat from escaping through the material. Most insulating materials have a thermal conductivity co-efficient of around 0.040 W/mK.


The U-Value or Thermal Transmittance is the measurement of the rate of heat loss through a building element such as a wall, floor or roof and is expressed as W/m² K. This measures how well parts of a building transfer heat so it is highly dependent on the thermal conductivity of the individual materials used to construct the building and the way they are assembled. The lower the U-value the better, because this means that the building envelope is resisting the transfer of heat. Generally this indicates high levels of insulation.


Yes, there are. Each country has its own maximum Thermal Transmittance (U-value) Regulations for various structures e.g. pitched roofs, flat roofs, external walls, floors, etc, tailored to climatic conditions. In England and Wales, these values are listed in Approved Document L of Building Regulations 2010, in Scotland see Section 6 of the Technical Handbook 2011, in the Republic of Ireland see Part L of Building Regulations 2011 and in Northern Ireland the regulations are in Part F 2006. These standards are constantly changing and getting more stringent as each country aims to achieve zero carbon new build homes in the near future.


It follows that the greater the insulation thickness, the lower the thermal transmittance or U-value. The table below illustrates the relation between U-values and the thickness of insulation with a thermal conductivity λ of 0.040 W/mK.


Thickness in mm 20 40 60 80 100 200 300
U Value – W/m²K 1.506 0.859 0.601 0.462 0.375 0.194 0.130


The heat accumulation capacity of wood fibre contributes significantly to the optimal internal climate of buildings, especially during the warmer summer months when internal spaces can overheat unpleasantly. The greater the accumulative capacity of the building materials, the better able the building is to maintain a more constant, comfortable interior temperature. This is particularly important in lightweight structures such as timber and metal frame buildings, where temperatures can fluctuate quite rapidly.


The thermal mass of a product is determined by a combination of the product’s density, its specific heat capacity and its thermal conductivity. Therefore Pavatex wood fibre insulation boards have very high thermal mass properties. The higher the thermal mass, the better able the building is to store excess heat during the day for any time between 10 and 12 hours, and then release it back into the building at night-time as it cools. This enables buildings to respond naturally to fluctuating temperatures and it helps to stabilise the interior temperature. This reduces the energy requirements of the building. It is critical to include high thermal mass products in lightweight structures e.g. timber frame buildings. See Summer Heat Protection for more information.


Pavatex wood fibre‘s capacity to disperse water vapour (diffusion ability) through capillary action is a very important property of the thermal insulation material, because a large amount of water vapour or condensation is generated inside buildings from bathrooms, cooking, breathing etc. The adequate transfer of water vapour through the complete building structure is critical so that interstitial condensation does not get trapped within the structure, as this would cause the structure to become damaged over time due to rot and mould growth, which would result in expensive remedial work.


The Water Vapour Diffusion Resistance Factor µ is obtained by dividing the water vapour diffusion coefficient in air, by the moisture permeability of a porous material. The µ factor therefore describes how many times better a product is at resisting the passage of water vapour, compared with an equivalent thickness of air when at an equal temperature. Materials with a Vapour Diffusion Resistance Factor of up to 10 are considered to have a very high diffusion capability and the Pavatex wood fibre products have a µ rating of 5 in wet conditions, which means that vapour passes through the boards, but at a controlled rate.


It operates on the principle that moisture can be adequately dispersed from the interior of the building to the outside but that the outside layers prevent moisture or rain penetrating from the outside environment into the structure of the building. This structure is diffusion-open or hygroscopic. The principle of these constructions is to use materials which become more vapour open as they go towards the outside of the building.