All information on this page is copied material from Gulvfakta, which is a technical reference material, Source: Gulvfakta

2.1.1.1 Materials for flooring
In this section, subfloors made of board materials are treated, e.g. chipboard, wood fiberboard and plasterboard. Both subfloors made as load-bearing subfloors and as floating subfloors are mentioned. The floor constructions mentioned in this chapter are intended for use with sheet materials. For beam constructions for wooden floors, please refer to the section on wooden floors.

Figure 1. The location of the floor substrate in the floor construction.

Glue and associated primer for gluing floor coverings to the subfloor are dealt with in a separate chapter.
Execution of the subfloor should, to the greatest extent possible, be included in the floor contractor's contract so that the responsibility for the execution with regard to the construction's appearance and usability is located in the same place.
Materials for flooring
As can be seen from Figure 1, the subfloor can consist of several layers. However, all of them will by no means always be needed. Furthermore, the order may vary depending on the current build. Some of the many materials that are used can also serve multiple purposes (have multiple functions), eg sand can act both as a screed and as an intermediate layer in floating constructions.

Two main groups of slab-based subfloors are:
Massively built constructions where there is a physical connection between the individual layers in the construction.
Example:
• Wood-based panels on wooden beam layers.
Floating constructions where the floor can move independently of the supporting surface.

Example:
• Leveled floor deck with plastic foil, on which wood-based boards have been laid out.

Floating slab floors are often used where there is a need for quick and dry leveling of a deck. In the following, a brief overview of the most important properties of the layers that can be included in a floor underlay is given. In addition, examples of a number of commonly used products are given, including generally available material information. It is the subfloor that is the basis for the finished floor's functional properties, e.g. with regard to:

Strength - should be chosen depending on use.
Flatness - requirements for screeding.
Moisture - constructive structure, moisture barrier.
Sound and gait - flexibility of the middle layer.
Lifetime - material selection, design, use.

2.1.1.2 Important properties of subfloors
In order for the overall floor structure to function as desired, there must be cooperation between the floor covering and its subfloor and also with the surroundings, e.g. the load-bearing structure, underlying terrain or surrounding walls. It is therefore necessary for the substrate to have a number of properties, which partly depend on the current floor covering and partly on building physical requirements for the entire floor construction.

When choosing a floor substrate, you must, among other things, take a decision on:
Requirements for the strength of the subfloor, e.g. for sheet material. Desire for the flatness of the substrate/finished floor, including the need for screeding and screeding.
The need for a moisture barrier. Requirements for strength and elasticity of the intermediate layer, depending on anticipated loads and wishes for sound reduction.

The required properties are not the same for all floor substrates. In the following, some of the properties of floor substrates which can be particularly important are briefly discussed:
Carrying capacity
The subfloor must be able to transfer the loads that can be expected in future use, without unwanted deformations or damage occurring.
Strength and stiffness/elasticity
The subfloor must be able to withstand the static and dynamic loads, e.g. from payloads, furniture, people and rolling traffic, which must normally be expected to occur in the intended use. For reasons of walking comfort, a certain flexibility (elasticity) may be desirable, while on the other hand, excessive deformations must not occur due to normal loads during use.
Flatness
The subfloor must be so flat that the floor can achieve the desired flatness. For thin floor coverings and non-load-bearing wooden floors, this means that the subfloor must be able to be laid out with the same flatness as desired for the finished floor, see more about this in the section on flatness.
Height leveling
The subfloor must be able to accommodate minor height differences in the underlying supporting structure.
Moisture barrier effect
To reduce the risk of damage due to moisture transport from below, e.g. due to construction moisture, it may be necessary to provide the floor construction with a moisture barrier, see more in the section on construction moisture.
Stability against moisture
The floor must not suffer harmful deformations due to moisture effects resulting from normal use.
Acoustic properties
The subfloor must have such sound technical properties that it can help reduce the transmission of airborne sound and footsteps, see more in the section on sound and floors.
Heat resistance
Floor materials to be used in connection with underfloor heating systems must be able to withstand the temperatures that can be expected to occur in the current construction.
Heat insulating effect
The subfloor must contribute to the thermal insulation of the deck construction.
Life
The subfloor must retain its properties to a satisfactory extent over a long period of time exposed to normal degradation factors, e.g. moisture or physical stresses from use.

2.1.1.3 Plate materials
In this description, board materials are assumed to be used in floating floors or load-bearing floors.
Thin chipboard and wood fiber boards can also be used to restore old wooden floors, etc.

Sheet materials for subfloors can be:
• Chipboard (including OSB boards)
• Plywood boards • Gypsum boards
• Wood fiber boards (incl. MDF boards)
Field sizes
Subfloors made of slabs must be divided into fields with expansion joints, which must be continued through the floor covering. The extent of the field sizes should not normally exceed 8 -10 meters for floating floors, depending on the type of slab. For larger field sizes, advice must be sought from the plate supplier. The number and location of joints is determined by the constructive structure of the floor, including the type of slab, the load, the expected moisture variations and the geometry of the room. Large mechanical loads, e.g. from heavy furniture or fixtures, can hinder the possibilities of movement and can necessitate that the field sizes be reduced.
Joints
Expansion joints in the load-bearing structure must always be passed through the floor structure including the floor covering. In floating floors, additional joints may be required depending on the structure, the geometry of the floor and the load. Further information about joints in floors can be found in the "Joint Map" published by the Joint Council for the Cooperation and Information of the Jointing Industry (FSO).

2.1.1.4 Wood-based boards in general
Particle boards, plywood boards, wood fiber boards and similar boards used in floor constructions in construction must be CE-marked. It is the plate manufacturer or the retailer who imports the plates themselves that is responsible for the CE marking. The harmonized standard DS/EN 13986, which is the basis for the CE marking, applies to production and use in Europe. As an addition to the standard, national regulations have been drawn up to the extent necessary to comply with building legislation - a so-called NA (National Application). In the Danish NA there is a requirement that the CE-marked wooden boards must comply with formaldehyde class E1 and that floor boards for load-bearing purposes must also comply with special requirements for strength and stiffness for point loads and dynamic loads, which correspond to the previous NKB regulations. The CE marking of wood-based boards will therefore contain the following information depending on whether the board can be used for a load-bearing subfloor or may only be used for a floating subfloor, i.e. fully supported subfloor.
Humidity conditions
Wood-based panels must be delivered with a moisture content in the range of 8 ± 2% (percentage by weight). A moisture barrier must be used if there is a risk of moisture being affected by the substrate. Due to the shrinkage and swelling of wood-based panels as a result of moisture variations, the possibility of movement must be ensured in the form of a joint along the walls and at penetrations in the floor surface. The width of the joint depends on, among other things of slab type and the size of the floor surface.
The place of execution
In order to avoid unnecessary dampness, laying should take place as late in the construction process as possible. Before laying, the building must be closed and dry, and the building must be heated. Work that can add large amounts of moisture to the building, e.g. brickwork and basic painting, should be completed.
Rooms in which wood-based boards are to be laid must be in equilibrium with a normal air humidity for the season, i.e. 35-65% relative humidity at approx. 20°C.

2.1.1.5 Floor chipboards
Floor chipboards are provided with tongue and groove on all four sides. For renovation and floating floor constructions in homes, floor chipboards are used in thicknesses down to 12 mm. For greater loads than in homes, e.g. in business and meeting rooms, the thickness should be at least 16 mm.
The surface of chipboard is a "better" substrate for flooring than plywood, as it is more even and uniform.

The boards are glued together in tongue and groove with PVAc glue or similar.

Table 1. Maximum spans for load-bearing sub-floors of 22 mm chipboard. The chipboards must be approved by the Board Inspection and the control mark by the factory.

Table 2. Tiling distances and screed dimensions for slab floors for use in homes.

The bonding class for floor chipboards must be adapted to the humidity conditions in the room where the boards are to be used. In humidity class I (ordinary indoor climate in heated rooms) glue class V20 is used, and in humidity class IU (unheated rooms or rooms with moderate moisture load) glue class V100 or V313 is used. Chipboard sub-floors should only be used as a working surface for subsequent craftsmen after careful covering. Further information on chipboard can be found in TRE 60 "Wooden boards" from Træinformation.

2.1.1.6 Plywood
For floating floor constructions, floor plywood is used, which is available in thicknesses down to 14.5 mm. Plywood boards for floors are normally provided with (approved) tongue and groove on the long sides. For floating floors, it is crucial that the boards are not skewed by the wind. Sheets with at least five layers of veneer should be used. When using thin floor coverings, the quality of the deck veneer is decisive for the appearance of the finished floor. For this purpose, special plastered or lightly plastered plywood sheets with an even surface should be used, where all holes and cracks are plugged or filled. Alternatively, a top plate can be laid, e.g. a chipboard or hard wood fiber board. Sheets are glued together with PVAc glue. For further information on plywood, refer to TRE 60 "Wood panels" from Træinformation.

2.1.1.7 Wood fiber boards
HDF and HB, i.e. boards with a density of at least 900 kg/m3, in thicknesses between 3 and 9 mm are used as a substrate for flooring. For straightening old wooden floors etc., hard wood fiber boards with a thickness of 3-4 mm are used, which are nailed to the substrate. For floating floors, boards with a thickness of 6-9 mm are used, provided with tongue and groove or rebated on all 4 sides. The plates must be acclimatised in the room in which they are to be laid out. The boards are glued together with PVAc glue. Board joints are offset by at least 300 mm. Sheets must be clean cut along all restrictions. Normally, it is not recommended to use folded wood fiber boards in rooms over approx. 25 m2. Further information on wood fiber boards can be found in TRE 60 "Wooden boards" from Træinformation.

2.1.1.8 Plasterboards
Plasterboards for floors can either be plasterboard or fiber plasterboard. Plasterboard can be laid out in 19 or 25 mm thickness. They can be supplied as special floor boards fitted with tongue and groove along all edges or as ordinary boards in 600 mm width, which are laid out in two layers with staggered joints. The density of plasterboard for floors is approx. 1100 kg/m3. Floor gypsum boards are reinforced with cellulose fibres. Fiber gypsum for floors is supplied as floor elements consisting of fiber gypsum sheets that are glued together offset from each other, so that a fold appears along the edges. The density is approx. twice as high as for wood-based boards, which makes plasterboard suitable for dampening airborne sound. Before applying thin carpet coverings or semi-hard floor coverings, the plasterboard must be fully leveled with a layer thickness of approx. 2 mm. For thicker floor coverings, troweling the board joints is sufficient. Plasterboards have very little movement due to moisture and can also be used in connection with underfloor heating, as they can withstand temperatures up to 40°C.

2.1.1.9 Laying methods
Floating sub-floors
Floating slab subfloors can move freely relative to the supporting sub-floor when the slabs shrink or swell (expand).
An intermediate layer is usually inserted between the load-bearing substrate and the subfloor, so that there is certainty that the floor surface can move freely. The intermediate layer can be made of materials that contribute to improving thermal insulation and acoustic properties. The stiffness properties of the plate layer and the intermediate layer must be chosen depending on the type of plate and the expected load. Floating floors are often used where there is a need for quick and dry leveling of a deck. If the intermediate layer is made of elastic materials, the floor surface can spring when walking, which makes the floor comfortable to walk on. Large mechanical loads, e.g. from heavy racks, point loads and counters, can hinder the floor's ability to move. In the case of floors with irregular geometry and where there are columns through the floor surface, the free movement of the floor must not be obstructed. If the floor surface is divided, it should be done as far as possible in rectangular fields, so that the expected movements in both directions are roughly the same.

Checklist for laying floating slab floors:
• The relative humidity in the building must be between 35 and 65%, depending on the season, and the temperature approx. 20°C.
• The building must be closed and the heating system must be installed and in use.
• The moisture content of concrete, lightweight concrete, etc. must be in equilibrium with the relative humidity normal for the season, i.e. the pore moisture content must be 35-65% RH. For concrete or lightweight concrete elements, it will take at least a few months before equilibrium is achieved. For concrete cast on site, an even longer time must be expected.
• Insulation materials, etc. must be dry.
• A moisture barrier, for example in the form of a 0.15 mm polyethylene film, must be laid out before laying the floor to protect against dampness from construction moisture.
• Wood-based panel materials must have a moisture content of 8 ± 2%.
• Glue, sealant and other auxiliary materials should be temperature-acclimated for at least a day before use, e.g. when stored in the rooms in which they are to be used.
Bearing floors
Load-bearing slab floors are understood to mean floors that rest on a linear support of joists or beams. The load of the floor is transferred through the plates to the underlying joists or beams. Beams are bricked up on an underlying construction of, for example, concrete or lightweight concrete, so that a flat base for the slab floor is achieved.
Beams are included in wooden beam layers above crawlspaces and in floor separations. Both beams and wooden beams offer good opportunities for placing sound and heat insulating materials in the cavity under the subfloor. The cavity can also be used for bringing forward heating, water and electricity installations.
Load-bearing slab floors can be made of chipboard or plywood.

Checklist for laying load-bearing slab floors:
• The relative humidity in the building must be between 35 and 65%, depending on the season, and the temperature approx. 20°C.
• The building must be closed and the heating system must be installed and in use.
• The moisture content of concrete, lightweight concrete, etc. must be in equilibrium with the relative humidity normal for the season, i.e. the pore moisture content must be 35-65% RH. For concrete or lightweight concrete elements, it will take at least a few months before equilibrium is achieved. For concrete cast on site, an even longer time must be expected.
• Insulation materials, etc. must be dry.
• Brickwork made with concrete must be hardened and dry.
• Moisture barrier, for example in the form of a 0.15 mm polyethylene foil, must be laid out before laying the floor to protect against dampness from construction moisture.
• Board materials must have a moisture content of 8 ± 2%.
• Wooden floor materials dried to the conditions of use should not be unpacked before laying.
• The moisture content of wooden beams and beams should correspond to that of the boards. The average moisture content should not exceed 12% for joists and 13% for beams, and no single measurement should exceed 14 and 15% respectively.
• Glue, sealant and other auxiliary materials should be acclimatized in terms of temperature for at least a day before use, e.g. when stored in the rooms in which they are to be used.

2.1.1.10 Substrate, intermediate layer, etc.
Moisture barrier
Before flooring is installed, the substrate must either be sufficiently dry, or precautions must be taken to protect the floor against moisture, which is usually done by using a moisture barrier. Moisture barrier is used especially with concrete if it is desired to avoid the long drying time, which can take many months, e.g. approx. 6 months for a 100 mm concrete 25 with one-sided drying. The need for the use of a moisture barrier is schematically shown in Figure 4, which originates from SBI instruction 178 "Damp insulation of buildings", see also in Gulvfakta's section Technology and quality for further information on building moisture and moisture measurements in concrete decks.
The term moisture barrier is used here in the same way as it is used in SBI's instructions and in TRÆ 41 "Laying wooden floors".
The term vapor barrier is used in other connections where moisture transport only occurs in vapor form, e.g. in walls and roofs.
The unit Z-value is used for diffusion resistance numbers instead of the previously used PAM. PAM values are converted to Z values by dividing by two, e.g. a material with a PAM value of 100 has a Z value of 50.

Figure 4. Terrain tires in heated buildings. Moisture-sensitive yellow coatings on concrete.

1. Diffusion-open floor covering, e.g. carpet without dense rubber backing. The concrete surface is dry.
2. A wooden floor is so sensitive to moisture that it always requires a moisture barrier on top of the concrete, which is not completely dry.
3. Diffusion-proof flooring, e.g. vinyl or linoleum, directly on dry concrete, i.e. concrete in moisture equilibrium with the highest RH that flooring and adhesive can withstand - often 85%.
4. Diffusion-proof flooring on a moisture barrier on the upper side of the concrete slab. The moisture barrier is necessary if the floor is laid before the concrete has dried.

The moisture barrier must prevent moisture in underlying constructions from penetrating moisture-sensitive materials in the floor construction. The moisture barrier must therefore be both tight against capillary suction and against water vapor diffusion, i.e. it must be dense and have a high Z value. Furthermore, the moisture barrier must be sufficiently robust to withstand handling on the construction site, e.g. withstand being stepped on in connection with laying out the floor. The requirement for the absolute size of the Z-value depends on the Z-value of the overlying layers. The moisture barrier must be specified by the designer. As a rule of thumb, it can be assumed that the Z-value of the moisture barrier must be 5-10 times as high as for the subsequent layers. In practice, meeting the requirements for the Z-value rarely causes problems, because for reasons of robustness, moisture barriers are usually so thick that a high Z-value is achieved with the types of materials used.

Commonly used materials for moisture barriers are:
• PE foil, thickness at least 0.15 mm for reasons of robustness. The Z-value for 0.15 mm PE foil is approx. 400 GPa s m2/kg.
From experience, thicker PE foils will be more robust during the construction period. Foils should be used that have documentation for diffusion density and durability, e.g. compliance with the Swedish Plastförbundets Verksnorm 2001.

Plastic foil is also a good sliding layer in floating floors, especially if it is used in two layers, or in combination with floorboard or similar products.
• Asphalt cardboard, 2 kg/m2, Z-value approx. 500 GPa s m2/kg.
• Molded asphalt, usually laid in a thickness of approx. 25 mm, whereby a Z value of over 1000 GPa s m2/kg is achieved.
• Epoxy system with documented functionality, e.g. according to the Swedish SP method 1310 (Statens Provningsanstalt).
• Special products from wooden floor suppliers, see the suppliers' instructions and product information.
• Special putty compounds, see the suppliers' instructions and product information.
It must be ensured that no perforation of the moisture barrier occurs, for example due to burrs in an underlying concrete layer. Protection of the moisture barrier can be done with an intermediate layer between concrete and moisture barrier.
Middle layer
• Intermediate layers are used in floating floors to ensure that the floor slab can move freely in relation to the supporting structure.
• In some cases, the intermediate layers can serve other purposes at the same time, eg sand is used for screeding, and insulating materials to improve heat and sound insulation.
• The intermediate layer must be chosen based on the desire to have a reasonably rigid floor that is not damaged by the loads for which the floor is intended, and which also does not cause inconvenience, e.g. vibrations when walking or annoying tilting of furniture and fixtures, due to floor deflections. On the other hand, for reasons of sound attenuation, there may be wishes to make the middle layer as pliable as possible.
When making a choice, both factors must be taken into account, if necessary.
Often the intermediate layers are combined. In floating floors, the substrate for insulation materials must, for example, have a flatness corresponding to the flatness requirement for the finished floor covering. This can be achieved, for example, by creating with loose granules before the insulation material is laid out.
Foam plastic, cork kraft paper and similar products
• Foam plastic, cork chipboard and similar products are laid out loosely under slab floors to equalize pressure and as a sliding layer.
• The products also contribute to improving the sound conditions by preventing the "clatter" against the supporting surface and by dampening the sound of footsteps and drums.
• Some of the products also act as a moisture barrier, so an additional moisture barrier is not necessary.
• Products recommended by the floor manufacturer/supplier should be used, so that there is certainty that the products have the desired properties, including durability.
Rubber cork/corkment
• Rubber cork/cork cement in strips is used as a pressure-distributing layer and contributes to improving the impact sound properties and the flexibility of the floor.
• The effect depends on the product's thickness and material composition. The materials can also be used glued to the substrate.
Flooring board
• Floorboard is used as an underlay for slab floors to reduce rattling noises.
• Floor board is an untreated board, usually with a basis weight of 500 g/m2.
Insulation materials
• Insulation materials are used in floor constructions to improve sound and heat insulation.
• In the case of beam or beam constructions, soft mineral wool can be inserted between beams and beams, where it e.g. can absorb sound.
• In floating floor constructions, the insulation is used to prevent the transmission of footsteps from the floor to the supporting construction, while at the same time transferring the load. For the sake of footstep sound, the insulation layer must be as flexible as possible, while for the sake of the wood floor's strength and stiffness it must be as hard as possible.
• The required stiffness of the insulation layer is determined based on the expected load, the thickness of the insulation layer and the floor material. It can be roughly assumed that mineral wool must have a density of 75-130 kg/m3 and polystyrene 30-40 kg/m3, depending on layer thickness, board thickness and load.
• Between the insulation boards and the board floor, a layer of cork parquet, ribbed cardboard or the like is often laid out to avoid annoying noise.
True
• Sand used as a substrate for floating floors must be well-graded, with a grain size of 1-4 mm and oven-dried. All fractions of the grain basket must be present, so that there is certainty that the sand packs properly during laying and compaction.
• Sand is laid out according to leaders. If the layer thickness exceeds 60 mm, laying must be done in several rounds with vibration for every 60 mm begun.
• Sand layer must be covered with a suitable covering material before laying sheet material, eg 0.2 mm polyethylene foil, asphalt cardboard or cork park layer.
Gypsum granules
• Gypsum granules must be well graded with a grain size of 1-5 mm. The density must be 400 - 600 kg/m3.
• Gypsum granules must be laid out at least 15 mm thick. For larger layer thicknesses, vibration must be done for every 50 mm begun.
• Leveled gypsum granules must be covered with a suitable covering material before laying sheet material, eg ribbed cardboard, floorboard or similar.
Perlite
• Perlite is a volcanic material with a density of approx. 150 kg/m3. Perlite must be laid out at least 15 mm thick. For larger layer thicknesses, compaction must be done for every 50 mm begun.
• Leveled perlite must be covered with a suitable covering material (board material) before laying floor boards.
Flax fibers Bitumen-impregnated
• Flax fibers must have a density of at least 150 kg/m3. The fibers are laid out along conductors with a layer thickness between 5 and 400 mm. It must be compacted for every 35 mm.
• Aligned flax fibers must be covered with a suitable covering material before laying sheet material, e.g. ribbed cardboard, floorboard or similar.

2.1.1.11 Expansion joints
Expansion joints in the load-bearing structure must always be passed through the floor structure including the floor covering.
In floating floors, additional joints may be required depending on the structure, the geometry of the floor and the load.

Figure 5. Example of execution of an expansion joint in a slab floor on joists.

Further information about joints in floors can be found in the "Joint Map" published by the Joint Council for the Cooperation and Information of the Jointing Industry (FSO).

2.1.1.12 Beam structures
Beams can be made of solid or laminated wood.
Solid wood beams must be sharp-edged battens with a width of at least 45 mm (planed measurement).
Beams in laminated wood (e.g. Kerto) must have a width of at least 40 mm, so that there is no risk of splitting.
The joists should be supplied as long as possible, as the best results are achieved with full-length battens. Lengths of up to 3.9 m are normal stock items, and larger lengths up to 4.8 m can normally be supplied to order.
Beams should at least be planed on the side facing the boards.
The joists must be so straight that their surface after laying deviates by no more than ± 2 mm on a 2 m straight beam.

After laying, there should be no more than 5 mm lateral deviations from straightness of 2 m (deviation from straight wood placed on the hollow side of the screed).
The joists must not twist more than, when laid out loosely with one end secured to the floor, a maximum "gap" of 2 mm per 2 m bedding length at a corner at the opposite bedding end. For a screed of e.g. 3.9 m, this corresponds to the twisting leading to a "gap" of approx. 4 mm.
The joists must be of a quality so that the requirements for studs correspond to the sorting rules for DK 18. This means that single studs must make up no more than 1/3 x the cross-sectional area and stud groups no more than 1/2 x the cross-sectional area.
The best result is achieved if the moisture content of the screeds when laid corresponds to that of the boards. This reduces i.a. problems with the squeak. The moisture content of the screeds must never exceed 12% when laid. This means that the average of the measurements taken must not exceed 12%, and that there should not normally be individual results higher than 14%.

Figure 6. Beam construction for floor slabs. All slab pieces should span at least 2 bays. All free board edges, e.g. along walls, must be supported.

Beam and beam distances for load-bearing slab floors appear from the tables in the sections on the respective slab types.
The specified distances ensure a reasonably stiff floor that does not cause annoying vibrations when walking, or cause furniture and fixtures to have annoying slopes due to the floor bending.
The support distance depends on the chosen material thickness and the expected load.

See also floor facts section on "Joints - material" and "Joint distances"