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Intermediate Floor: Material Layers and Characteristics

Choosing materials and the right material layers to design intermediate floors with optimal structural, energy, and acoustic performance

The intermediate floor is a horizontal enclosure that divides two internal spaces of the building belonging to the same housing unit or different units. It can have variable configurations and materia layers depending on the intended use of the enclosed spaces.

Let’s see the layers that compose it, the thicknesses involved, and the main characteristics.

  1. Ceiling slab
  2. Attic floor
  3. Intermediate floor
  4. Ground floor slab
Schematic representation of the intermediate floor

Schematic representation of the intermediate floor

Intermediate floor material layers

The material layers and thickness of an intermediate floor can vary depending on the use and property of the spaces, the chosen technological solutions, and the desired performance. Generally, the stratigraphy of an intermediate floor consists of:

  • flooring (common types include stoneware, parquet, terracotta, ceramic, resin);
  • screed for load distribution;
  • flooring insulation (may be absent in single-family buildings);
  • plant substrate;
  • thermal insulation (used when the floor is a heat-dissipating surface because it borders unheated spaces and does not meet the transmittance values required by the regulations);
  • floor structure (joists, hollow bricks, etc.);
  • plaster or other finishing layer of the floor intrados.

In the case of underfloor heating, radiant panels are placed below the screed for load distribution (in this case, it is also called a thermoconductive screed) and above the insulating layer that helps limit heat loss to the spaces below. Let’s delve into this solution further.

Floor with radiant heating

The correct material layers of the intermediate floor with radiant heating depends on the functionality of all components. In general, the radiant system is placed above the lightweight leveling screed, which also houses other systems (corrugated conduits for electrical wiring, drainage pipes, water distribution, etc.).

In order, the layers to consider, in addition to the structural thickness of the floor, are:

  • flooring: any type of flooring can be installed on a radiant system (stoneware, parquet, terracotta, etc.);
  • screed for load distribution: thickness from 3 cm (self-leveling rapid drying type) to 4.5 cm for traditional solutions;
  • radiant coil;
  • support layer for the radiant coil: can be cast in place or prefabricated and dry-laid;
  • protective layer for the insulating layer: possibly placed on the insulation to protect it from the screed pour;
  • thermal insulation: to be placed under the radiant panels to prevent heat loss to the spaces below. The thickness varies depending on the type of underlying space (heated, unheated) and is generally between 3 and 6 cm;
  • acoustic insulation: this layer can be independent or pre-coupled with the thermal insulation layer (with a rubber-based sheath);
  • vapor barrier: to be positioned according to the type of floor (ground floor, on heated or unheated intermediate floor, etc.) and flooring. It is important to remember that its function is to protect the insulation from moisture, so it is always placed near the insulation and on the side most exposed to condensation;
  • leveling screed that houses the systems (electrical, plumbing, drainage, etc.) of about 5-8 cm, preferably lightened with loose insulating material (cork, perlite, expanded clay, etc.). When there is not enough thickness, you can opt for a “channel” running along the perimeter of the walls that houses the systems and does not overlap with the radiant floor package.

Floor characteristics

The floor is the final layer of the intermediate floor, the finishing layer, and currently there are many types of indoor flooring available. The most innovative ones feature large formats (up to 300 x 150), very thin thicknesses (3.5 mm), lightweight, flexible, and resistant materials thanks to reinforcement with fiberglass. However, there are also trends inclined towards rediscovering traditional materials such as cement tiles, majolica, etc.

The choice is vast and includes floors made of:

  • ceramic
    • single-fired;
    • double-fired;
    • terracotta;
    • stoneware;
    • clinker;
    • majolica;
    • red single-fired;
    • light single-fired.
  • stone
    • marble;
    • granite;
    • travertine;
    • stone
      • volcanic;
      • limestone;
      • sedimentary;
  • wood
    • maple;
    • oak;
    • cherry;
    • ash;
    • teak;
    • walnut;
  • resilient
    • rubber;
    • vinyl;
    • linoleum;
    • resin.
  • micro cement
  • beaten
  • kerlite;
  • etc.

Regardless of the chosen type, a floor must meet the following requirements to be compliant:

  • abrasion resistance: surface mechanical resistance;
  • chemical attack resistance: material’s resistance to chemical agents such as food substances, detergents, various liquids;
  • hygiene: the ability to effectively clean surfaces to remove dirt, germs, and bacteria;
  • light resistance: some materials change color or may fade or yellow due to exposure to sunlight or artificial light;
  • fire resistance: material’s ability to withstand flame exposure.

Intermediate floor thickness

The thickness of the intermediate floor depends mainly on two variables:

  • the structure;
  • the functional layers.

To calculate the thickness of the structural part, a structural calculation software is needed. Generally, the thickness of the structural part varies based on the span the floor must cover, the construction type (reinforced concrete, steel, wood, etc.), material strength, expected project loads (accidental, permanent, etc.), regulatory requirements, etc.

The thickness of the functional layers, on the other hand, depends on the type of layers involved. Specifically, it depends on the thickness of the subfloor, the presence of the insulating layer, the systems it must accommodate, the level differences to cover, etc.

Therefore, the floor thickness cannot be uniquely determined.

Once the design thickness of the intermediate floor is established, you can proceed with the graphic representation and 3D modeling necessary for:

  • architectural design drafting;
  • structural calculation of the floor;
  • energy certifications and verifications.

In particular, to represent all layers of a floor and automatically obtain legends and diagrams with all layers and their respective thicknesses, you can use a BIM architectural design software. In practice, you create the 3D model of the entire building, assign material layers to the intermediate floor, creating it from scratch or modifying an existing one in the library. The complete BIM model with all material information can be exported in IFC format and used as an energy model for calculating transmittance, energy checks, etc., or for structural calculations and verifications, with a structural calculation software.

Subfloor

The subfloor is the layer following the structural part of the floor and serves to level irregularities, accommodate and protect systems, provide thermal and acoustic insulation.

The thickness of the subfloor varies greatly depending on the type and quantity of pipes it houses. Often, the subfloor is made with lightweight premixed materials. The advantages are numerous to limit weight and not excessively burden the floor structure. This attention is particularly required in restoration works of historical buildings and renovations when there is a need to avoid loads not considered in the structural calculation. Additionally, the use of a porous material improves insulating properties and acoustic performance of the floor.

The subfloor can be single-layered or double-layered if it includes insulating or lightweight material.

A double-layered subfloor that ensures good thermal-acoustic performance, consisting of an insulating/lightening/compensation layer, anti-impact mat, and finishing screed, requires an ideal thickness between 12 and 18 cm.

Acoustic insulation

Sound waves propagate easily in a building structure. To ensure the maximum levels of permissible impact noise according to regulations, it is essential that intermediate floors, as well as partitions and vertical closures, contribute to this purpose.

Systems to prevent impact noise propagation are varied, including:

  • use of resilient flooring (e.g., carpet, rubber, vinyl) or elastic mats that reduce impact energy at the time of impact and should be placed not only on the floor but also under the partitions;
  • use of techniques and materials capable of blocking vibration and preventing propagation (floating floor) by interrupting the structure’s continuity;
  • installation of a suspended ceiling with anti-vibration hooks and plasterboard counter-walls. This technique isolates the noise only in the ceilinged environment.
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