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Thermal Insulation in Buildings: Basics

When tackling any construction or renovation project, choosing the right materials is a crucial step. It's essential to select the best materials to ensure nothing goes wrong with our project. One of the main properties to keep an eye on is the thermal insulation capacity of the materials we plan to use.

In this post, we'll explain the key factors to consider when choosing between different insulating materials for your projects. Discover the fundamental aspects of achieving effective thermal insulation in your building right here.

Definition

At Panel Sandwich Group, we pride ourselves on offering top-quality products, including those that provide the best thermal insulation. The concept of thermal insulation can be summarized as a property associated with the ability to transmit heat. Essentially, to measure the level of thermal insulation of a material, we must consider its ability to reduce the transmission of heat. This term, which we will explain further, is also known as thermal resistance.

This means that the key to the thermal insulation of a material lies in its ability to reduce heat transmission, so it is enough to know the thermal resistance of the material to know if it is a good insulating material. But before knowing what thermal resistance is, it is necessary to explain how heat is transmitted. Heat transfer is the phenomenon that occurs when two or more objects interact and their heat energy is transferred by different types of particle movements and chemical concepts. These vary depending on the type of transmission form involved, each of which involves different functions and processes.

Ways of heat transmission

Heat transfer between materials can occur in three distinct ways, always following the same pattern of transfer direction (from higher to lower temperature).

Basic Concepts of Thermal Insulation in BuildingsConduction Thermal Insulation

1. Conduction

This process is based on the direct heat flow through matter as a consequence of their physical contact. This direct contact involves the transfer of heat energy between the two bodies, or parts of them, which are usually at different temperatures. The hottest areas are those with the highest thermal energy, while the coldest areas have the lowest thermal energy.

This system of heat transmission, consisting of the movement of atoms within a body, is predominant in solid bodies. Therefore, it is very important in the thermal insulation of buildings since most construction elements are installed in contact with each other and the conduction process will influence their insulation.

2. Convection

A process based on the transfer of heat within gaseous or liquid elements. Therefore, heat is transmitted by the physical movement of hot molecules present in areas with a high temperature to areas with a low temperature and vice versa, thus balancing the different temperatures. Natural convection is produced by the difference in densities resulting from a difference in temperatures.

In buildings, heat flow convection is upward. Therefore, having a roof with good thermal insulation will make it possible to take advantage of the heat generated inside the house.

In addition to gaseous elements, the convection process is of great importance in fluids, hence the existence of a process called surface conduction. The heat flow that occurs between the surface of a material and a fluid, for example, between the outside of the tile and the rain or dew water, produces a heat transfer by conduction through the thin layer of the fluid next to the surface.

This process highlights the importance of ventilation and the elimination of condensation humidity. This is due to the fact that, even if the thermal insulation of the roof or facade is correct, the appearance of humidity in elements that are in contact with thermal insulating materials will result in greater surface conduction. Likewise, the presence of humidity in a given construction solution leads to high energy consumption by cooling the interior temperature of the building.

Convection Thermal InsulationRadiation Thermal Insulation

3. Radiation

The radiation process is based on the transmission through space of electromagnetic waves. These waves are invisible and the heat energy is emitted by infrared radiation by all matter with a temperature above 0ºC.

Thermal radiation is the result of the temperature alone. Radiation depends on the thermodynamic temperature of the emitting body and is independent of the temperature of the receiving body or the environment. In other words, the energy radiated by all bodies is a direct consequence of their temperature.

Concepts to be considered

When studying and analyzing the thermal insulation capacity of any building element, we must know how to interpret certain values. In the following, we will briefly explain Thermal Resistance, Thermal Conductivity and Thermal Transmittance.

1. Thermal Resistance or R-Value

This is a concept that is key to measuring the level of thermal insulation of a building material, since it refers to the ability of a material to insulate thermally. In other words, its ability to prevent heat from passing through conduction.

For its calculation, it is also necessary to know the thickness of the material (e) and its thermal conductivity (λ):

R = e/λ

In the case of a construction element consisting of several thermally homogeneous insulation layers, the thermal resistance of each material is added together to obtain a total thermal resistance value (RT).

2. Thermal Conductivity (λ)

From the previous concept we can deduce the importance of thermal conductivity (λ). It is a thermal property characteristic of a homogeneous material, and is equivalent to the amount of heat per unit time that passes through a layer of thickness and unit surface area of material, per unit temperature difference. In other words, it represents the capacity of a material to allow heat to pass through by conduction and per unit of measurement of one meter. The lower its value, the less heat capacity it has and, therefore, the better thermal insulator it will be.

But it is not only important that the thermal insulation material has good thermal conductivity. In order to meet the thermal insulation objective, it is also essential to dimension the appropriate insulation thickness.

Its unit of measurement in the International System is the Watt divided by meter per degree Kelvin (W/m.ºk). As a general rule, we will consider a building material with good thermal insulation only if λ < 0.065 W/m.ºk.

Insulating Material Quality

In the following table, you will be able to check the approximate values of thermal conductivity (λ) of the main thermal insulating materials (these data may vary depending on the density of the material):

THERMAL INSULANTS

Material

λ (W/m2.k)

Expanded Polystyrene

0, 031 - 0, 050

Extruded Polystyrene

0, 029 - 0, 033

Rockwool

0, 031 - 0, 045

Polyurethane (PUR)

0, 022 - 0, 028

Polyisocyanurate (PIR)

0, 022 - 0, 035

3. Thermal Transmittance or U-Value

You cannot finish reading this post without knowing the meaning of this concept, so often used in the construction world. Thermal Transmittance (U= W/m2K) refers to the amount of heat that flows, per unit of time and surface, through a construction element when there is a thermal gradient of 1ºC or 1ºK of temperature between the two environments that it separates. We can then deduce that Thermal Transmittance is inversely proportional to Thermal Resistance: the more resistance of the materials that make up an envelope, the less heat is lost through it. In other words, we are talking about the capacity of a building element to transmit heat in its real position:

  • The higher the U, the lower the thermal insulation effect of the element.
  • The lower the U, the better the thermal insulation and the lower the heat loss through the element.

In conclusion, the ideal insulation is one that does not transmit heat (U= 0).


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