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Building envelope

Introduction

One thing is certain: Without a modern envelope, no building can achieve energy efficiency. Take a look at the latest solutions for insulation, sealing, windows and facades!

Building envelope

Buildings offer huge potential for energy-saving. In Germany, heating and hot water requirements alone account for approximately 35 percent of total final energy consumption (see German Energy Agency, in German). This is an important cost factor for companies and private individuals alike.

Older houses in particular consume up to five times more energy than new builds, with the largest share of heat being lost through their external surfaces (see German Energy Agency, in German).

Important factors in the refurbishment of the building envelope are the insulating material, the avoidance of thermal bridging, windows and glass constructions and a high degree of air-tightness overall. Key considerations in all cases are an individual evaluation of the entire building and skilled, professional planning and realisation.

In addition to reducing energy costs and CO2 emissions, optimising the building envelope also enhances indoor comfort and increases the value of the property. An effective envelope protects the building from cold in the winter and from heat in the summer. It is therefore also beneficial in hot regions.

Germany has been investing in energy-efficient building and renovation for many years and has therefore acquired considerable experience in this area

Image Copyright: AHK Baltikum

© AHK Baltikum

Insulation options can be differentiated according to various insulation levels and insulation materials. The insulation levels can be classified as exterior, interior and core insulation.

Insulation materials

Insulation materials are mainly distinguished between organic and inorganic insulation materials. Examples of inorganic insulation materials are mineral wool or ex - pand ed granules. Organic insulation materials can be broken down further into fossil-based insulation materials, such as polystyrene, and renewable insulation materials, such as
those based on wood fibre, hemp or seaweed.

The ability of an insulation material to transfer heat is specified by its thermal conductivity: excellent insulation is obtained from materials with low thermal conductivity. In insulation materials, the range extends from approx. 0.025 watts per metre and Kelvin (W/(m·K)) for PUR insulation materials up to 0.045 W/(m·K) for wood fibre panels. Mineral wool and polystyrene have a heat conductivity of approx. 0.035 W/(m·K). In addition to heat conductivity, other properties play a role in the selection of a particular insulation material, e. g. protection against overheating in the summer months, fire protection and even permeability to water vapour.

Exterior, interior and core insulation

Among the various options for insulating buildings, exterior insulation is the easiest and least problematic from a structural perspective. Interior insulation, on
the other hand, is exposed to various stresses and can lead to the formation of mould if not installed properly. It also restricts the use of the living or utility space.

Interior insulation is used primarily when insulation measures cannot be used on the exterior facade, for example in the case of listed facades. Core
insulation is suitable for renovating double exterior walls, which have a layer of air between the interior and exterior wall. The potential insulation strength is dictated by the width of this layer of air, but in practice it is often significantly constrained, for example by residual mortar.

Core insulation is suitable for renovating double exterior walls, which have a layer of air between the interior and exterior wall. The potential insulation strength is dictated by the width of this layer of air, but in practice it is often significantly constrained, for example by residual mortar.

Image Copyright: RKW Architektur + Städtebau Fotograf: Carsten Costhard

© RKW Architektur + Städtebau Fotograf: Carsten Costhard

Avoiding overheating

While heat losses should be avoided and solar gains should be increased primarily in moderate and cooler regions, the focus in warmer regions is on avoiding overheating. This
can be achieved through effective sun protection in transparent structural parts or – and this has a more effective impact – by means of climatically adapted building concepts, which facilitate a high degree of shade or natural ventilation and cooling. These passive systems and strategies help to save valuable energy.

Reduce heat loss

The airtight installation of modern windows can significantly reduce heat loss within the building envelope. Modern windows generally consist of two to three panes of glass, with the spaces in between filled with inert gases such as argon, krypton or xenon. This layer of gas acts as thermal insulation. Barely visible coatings on the glass, which allow only radiation with certain wavelengths to penetrate, provide another layer of thermal insulation. This means, for example, that visible light can pass through during the summer, while long-wave heat radiation is reflected.

Modern window frames are very well insulated and are fitted with a multi-chamber profile to optimise a building’s energy efficiency. The material in the glass spacers also has
a strong influence on the transfer of heat through the windows. Plastic spacers with low thermal conductivity have an advantage over the traditional aluminium spacers.

The best thermal insulation is futile if the building envelope is permeable, causing increased ventilation heat loss. The airtightness of the building envelope is therefore another important factor in the energy-efficient heating or cooling of a building. Uncontrolled ventilation losses through doors and windows that are not properly sealed or through incorrectly sealed penetrations in the building envelope (e. g. through cables or pipes) must therefore be avoided as much as possible.

To achieve a high level of airtightness, attention must be paid to the use of suitable structural components. Alternatively, a separate airtight layer must be installed on the inside of the building envelope. This can be achieved with the use of films or by taping the joints in the wood frame construction. Another option is to carefully apply a layer of plaster on the inside of the exterior walls in the masonry.

The internationally established blower door test, a method to measure pressure differentials, is usually used to detect the presence of any leaks.

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