Facade insulation: external insulation - the optimal building physics insulation solution

Around 30 percent of the heating energy used is lost over the outer walls of an uninsulated house. Efficient facade insulation therefore can not be dispensed with. In new buildings, an external insulation of the facade is basically made. Various methods and systems are available for this.

How much energy is lost in a building over an uninsulated wall, depends on the surface and the structure of the facade. In addition to relevant energy savings, a facade insulation, however, has a few more tasks to fulfill. On the one hand, it serves to protect the building fabric. Exterior walls without thermal insulation have low surface temperatures both outside and inside during the cold season. Water vapor diffusion from the interior of the building into the masonry creates the risk of moisture damage and mold growth. Professional façade insulation prevents condensation from settling in the walls or in the insulating layer. Especially with ventilated facades moisture damage and mold formation are excluded. In addition, the facade insulation also makes a significant contribution to the sound and heat protection of the house.

Table 1: Cost per m2 for different types of facade insulation

DämmungsartCost per m2
EIFS100 - 150 euros
Ventilated curtain wall170 - 300 euros
Cavity wall insulation15 - 30 euros
internal insulation40 - 150 euros

Facade insulation: external or internal insulation

The rule for the facade insulation is the external insulation, it is considered as building physics optimal solution. Interior insulation is mainly used when external insulation of the building is not feasible. Typical areas of application are old buildings and monument renovations, where the original façade is to be preserved. For new buildings, interior insulation plays virtually no role.

Advantages and disadvantages of external insulation of facades

A major advantage of external facade insulation is that no usable space is lost inside the building. In renovations, thermal insulation and the visual renewal of the façade can be combined. Depending on the construction method, external insulation may be cheaper than internal insulation, but the required equipment of the house will increase the labor and thus the cost.

Exterior insulation of facades - only by a specialist company

An external insulation of facades belongs fundamentally in the hands of a specialist company. The constructions can influence the building statics and require comprehensive planning and craftsmanship. The work of architects and builders merges seamlessly. As a rule, the external insulation of the façade, including the insulation materials used, must be approved by the building authorities.

Which requirements apply to the thermal insulation?

The minimum requirements for the thermal insulation of facades are specified by the Energy Saving Ordinance (EnEV) 2014. The heat transfer coefficient (U-value) of the facade and all other insulated house areas must be at least 0.24 W / m2K. Many builders, however, opt for a stronger insulation. In addition to the desired energy saving effects, the desire for optimal sound and heat protection through the insulating layer also plays a role here. Depending on the chosen insulating material, the facade insulation also optimizes the fire safety of the building.

Tips & Tricks

About 25 percent of the heat energy is lost unused over an uninsulated house facade, an efficient facade insulation is therefore an absolute must. The exterior insulation of facades is usually done by thermal insulation composite systems (ETICS). A ventilated curtain wall can be an optimal alternative in terms of building physics, as well as allowing greater freedom in the design of the exterior cladding of the façade.

Different methods for external insulation of facades

Load-bearing wall constructions consist of masonry, artificial or natural stone, concrete or reinforced concrete. In new buildings, they are usually constructed as single-shell, warm facades. The thermal insulation layer is applied directly to the wall construction and then clad with plaster or insulating clinker. Most of the warm facades are designed as a lightweight outer wall with a surface weight of = 150 kg / m2 and a plaster facade, as a construction and insulation solution is a thermal insulation composite system (ETICS) use. The warm facades also include curtain walls ("curtain walls"), which are mainly used on larger building complexes. They are not identical to a ventilated curtain wall, which is a cold façade based on a two-shell wall construction. Core insulation plays a role, especially in old building renovation, if a two-shell wall construction is given.

Thermal insulation composite systems (ETICS)

ETICS are system solutions for the thermal insulation of buildings, which are fastened directly to a load-bearing wall. They consist of coordinated building materials - and the insulating material is the core of the system according to which the plaster and plaster thicknesses used are based. ETICS with mineral wool (glass wool, stone wool) or EPS / Styrofoam so far hold the largest share in this market segment, but here, too, natural building materials are on the rise. For example, an ETICS with wood fiber insulation boards and a mineral plaster is an optimal solution for a diffusion-open facade insulation with excellent moisture balance and good sound and heat protection.

Table 2: Selected insulation materials for ETICS

insulationThermal conductivity (W / mK)Minimum insulation thickness (cm)Cost / m2 (EUR)
glass wool0,032 – 0,0401410 – 20
rock wool0,035 – 0,0401410 – 20
EPS / Styrofoam0,035 – 0,045145 – 20
wood fiber0,04 – 0,0551840 – 50

Construction of a ETICS

Components of a ETICS are insulating panels, a reinforcing layer and a reinforcing mesh. The completion of the system is given by the exterior plaster. The assembly of ETICS is usually carried out by stucco workers.

Building regulations

There are no binding standards for ETICS. They require individual building inspectorate approval, for which their suitability for a specific building must be proven. All components of an ETICS must be supplied by the same manufacturer, otherwise the façade will de facto be built illegally.

curtain walls

Just like façade insulation with a ETICS, a curtain wall is a warm façade - a single-shell construction that does not have a rear ventilation level. Curtain facades gained importance for the first time in the second half of the 19th century. They were used from the beginning mainly for industrial buildings and public buildings. In private house construction, they play and play a role especially in very high-quality architect's houses. Their design is described by the DIN EN 13830 standard.

Construction of a curtain wall

Curtain walls are fastened with their substructure to supporting columns or the storey ceilings. Apart from their own weight, they carry no other static loads. The removal of the vertical and horizontal loads of a curtain wall is usually done on each floor, by inserted structural components but also a load transfer over longer distances is possible. They are fastened to the load-bearing structure with adjustable, corrosion-proof anchor bolts, brackets or brackets, the location of which is determined during the rough construction planning.

Materials for a curtain wall

Aluminum, steel or wood are used as load-bearing materials for curtain walls, and the outer skin of the façade can be made of plastic or glass. Self-supporting sandwich elements (sandwich panels) were specially developed for this facade construction. Their double-sided cover layer made of aluminum or steel sheet is shear-resistant connected to an insulating core, which usually consists of PUR / PIR or mineral wool.

Curtain wall and transparent thermal insulation (TWD)

Modern curtain walls can also be based on transparent thermal insulation (TWD). TWDs are made of materials that combine excellent thermal insulation with high light transmission. Due to their honeycomb, hollow chamber or capillary structure, they are able to scatter incident light and to convert its energy into heat in an absorption layer underlying the building's outer skin. With these properties, transparent thermal insulation is a passive area of ​​application of solar thermal energy.

Ventilated curtain walls

Ventilated curtain walls have their roots in traditional construction of rural areas. Today, they are always used when a façade is not only plastered, but is to be individually designed using cladding made of stone, wood, slate or other materials. The method is suitable for new buildings and renovations as well as for any facade sizes. From the point of view of building physics, a ventilated curtain wall is an optimal solution for external facade insulation: thanks to the integrated rear ventilation level, it enables excellent moisture balance; both moisture and moisture are reliably dissipated. Moist external walls dry out in a very short period of time.

Two-shell cold facade

A ventilated curtain wall is a so-called cold facade, as between the outer wall cladding and the insulating layer is a cold air layer. The system components of a ventilated curtain wall are defined by the product standard DIN 18516-1. The constructions must be approved by building authorities. As an insulating material, a variety of materials - including various natural materials - are used. In practice, these facade linings are very often performed with mineral wool.

Construction of a ventilated curtain wall

On the supporting outer wall, a substructure of aluminum profiles, wooden slats or - in heavy exterior wall cladding - steel anchors mounted. The interstices of this substructure are then filled with the insulating material. The insulation is protected by a windproof layer from the weather, which may consist of wood or other material. On top of this is a slatted structure, which serves as a mounting level for the suspended outer cladding; between it and the outer facade curtain is the ventilation layer. Through a ventilated curtain wall, the functions of thermal insulation and weather protection are largely separated from each other, which, among other things, minimizes the susceptibility to damage of such wall systems.

Cavity wall insulation

Core insulation (hollow wall insulation) is mainly carried out in the context of old building renovation, provided that the outer wall consists of double-shell masonry. Such a two-shell construction consists of an outer facing masonry as a weather protection and an inner facing shell for thermal insulation. In older buildings, these cavities are often not or only insufficiently insulated, resulting in high energy losses.

Core insulation - the economical alternative to ETICS

A core insulation can be an uncomplicated and cost-effective ETICS alternative. The insulating material - for example, mineral wool or plastic granules, perlite or expanded glass - is introduced into the cavity by means of blown insulation. Insofar as it is completely filled with the insulating material, the insulation is automatically EnEV compliant. Even with this type of insulation, the expertise of a specialist is necessary, which checks the masonry in terms of its moisture content and possible damage and makes the choice of insulation. Due to the rear ventilation, the insulation must be hydrophobic (water-repellent). From an energetic point of view, a core insulation is rather a compromise, since the thickness of the insulation depends on the cavity width and thermal bridges can not always be completely excluded.

Exclusion of thermal bridges

The exclusion of thermal bridges generally plays an important role in the external insulation of facades. Particularly sensitive areas are, for example, window openings as well as the transitions to the roof, balconies, bay windows and the basement area / basement area. If necessary, the airtightness of the façade can be checked by a blower door test (differential pressure measuring method).

Tips & Tricks

In old buildings with double-shell masonry comes as a very economical solution for the facade insulation and a core insulation in question. It is made as a blow-in insulation with water-repellent insulation materials. The cost is about a quarter of the investment in an ETICS.

Video Board: The Benefits of External Wall Insulation for the Home