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Detect and eliminate thermal bridges in the old building
Detect and eliminate thermal bridges in the old building

Video: Detect and eliminate thermal bridges in the old building

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Video: Thermal Bridging: Energy Loss Through the Walls of Your Home 2023, February
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Thermal bridges occur in old buildings, but also new buildings. A lot of valuable energy is lost through it. But you can do something about thermal bridges. In this article we explain how we build thermal bridges, give typical examples and show what can be done about them.

Table of contents Table of contents Recognize and eliminate typical thermal bridges in old buildings

  • Thermal bridges or cold bridges?
  • Consequences of thermal bridges
  • Three types of thermal bridges
  • Where thermal bridges occur more often
  • Make thermal bridges visible and document them
  • Measures against thermal bridges

Table of contents Table of contents Recognize and eliminate typical thermal bridges in old buildings

  • Thermal bridges or cold bridges?
  • Consequences of thermal bridges
  • Three types of thermal bridges
  • Where thermal bridges occur more often
  • Make thermal bridges visible and document them
  • Measures against thermal bridges

Thermal bridges are areas of building components - especially the building envelope - where heat escapes more strongly than in other areas. This problem occurs especially during the heating season. The cause of thermal bridges is often the faulty insulation of parts of the building. Components with low thermal insulation cool down faster than well-insulated ones. Due to the low surface temperature, moisture can precipitate and dust settles. As a result, mold can form.

Thermal bridges or cold bridges?

Colloquially, thermal bridges are often referred to as cold bridges - this term is probably the more common one. Physically, however, the term cold bridge is not entirely correct, because the heat migrates more strongly here, but no cold comes in.

Consequences of thermal bridges

The increased heat conduction of thermal bridges causes various problems, from building damage to health risks:

  • Increased heating requirements: heat flows from inside to outside via thermal bridges, which means that you have to heat more, which also affects the comfort in the room. Cold surfaces ensure that the resident believes he is feeling a "train". In reality, it absorbs significantly more radiant heat than at higher surface temperatures. The higher heating requirements result in higher heating costs.
  • Condensing water on the walls: In the area of ​​thermal bridges, at low outside temperatures, the surface temperature of components on the room side drops more than in the surrounding areas. As a result, the room air humidity condenses on the component surface.
  • Mold: There is a risk of mold growth on thermal bridges. Mold does not only appear when condensation fails, but can already appear on the component surface at a relative humidity of 80 percent. Some molds even develop at 70 percent. Mold spores are not only unsavory to look at, they can also endanger the health of house residents.
  • Construction damage: If condensation forms in the area of ​​cold bridges and the moisture penetration lasts longer, this can lead to construction damage in extreme cases. The wall, once moistened, then cools further on the inside due to the increased thermal conductivity, which increases the thermal bridge effect and further increases the occurrence of damage.
Wärmebild undichte Einbaufuge am Fenster
Wärmebild undichte Einbaufuge am Fenster

The thermal image shows an installation joint on the window that is not completely sealed. As a result, drafts and mold can develop.

Photo: FLiB eV / txn

Three types of thermal bridges

There are three types of thermal bridges:

1. Geometric thermal bridges occur wherever a small heat-absorbing surface on the inside of the building meets a larger heat-emitting outside of the building. Examples of typical places are outer edges, dormer windows and oriels. Geometric thermal bridges cannot be completely avoided. However, good thermal insulation of the outer wall significantly reduces its impact.

2.Constructive thermal bridges arise when components penetrate from the inside out, when the insulation level is interrupted or when the regular cross-sections of a wall are reduced, for example with radiator niches. Other examples include a reinforced concrete column that interrupts the outer masonry, an insufficiently insulated lintel or an overhanging reinforced concrete slab (balcony). The fault zone of a cold bridge - that is the area of ​​temperature reduction - also extends into the surrounding component.

Thermal bridges can also result from improper execution, for example gaps in the insulation or poor connections between the outer wall and windows. In single-shell, uninsulated masonry construction, gaps at the end of a row of stones are often simply filled with mortar, which conducts the heat much more than the stone.

3. Environmental thermal bridges occur in areas with different air and surface temperatures. For example, there are uneven heat flows near radiators.

Dämmung Fenster Wärmebrücke
Dämmung Fenster Wärmebrücke

The insulation of the house reduces the negative effect of thermal bridges. However, it is important that connections between parts of the building - such as here between the window and the roof - are properly sealed.

Photo: German Federal Environmental Foundation (DBU)

Where thermal bridges occur more often

Thermal bridges appear more in energy-efficient buildings than in non-thermally insulated old buildings. The differences in wall surface temperatures such as “cooling fins” are particularly noticeable there. The proportion of heat lost through cold bridges also increases significantly in insulated buildings.

On the other hand, old buildings from the 1950s to 1970s also have specific weak points that favor the formation of thermal bridges:

Cantilevered balcony slabs: Balconies and loggias in which the floor ceiling becomes a balcony slab and protrudes from the heated interior into the cold exterior are typical design-related thermal bridges in buildings from the 1950s to 1970s. The insulation is pierced by the highly thermally conductive reinforced concrete slab. This construction creates a constant heat flow to the outside in winter. The consequences are a strong cooling of the ceiling in the rooms and frequent moisture damage. The situation is similar with stair landings in the entrance area, where the basement ceiling is led from the inside to the outside without thermal separation. The ideal solution is to place balconies in front of the facade completely separately.

Roller shutter boxes: A typical 1960s is the uninsulated roller shutter box, which becomes a thermal bridge. Here the outer wall cross section is weakened, the effect is exacerbated by the leak, the cavity and the lack of thermal insulation of the construction.

Radiator niches: Many houses built in the 1960s had a radiator niche. Due to the weakening of the outer wall and due to the high temperatures of the radiator in winter, a constant heat flow to the outside is created - a classic thermal bridge.

Attic constructions from past decades: In the 1960s and 1970s, the attic of a flat roof was often formed by the outer wall that extended beyond the flat roof. If it is not insulated all round during a renovation and connected to the roof surface, it represents a thermal bridge.

Connection window / insulated outer wall: If there is a gap between the window frame and the external insulation with uninsulated masonry, a lot of heat is lost in the window reveal. The soffit and frame remain cold and often become damp.

Downpipes in the outside walls: Downpipes laid in outside walls (again the 60s and 70s) weaken the already small cross-sections of the outside walls. In addition, the high temperature differences to the adjacent components can lead to condensate damage.

Thermografie Fassade Altbau
Thermografie Fassade Altbau

Thermography reveals the weak points in the old building - the heat escapes through the uninsulated facade, through windows without heat insulation glazing, through uninsulated roller shutter boxes, heating niches and pipes in the outer wall slots.

Photo: Association of Private Builders (VPB) / Regional Office Emsland

Make thermal bridges visible and document them

With the help of thermography, thermal bridges can be made visible. The images help to easily identify weaknesses in the building envelope and irregularities in components.

With careful planning, it is worthwhile to balance the thermal bridges individually, in accordance with DIN V 4108 - 6: 2000.11 in conjunction with other recognized rules of technology. This is usually done by a specialist planner. The runner of a new building should ask the planners how thermal bridges have been balanced and minimized.

Special rules apply to the calculation of old buildings. In concrete buildings with many jumps and cantilevered components, the thermal bridges can make up more than 20 percent of the total heat losses. If such buildings are insulated without removing the cold bridges, the relative proportion of these losses increases even further. In addition, structural damage from condensation is likely.

Measures against thermal bridges

The reduction and elimination of thermal bridges must be the goal for energy and health reasons. The bridges can be reduced with internal or external insulation - but only with the appropriate know-how, because incorrect insulation does little to combat thermal bridges.

In principle, the heat-insulating shell should completely encompass a building. The insulation effect should be very good wherever possible. However, this cannot always be consistently observed. Slightly reduced insulation effects can therefore be permitted at exceptional points. However, you should keep the following in mind:

  • Isn't it possible to completely avoid a thermal bridge? For example, can the balcony be presented separately instead of a cantilevered panel, i.e. thermally separated from the building?
  • The insulation layers of various components should merge seamlessly at the joints, such as the outer wall insulation in the insulation of the sloping roof.
  • If insulation of different thicknesses adjoin one another, the center lines of the insulation layers should merge. A possible, but more expensive alternative is the overlap of the insulation layers.
  • The angles at which external components meet should be as obtuse as possible. Angles that are smaller than 90 degrees have a high thermal bridge effect.
  • If components that penetrate the insulating shell cannot be avoided, other factors should try to reduce the thermal bridge effect.
  • Thermal separation with high-quality insulation is a very good, but often expensive solution. Insulated cantilevers are an example.
  • Use of materials with the lowest possible thermal conductivity for the penetrating component, such as gas concrete block, lightweight concrete or pore brick.

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