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Thermal protection in retrofits

It can be proved that insulation of buildings leads to significant energy savings and also protects the building substance - not only in new constructions but also in modernised old buildings. Thermal comfort in the home is also improved by thermal insulation.

An old building before renovation:
Location: 4 Jean-Paul-Platz, WBG Nürnberg

Renovated building - with Passive House components:
The modernisation includes very good thermal insulation of all
exterior surfaces, including new windows and heat recovery.
Planned by Dr. Burkhard Schulze Darup.

Problems due to moisture build-up

Research shows that increasing the insulation thickness of an external insulation system minimises problems associated with thermal bridges. With excellent external insulation there are no problems with damp due to humidity in the interior. The following diagrams illustrate this using an example of a room with an external edge on the ground floor. Even if a cabinet is situated in the corner of the room, condensation can be prevented – if the wall is well-insulated enough. You can find additional details about this and the modernisation project in the Protocol Volume [AkkP 24] about the modernisation of old buildings.

Old building - situation at the facade without insulation Refurbished old building with good external insulation (200 mm)

A situation usually found in a partially modernised existing building: new windows were installed, but no insulation was added to the exterior walls. Under winter boundary conditions (outside -5°C; inside 20°C) the resultant surface temperatures within the home fall to 9°C, behind the cabinet in the corner the temperatures can drop below 5°C. At these low temperatures the air contains very little moisture. Therefore the relative humidity rises to high values, and these conditions are perfect for mould growth. In the uninsulated old building, mould damage due to the increased humidity is predetermined.

That better insulation eliminates the danger of mould growth is not just luck or limited to the case shown here. By increasing the insulation of the wall, interior surface temperatures rise. Due to the cross heat flow, this occurs even in the critical thermal bridge areas. Systematic investigations show that adequate additional insulation raises the temperatures at all critical connection points so far that the relative humidity remains under 80% everywhere and therefore problems with humidity do not occur [AkkP 24] .

Picture of the building site:
Installation of 200 mm of thermal insulation. Over each
window, a strip of non-inflammable \ mineral wool
insulation is inserted.

(Photograph: Schulze-Darup)
Picture of the building site: The stopping over the old ex-
terior plaster can be seen as well as the insulation which
is fitted tightly under the window sill. You can find
thermographic images here: Outdoor thermography.

(Photograph: Schulze-Darup)

Heating demand

Particularly remarkable about the heating energy balance of old buildings are the high heat losses through external walls are (see diagram below). It is particularly important, not only from the building physics point of view, but also from an energy-economic perspective, to improve the thermal protection. The view is often expressed that external walls should be excluded from thermotechnical modernisation measures, but this is not appropriate at all. Especially the external walls must be well-insulated, mainly from the health point of view (see paragraph above Problems due to moisture build-up about the prevention of mould growth by using good insulation).

In various demonstration projects e.g. in Ludwigshafen, in Nuremberg and in Tevesstraße (Frankfurt), the heating demand was reduced to less than 30 kWh/(m²a) and in some cases it was reduced to 15 kWh/(m²a), which is the Passive House standard value for new constructions. Old buildings are thus significantly improved.

Energy balances

These energy balances have been balanced using the Passive House Planning Package (PHPP). This tool allows substantial balancing and optimisation of the measures for existing buildings also.

Energy balance of the old building (before):
The high specific losses through the exterior walls (blue) and
the attic roof (light red) are particularly noticeable. Solar gains
don't count here, because the losses are so high and have to be
balanced by the heating system (red), which gives an energy
consumption of more than 200 kWh/(m²a) before the refur-
bishment (20-litre house).

Energy balance after the successful refurbishment: The same
criteria for the energy balance of the refurbished building were
adhered to. Due to the good thermal insulation, the losses
diminished to very small values. Solar gains and internal heat
gains change only a little, but now they cover nearly half of the
losses. As a result, the heating energy requirement after the
refurbishment is very small, mathematically it is 27.4 kWh/(m²a)
(2.7-Liter-house), resulting in energy savings of 87%.

Because the exemplary refurbishment of the building in Jean-Paul-Platz 4 in Nuremberg as described here was actually accomplished with the quality indicated, the measured results for heating energy consumption can be compared with the calculated results afterwards. The actual measured heating energy consumption for the first year was 26.9 kWh/(m²a) - which confirms the calculation results for the project.

The graph below compares the calculated results with those measured: The monthly values during the first year after the modernisation add up to 26.9 kWh/(m²a), in the second year it was 24 kWh/(m²a). The measured consumption is therefore even smaller than the computed value (PHPP computation, represented as red columns). The heating energy consumption in this building was reduced by a factor of 8 due to the refurbishment: the remaining consumption is extremely small, it amounts to only about 12% of the original value.

The consumption measurements documented in this diagram
were performed by the FIW Institute in Munich. The measure-
ment results for the whole building are represented as blue

In the illustration, it can be seen that the individual consumption values of the different apartments vary. This is due to differing room temperatures and also due to the frequency of window opening by the tenants in winter. That this is the case, can be seen in this thermographic image. That the energy consumption even in such apartments is higher than average, but not excessively high, is shown by the diagram above. The largest individual consumption is about 40 kWh/(m²a), still more than 80% less than the average consumption in the building prior to modernisation. A discussion about the opening of windows in Passive Houses can be found here: Opening windows in the Passive House? – It’s possible and allowed!.


Based on these example, we can see that excellent thermal protection is of considerable importance for the modernisation of existing buildings too. It provides greater protection from moisture damage, improves the thermal comfort through higher surface temperatures and doubles the useable energy savings potential.

See also


[AkkP 24] Einsatz von Passivhaustechnologien bei der Altbau-Modernisierung; Protokollband Nr. 24 des Arbeitskreises kostengünstige Passivhäuser Phase III; Passivhaus Institut, Darmstadt 2003.

planning/thermal_protection/thermal_protection_works/insulation_prevents_structural_damage_evidence_no.4_measurements_in_a_retrofit.txt · Last modified: 2014/09/18 18:19 by