Modernization of Old Buildings:
High Energy Efficiency is Better

The translation of this page was made available by support of Intelligent Energy Europe

Rennovated buildings usually have an existing heat dirtribution system and there is no reason not to use the very same system after renovation. With the renovation the heat requirement is reduced, then the system temperatures can also be reduced. Therefor, high efficiency boilers and heat pumps can then be used. Good thermal insulation and high efficency mechanical equipment go hand in hand.

Old building before upgrades

Location: 4 Jean Paul Place, WBG Nuernberg

Rennovated building - with Passive House components

The modernization included very good thermal insulation of all exterior surfaces, new windows and balanced ventilation with heat recovery.
Planning by Dr. Burkhard Schulze Darup.

Research shows that increasing insulation levels minimizes problems associated with thermal bridges such as condensation. The following diagrams illustrate this. If the wall is well insulated, as seen on the right, the moisture problems in the room are eliminated. You can find additional details on the this project in the document: "Modernization of Old Buildings" [ AkkP 24 ].

Old building - situation at the front without insulation

Example of conditions one usually finds in a partially modernized 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 dwelling range down to 9°C: Behind a cabinet against an outside edge, the temperatures can drop below 5°C. At these low temperatures air will hold very little moisture. Therefore the relative humidity rises to high values, good conditions for mould growth.
In the uninsulated old building mould damage is caused by the increased humidity.

Well insulated (200 mm) building after renovation

The concept that better insulation reduces the danger of mold growth is not limited to the case shown here. By increasing the insulation of the wall, interior surface temperatures rise. Systematic investigations show that adequate insulation all critical connection points raises surface temperatures high enough so that the relative humidity remains under 80% everywhere and therefore problems with humidity are eliminated.
Source: [ AkkP 24 ]

Building site picture: Installation of 200 mm of thermal insulation. In each case, a strip of non combustible mineral wool insulation is placed over the windows.                                               (photo: Schulze Darup) Building site picture: The old exterior plaster is primed before the insulation is placed against it, also note how the insulation fits tightly under the window sill.   (photo: Schulze Darup)

Contrary to popular prejudices, it is beneficial, when rennovating, to make the building very airtight. Unsealed gaps and cracks allow water to get into the wall when it condenses out of the air passing throught the wall. The planning principles for new buildings can successfully be transferred to the modernization of old buildings. In implemented renovations, the attained airtightness has been surprisingly good. Therefore, we must refer to how important controlled ventilation of dwellings becomes: "Those who demand airtightness, must also provide sufficient ventilation."

Old building - often extremely leaky

Old wooden windows;         Timber beam attic floor;           ribbed slab for main floor.

In this old building an air leakage of 4.9h -1 was measured. Is it possible to improve such an old building to the same airtightness as a new high-quality building?
(additional information in: [ AkkP 24 ].)

Rennovated building with good airtightness

It is! The air tightness level formed by a priming the old external plaster (the insulation is seen in the bottom of the middle photo), the floor was made airtight by an airtightness barrier (right photo; important: the thermal insulation installed on top of the airtightness barrier next).

The air leakage after the renovation was with 0.35 h-1.

After a careful thermal bridge free modernization the windows often remain the most significant weak point. It has been shown, however, that high comfort levels and the elimantion of condensation is achieved when the Passive House windows are used and the window installation is done using Passive House methodology.


Old building - old, poorly insulated and leaky windows

Old wooden windows; leaky and poorly insulating - replacement is overdue.


Cold interior surfaces of an old window (here between 12 and 14°C) lead to wasted energy and make the occupant feel cold through radiative losses (IR-image: Feist, in the PHI office space)

Passive house window - the best choice

The new window installed: A warm window with triple glazing, warm-edge spacers and a highly insulated frame. This window will be considered to be high performance for the next 50 years.

In contrast, Passive House windows have high internal surface temperatures: Both for the glazing (here: 17 °C) and at the framework. This creates good comfort for the occupants in the room. (IR-image: Feist, in the Passive House Darmstadt Kranichstein)

Providing sufficient fresh air is a main focus in rennovating an old building. The typically recommened "twice daily intermittant ventilation" is not sufficient for the removal of room air pollutants. With highly airtight building envelope, the safeguarding of the necessary ventilation of dwellings is an indispensable component of a responsible renovation. This statement applies to the modernized of old building even more than with new buildings: Adequate air exchange must be ensured.

The most important task in cold climates is dehumidifying from kitchen, bathrooms and toilet rooms. An exhaust register must be located in all rooms where humidity is generated. The amount of fresh air brought in should not be too high, however, because then the air can possibly become "too dry". Information about ventilatoin for good comfort and health can be found here: [ AkkP 30 ].

Particularly remarkable with the heating energy balance of old buildings are the high losses through the exterior walls (see the portion with the balance in the following diagram on the left side). It is particularly important then, not only from the building design viewpoint, but also from an energy-economic perspective, to improve the thermal resistance in the walls. The often expressed view not to add insulation to the exterior walls of old buildings, is wrong. That the exterior walls must be better insulated comes not only from an energy perspective but also from a in door air quality one (See the paragraph above over mould avoidance by good thermal insulation).

During the demonstration projects in Ludwigshafen and Nuernberg the heating energy requirement was reduced to under 30 kWh/(m²a). Old buildings thus experience a factor 8 improvement. Such drastic improvements were not considered to be realistic until recently, even in the building industry. The results of measurement from the demonstration projects, documented in [ AkkP 24 ], show that there is a strong relationship between values determined through computer simulation and the measured results.

Energy balance of the old building (before) 2)

The high specific losses through the exterior walls (blue) and the attic cover (light red) are remarkable. Solar gains play nearly no role, because the losses are so high. These high losses have to be balanced by the heating system (red), which amounted to a an energy consumption of more than 200 kWh/(m²a) (20-litre house) before the renovation.

Energy balance after the successful renovation 2)

The energy balance of the renovated building is much better. Due to the good thermal insulation, the losses are diminished to very small values. The values of the Solar and internal Heat gains changed very little, but now they counteract nearly half of the losses. As a result, the heating energy requirement is very small after the renovation: The modeled energy consumption is 27.4 kWh/(m²a) (2,7-Liter-Haus) resulting in energy savings of 87%.


Because the exemplary renovation at the building Jean Paul place 4, described here, was actually accomplished in Nuernberg with the presented quality, the measured results for heating energy consumption can now be compared with the modeled results. The actual measured heating energy consumption for the first year was 26.9 kWh/(m²a) - which confirms the modeled results. The graph below compares the modeld results with the measured:

The consumption measurements documented in this diagram were performed by the Munich Institut FIW. The results of measurement for the whole building are represented as blue squares. The monthly values during the first year after the modernization add up to 26.9 kWh/(m²a), in the second year it was 24 kWh/(m²a). Measured consumption is even smaller than the modeled amount (PHPP computation, as red columns represented). The renovation reduced heating energy consumption in this building by a factor 8: Remaining consumption is extremely small, it amounts to only about 12% of the original value. Note the significant variation between the values of individual dwellings: This is due to different living habits of the inhabitants (e.g. different thermostat settings, having windows open during the winter). Despite this, it can be seen that even then, energy consumption remains low, the largest individual consumption is approximately 40 kWh/(m²a), still more than 80% less the average consumption in the building prior to renovation. You find a discussion about opening windows here: "may one open the windows in a Passive House?" (German)


In the meantime additional examples of renovations using passive house components were implemented. Among them also the following example of a Passive House renovation of the GAG in Ludwigshafen (PHIB: Passive house in the building stock).

Old Building in Ludwigshafen
Before Renovation

After Renovation: A Passive House
Ludwigshafen, GAG

Passive House components are suitable for use in modernization of existing buildings. These measures reduce the risk of moisture damage, improve the occupants thermal comfort through higher surface temperatures and double the energy savings of a typical renovation

Using highly-efficient components in a high-quality modernization is more attractive because the quality of life for the inhabitants increases noticeably

On the other hand modernization measures in existing buildings are a motor for the economic situation. The results show that there is a dramatic potential for CO2 savings: The CO2 reduction obtained in the example renovations amounts to over 75%. The efficiency improvement makes an increased meaningful use of renewable sources of energy possible. With these measures, implemented today, we can prevent the most catastrophic consequences of climate change.


1) The principle reads: Constructions must be airtight on the warm side (thus on the interior side of the thermal insulation in cold climates). The construction should be open to vapor diffusion on the cold side. The example project followed these rules: You may find detailed documentation in: [ AkkP 24 ]

2) These energy Balances were determined using the Passive House Planning Package. (PHPP). This tool also allows the energy optimization of old buildings.

The passive house and the modernization with passive house components are not theoretical concepts. Thousands of buildings (examples) are already implemented. The principles represented in the context of this basic information work satisfactorilly in practice.

One can visit passive houses: Once a year there is the day of the passive house. On this day hundreds of passive house inhabitants open their houses to the public, in order to make it possible for those interested to experience what life is like in a Passive House. The day of the Passive House is organized by:


On the IG Passivhaus site, you can find architects in your area with experience in energy-efficient modernizations.

Current results from exemplary modernizations are presented at The Passive House Conference in working groups.

More on the current passive house conference:


[ AkkP 24 ] Passive House Technologies used in the Modernization of Old Buildings; proceedings NR. 24 of the working group economical Passive Houses, 1. Edition, passive house Institut, Darmstadt 2004 (German, see the publication list, pdf, 200kB)

[ AkkP 30 ] Ventilation for Old Buildings: Solution variants; 1. Edition, Passive House Institut, Darmstadt 2004 CGerman, see the publication list, pdf, 200kB)

[ AkkP 32 ] Factor 4 also with sensitive old buildings: Passive house components + internal insulation; 1. Edition, passive house Institut, Darmstadt 2004 (see the publication list, pdf, 200kB)


Find information on the passive house concept here.

Find information on the economics of passive houses here

Contend of all pages of this site: directory passive house.

Go to thepassive house of the institute homepage:

(last changed: 6.05.2007 / author Dr. Wolfgang Feist; thanks to David Stecher for proof reading of the 1st edition
© Passive House Institute; unchanged copy is permitted, please give reference to this page)