green LIGHT: light, fresh air, exterior space, greening in the large volume PassivHaus

theoretical topics: Optimization of natural light, ambient humidity and of private exterior space, planted over buildings, evaluation of the energetic performance and special challenges of large volume "Passivhaus" residential buildings. applied research: concept for the renovation of a 13 storey residential building for senior citizens built in 1974 to PassivHaus standards, applying the results attained in the theoretical part.

Content Description





Energy efficiency and Passivhausstandards have made their way to public awareness already. Dealing with sustainability, not only the standards for the energy efficiency of buildings have to be thought over, but also the building types on the whole.

The fact, that the single family home can only achieve very modest objectives in terms of primary energy per person due to its implications on infrastructure and traffic is still unanchored in public awareness.

Passivhausstandards will sooner or later increasingly find their way into building refurbishment. Renewing the windows with triple glazing using conventional fitting details will definitely reduce day lighting conditions in the rooms.

It has to be avoided, that with using triple glazing in refurbishment as well as in new buildings thermal comfort increases while visual comfort decreases. It has to be avoided, that the refurbishment solutions of today include the refurbishment demands of tomorrow. Thermal refurbishment can only meet a small part of the refurbishing demand. Functional faults and the lack of modern living quality must not be lost out of sight.


In this research paper you will find answers to the questions - what the contemporary requests for day lighting standards in living spaces are and how the amount of daylight in the room can be optimised.

  • how a private exterior space has to be constructed, so that there should not occur any discrepancy between usable width and illumination of the rooms behind.
  • how residential buildings can be planted over sustainably and professionally
  • what possibilities there are for the ecological conditioning of the ambient humidity of the air, and what special plants will contribute to this topic
  • how the large multi storey passiv haus performs energetically in comparison to a passiv haus single family dwelling, what differences there are to be pointed out, and what special needs there are for passiv haus standard in multi storey housing.
  • how the renovation concept for a large multi storey residential building to gain passiv haus standard will look like.


The contribution of this research work is on the one hand to explain the considerably higher energy efficiency of buildings of large volume and to demonstrate the topic by comparison and on the other hand to offer sustainable, interesting and first of all attractive alternatives to the building type of single family houses for dense urban areas.
The attractivity of a flat is highly determined by the criteria of brightness, private exterior space an the quality of the surrounding quarter. We are convinced, that these elements of comfortable contemporary living have to be regarded essential (as well in renovation as in building construction) and we want to point out some solutions.

Methods and data

Basic research has been supported by internet and literature inquiry and our practical experience as architects. The U values have been calculated with the simulation tool "archiphysik", the demand of thermal heat and the heating load have been calculated with the tool PHPP 2004 of "Passivhausinstitut Darmstadt".

Other calculations have been carried out with an excel software, the daylighting simulations have been carried out with the tool Relux 2005. The simulation of the thermal and hygric conditions have been carried out with simulation tool Trnsys 16.

The calculation of the thermal bridges has been carried out with the simulation tool WAEBRU 6.0. The daylight measurements were done with a specially constructed model, and a Lutron LX-107 luxmeter.

All specifications to the topic of planted over buildings result from the over 20 years experience of C. Haas in this field, and from her cooperation with the "Verband für Bauwerksbegrünung"-the Austrian organisation for planted over buildings.

All of the planning has been done in form of integrated planning, with discussion and dialogue between all projects partners right from the beginning.

Results and conclusions

Results: large volume buildings in comparison to single family dwellings

In the chapter 'overall and geometric data' of residential buildings dealing with their energy consumption the overall and geometric parameters, which predetermine the energy consumption of a building are explained and several examples are provided.

In the chapter 'U values' we show, how the insulation material thickness of the building shell may decrease with increasing building dimensions. In the chapter 'compact form' it will be demonstrated, that a highly structured single family home will take 20 times as much insulation material per m² of floor area as a large volume residential building with equal energetic standard. In the chapter 'windows' we will show, that in large volume buildings of passiv haus standard (U values of the wall about 0,25 W/(m²°K) and the use of large undivided glass panels with slim frames even shaded east and west orientated windows will average to a better energetic balance than the described insulated wall.

In the chapter 'optimising insulation thickness' an optimised thickness of insulation of the bottom floor slab (all regarding passiv haus standards)has been calculated to be about 70% of the insulation thickness of the roof.

In the chapter 'heating load' we show solutions for apartments in the corner or at the fringe of a large building. Those apartments possess more exterior walls than other apartments and provide therefore more difficult conditions for being heated only by the air. Rounded forms and slim dimensions of the construction (of the exterior walls) can reduce the heating load of the apartment by 10%.

Solutions for corner apartments by means of building services provide a simple water based heating system above the doors of the rooms. Extra costs for this system are about 8-10 € per m².

Results: daylight optimisation

Definition of a new contemporary standard
In general the chapter of requests for brightness, glare, sunlight and contact to the outside world in DIN 5034 seems to make sense. Apart from contemporary requests in the DIN 5034 the following should be regarded:

  • Only the net glazed area should be part of the evaluation.
  • The recommendations in the DIN should be multiplied by a factor of 1,5. This will take into consideration that in the near future triple glazing with a lower light transmission will become standard for housing.
  • Overshadowing by neighbouring buildings should be limited by not exceeding an obstruction angle of more than 30° or a 2:1 ratio of distance and height.

Applying these three additional demands to the DIN, the solution will be a window with a net glazed area of 25% of the usable room area. Using large unpartitioned windows, and partly fixed glazing elements, the area of the wall opening will thereby rise to 30%-35% of the floor area. Restrictions caused by balconies have to be considered separately. It does not seem to be sensible to commit to a certain daylight factor as a method of evaluation at this juncture, due to a lack of congruence between measurements in the physical model and the day lighting simulation tools.

Optimising the amount of light per window
In the physical model we measured several variations of the window reveal. They all differed little as long as they were painted white. Therefore slanting the reveal e.g. does not seem to be a favoured solution.

It is most important to design the net glazed area as large as possible. We show some solutions how that could be done in passiv haus standard. With normal window dimensions and passiv haus standard the frame takes about 50 % of the window area. By the use of slim frames, unpartitioned windows and partly fixed glazing, the net glazed area can be increased up to 60%.

Results: dedicated exterior space

Planning a balcony in multi storey housing is always a controversial issue: on the one hand, it should have maximum usable width, on the other hand, it should not reduce the light in the room behind. The reduction of solar gains we regard of minor priority, compared to the benefits of a large exterior space for the apartment. We are setting up the demand, that with a balcony the day lighting conditions in the room behind shall not fall shorter than 70% of the unshaded room. Out of the large amount of various measures we simulated, only one seemed to be promising for multi-storey residential buildings:

To place the balcony 40 cm higher than the floor of the room behind. This measure allows amply exterior space. It matches the day lighting demands, the useable width will be 1,8 M all over the facade. By placing a second level in front still higher the usable width can yet be extended. In the last chapter we examined the shading influence of an adjacent building on the daylight conditions on ground floor level. 45° of shading, combined with a standard balcony above, provide unbearably bad daylight conditions. The angle of shading should not exceed 30° or aproportion of 2:1 (width to height)

Results: planting over buildings professionally

ecological aspects and aspects of health
Planting over buildings is of essential importance relating to the reduction of heat in summer, rainwater retention, the absorption of pollutants and dust, setting up an insular biotope of high ecological value, the reduction of the U value of the construction, the cushioning of high frequency radiation and relating to therapy and health.

Economic aspects
Roof greening is self financing, because the costs for construction and maintaining are countervailed by less expenses for insulation material, less expenses for maintenance and repair of the sealing. Reduced costs for city sewage treatment plants due to rainwater retention are not yet included.

Facade planting and roof greening
Relevant parameters for professional planting of large buildings are dealt with in the chapters vegetation, techniques and maintenance.

Dealing with planting facades directly without any twining scaffold there are no sufficient data available to assess the risk of a damage or root penetration of the insulated façade. We do not even have sufficient information, whether there is any risk for these facades at all.

Planting of dedicated exterior spaces
Several variations of plantings for little space are described, which can provide a screen from view, from wind and from sun.

Shading windows with plants
Windows directed east or west can be equipped with temporary greening instead of an exterior shading device. Examples for plants, planting boxes and maintenance advises are given.

Time and decision layout
Façade and roof planting is possible at low costs, if specialised consultants are involved early and can work simultaneously with the architects. In the time and decision layout the decisions to be made are related to the planning process of the architect.

Results: optimising the ambient humidity of the indoor air

Passiv haus standard provides a technology for the first time in history, with which physiologic requirements of man can be met as well as buildings can keep out of claims of structural damages. Even under disadvantageous conditions there will not occur any room temperature below 15° C ( even in edges, behind furniture) .

In our climate an ambient humidity of the air of 40%-60% is the optimum for human beings, physiologically speaking we should prefer the upper limit in winter and the lower limit in summer. In the following chapters indoor humidity sources are described in detail. 4 static balances for a 75 m² flat with a different number of occupants and professions show the range of humidity demand in winter.

Humidity production with plants, thermal and hygric simulation
The impact of the plant cyperus alternifolius on the ambient humidity of a room of 12 m² was object of the investigation.

2 different room, 2 ways of positioning the plants, and 11 variations have been simulated. We can show, that highly transpiring plants, such as cyperus alternifolius will achieve excellent results. The rooms should have slightly larger windows than normally, so that the plants will gain a large amount of daylight even in winter, the plants should be positioned directly in front of the window in winter, and should be moved to the back during march and October and should be transferred to the balcony in summer. To achieve an ambient humidity of 45% in Winter the plants have to be additionally lit with artificial light. Humidity absorbing surfaces like loam or wood have positive, regulating influence on the indoor climate. Humidity peaks can thus be reduced. In the future, a combination of plants with moisture recovery would be the optimum, and most energy efficient.

Results: reconstruction concept for a residential home for the elderly in Penzing

The residential building in Penzing is a 13 storey reinforced concrete construction with a 3 storey part for kitchen and services, all built in 1974.

Renovation demand
The heat consumption of the building at the moment is about 167 kWh/m²,a on average. The residential part of the building has a very bad proportion of surface to volume at the moment, due to large cut-in loggias which enlargen the surface drastically. The apartments are too small , the bathrooms are old and lack handicapped accessibility, the room temperature of the apartments differs considerably between ground floor and highest level. The dining and reception hall gets much to warm in summer, there is also no cooling in the kitchen area.

Renovation concept
The loggia is going to be integrated into the living space. The heated living area is thus increased by 26%, the surface is minimised. The proportion of surface to living area is thus cut in half.

The overall surface of the residential part is reduced by 23,5%. The new proportion of surface to volume is 0,18. Heat insulation: 30 cm at the wall, 52 cm on the roof, new triple glazing with passiv haus standard.

building services: a semi-central ventilation system is regarded best. two ventilation appliances per storey will supply 10 apartments each with fresh air. Heat and moisture recovery >80%. The heat dissipation in the rooms will be made by the so called "thermal fresh air box"

Balcony and façade planting
The new layer of balconies and façade planting will be positioned independently outside the building, with selective junctures only.

In a distance of 30cm from the railing and the planting boxes diagonal cables of stainless steel cover the 13 storey high façade as a twining scaffold for the plants. Form and function have been put together to a unity of design.

PHPP and future energy demand
The proposed measures will guarantee passiv haus standard in the residential part, in spite of the high, unrecoverable energy losses in the heated bottom floor. The calculated thermal heat demand is 12,5 kWh/m²,a In the service area passiv haus standard will not be obtainable. However, the thermal heat demand for the service area may be lowered to 55 kWh/m² a. On an average the renovated building will achieve a thermal heat demand of 20,3 kWh/m²,a. Thus the thermal heat demand can be cut down from 140 kWh/m²,a to about 15 % of this initial value.

Functional renovation
Functional renovation includes primarily the rearrangement of the service zone in the apartment : entrance, bathroom, kitchenette, sleeping alcove. Handicapped accessibility according to ÖNORM B 1600 and 1601 can be obtained, the demanded increase of floor area will add up to 26%.

The ventilation system with heat recovery, which is necessary anyway for the purpose of energy saving will offer a decisive gain of living quality, especially in a residential home for the elderl

Project Partners

Projectleader: Arch. Dipl. Ing. Ursula Schneider
pos architekten ZT KEG
  • Belichtung:
    Pokorny Lichtarchitektur
    DI Klaus Pokorny
  • Simulationen, Baupyhsik:
    IBO Österreichisches Institut für Baubiologie
    DI Thomas Zelger
  • Haustechnik:
    Ö koplan Ges.m.b.H.
    Ing. Alexander Petz
  • Garten&Landschaftsplanung:
    Dipl. Ing. Christine Haas


pos architekten ZT KEG
Arch. Dipl. Ing. Ursula Schneider
Maria Treu Gasse 3
1080 Wien
Tel: 01/4095265, Fax: DW 99