Retrofit of an urban apartment building

near „Passive House“ standard (Zurich)

Viridén Karl Dipl.Arch.HTL

Viridén + Partner. Häringstrasse 20. 8001 Zürich. Switzerland.

Phone: +41 1 260 77 55. Fax: +41 1 262 48 72. E-mail: viriden@viriden-partner.ch

INTRODUCTION

The passive solar house standard is highly relevant when it comes to new buildings. But in fact, it

is possible to come near to achieving this standard in restoration projects too. In Switzerland,

refurbishment and renovation projects are very important, since the majority of the existing build-

ings cannot simply be replaced by (passive) new buildings with a low energy consumption. Very

often, the chances of achieving the aim of a passive solar building depend on the basic condi-

tions, and, in particular, on the attitude of the client.

In Zurich, the refurbishment of a 107-year-old property due for demolition was designed to meet

the passive solar house standard, despite the protected status of the building. The renovation work

was carried out according to the criteria for sustainability presented in the handbook “Eco-logical

Construction Practice” 1)

. It is the first refurbishment project of this kind in Switzerland.

© Nina Mann

Figure 1 Rebuilding the attic floor with prefabricated elements

INITIAL POSITION AND CHALLENGES

Since the 107-year-old multi-residential house was in a relatively poor condition, a complete

renovation was necessary. The building is located in the middle of the city of Zurich, in the 'Kreis

4' district; it stands between a building of the same height on one side and a two-storey building

on the other. The street-side façade has to meet the requirements of a preservation order. Since

the rear façade facing onto the courtyard is only 4 metres from the nearest building, it is subject

to the corresponding planning and building regulations with regard to thermal insulation meas-

ures. The interesting challenge in this renovation project was to create high quality housing

which would attract “good” tenants to an area in the neighbourhood of Zurich's red light district.

This aim has been achieved with the current tenant profile.

PASSIVE SOLAR HOUSE STANDARD IN THE REFURBISHMENT

It is difficult to achieve the passive solar house standard in any renovation project. However,

when a façade has to meet the requirements of a preservation order, it is virtually impossible. The

challenge presented in designing and carrying out the refurbishment is far greater, since the exist-

ing substance of the building and all its unknown quantities such as leakages, thermal bridges etc.

have to be taken into account.

Apart from the installation of comfort ventilation, renovation work on the building envelope aims

to achieve U values of under 0.15 W/m2 K. This means a very low heating requirement, if possi-

ble under 15 kWh/m2a NF. In this case, fulfilling the primary energy consumption at under 120

kWh/m2 a net floor area was easily achieved. In addition, however, the building envelope has to

be made as airtight as possible, i.e. to achieve an air change nL50 value of 0.6 h-1

.

The decisive criteria for the passive solar house standard (for new buildings) were fulfilled, ex-

cept for the building envelope and the air-tightness. The heating requirement is slightly higher

because it was not possible to insulate the street-side façade more effectively. The required air-

tightness was not achieved either. The whole building envelope has a nL50 value of about 2, with

the four wood storage heaters and the basement.

© Nina Mann

Figure 2 Before and after renovation

REFURBISHMENT CONCEPT

Basically, the original structure and configuration of the building was maintained. Although the

rooms are small, the flats have a certain charm and offer high-quality space. These features were

enhanced in the refurbishment. Following the principles of ecological building, as little as possi-

ble was demolished and as much as possible was retained. The existing doors, door frames, wain-

scoting and suchlike were restored and repainted. The attic floor, however, was in such a poor

state that it had to be completely demolished and rebuilt with prefabricated wood elements.

The shape of the building displays a favourable ratio of surface areas to net floor area (A/NF =

1.5). The building envelope was improved to above average in terms of thermal insulation: the

insulation layer is between 16 and 40 cm thick. About 70% of the building envelope has an aver-

age U value of 0.15 W/m2 K.

Owing to the preservation order requirements, visible changes to the street-side façade, which

comprises 20% of the building envelope, had to be kept to a minimum. However, we were able to

place a 3 cm thermal insulation layer both outside and inside, which meant that we reached a U

value of 0.43 W/m2 K.

The remaining 10% of the building envelope consists of windows with a U value of under 0.7

W/m2 K (the U value of the glass is 0.5 W/m2 K). On the street-side, the thermal insulation of

the window frames was improved by placing a soft fibreboard between the walls and the window

frames. On the rear façade, the external thermal insulation was extended over the window frames.

© Nina Mann

Figure 3 Two-bedroom-flat on standard floor

SERVICE INSTALLATIONS

Before the refurbishment, the building was heated by means of individual paraffin oil heaters and

electric radiators. There was still no conventional heating system, built-in heat emitters or under-

floor heating one hundred years after construction.

The aim was to keep the energy consumption for heating, ventilation and hot water as low as pos-

sible and to make extensive use of renewable energy. The energy required for heating and hot

water is collected in a storage cylinder (2,600 litres) with an integrated boiler from a solar panel

system (15m2) and an air/water heat pump (9 kW).

The heat is distributed via the ventilation system with heat recovery as warm air heating. Each

flat has its own system unit, which can be adjusted independently.

If the outside temperature falls below -2°C, the warm air heating is unlikely to be sufficient, and

the remaining requirements must be covered by the wood storage heater in each flat.

ENVIRONMENTAL POLLUTION REDUCED BY A FACTOR OF 10

Compared to the former situation, the primary energy consumption for heating, hot water, venti-

lation and domestic electricity has been reduced by a factor of 10. Before the refurbishment, the

0

100

200

300

400

500

600

700

800

900

1000

before renovation after renovation conventional

primary energy consumption amounted to about 1,000 kWh/m2a net floor area; the aim was to

reduce this to 100 kWh/m2a NF (electricity consumption multiplied by 2.97, oil x 1.09, gas x

1.07, wood x 1.01).

Figure 4 Primary energy consumption (PEI) in kWh/m2 year net floor area, according

to „Passivehouse“ standard.

HEATING REQUIREMENT 5 TIMES LOWER THAN REGULATIONS DEMAND

The heating requirement (Qh) is five times lower than the regulations demand. For the refurbish-

ment on Magnusstrasse 23, the heating requirement (Qh) limit set by 380/1 lies at 107 kWh/m2a

NF, while the value planned is only 20.9 kWh/m2 a NF.

ECOLOGICAL CONSTRUCTION

A great deal of importance was attached to ecological considerations. The flow of materials (in

both demolition and installation work) was kept to a minimum. The project focussed on applying

the requirements of our own publications such as 'Eco-logical Construction Practice' 1)

and the

SIA D0122 'Ecological Aspects of Building' 2)

. We also worked in collaboration with the Centre

for Sustainable Design, Planning and Construction at the Zurich University of Applied Sciences,

Winterthur.

CONCLUSION

Magnusstrasse 23 now undercuts the Minergie new building standard by a factor of 2 and the

Minergie refurbished building standards by a factor of 4. In order to reach the passive solar house

standard, the street-side façade would have to be insulated to the same extent as the rear façade.

However, in spite of this shortcoming, it is clear that a refurbishment can reach a far higher stan-

dard than ordinary new constructions if sensible measures are taken.

© Nina Mann

Figure 5 Interior spaces

Monitoring success

Magnusstrasse 23 will be monitored as a pilot and demonstration project over the next two years

(2001 – 2003) and its performance evaluated as comprehensively as possible. The question also

arises how far the passive solar house standard can function in a refurbishment.

Several factors which were taken into account in the refurbishment plans remain uncertain; for

example in the ground floor flat, the effects of the thermal bridges cannot be monitored precisely,

in spite of efforts to allow this. Furthermore, for privacy reasons, the inhabitants tend to close the

blinds more often than expected, which reduces the anticipated solar energy gain. In order to

compensate for this, they can use the wood storage heaters to generate more heat as required.

We are very interested to see what developments occur in refurbishments based on the passive

solar house standard.

Project team

Karl Viridén, Viridén + Partner, Zurich

Prof. Peter Hartmann, Zurich University of Applied Sciences, Winterthur

Heiri Huber, Hochschule für Technik und Architektur HTA Lucerne

René Naef, naef energietechnik, Zurich

Sponsors

Amt für Abfall, Wasser, Energie und Luft, AWEL, Zurich

Bundesamt für Energiewirtschaft, Berne

Competair (Maico), Thalwil

EWZ Stromsparfond, Zurich

Flumroc AG, Flums

Suprag AG, Telekommunikation, Zurich

Building data

Multi-residential building with 4 flats

Year of construction 1894

Refurbishment April 2001

Location Zurich

Area of plot 111.4 m2

Area covered by building 97.8 m2

Building envelope figure (A/NF) 1.5

Net floor area (according to passive solar building standard) 375 m2

Architects Viridén + Partner and Prof. W.

Dubach, Arch. SIA / BSA, Zurich

REFERENCES

1 Preisig H.R., Viridén K., Dubach W. 1999. Ecological Aspects of Building. SIA Zurich, Do-

cument D 0122 3rd

impression

2 Preisig H.R., Dubach W., Kasser U., Viridén K. 2001. Eco-logical Construction Practice:

manual for cost-conscious clients. Werd Verlag Zurich