format10_en.pdf

FORMAT
built Office building in Hanover
explained German Energy Conservation Act 2009
conceived Back to the city
explored Future of housing construction
Xella
10October 2008

2 | 3
built
Speed and precision
The construction of a new administrative building for a tax consulting firm illustrates that pre-fabricated wall
solutions can fulfil all the economic, ecological and structural requirements to be met by modern building
materials. The shell of the 56 metre long three-storey office building in Hanover was completed in only six
weeks. In particular, the use of pre-fabricated Ytong wall panels permitted this short construction period.
Autoclaved aerated concrete, a building material with a very high heat insulation factor, moreover enabled
energy-saving construction in accordance with the German Energy Conservation Act (Energieeinsparverordnung
– EnEV) as well as optimum noise insulation and fire protection.
The use of pre-fabricated wall elements for the new Alcontas office building offered numerous advantages.
Alcontas office building, Hanover
- Architect:
Dipl.-Ing. I. Schierz, Hanover
- Owner:
Steuerkanzlei Alcontas,
Hanover
- Building contractor:
Bausatzhaus van Elst GmbH &
Co. KG, Bergisch-Gladbach
- Products:
Ytong wall panels in a custom
format (h = 2.925 metres,
d = 36.5 centimetres), Ytong
solid roof
The new administrative building of the Alcontas
tax consulting firm is located at the intersection of
several main roads in the centre of Hanover, Germany.
The narrow and long three-storey building
with a recessed storey at the top was fitted into the
trapezoid plot of land. Its plain facade is structured
by staggered rows of large windows of different
sizes.
Initially, the building was to be erected using
traditional masonry construction. However, for
cost reasons, more efficient construction methods
that permit to build high-quality buildings in a
short period of time were also considered. Finally,
the client and the architect opted for Ytong autoclaved
aerated concrete, which reduced the construction
period by three months. The wall panels
were made precisely to measure by computercontrolled
machines at the factory and laid in
bonds by programmed brick-laying robots on the
building site. With its clear cubic form, the new
Alcontas building was ideally suited for the use of
Ytong wall panels. While three weeks had initially
been allowed for the completion of each storey in
conventional brickwork, the use of wall panels
permitted this period of time to be reduced to one
week per floor. It thus took only six weeks to complete
the shell of the building.
Pre-fab elements for faster construction
The time required to complete the subsequent
construction phase was also reduced. For example,
the high dimensional and angular accuracy of
the wall panels meant that windows and doors
could be ordered well in advance and the windows
could be installed right after completion of the
building shell.
In total, some 478 cubic metres of wall panels
were needed. The outer walls were 36.5 centimetres
thick, while the inner walls had a thickness of

The very high dimensional and angular
accuracy of Ytong wall panels allowed the
windows and doors to be ordered well in
advance.
Ytong wall panels
Ytong wall panels are pre-fabricated
wall elements made of
autoclaved aerated concrete. They
are made precisely to measure in
a computer-controlled production
process. The elements are laid in
bonds like traditional bricks.
Programmed brick-laying robots
apply mortar and lay the bricks.
They precisely adhere to the
required height, length and overlap,
thereby ensuring a dimensional
accuracy that cannot be
achieved at the building site.
Openings for windows as well as
lintels and recesses for other
structural members are also
taken into account.
17.5 centimetres. The wall panels used for this
building had a special height of 2.925 metres. As a
result, a levelling layer at the top and at the bottom
could be dispensed with. The pre-fabricated elements
were delivered on time in line with the
building progress and daily requirements and
installed level and flush in accordance with the
assembly plan. The wall panels were set in mortar
beds on slabs that had previously been levelled
out. After they had been secured, the butt joints
were filled with mortar. Due to this fast assembly,
only very little building moisture penetrated into
the shell, which resulted in a short drying period. A
crane on the construction site or a truck-mounted
crane moved the panels from the truck directly to
their final location.
For time reasons, solid concrete ceilings in the
statically required thickness were used. This also
had advantages for the construction of the setback
storey: It permitted to distribute the existing
loads to the wall structures below it. The solid roof
made of Ytong roof tiles speeded up construction
even further. Moreover, the Ytong roof ensures
heat insulation in the summer and prevents excessively
high temperatures within the building.
Freedom of architectural design
The use of pre-fabricated Ytong wall elements
had numerous advantages – starting with the freedom
of architectural design, which was fully preserved.
The architect was not subject to any planning
constraints and could realise his original plan
while taking the owner’s requirements into
account.
Computer-controlled production meant optimised
consumption of materials and low manufacturing
costs. At the same time, the building
progress could be precisely planned and schedules
could be adhered to, which provided the basis for

The use of pre-fabricated wall and roof elements permitted to reduce the
construction time by three months.
4 | 5
exact cost estimates. In addition, the pre-fabrication
stage was independent of weather conditions
and thus contributed to the strict adherence to the
time schedule.
The constantly high quality of the wall panels
achieved through the automated production process
facilitated and accelerated the completion of
the building. Once delivered to the site, the elements
only needed to be assembled without any
time-consuming sawing. This also helped avoid
building site rubble and protect the environment.
Optimised heat and noise insulation as well as
fire protection
All in all, the use of wall panels simplified the
logistics at the building site, which permitted to
reduce building site facilities to a minimum. In
addition to an optimised construction process,
structural reasons played a key role in the selection
of the building material for the office building
of the tax consulting firm. Right from the start, it
was planned to use autoclaved aerated concrete
for the new building. Thanks to its good heat insulation
properties, the wall elements only had to be
36.5 centimetres thick to meet the heat insulation
requirements of the German Energy Conservation
Act. This allowed to dispense with expensive additional
heat insulation of the outer walls. Ytong’s
typical pore structure provides a good heat insulation/storage
balance for a pleasant room climate.
Moreover, Ytong autoclaved aerated concrete
also has advantages with respect to noise insulation.
In case of composite heat insulation systems,
resonances can occur between the solid wall and
the insulation. A monolithic, homogenous material
allows to eliminate this weak point. Given that the
building is located close to the intersection of several
busy motorways, this was a welcome additional
benefit.
Wall panels made of autoclaved aerated concrete
are incombustible (building material class
A1) and fully recyclable because they are manufactured
in an environmentally friendly production
process using natural resources. As solid building
materials, they are particularly durable and longlasting,
which keeps the maintenance costs of
buildings made of autoclaved aerated concrete
low.

Reduction of CO 2 emissions
According to the plans of the
Federal Government, CO 2 emissions
in Germany are to be cut by
40 percent by 2020 compared to
1990. In absolute figures, this is a
reduction by 260 million tons of
CO 2 compared to the current
values.
explained
EnEV 2009 - the new German Energy Conservation Act
The amendment of Germany’s EnEV Energy Conservation Act was adopted on 18 June 2008 even though
the consent of the upper chamber of parliament is still pending. The new EnEV, which for the first time prescribes
the use of renewable energies, is to enter into force on 1 January 2009. The stricter energy efficiency
requirements under the amended EnEV will create new challenges for the planning and construction of brick
buildings.
Improving the energy efficiency of buildings is
currently one of the key tasks for reducing the
consumption of primary energy. Rising energy
prices have increased the readiness of owners and
planners to consider energy-saving options for
buildings. Even so, energy-optimised buildings
nevertheless still account only for a small percentage
of new buildings today.
The ministerial draft of the German Energy
Conservation Act 2009 contains a number of major
changes compared to EnEV 2007. The primary
energy consumption for heating, hot water and air
conditioning of new residential buildings has to be
at least 30 percent below the maximum values
prescribed by EnEV 2007. The energetic requirements
to be met by the building shell will also
increase: As of next year, transmission heat losses
have to be cut by at least 15 percent compared to
the current regulations.
Increasing energy efficiency
With a market share of over 80 percent of new
buildings in Germany, brick buildings still play a
prominent role when it comes to optimising the
building shell. There is a variety of different
approaches which - alone or in combination - permit
to increase the energy efficiency of buildings.
In this context, the building shell and hence the
brickwork are of primary importance. For in addition
to improving the efficiency of the installations,
energy optimisation starts with a well-insulated,
area-optimised building shell – be it to reduce
transmission heat losses, avoid overheating in the
summer or make use of internal heat.
Given the importance of the building shell, it is
not surprising that every amendment of the EnEV
has a direct impact on the structure and construction
of brickwork. The stricter requirements with
respect to the primary energy consumption and
the avoidance of transmission heat losses of a
building in connection with the requirement to use
renewable energies will result in only a few
changes to the currently used structure. Energetically
correct and sensible detailed solutions will
play a greater role. Thermal bridge allowances of
0.05 W(m²K) do not have to be made for wellinsulated
brick buildings. Today, there are already
bricks whose thermal conductivity differs only
slightly from that of classical insulating materials.
Changes for brick buildings
Blower door measurements can be expected to
become standard practice for new buildings
shortly. However, air-tightness is no challenge to
brick buildings because a layer of plaster on one
side of the wall usually suffices to minimise ventilation
losses. Provided that the renewable energies
heat regulations as included in the draft of
the EnEV will be effective, the changes for brick
buildings will probably be rather limited, with the
exception of the planned new verification procedure
for residential buildings.
Based on the Federal Government’s Climate
Protection Programme, even more stringent
requirements are scheduled to be introduced in
2012.

The winners at a glance:
1 st prize (EUR 6,400):
frank&friker Architekten,
Munich
Award (EUR 2,400):
ahoch4 Architekten Ingenieure
Designer, Zwickau
Award (EUR 2,400):
usp architekten, Berlin
Award (EUR 2,400):
Eberhard Möller, Architekt,
Munich
Award (EUR 2,400):
Ulmer TM Architekten, Berlin
6 | 7
conceived
Back to the city
For a long time, a house with a garden on the outskirts of a big city was the dream of many home owners.
Those who could afford it, built or bought a house in the suburbs and mowed their lawns on Saturdays. This
trend has changed – according to forecasts, housing demand in sought-after cities will continue to increase.
In Berlin, Hamburg, Frankfurt and Munich, residential or free plots of land in attractive city centre locations
are rare, though. But necessity is the mother of invention and architects have started to look at vertical extensions
as a way forward in densely populated metropolitan areas.
Xella, the manufacturer of building materials,
noted this interesting trend and organised the
“Zurück in die Stadt” (Back to the city) competition
in cooperation with DETAIL magazine. The Association
of German Architects accepted the patronage
of the competition. Participants were invited to
address the issue of growing housing space shortage
in our cities through the development of a
vertical extension concept for densely built-up
downtown areas. The Ytong solid roof had to be
part of the design and the prototype’s adaptability
to real-world conditions had to be proven on two
actual construction sites in Berlin and Munich.
5 out of 64
In total, 64 projects were submitted and
assessed by a jury of experts. The winners of the
EUR 16,000 competition have now been chosen.
Headed by Prof. Dr. Thomas Jocher (Fink + Jocher,
Munich), the jury was comprised of Elke Delugan-
Meissl (Delugan Meissl associated architects,
Vienna), Petra Hölscher (Xella Deutschland GmbH),
Prof. Daniel Kündig (UC'NA, President of sia,
Zurich) and Christian Schittich (Senior Editor of
DETAIL). In addition to the first prize, four other
1 st prize:
frank&friker Architekten, Munich
projects were singled out for awards. A project in
Berlin is already planned and partners or customers
providing roofs for the realisation of the new
adaptive housing concepts will now be recruited.
The prizes were presented during the “Großstadt”
evening event on 3 June 2008 on the occasion
of the 4th Münchner Architekturwoche (Munich
Architecture Week). The winners of the first prize,
Tina Frank and Jochen Friker, Munich, managed
to architecturally redefine the roof and thus the
crown of the city. Their design convinced the jury
through the modulation of the roof landscape with
its protrusions and recessed atriums. The treatment
of the atriums and roof shapes in combination
with the proposed structure and precise location
of the sanitary facilities ensure high flexibility
and adaptability to different roof sites. The members
of the jury moreover praised the high quality
of the room sequences, cross-references and
natural light sources, which are achieved despite
the simple layering of the rooms and permit highquality
living even in case of deep floor plans.
Three conical modules that can be combined
with each other are the basis of the design proposed
by ahoch4 Architekten Ingenieure Designer,
Zwickau. This project focuses on the height of the

Award: ahoch4 Architekten
Ingenieure Designer, Zwickau
building site, its spatial separation despite its location
in the city centre as well as the view and lighting.
The sloped sides and roofs form a structural
unit and ensure sufficient shadowing of the glass
fronts. Each module seems to be independent of
the others and remains clearly visible from outside.
Award: usp Architekten, Berlin
usp architekten, Berlin, proposed a simple and
compelling, thoroughly designed module, whose
units are held together by consistently shaped
facade elements that consist of two layers.
According to the jury, the special feature of the
design submitted by Eberhard Möller, Munich, is
the successful integration of the vertical extension
into the existing building or surrounding area. This
is achieved by means of large box-shaped outdoor
sitting areas, which are also the dominant element
of this design.
Award: Eberhard Möller Architekt, Munich
Inspired by a tree crown, the extension designed
by Ulmer TM Architekten, Berlin, grows into all
directions. A free, flexible system creates a small
city on top of the city with different room qualities,
places and atmospheres. Its small scale facilitates
its integration in different situations as well as its
technical realisation.
Award: Ulmer TM Architekten, Berlin

Chamber recognitions:
Hessian Chamber of Engineers:
7 credits towards authorisation to
sign stability and heat insulation
proofs and 7 credits towards
authorisation to sign construction
plans
Hessian Chamber of Architects:
5 further education credits for
architects
North Rhine-Westphalian
Chamber of Engineers:
2 credits
North Rhine-Westphalian
Chamber of Architects:
2 credits, architecture and interior
design
8
explored
Looking at the future of housing construction
The 5 th Forum "Massiver Wohnbau" series is taking place in autumn 2008. This year, Xella’s training programme
will focus on the future of housing construction under the motto “Wegweisend” (Ground-breaking).
As always, renowned speakers will illustrate in their visionary and practice-oriented lectures how you can
ensure your future success by selecting the right strategies today. Register now!
The subjects and speakers:
Auf die Zukunft bauen - Planen, Bauen, energetisch Sanieren im 21. Jahrhundert
(Building on the future – planning, building, energetic refurbishment in the 21st century)
Dr. Franz Alt, editor, presenter, author
Bauen mit Energie - Übersicht der Fördermöglichkeiten
(Building with energy – overview of subsidies)
Peter Friemert, architect and Managing Director of ZEBAU,
Zentrum für Energie, Bauen, Architektur und Umwelt GmbH
Alles im Lot? Maßtoleranzen bei Wandkonstruktionen und Bekleidungen
(All levelled out? Dimensional tolerances of wall structures and panelling)
Dipl.-Ing. Ralf Ertl, consultant engineer, publicly appointed and sworn expert
Wettlauf um die Frauen - Frauen sind die Bauherren der Zukunft
(Competing for female customers – women are the building owners of the future)
Helmuth Muthers, independent strategic consultant
EnEV 2009 - Hülle mit Köpfchen - Anforderungen aus der EnEV 2009 und Lösungen mit Xella
(EnEV 2009 – smart building shells – requirements of EnEV 2009 and solutions by Xella)
Dipl.-Ing. Thorsten Schoch, Managing Director of Xella Technologie- und Forschungsgesellschaft mbH
The forum dates:
21. 10. 2008 Cologne – Dorint Hotel an der Messe
28. 10. 2008 Osnabrück – Steigenberger Hotel Remarque
11. 11. 2008 Hanau – Congress Park Hanau
12. 11. 2008 Pforzheim – Reuchlinhaus-Schmuckmuseum
13. 11. 2008 Fürth/Nuremberg – Hotel-Pyramide
19. 11. 2008 Hamburg – Empire Riverside Hotel
20. 11. 2008 Berlin – Meilenwerk
For further information and to register, please visit www.xella.de/veranstaltungen
The attendance fee is EUR 75 (plus VAT) for the first participant in the event and EUR 50 (plus VAT) for
each additional participant from the same company. Drinks, light lunch and dinner are included.
Editorial information
Xella International GmbH
Franz-Haniel-Platz 6-8, 47119 Duisburg
www.xella.com, kommunikation@xella.com
Design: Konradin Relations, Leinfelden-
Echterdingen, www.konradin-relations.de