Stefano Paolo Corgnati
Vice-president of REHVA,
TEBE Research Group, DENERG,
Politecnico di Torino, Italy,
TEBE Research Group, DENERG,
Politecnico di Torino, Italy, email@example.com
GOODFOR architecture and design, Torino, Italy
In keeping with the
European definition of nZEB , the CorTauHouse represents an Italian
significant design experience in which the architectural quality in renovating
a traditional rural building is combined with the use of high-performing energy
solutions. The nZEB realization challenge is presented here in the form of
interview with the designers.
Keywords: nZEB, energy efficiency, cost control, traditional rural building, building system, architectural quality.
The CorTau House is a single-family house, realized by
renovating a “curmà”, a traditional rural building, located in Livorno
Ferraris, in the Northern Italian region of Piedmont. The construction of the
building, started in March 2014, is still in progress but this nZEB already
represents a good example for the replicability and implementation of a
high-performing house model at the regional and national levels. The project and
realization of the building are described from the project owner/building
system designer, S.P. Corgnati, and from the architectural designer, M.
A first question to the
project owner: what led you to realize a nearly Zero-Energy Building?
possibility to ensure the energy independence of the building from fossil
energy sources: the CorTau House (Figure 1) is indeed “all electric” and meets the energy demand
through self-generation of electricity from a solar PV system. Moreover the
project pursues the dual objective of combining the nZEB requirements 
with architectural quality principles and with the renovation of a traditional
rural building widely diffuse in Piedmont.
Figure 1.The designed CorTau House, south front.
Which are the main
benefits deriving from this kind of building?
advantages, in keeping with the nZEB philosophy, are surely a considerable
reduction of the energy required for conditioning the house and the meeting of
energy needs through the use of on-site renewable sources, including the sun
and the heat extracted from groundwater.
Which elements have played
a decisive role in designing and realizing the building? How influential have
been the context, the previous existence of a traditional building and the
current energy efficiency legislation?
traditional rural framework has surely influenced the project, whose aim is to
preserve and to enhance the distinctive features of the building (Figure 2). The roof covering in tiles
and the wooden roof structures have been maintained, so as the brick pillars.
The design team also had the good fortune to reinterpret an ancient intuitive
know-how in a scientific way, according to bioclimatic architectural principles:
the existing building indeed, fully opened on the south side, presented a
closed façade on the north side (Figure
3): the project has been adapted to this simple existing structure,
optimally suited to achieve excellent energy performances.
technological and structural solutions have been adopted?
architecture study is used to work with reinforced concrete septa, which have
the dual function of acting as structural elements and including the building
systems. Moreover, massive structures are adopted in order to get the
most out of the thermal inertia of the building envelope,
considering the temperate climate of the context. The result is a building
characterized by parallel axes that incorporate the building systems in a
north-south direction and by horizontal surfaces enclosing the living space:
there is a symbiosis between the building structure/envelope and the
technological aspects characterizing the living space.
With regard to the building envelope, there is a clear separation between the
highly insulated opaque components, characterized by external insulation, and
the transparent surfaces, in order to minimize the creation of thermal bridges.
Apart from building
envelope measures, which energy efficiency strategies have been adopted with
regard to the building system?
mechanical ventilation system with heat recovery and dehumidifier is
combined with radiant floors for heating and cooling: a geothermal heat
pump provides the production of cold and hot water for the radiant panels and
Domestic Hot Water (DHW). All the electricity needs of the building for
lighting, cooling and interior equipment are covered from a 7 kWp
grid-connected photovoltaic system installed in the roof.
Figure 2. Picture of the pre-existing rural building,
Figure 3. Volumetric representation of the pre-existing
rural building, south front.
Acoustic solutions have
been considered too?
S.P.C.:In the CorTau House the soundscape design concerns not only
the building itself but also the garden. The main acoustic protection of the
house is indeed provided by tree planting and hedges, which have the
additional functions of solar control and privacy screening. With refer to the
building, reinforced concrete septa placed between living and sleeping areas
provide the acoustic insulation of these two macro-areas of the house.
Among the adopted design
measures, which ones revealed to be priority for the nZEB realization? On the
contrary, which solutions have been ruled out and why?
S.P.C.:The project experience has highlighted the importance of individuating the correct relationship between opaque and transparent surfaces in relation to different room exposures, in order to correctly design external sun screens and to control the solar radiation. The optimization of the building energy performance is based on passive energy solutions: since the first concept, the architectural design and the energy-saving project have been complementary and decisive in the evolution of the project. The project originally involved an articulated system of reinforced concrete septa and slabs: this solution has been ruled out in the final project. The structure has been simplified, giving way to clearer separation between opaque and transparent surfaces, in order to avoid thermal bridges and to control the construction costs due to concrete paving.
A fundamental strategy
towards nZEBs is an integrated design methodology: how did the architectural
project evolve in order to achieve the goals of energy efficiency and cost
architectural design work has been carried out in parallel with the building
system design from the preliminary phases: the creative role of the
architectural designer has been driven by nZEB energy goals, together with the
property owner’s request of cost control, with reference both to the investment
costs and to the future running and maintenance costs. As said before, in a
previous stage of the project (Figure 4),
the house was characterized by an articulated structure with
stepped levels, including a basement used as a garage. In order to control
the costs, the project has been modified, proposing in the final version a
one-storey residential unit with reduced net floor area and volume (Figure 5 and Figure 6). The interior spaces and structures of the house have
thus been optimized, ensuring reduced energy losses and, consequently, lower
energy needs for heating and cooling in future. Moreover, costs for excavations
and costs due to the realization of a second staircase and to the installation
of a distribution manifold for the first floor have been avoided.
What about the building
estimated energy performance? How have the consumptions been calculated?
with the definition of nZEB , the energy consumption of the house is nearly
zero: the low energy demand is covered through self-generation of electricity
from PV system. The energy performance of the building has been calculated in
the preliminary phases of the project through calculation software based on the
European standards. At a later stage the energy consumptions of the building
have been calculated using dynamic energy simulation tools for comparing the
estimated final energy demand profiles and the energy production ones.
Figure 4. The first concept of the house, south front.
Which difficulties did you
encounter during the nZEB design and construction phases?
M.L.: The building site is a “hostile”
place because of the co-presence of different professional figures. In order to
achieve the nZEB design goals in terms of architectural quality there is a
strong need for collaboration and cooperation between the designers, the director of
works and the construction company: only through an agreement between all the
parties interesting results become possible. I like to think that the project
is a thought, which is made of different nuances. The construction company
provides not only for skilled manpower but also for ideas and support; the
designers have to integrate and implement the project on the basis of these
technical suggestions, though maintaining the basic features of the
The quality of the final work is surely prime in order to achieve the prefixed targets; did you encounter any problem in finding materials and trained manpower?
didn’t encounter relevant problems thanks to a great synergy with a highly
qualified construction company. The manpower and the technicians on site
revealed to be trained in the construction of high quality buildings:
the attention given to building details is a fundamental aspect for the
achievement of the result.
How much does the
realization of a nZEB cost with respect to a “traditional” building? How long
is the estimated payback period of the investment extra-costs?
are clearly related to the adopted solutions: for example in this case the
architectural and structural use of massive concrete structures has affected
the construction costs. The investment extra-costs are about 30% higher than
the costs to be bared for the realization of traditional buildings, considering
standard finishes. This percentage of extra-costs is however more elevated than
for other nZEBs because of a decisive boost to experimentation with regard
to the building system, which could be simplified. In relation to the
investment extra-costs, the payback period has been estimated of less than a
decade, a reasonable period considering that the investment is made in a
primary residential property.
Are tax deductions or
other financial subsidies granted for the realization of a nZEB at the national
or regional level? In your opinion are they suitable?
S.P.C.: In Italy energy retrofits are strongly subsidized
in terms of tax deductions for interventions of building renovation and energy
efficiency. In 2014 and 2015 for refurbishment works on real estate property it
is possible to benefit from a tax deduction of 50%, for building renovation,
and of 65%, for energy retrofit actions, over ten years, on a maximum spending
limit respectively of 96,000 € and 100,000 € per real estate unit. Financial
subsidies are nowadays fundamental in order to incentivize energy efficiency
plan of the house.
Figure 6. Transversal section.
This building can be taken as a model for the future realization of new nZEBs and for their distribution at the national and regional levels. Which design and construction “rules” followed for this case study could be replicated for other ZEBs?
S.P.C.:The “curmà” is a typology of widely diffuse building in the Northern Italian rural areas: the CorTau House shows a new possible way to interpret its renovation and re-functioning. A replicable “rule” is surely the idea of preserving the existing structure and adding to it a new building organism characterized by innovative energetic and architectural performances.
with the above but I would also like to underline that in my opinion there is
not a correct or wrong model for designing a building: the building quality is
the result of a correct balance between several elements, different for each
project. The CorTau House is an example of nZEB located in a
rural Po plain scenario; a good model of nZEB surely fits into the context and
is designed on the basis of the specific needs, climatic conditions and
traditions of the place in which it is realized.
Is there any other theme
you would like to highlight?
S.P.C.:In our climatic
conditions the nZEB design challenge can be summarized in two basic concepts: the
careful design of the building considering both the winter conditions and the
summer ones and the control of humidity – fundamental for a building surrounded
by rice fields. The compensation between the building behavior during winter
and summer seasons represents the basis of the reasoning intended to emphasize
the passive design.
that this design experience also highlights another issue: this house
represents a good project in relation to the urban space, nowadays degraded in
Italy. In this sense the CorTauHouse
can be assumed as a model for sensitive zones, in order to demonstrate that
also controlling costs high results in terms of quality of life are achievable.
 Directive 2010/31/EU of the European
Parliament and the Council of 19 May 2010 on the energy performance of
 REHVA nZEB technical definition and system
boundaries for nearly zero energy buildings, 2013 revision for uniformed
national implementation of EPBD recast prepared in cooperation with European
standardization organization CEN. REHVA, Federation of European Heating,
Ventilation and Air-Conditioning Associations, Report No 4, REHVA 2013.
 ECOFYS, Towards nearly zero-energy
buildings - Definition of common principles under the EPBD. Final report, February