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Casa Bunyesc: Passive house in Lleida, Spain

Il Caso Evidenziato June 2017
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A single-family house with a shared party wall between adjoining buildings which is comprised of a ground floor, first floor and basement for office and housing.

The Casa Bunyesc Project began as a challenge to discover the comfort behavior of a single-family house. It was built with an envelope system featuring a wood frame and low thermal inertia and using local sheep wool as insulating material, while taking into account the mild semi-arid climate which often has exceptionally hot summers. The house has been monitored in different stages and is one of the first buildings to achieve a Passivhaus standard in Spain.


After construction, a family of 4 moved into the house and their energy behaviour was monitored in order to assess the energy design and systems. Since then, it has progressively evolved to become to a positive energy house by generating its own energy which also verifies how it could become self sufficient.


In 2011, an extension was built on the adjacent plot with a small storage room and a porch. In 2016, another addition was built. This addition is comprised of a small meeting room with a bathroom and a kitchen-office area.





C/ Arboretum, 21, 25198 Lleida, Spain


Project team


Project management, architect design, thermal and structural calculations: Josep Bunyesc

HVAC and electricity systems: Jorfe instal·lacions

Wood frame manufacturer: Sebastia Disseny Estructural SL


Time schedule


Design: October 2008 – April 2009

Construction April – September 2009 (small addition to house was made in 2016)

Occupation in September 2009


Building use and area


The Casa Bunyesc is a single family house comprised of a basement, ground floor and first floor. The basement has an office, a warehouse and a facility room. The ground floor has a hall, bathroom, kitchen-dining room and an auxiliary room. The first floor has three bedrooms, a bathroom and a small room. The hall is located in the central part, has a south-eastern orientation, and is the center of distribution to the different comfort areas. It also provides natural light for these areas.


Total Constructed Floor Area: 241.5 m2 (originally) / 287.7 m2 (after expansion)

Total Usable Floor Area: 189.7 m2 (originally) / 236.3 m2 (after expansion)

Total Treated Floor Area: 78.5 m2 (originally) / 98.7 m2 (after expansion)


Construction costs


Total project cost: 200,000 €

Ground works: 5,000 €

Structure works: 110,000 €

Finishing works: 70,000 €



Envelope performance


The main goal of the project was to achieve a good comfort level for the user more so than a minimum reduction of energy demand. According to sustainable and health factors, the building envelope has local sheep wool as insulation and local wood as a frame structure and achieves a wall façade thickness between 18 and 24 cm. The local wooden frame modules are composed of laminated pine wood with oriented strand board (OSB) finished on the inside and a breathable board on the outer side in order to avoid condensation and to eliminate thermal bridges. Moreover, the whole envelope system is easily detachable in order to allow possible future extensions or replacements.


Detail of envelope elements:

-Exterior walls: U-value average is 0.22 W/m2.K.

-Ground: U-value average is 0.37 W/m2.K

-Roof: U-value average is 0.18 W/m2.K

-Windows: U-value average is 1.1 W/m2.K


In 2016, there was a small building addition with new finishing materials on the south wall façade. An 8-cell polycarbonate fiber board was used on the outer side to provide solar energy and natural light and compacted earth or water in transparent droplets inside to provide thermal inertia. This new envelope system has a U-value average of 0.7 W/m2.K, which reduces the heating demand more in winter, maintaining the daily temperature during the night. In summer, this system has a simple solar protection such as shutter blinds and some natural ventilation, which therefore makes it unnecessary to use the air conditioning system. On the north side of this extension, the wall façade was used with a new outer finishing for the wood frame, burnt pine wood as natural protection for water and insects, which leaves the wood black without the necessity of painting and maintenance.



Energy consumption


Heating demand: 7 kWh/m2.year

Primary energy consumption: 52 kWh/m2.year

Energy label: A

Calculation method is according to RT 2012


Electric final consumption: 14 kWh/m2.year.


Renewable production

-24 m2 of PV cells connected with batteries for accumulation of electricity, allowing up to 8 months a year without connection to the grid.

-2.380 kWh/year of PV production (30% provided for charging a hybrid car (600 kWh/year is equivalent to 3,000 km/year and saving around 150l of gasoline consumption)



Energy systems


Heating and air-conditioning system with mechanical ventilation and extra heat supply (support) from wood stove.

A double-flow mechanical ventilation system with heat recovery allows for more efficient air renovation. In addition, this ventilation system is connected to geothermal pipelines which assures pre-treated air through heat exchange on the ground level.

In winter, even on the worst days (foggy), the whole heating demand is covered by underfloor heating provided by a wood stove (which was electric until 2012) installed in the basement.


DHW system through solar thermal.

Solar thermal panels are installed on the south façade to heat water when it is needed. The vertical orientation allows for more heat more in winter than in summer due to the different sun altitude, therefore avoiding overheating and preventing possible incidents. This is an auxiliary system which is connected to the heating system, although is rarely used.



Awards and recognition


Candidate of the Green Building Solutions Awards 2015 (

Selected candidate project representing GBCe in the International Conference “Sustainable Building 2011” in Helsinki (

Finalist of BEAU XI Biennal arquitectura espanyola 2011

Finalist of premis Catalunya Construcció 2010 in the building innovation category

Finalist of the 3rd mostra d’arquitectura in Lleida 2010



Additional information


Summary and photo gallery:

Lessons learnt

The location of the Casa Bunyesc in Lleida presents a complicated climatology in winter, as there are only about 30 days of sunlight due to fog. Throughout the whole year, the house has needed 420 kWh of electricity that did not come from the photovoltaic cover. As a result, 85% of the total annual energy consumption for the home, office and car load comes from the photovoltaic generation of the roof itself. In other Mediterranean regions without fog, it would be easy to self sufficient, as 90-95% of the energy consumed in the buildings, could be produced with photovoltaic energy of the building itself. In buildings of tertiary use, which concentrate the consumption during the day, the local photovoltaic capture would allow to save a good part of the energy from non-renewable sources.

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