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Passivistas - The House Project: Retrofit towards nZEB 2020

Highlighted Case September 2016
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The first Passive House certified renovation in Greece


The existing building, a typical 1960´s Athens single-family house, was selected for a full refurbishment using Passivhaus standards. The bearing structure was originally made by reinforced concrete with no insulation in the walls, a flat roof with access from an external staircase and single-glazed windows with wooden frames. Oil stoves and conventional radiators, a traditional fireplace, two old cooling units and an electric water heater were used as the original HVAC and DHW systems. Before renovation, the building was unoccupied for at least 5 years and annual primary energy consumption was estimated around 300 kWh/m2.year.



Renovation targets


For the project team and the members of the Helenic Passive House Insittute (HPHI), the aim of “Passivistas: The House Project” was to be considered an exemplary case study for nZEB buildings in Greece reaching the objectives of the 2020 roadmap. The idea or objective that “consuming much less energy is achievable and cost effective” being paramount to the project. The building is comprised of two storeys which has now been divided into two independent spaces on each floor; an office (semi-basement) and a house (ground floor)

The energy upgrade was centered on achieving energy consumption targets defined by the EnerPHit standard criteria:

maximum needs for heating or cooling ≤ 15 kWh/m2.year
maximum total energy primary needs, including electricity consumption ≤ 120 kWh/m2.year


Energy efficiency improvements


The main energy efficiency measures carried out were the following:

  • external insulation of the entire façade and roof
  • replacement of windows and frames with triple glazed windows
  • optimization of shading and solar gains through automatic blinds and a surrounding garden
  • improving airtightness of the building, paying special attention to even small amounts of uncontrolled leakage through frames, electrical and plumbing gaps by using methods such as airtight membranes sealed with special silicone
  • installation of a heat recovery ventilation system for each space (house and office) to improve the indoor air quality and for preheating or precooling the air
  • installation of a split cooling and heating system (one in the living room and other in the office) to cover occasional heating and cooling demand when necessary
  • installation of a solar thermal system for hot water
  • removal of conventional radiator system and all other old units, as well as the fireplace
  • use of energy efficient elements for the lighting system 
  • high-efficiency appliances
  • automatic display monitoring system for control and measures
  • installation of a PV system to cover all the energy consumption needs (still pending)





Anastaseos 112, Papagos 156 69, Greece



Project team


Project management: Stefan Pallantzas (civil engineer)

Energy certification: Lymperis Liberopoulos and Royal Karachaliou (architects)

Energy concept and supervision (regarding PHPP): Nasia Roditis (architect), Angela Stathopoulos, Elias Egoumenidou and Stefan Pallantzas (civil designers)

Renovation design: Euterpe Tsouti and Fani Kalamatianou (architects)

Thermal analysis: DI Ioannis Pappas (mechanical engineer)

Thermal engineering: Stefan Hatzoulis (civil engineer)

PV system design: Pericles Kottaridis (mechanical engineer)

Accoustic study: Mersin Vitali (civil engineer)



Time schedule


Built: 1964

Renovation design process: 2014

Renovation works: July - October 2015 (split heating and cooling system and PV system were installed during 2016)

Monitoring: since October 2015



Building use and area


After renovation, the single-family house was converted into two separate spaces:

  • house (ground floor) comprised of a living room, kitchen, bathroom and two bedrooms. During the 7 consecutive years following the renovation, this space will act as an open residence for guided visits, lectures and presentations to public and professionals.
  • office (semi-basement) comprised of a reception area, meeting room and bathroom. This space is to be used as the headquarters of the Hellenic Passive House Institute as well as a venue for seminars, training, and a materials showroom.



Surface area


  • Plot Area: 520 m2
  • Total Constructed Floor Area: 142.4 m2  (ground floor 98.8 m2 and semi-basement 43.60 m2)
  • Total Treated Floor Area - TFA: 114.6 m2 (ground floor house 85 m2 and semi-basement 30 m2)



Construction costs


Whole renovation cost (VAT and taxes included): 76,900 €

Renovation cost for energy efficiency improvements (VAT and taxes included): 57,150 €

Seventy percent (70%) of the whole renovation cost was funded from sponsors -companies that gave all material and equipment needed ( Ten percent (10%) of this cost was covered by an international crowdfunding via Indiegogo (

The cost for the renovation was only 7% more than the present building standard cost in Greece.



Envelope performance


The existing building was made of reinforced concrete slabs and perforated brick walls and was completely uninsulated, with major thermal bridges all around its perimeter due to balconies and projecting structural elements. It also had wooden frame windows with single glazing.


According to PHPP results, the need to add external insulation on all surfaces in contact with the outside air and to replace all windows and doors (including frames) were contemplated. The dimensions of the southern windows in the kitchen and the bathroom were increased and all windows were converted to a single opening in order to increase the glazing area.


All existing thermal bridges were resolved in order to have the least possible influence on the heating or cooling needs for the building. The salient structural elements of the façade (balconies and canopies) were covered entirely with 5 cm of expanded polystyrene (EPS) and 4 mm of acrylic plaster. Special ceramic exterior tiles with extruded polystyrene were used on the floor to minimize the thermal bridging.


Details of the envelope elements after renovation:

  • External wall façade (U-value: 0.178 W/m2.K): 3 cm interior plaster / 6 cm perforated brick wall / 8 cm air space / 6 cm perforated brick wall / 3 cm exterior plaster / 15 cm EPS Neopor rigid foam insulation / 0.4 cm acrylic plaster
  • Roof (U-value: 0.1 W/m2.K): 2 cm plaster / 13 cm reinforced concrete / 5 cm screed concrete / 30 cm EPS Peripor thermal insulating material
  • Ground floor (U-value: 0.486 W/m2.K): 13 cm reinforced concrete / 5 cm screed concrete / 3 cm old tile / 5 cm EPS Neopor / 0.2cm membrane / 0.7 cm laminated floor
  • Windows (U-value: 0.92 W/m2.K): thermally separated aluminum frame with fiberglass / triple glass (0.50 W/m2.k and solar factor 0.54)
  • Doors (U-value: 1 W/m2.K)



Energy consumption


According to the PHPP tool v9 results:


Heating Demand (after renovation): 11 kWh/m2.year
Cooling Demand (after renovation): 12 kWh/m2.year
Primary Energy Renewable Demand (after renovation): 51 kWh/m2.year
Total Primary Energy Consumption (estimated before renovation): around 300 kWh/m2.year
Total Primary Energy Consumption (after renovation): 93 kWh/m2.year (15-20% of the consumption of the existing building)


First Monitoring results between November 2015 and September 2016


During the first winter, an air pre-heater (direct, electric) was used to heat the house. The system worked properly and consumption was in line with the PHPP calculations. According to PHPP the total final energy for heating should have been 1,307 Kwh and the measured energy was 984.19 Kwh. The reason for this difference was that the office was not occupied in December, and the second part of January and beginning of February were warmer than the average climate data.


In the residence, the heating period started 16 December - 17 February. In the office, the heating period started 17 January - the end of March. During heating period the average temperature in the residence was between 19.4 and 21.1 degrees Celsius. There were no differences in several rooms. Thermal imaging showed that there were no cold surfaces or visible thermal bridges.


The cooling period for the residence started 19 June - 9 September. The total energy used for the cooling of the residence was 136.17 Kwh and the average temperature of the residence (Living Room) was 25.01 degrees Celsius. The average temperature in the Bedroom was 0.5 degree higher, but was still comfortable.


The Total Energy measured in a 4 month period (1/6-30/9) was 846.05 Kwh this was much better compared to the PHPP calculation (1,168.60 Kwh). The addition of a split heating and cooling system (one in April and the other in August) and a PV system (October 2016) will improve the coverage of the needs for the next measurements.



Energy systems


Heat Recovery Ventilation system

One ventilation system was installed for each space (house and office). For the house the normal air-flow is 110m3/h. For the office a bigger unit was chosen with a 250m3/h capacity to cover the presence of nearly 10 people (e.g. during training courses). Both units are installed for the improvement of indoor air quality and preheating or precooling the air. Each ventilation unit consists of air exhaust fan, a fresh air supply fan, the alternator heat exchanger, air filters and shell.



Auxiliary split heating and cooling system

In this project all the heating and cooling needs of each space are completely covered by a simple split heat pump of 2 KW. One unit is located in the living room of the house and the other in the office.



Solar thermal system for hot water

The hot water is heated by a solar water heater with a capacity of 200 liters. Both the water tank and 4.2 m2 panels are installed on the roof of the building which covers 85% of the building in hot water needs.



Solar shading system

All southeast, southwest and northwest windows have automatically controlled roller blinds for temporary shading in summer. All windows except one in the kitchen, can be opened or tilted for natural night cross-ventilation in summer and have screens on the outside. The two balconies on the southwest and northwest side of the building will have horizontal shades which are placed in order to create an air space between the windows and the the balcony sitting area during midday and afternoon hours in summer.



PV system (to be installed in October 2016)

The installation of photovoltaic panels with 4kWp (around 14 panels) will cover all the needs of energy consumption of the building.



Airtightness average: 0.56 1/h at n50



Awards and recognitions


The Project was certified as an EnerPHit Classic in February 2016 by PHI (
Project selected among 350 candidate projects to be presented in the 20th International Passive House Conference in Darmstadt (
Project awarded in the Energy Mastering Awards 2015 as the best energy-saving practice in Greece (



Additional information


Project Description (Passivhaus database):
Project Description in English (presentation):
Project Description in English (webinar video):

Detail of the surroundings (video):

Insulation Works (videos): part 1 ( and part 2 (

Blower Door Test (video):

Lessons learnt

The way of design and step-by-step implementation, and the subsequent monitoring and metering of the pilot project will promote collaborative processes among executives of HPHI, certified passive building designers, engineers and technicians from all sectors and commercial and technical department of companies manufacturing and marketing passive house components. It will offer to every citizen through open public data all the information required on how to drastically save energy in their house while improving the quality of life and at the same time will contribute substantially to the fight against global warming.

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