Traveling with Xella - Passive House in Pilsen

Surprising Indoor Comfort
The model house in Plzeň serves as a training and demonstration center for the general public. Its owner, David Koranda from the company Setrite, which operates the model house, points out an interesting fact. “At seminars on low-energy and passive houses, discussions continually revolve around the increased construction costs and their return on investment. Many visitors who come to us think that they will only take away information about savings and technologies. However, anyone who visits us is surprised at how good it feels to breathe here. The question of better indoor climate is unjustly somewhat sidelined, even though this aspect is, in my experience, the greatest advantage of modern passive houses. Energy consumption doesn’t bother you if it’s low enough, but the comfort of the interior is something you feel at home permanently,” added David Koranda based on his experience with his own low-energy house.



Betting on Masonry Walls
The passive house in Božkov was built on a south-facing slope overlooking a green valley. It consists of two functionally separate parts. One is residential, and the other houses the headquarters and training center of the company Setrite. According to David Koranda, choosing the building material was a strategic decision in the design of the building. “Our goal was to show people that building a passive house is not as complicated as is often claimed. Therefore, we wanted to build the house from traditional masonry material that is familiar to people and meets above-standard thermal insulation parameters for exterior walls. We didn’t want to go for timber constructions, which are not emotionally close to many people and also offer a different climate than traditional masonry buildings. Fired materials did not convince us for thermal-technical reasons. Among the masonry materials, Ytong emerged as the most suitable. The high precision of masonry, along with the excellent insulation, justified the choice of aerated concrete. Low-energy buildings, which require precision in every detail, must have a very precise masonry system. Similar parameters are best met by Ytong aerated concrete on the current market,” said David Koranda regarding the building material.

A Genuine Passive House
According to David Koranda, it is not about whether the calculated heat consumption for heating in passive houses is 12 or 17 kWh/m2 per year. This is influenced in real practice also by the way the house is used and many other aspects. “The point is that when you feel comfortable at home in winter at 23 °C, you don’t have to worry about heating bills. However, if you demand an unusually high temperature indoors, the concept of a passive house loses its meaning, and heating costs unnecessarily rise.” But in the case of the model house, the builder aimed to reach the declared values of a passive house, which is a maximum annual heat consumption of 15 kWh/m2 of usable floor area. Therefore, they used a rather extreme composition for the outer walls with insulating Ytong Lambda blocks with a thickness of 500 mm and additional insulation with a 200 mm thick layer of foam polystyrene. The heat transfer coefficient for this 70 cm wide exterior wall reaches 0.09 W/(m2. K). The wall offers truly exceptional thermal insulation, sufficient thermal accumulation, and above-standard comfort in the indoor climate. High thermal accumulation guarantees summer thermal comfort, which can be an issue in lightweight passive wooden buildings. The disadvantage of this construction is the greater thickness. “This is a model house that shows the directions and possibilities of contemporary construction. In everyday practice, it is possible to build a low-energy or passive house using more slender constructions, which we plan for future projects,” said David Koranda about the choice of exterior walls. However, the high thickness of the exterior walls also had its advantages. In the model project, there was the possibility of routing air conditioning inside the walls. Similarly, this was true for other technical installations in the house. “We did not deal with any channels in the floor or suspended ceilings; instead, we simply routed air distribution into the aerated concrete walls. Thanks to the good machinability of Ytong, we simplified and reduced the cost of the work significantly,” explained a representative of the builder.

Essential Recuperation
No passive house can do without forced ventilation with recuperation. “Controlled ventilation can save significant amounts of heat, but most importantly, it ensures a more comfortable and healthier indoor climate. The quality of indoor air remains consistently the same, according to set parameters, and does not fluctuate depending on how regularly users open windows,” said David Koranda. Fresh outdoor air is warmed in the recuperation unit from the extracted spent air and is also filtered, so it is free from dust and various allergens. Ventilation can be automatically regulated according to various air quality parameters, such as the CO2 content or humidity. The benefits are noticeable throughout the day, but especially at night when, in regular houses, the quality of the indoor climate significantly decreases.

The Passive House in Božkov utilizes a compact Nilan unit with an air-to-water heat pump for ventilation and heating. The entire unit is about the size of a refrigerator with a freezer. In addition to air recuperation, it also provides hot water heating using a heat pump that utilizes residual energy from waste air in winter and from supply air in summer, which it cools according to the user’s request, thus replacing air conditioning. The unit is also equipped with an electric heating coil that provides hot water for the underfloor heating circuit. The advantage of the system is that it only requires connection to the electric power source and has very favorable investment costs comparable to conventional heating systems.



Structural and Material Solutions
The house is built on strip foundations. Thermal bridges between the foundation and walls are eliminated by using foam glass Perinsul Foamglas. This also interrupts the thermal bridge at the threshold of the entrance door and at the location of the eaves on the exterior and interior walls. The roofing of the lower part is monolithic reinforced concrete, while the upper part is covered with a flat roof with a wooden structure with a minimal slope.

Basic Information About the Passive House in Plzeň

• Construction location: Plzeň-Božkov

• Purpose of the building: family house, b.j. 4+1 and separate office space

• Investor: Setrite Ltd.

• Project author: Ing. arch. Martin Spěváček

• Floor area: 160 m2

• Specific heat consumption for heating: 15 kWh/m2 per year

Composition of External Structures

• Uexternal wall = 0.09 W/(m2. K) – internal plaster; calcium-silicate block 15 mm; Ytong Lambda 500 mm; foam polystyrene 220 mm; external thin-layer mineral plaster 3 mm

• Uroof = 0.09 W/(m2. K) – drywall cladding 12.5 mm; insulation Rockwool Airrock 100 mm; vapor barrier 0.1 mm; insulation Rockwool Airrock 500 mm between wooden trusses; diffusion foil Tyvek Solid 0.23 mm; ventilated air gap 40 mm (counter-battens); OSB boards and waterproofing

• Ufloor = 0.13 W/(m2. K) – leveling and wear layer 20 mm; concrete screed 60 mm; separating foil 0.2 mm; foam polystyrene 300 mm; moisture insulation (mPVC) 0.8 mm Uwindows = 0.75 W/(m2. K) – single with thermal insulation triple glazing and two selective layers

• Udoors = 1.20 W/(m2. K) – entrance doors with a polyurethane foam core