Try living in a passive house

So far, only a few people have had the opportunity to gain personal practical experience with a passive house, and even fewer have succeeded in conveying this experience to the general public. An interesting initiative in this regard is the construction of a model passive house in Plzeň-Božkov, which has been functioning as a training and demonstration center for the general public since March.

“The interest of the public has truly pleasantly surprised us; since March, several hundred people have visited our training center. Serious prospective builders of passive houses can spend several days in the model house to personally experience what life is like in such a standard,” says David Koranda from the consulting and development company Setrite. According to him, passive houses are not just about minimal energy consumption but also offer comfort and a healthy environment for their users. “At seminars on low-energy and passive houses, discussions repeatedly center on the increased construction costs and their payback. The question of indoor climate remains in the background. Based on my experience, quality climate is the greatest advantage of modern passive houses. Energy consumption doesn't bother you if it is sufficiently low. However, you feel the comfort of the interior permanently at home,” continues Koranda.

Traditional masonry walls
The passive house in Božkov, designed by architect Martin Spěváček, has risen on a south-facing slope with a pleasant view into a green valley. It consists of two functionally separated parts. One is residential, while the other houses the office and training center of the company. According to Koranda, the choice of building material was a strategic decision during the design of the building. “Our goal was to show people that building a passive house is not as complicated as it is often claimed. For this reason, we wanted to build the house from traditional building materials, which are closer to people than wooden constructions – many people find them uncomfortable due to the different climate they offer compared to traditional masonry buildings. Among the masonry materials, the autoclaved aerated concrete Ytong emerged as the most appropriate. In addition to its superior insulation, it also offers high accuracy in masonry, which plays a crucial role in low-energy constructions,” Koranda states about the building material.

Above-standard construction
According to Koranda, in passive houses, it is not about whether the calculated energy consumption for heating is 14 or 20 kWh/m² per year, as this is influenced by many aspects during normal house operation. “The point is that when you feel comfortable at home during winter at, say, 23 degrees, you simply do not have to worry about heating bills.” However, in the case of the model house, it was a concern of the builder to safely achieve the generally declared values of a passive house, specifically an annual heating consumption of a maximum of 15 kWh/m². Therefore, relatively extreme insulation composition was used for the outer walls, made from Ytong Lambda insulating blocks with a thickness of 500 mm and 200 mm of polystyrene with a thermal transmittance coefficient U = 0.09 W/m²·K. This construction offers truly exceptional thermal insulation, adequate thermal accumulation, and above-standard comfort in the indoor climate. The disadvantage of the construction is its greater thickness. “This is a model house that shows the directions and possibilities of contemporary construction. In regular practice, a low-energy or passive house can be built from autoclaved aerated concrete even using slimmer constructions, which we are planning in upcoming projects,” Koranda says regarding the choice of outer walls.

Aerated concrete variants
His assertion is confirmed by the words of Karel Ryneš, the technical advisor for the Ytong brand: “The Ytong Lambda outer wall, available to builders in two thicknesses (37.5 cm and 50 cm), is recommended without insulation for the construction of energy-efficient and low-energy houses. The blocks are suitable for houses in category B of the Energy Labels and, under certain conditions, even for category A houses. Our recommended construction solutions for both label categories are intended to serve investors not only as a guarantee of the energy standard of the future house but also as a guarantee of reasonable investment costs for construction. The price of energy-efficient autoclaved aerated concrete houses does not have to differ significantly from conventional houses.” The recommended systematic solution for passive houses made from autoclaved aerated concrete was not available during the design and construction phase of the model house in Plzeň. However, that has changed today. Earlier this year, the producer of aerated concrete introduced a novelty Ytong Multipor – super-insulating aerated concrete slabs, which they now recommend as external insulation for aerated concrete walls of smaller thickness (30 cm). “The resulting layer with a thickness of 50 cm is indistinguishable from ordinary masonry at first glance. The outer walls are equally thick, solid, and load-bearing, but they have two and a half times better insulating properties. Unlike commonly used insulated walls, the sandwich with Multipor is a diffusion-open wall that does not suffer from condensation and breathes optimally. This ensures that the entire wall is durable and provides extraordinary qualities for the indoor environment of buildings,” adds Karel Ryneš.

Necessary recuperation
An undeniable advantage of the solid masonry used is its high thermal accumulation and positive impact on the humidity climate of the interior. The high accumulation of the building guarantees summer thermal comfort, which can be a problem, for example, in lightweight passive wooden constructions. However, no passive house can do without forced ventilation with recuperation, which allows for the introduction of the necessary amount of fresh air into the living spaces. One advantage of the thick outer walls in the model project was the possibility of easily conducting the air-conditioning systems within the walls. “We did not deal with any ducts in the floor or suspended ceilings; we simply milled the air distribution into the walls. Thanks to the good processability of Ytong, we significantly simplified and reduced the cost of work,” says the builder's representative. The passive house in Božkov utilizes a compact recuperative unit with a heat pump for ventilation and heating, which is additionally equipped with an electric heating coil. This ensures the reheating of warm water for the underfloor heating circuit. The advantage of the system is the connection only to a source of electric energy and very favorable investment costs, comparable to a conventional heating system. Thanks to the heat pump, the whole house can use a preferential electricity rate, further lowering its operating costs. The consumption of household appliances, in fact, tends to be greater than the energy consumption for heating in similar houses. Significant savings also arise from the fact that there is no need for a gas connection and expensive chimney structure. Therefore, the used ventilation and heating system overall brings significant investment savings, which can cover the costs of the house's top-quality outer shell.