What is a passive house?

5 BASIC PASSIVE HOUSE PRINCIPLES

A passive house is almost self-sufficient. The house is able to exist almost independently of external resources.
It absorbs heat from the sun and the earth. It interacts with the environment and enables you to feel in harmony with nature.

Excellent heat insulation

High quality windows and solar energy gains

Ventilation with
heat recovery

Airtight building envelope

Thermal bridge
free constructions

The idea of a passive house comes from a Swedish architect Bo Adamson and a German civil engineer Wolfgang Feist. In 1988 they created the concept of a Passive House, which constituted the basis for the first passive house built in Darmstadt, Germany in 1991. It was a semidetached house with four apartments, each having a total living area of 156 m². Since then passive houses have gained popularity around the world, especially in Central Europe and Scandinavia.

What is the difference between passive houses and traditionally built houses? The difference of a passive house is in its high thermal insulation and airtightness, which significantly reduces heat losses. At the same time these buildings are designed in a way to prevent them from overheating and ensure comfortable indoor climate both in winter and summer.

In order for a house to be considered passive, it must meet the following requirements:

the annual specific heat consumption for space heating is less than 15 kWh/m² OR the maximum heating load per square meter of living space does not exceed 10 W/m²
the annual specific space cooling energy consumption does not exceed 15 kWh/m²
the overheating frequency (indoor temperature more than 25°C) is less than 10%
airtightness test n50 ≤ 0.6 air change/h
the total annual primary energy consumption is less than 120 kWh/m²

New technologies are being developed, more precise measurements enable improvements in construction process, however, the basic principles of passive houses laid down thirty years ago have remained the same.

EXCELLENT HEAT INSULATION

One of the cornerstones of passive houses is excellent thermal insulation for the roof, exterior walls and foundations. It is essential that their thermal transmittance value or U-value is less than 15W/(m2K). It corresponds to an insulation layer of at least 250-300 mm. Taking into account climate conditions it is thicker in Latvia. For example, for pre-fabricated wooden houses this layer reaches 400 mm or more.

It is essential that for every single passive house we develop a full energy efficiency calculation is conducted. The calculation evaluates impact of design decisions and engineering solutions of every building on the overall energy efficiency of the house.

HIGH QUALITY WINDOWS AND SOLAR ENERGY BENEFITS

To maximize the use of solar energy, it is essential to choose the best facade orientation. The best façade orientation of the passive house is towards the south. However, since glazed window surfaces have a high total solar transmittance ratio, it is necessary to think about the shading in order to prevent the building from overheating. The Passive House Standard states that the frequency of overheating (above 25 degrees Celsius) for a passive house should not exceed 10%. Anyway, the window U-values in the passive house should not be more than 0.8 W / (m2K). To achieve this, it is essential to use high quality insulated window frames and triple-glazed window panes. Besides, to protect the house from overheating, if it does not have roof overhangs, windows can be equipped with external shading.

VENTILATION BY MEANS OF HEAT RECOVERY

Ventilation is essential in every home to provide a good indoor air quality and a healthy indoor climate throughout the year. Relative humidity in the house is considered to be optimal if it is in the range of 35 to 55%. In order to prevent air dryness, ventilation in the passive home should be adjusted to the amount of fresh air consumed. Therefore, when choosing a ventilation system, it is important to know the amount of people living in the house. Accordingly, a ventilation unit is selected which simultaneously provides both air circulation and air extraction, and, if necessary, it can be used for heating as well.

An energy efficient ventilation system removes warm and damp air from the kitchen, bathroom and toilet. Fresh air is supplied in the living room and in the bedrooms. However, everything shall be calculated exactly, since the total electrical consumption of ventilation unit in the passive house shall not exceed 0.45 Wh/m³.

AIRTIGHT ENVELOPE

In order to prevent uncontrolled air movement and consequently heat loss, an external envelope of the passive house shall create an undisrupted airtightness layer.

Airtightness of insulated structures is important for several reasons, as it not only reduces cold air infiltration into the building, which may result in a condensation in building structural elements as well as increase the energy consumption of the building, but also protects the envelope from warm and wet air exfiltration from the building. As a result, the structures are protected from condensation and mold formation on them.

To ensure that there is an airtight layer between the wooden panels, at the joints and corners, the joints are covered with special adhesive tape. In order to check if the building's air-tightness criteria meet requirements of the standard EN 13829, the Blower-Door test, a special pressure differential measurement method, is used.

STRUCTURES WITHOUT THERMAL BRIDGES

Thermal bridges or imperfections in structures and insulation of the building may adversely affect its energy efficiency. Such thermal bridges are formed in places where the material with high thermal conductivity penetrates the thermal insulation layer or passes through it. Such a risk exists, for example, at the console balcony plate, in the floor and in the wall connection areas, or in the mounting points of facade heat insulation composite systems. In passive houses such thermal bridges should be avoided. To achieve this, it is essential to choose correct architectural solutions for buildings. Insulation and installation of the windows shall be made in such a way, as to avoid the thermal bridges in the building's envelope.