Energy efficient house. Why it pays off?

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In recent years, a dynamic development of the building industry can be observed. This is not only connected with the number of buildings and new investments, but also with the development of technical thought, widely understood “know how” and increased awareness of the society in issues related to caring for the environment.

What is an energy-efficient house?
The above-mentioned factors determine the growing interest in energy-efficient construction. What is an energy efficient house? It is a so-called low-energy house, which has a heat demand between 30 kWh/ (m²-year) and 60 kWh/ (m²-year). The design of a low-energy house must meet a number of requirements in order to be recognised as a low-energy house. This usually involves unconventional solutions and higher construction costs.

Passive house vs. low-energy house – the most important differences
Very often low-energy houses are confused with passive houses. Both are closely related, but there are differences between them. The basic parameter that differentiates the two types of construction is the demand for primary energy (needed for heating, hot water, operation of household appliances). As mentioned above, in the case of an energy-efficient house, this is between 30 kWh/ (m²-year) and 60 kWh/ (m²-year), while a passive house has a demand of 15 kWh/ (m²-year). Another difference is the average U-value for external walls. In the case of an energy-efficient house, it should not exceed 0.20. For a passive house, the maximum value is 0.12. Similarly to the external walls, the U-values for windows and doors are also specified. They are 1.3 and 0.8 respectively. Analysing the above data, it is easy to see that a passive house is an extremely energy-efficient version of a low-energy house. The differences between an energy-efficient and a passive house significantly affect the construction costs.

How to build an energy efficient house?
To build an energy-efficient house, you need to start with a special design, which unfortunately is more expensive than for traditional houses. This design specifies exactly what to build the low-energy house with. The body of the building should be simple, based on a rectangle, and the walls and roof – have as few bends as possible. On the south side, as much glazing as possible should be placed, while the north side should be built-up, without window openings. This layout of the building determines the arrangement of rooms. Living rooms should be located on the southern side, while the northern side is usually intended for utility rooms. The U-values mentioned above are very important. In order to obtain them, it is necessary to apply thermal insulation layers of at least 20 cm in walls and 30 cm in the roof or flat roof. Generally speaking, you should strive to eliminate thermal bridges, so you need to take care of the right doors and windows. The architecture of low-energy houses makes them look quite specific and even modernistic. This can be a problem in obtaining planning permission, especially in regions where the development conditions place great emphasis on tradition.

Energy efficient house – parameters
In addition to the previously mentioned U coefficient and energy demand, energy-efficient houses must meet a number of other requirements. The first of these is the Energy Demand index. This is the final energy demand, taking into account transmission losses. Another indicator is EUco, which determines the amount of energy needed for heating and ventilation. This indicator shows the degree of protection against heat loss. According to the ISO standard, for low-energy houses the EUco is between 30 and 70 kWh/(m2-yr). The latest regulations for low-energy houses have been in force since 2014.

Low-energy house – costs
How much does an energy efficient house cost? Building a small, energy-efficient house requires more money than for traditional buildings. The main factor influencing this are the material costs. This is the case with walls, the cost of which for a small low-energy house is about 15 000 Polish zł, while in the case of traditional houses it is about 10 000 zł. The zero state of an energy-efficient house is also more expensive by 5,000 zlotys. Here we are talking about the amount of around 20 000 zlotys. When building a low-energy house, you can save money when planning the roofing, because it is not recommended in such construction to design dormer windows or caves, which create additional costs when building traditional houses. The low-energy house is about 30% more expensive than a simple house, still the most popular one.

Low-energy house – building cost vs. profit during use
The profitability of the low-energy house is best illustrated by comparing the use costs of the above mentioned buildings with traditional houses. Heating an average house with coal costs about 4,000 PLN per year, heating with oil costs 7,000 PLN, heating recommended in energy-efficient houses (heat pump) will generate a cost of about 2,000 PLN. It should also be noted, that low-energy houses are very often equipped with a photovoltaic installation, which reduces the cost of electricity consumption by the heat pump. The architecture of a low-energy house also provides measurable benefits in terms of comfort. The south-facing glazing, mechanical ventilation and ergonomic arrangement of rooms have a positive impact on the well-being and mood of occupants.