Energy-efficient houses by building on wooden structures or thermal rehabilitation

Energy efficiency in the home is a topic that is given major importance in European countries and the issue of reducing fuel consumption in the home is treated very seriously. New houses are being built with the idea of the lowest possible future energy costs, even zero, using the best insulation materials, ingenious jointing solutions to eliminate thermal bridges or triple-glazed windows.

Directive 2010/31/EU The European Parliament and Council Directive on the energy performance of buildings, published on 19 May 2010, requires new buildings to become more efficient and sets a deadline of 2020 for all new buildings to be nearly zero-energy buildings (nZEB). For new public buildings, the deadline is the end of 2018, which means that the Directive is already in force for them. Directive 2012/27/EU on energy efficiency also obliges Member States to set efficiency targets by 2020.

At the beginning of 2016, the Government adopted an Emergency Ordinance which stipulates, in line with the European Directive, that all new buildings received on the basis of building permits issued from 31 December 2020 onwards must have a near-zero energy consumption. In the case of public buildings, the ordinance is valid from 31 December 2018.

Thermal insulation of old houses

In Romania, the most important energy consumer is the building sector, whether private or public. At the level of a building, heat consumption for heating and domestic hot water accounts for about 70% of total energy consumption. A problem is the residential sector, due to the age of buildings. According to data National Institute of Statistics, 31% of residential buildings are built before 1961, 19% - between 1961 and 1970, 23% - between 1970 and 1980, 14% - between 1981 and 1990, 7% - between 1990 and 1999, 6% - after 2000. All these buildings should be made energy efficient by insulating them.

Thermal insulation aims to restrict the flow of heat, thus reducing energy consumption for heating or cooling. Heat flow is determined by the temperature differences between the inside and outside of the house. In winter, the heat in the house tends to go out, and in summer it tends to go in. Now, in order to continue to have a comfortable environment in the home, we supplement the drop or rise in temperature with energy consumption. It is proven that the greatest heat loss - up to 70% - occurs through the exterior walls and roof. Sensitive areas include windows, doors and floors, but for a significant reduction in heating and cooling costs, attention should be focused on the biggest heat 'losers', i.e. the external walls and roof.

There is thermal insulation solutions for all types of houses, whether concrete, brick, timber, log, prefabricated walls, steel or mixed. Viable solutions have been found for old houses, even those with carved exteriors. From studies done in Germany on renovated and thermally insulated old houses resulted in energy costs being reduced by at least 65%, and in many cases by more than 90%.

Energy efficiency of wooden houses

The whole energy-efficient homes "craze" started after the 1973 oil crisis. Governments were so frightened by the prospect of running out of heating that they pushed for the introduction of energy efficiency calculations into home design. This evolved into European Community directives requiring houses to be built to operate with near-zero energy consumption, with some of the energy needed being produced by the houses themselves.

Building an energy-efficient house involves several aspects, and thermal insulation is not enough. The house must provide green energy sources with solar panels, have windows with 3 rows of glass so that heat exchange is very low, provide indoor air circulation with heat recovery and reuse. Wooden houses are the most thermally efficient because wood by its nature is an insulating material. They are also very well insulated due to their construction.

Types of wooden houses

Houses on wooden structure. They involve building a structure on site from wooden posts, frames and beams and forming the walls between the structural elements using OSB and insulation materials. Even if no insulation was put in (which is usually not the case), and the walls were just sealed on either side with OSB or drywall, the layer of air inside would act as a thermal insulator.

Houses made of prefabricated structures are made in the factory and only assembled on site. The walls are made of several layers of different materials that ensure very good energy efficiency. The processing is done with high-performance machinery so that the walls are joined on site easily and without loss, and the pieces fit together perfectly. In addition to very good energy efficiency, this type of house has the advantage of a short construction time and a clean construction site.

Round wooden houses or square. The walls of these houses result from the successive stacking of wooden beams or logs. Basically the whole wall is made of wood - a very good thermal insulator. The processing or construction solutions are chosen so that the joints are well made and the wall does not 'split' if the wood dries out. Insulation material (mineral wool, wool, polyurethane foam) is placed between the logs and the beams to increase the efficiency of the insulation. The houses are warm in winter and cool in summer, ensuring the comfort of those inside.

Houses in CLT panels. The thickness of CLT allows it to be used as a structural element with outstanding strength and stiffness properties. The structure of the house consists of CLT panels which are used for walls and floors. CLT - industrialised wood - has significant advantages in terms of fire resistance, energy efficiency, acoustic performance or stability over time.

The Passive House concept

Passive house is a concept that, although older, has become very relevant nowadays as people have become aware of the environmental and economic impact of energy consumption for home comfort. It all started with Wolfgang Feist, a German physicist, who built the first passive house. Find the full story here. Passive house design aims to reduce energy consumption and use renewable energy so that the house is independent of utility companies.

In general, this type of housing combines building systems and materials that work to our advantage to achieve pleasant and healthy conditions in the home. To make such a house you need to understand how it works. It's about using architectural strategies and natural products to achieve indoor comfort with minimal energy requirements that are covered by clean, cheap renewable energy. Architectural strategies are simple ideas, such as facing windows to the south or covering a terrace to protect it from the summer sun, but with an impact on energy consumption. In other words, resources such as natural light, solar energy, rainwater or natural ventilation are used as much as possible to achieve maximum year-round comfort. The materials used are important not only to achieve energy efficiency in the home but also in terms of carbon footprint. Wood is preferred, not only for its excellent insulating qualities, but also because it is natural, biodegradable and recyclable.

The passive house is very well insulated and has such high-performance windows that it no longer needs a traditional heating system. Heat losses are so low that heating and cooling energy savings of up to 90% are achieved compared to traditional houses and over 75% compared to new builds. The energy source inside the building is the body heat of the inhabitants or solar heat entering the building. A mechanical ventilation system constantly introduces fresh air filtered of dust and pollutants for superior air quality. A highly efficient heat recovery unit allows the heat contained in the exhaust air to be reused.

Passive house standard

In order to be certified as a passive house, a building must comply with several principles and meet certain performance criteria set by Passivhaus Institute from Germany. The principles are:

• Continuous thermal insulation made with quality materials of the required thickness;
• high-performance windows and doors;
• solar gain in winter. The house is positioned in relation to the sun, large windows are fitted on the south facades and on the north facades the number of windows is kept to a minimum;
• mechanised ventilation system with heat and humidity recovery.

The performance criteria are based on annual energy consumption:

• heat load for heating max.10W/m²;
• heat requirement for heating max 15 kWh/m²/year;
• space cooling requirements max 15 kWh/m²/year;
• maximum 42 kWh/m² total annual energy requirement.
• high air tightness n50 ≤ 0.6 shifts per hour.

The certification system is based on auditing buildings for thermal insulation performance, heat loss control, indoor air quality, solar energy use. The certificate certifies that the dwelling has very low energy consumption - close to 0 - for heating and cooling compared to a conventional dwelling. There are Passivhaus Institute accredited companies in Romania that can design and accredit a passive house. There are also courses for all builders and architects interested in this type of construction.

We all want to pay the lowest possible energy bills. We all want to live in homes that are warm in winter and cool in summer. Soon this desire will become an obligation. We need to understand the European Commission's approach as beneficial both for us and for our big home - the Earth. And that is why we need to think as seriously as possible about the energy efficiency of our homes and try to improve it.