YTONG LAMBDA pro

The topic of low-energy buildings has been "in vogue" in our country for several years, however, actual construction still significantly lags behind the frequency of professional discussions and articles on this subject. While ecological houses made from straw and several quality passive houses, "ordinary" low-energy and energy-saving houses already stand, they are still as rare as hen's teeth. The average new building in our country is still far from the standard of energy-efficient houses, let alone low-energy houses. On a mass scale, only the information that houses need to be insulated has so far been instilled.

Let's try not insulating for a while

The actual return on the insulation of new exterior walls is rather in the dozens of years than in single years. In the budget of a three to four million CZK family house, an extra 150,000 CZK (about 200 m² of facade at 700 CZK/m²) is not such a big item, but you would have to save at least 10,000 CZK annually on heating for this investment to pay back within fifteen years. Furthermore, if the user in the insulated house with tight windows monitors humidity and ventilates properly, the achieved energy savings will not be substantial. If there is no ventilation, savings will come at the expense of the quality and hygiene of the indoor environment. Currently, the insulation of facades is more of a "just in case" solution aimed at eliminating thermal bridges in poor-quality or poorly executed exterior walls of conventional new buildings, rather than a systematic solution for low-energy buildings. I certainly do not want to claim that insulation is pointless. I just want to point out the interesting fact that common low-energy buildings with an annual heat consumption of around 50 KWh/m² can manage without relatively expensive and labor-intensive insulation. For those 150,000 CZK, you can also acquire a fairly sophisticated controlled ventilation system with heat recovery for an ordinary family house, which can save a similar amount of energy as the mentioned facade insulation. Moreover, with a simultaneous improvement of the building's microclimate, so the house's investor will feel the benefits of this solution immediately after moving in and not after 15 years. Without increasing the insulating capabilities of the outer shell, however, such measures will logically not lead to low-energy buildings. In combination with additional insulation of the building, the increased investment is already doubled (about 10% of the construction budget) and achieves even worse return (even 50% energy savings for heating cannot realistically exceed 20,000 CZK per year for an ordinary family house).

Family House Bungalow - YTONG LAMBDA 500 mm

Family House Bungalow - According to the Standard

A certain solution in this regard is represented by the aerated concrete precise masonry system. The easy cutting and processing of aerated concrete lead to the fact that even more complex shapes and wall structures are built from a homogeneous thermal insulating material, not from a heterogeneous mixture of mortar and bricks as in other systems. In an aerated concrete wall, there is also no significant "weakening" of insulation capability by thermal bridges at the joints of individual elements. The reason is the high precision of individual blocks and the precise gluing on thin-layer mortar, enhanced by the large dimensions of lightweight aerated concrete elements. Uniform properties of aerated concrete in all directions also help successfully resolve most key details and potential thermal bridges (window reveals, foundation of the masonry, plinth, attic walls, etc.) without additional complex modifications. Any internal wiring in the external walls minimally weakens the wall again thanks to the easy processability of the material and does not create thermal bridges like in some fragile or hollow masonry elements. Even the average mason can, therefore, build from aerated concrete on a real site without special tools and various shapes walls with thermal insulation parameters truly comparable to the values declared by the manufacturer.

YTONG LAMBDA

These values are also significantly improved by this year's novelty in Xella's range - YTONG LAMBDA, intended specifically for low-energy single-layer buildings. It is a new class of white aerated concrete P2-350, which has already been successfully applied in some European markets. The exterior insulating blocks retain most key parameters such as precise fast masonry, guaranteed compressive strength of at least 2 MPa (the same as the existing material P2-400), non-combustibility, and high fire resistance, comparable acoustic parameters, and the ability to naturally regulate the humidity microclimate in the interior of the building. The novelty is the reduced bulk density of the material from 400 to 350 kg/m³ while maintaining the same load-bearing capacity of the masonry. As a result, walls made from YTONG LAMBDA blocks achieve unique insulation capabilities (λ = 0.085 W/mK), which are closer to the parameters of thermal insulations than the properties of load-bearing masonry elements. With a thickness of 375 mm, the exterior walls from YTONG LAMBDA blocks without plaster achieve a heat transfer coefficient U = 0.23 W/m²K, which even exceeds the values recommended in the standard ČSN 730 540 for low-energy buildings (U = 0.25 W/m²K). At a thickness of 50 cm (made only on order), the walls even exceed the recommended values by about 30%, and are thus suitable for the implementation of the most economical buildings without additional insulation. With implementation at conventional prices, with the certainty of achieving the declared parameters by conventional craftsmen, and in unbeatable time. Unlike other masonry constructions, these are not hypothetical values achievable only at the cost of increased labor intensity or more complex logistics on site as in the case of systems with a high number of different shapes and masonry elements. In combination with comparable constructions for other exterior parts of the building and with the previously mentioned controlled air exchange, YTONG LAMBDA allows achieving truly quality low-energy and energy-efficient houses on a mass scale. Its use in conventional buildings without comprehensive low-energy solutions will yield the same results as additional facade insulation. However, logically with significantly lower overall costs, which will not exceed investments in ordinary single-layer walls. Energy savings for specific buildings For a specific illustration of energy savings when using YTONG LAMBDA exterior walls, I calculated annual energy losses due to heat transfer through the exterior walls for two very different houses (Tab. 2). The table does not take into account losses from infiltration and ventilation or heat gains of the buildings. The first example is one of the first domestic implementations from YTONG LAMBDA blocks (wall 500 mm) in a low-energy standard (Uwindows = 0.95; Uroof = 0.13–0.16; Ufloor = 0.22 W/mK) - a single-storey family house bungalow in Černá Hora (Fig. 1). The second is a low-energy family house (Passive House - real load-bearing walls made from aerated concrete blocks with a contact and partially ventilated insulation system with a thickness of 20 cm, Fig. 2) with significant passive solar elements. From Table 2 and the attached graphs, it is evident that heat losses through the exterior walls do not account for more than 50% of total losses even in standard (code-compliant) buildings. When using YTONG LAMBDA insulating blocks, a realistic reduction down to one-fifth of total heat loss through walls is possible. The graphs show that even this reduction manifests itself in the annual balance as a significant saving of consumed energy. The price difference between a quality single-layer wall made of aerated concrete and a multi-layer insulated construction can be used for further loss reduction, for example, at the windows, for systematic elimination of thermal bridges, or for the previously mentioned reduction of losses through ventilation with the help of heat recovery. Particularly when combined with controlled heat ventilation, such a solution becomes investment-wise comparable with a conventional insulated house. It brings benefits not only in terms of the home's energy balance but also in the quality of the building's microclimate.

Fig. 1: Family House Bungalow

Fig. 2: Low-energy Family House Passive

Table 1:
Total energy savings

Table 2:
Losses through exterior walls of two specific buildings at different wall parameters