Multi-storey buildings made of aerated concrete

YTONG aerated concrete is intensively used especially in the construction of residential and civil buildings, thanks to its very good physical properties. This mainly includes positive thermal insulation capabilities, adequate heat accumulation, and resulting thermal inertia in both summer and winter, as well as health safety and suitable diffusion moisture properties.

While the design of aerated concrete is common practice for typical low-rise buildings, it requires more consideration of statics and the use of different classes of aerated concrete in multi-storey buildings. The following examples of the application of aerated concrete in multi-storey residential or administrative buildings clearly demonstrate the various ways of using YTONG blocks and their main advantages. Nevertheless, it is always an economically efficient solution and ensures the safe achievement of the relevant regulatory requirements.

LIGHTWEIGHT FILLING WALLS

The most widespread example of using aerated concrete is in monolithic skeleton buildings. The combination of low weight, simple masonry technology, and very good thermal insulation properties makes YTONG blocks an optimal material for filling and external walls of these buildings. This material has similar thermal accumulation and acoustic parameters as traditional masonry elements, but with significantly lower weight. Therefore, it introduces much lower loads into the skeleton. From a static perspective, it is thus possible to design walls and partitions more freely throughout the layout of the individual floors. The load-bearing system can be dimensioned for smaller stresses. The result is often significant savings in reinforced concrete in the load-bearing skeleton. Another advantage is the easy bonding of blocks with thin-layer mortar and the simple cutting of aerated concrete. This guarantees precise masonry with minimal waste, without thermal bridges, and without cumbersome forces, mixers, or demanding hauling of mortar. The mortar consumption compared to other masonry is minimal; moreover, the dry YTONG mixture is prepared directly on the construction site using an ordinary drill. To meet the norm's requirements for the thermal resistance of external walls, walls made of 30 cm thick YTONG external blocks are sufficient. However, due to the need for external thermal insulation of facades because of thermal bridges in the form of reinforced concrete ceilings, blocks of thickness 20 or 25 cm are usually used. When applying contact facade insulation, insulation thicknesses over 8 cm are suitable. A similar external shell achieves low energy building parameters with a total thickness of around 30 cm. Compared to fired masonry, YTONG needs smaller insulation thicknesses, thus saving valuable built-up space. For acoustic and inter-apartment walls, P6 - 700 blocks with a thickness of 375 mm can be used. However, due to the lower built-up area, it is more suitable to use Silka aerated acoustic blocks (thickness 24 cm) from the same manufacturer, Xella CZ.


A skeleton with YTONG filling walls (residential buildings in Olomouc and Uherské Hradiště)

Residential building in Kunovice (masonry system from aerated concrete)

WALL SYSTEM

Aerated concrete is less commonly used for traditional wall structures of multi-storey buildings. However, the YTONG system can bring significant advantages to both the investor and the implementing company in these buildings.

Load-bearing and acoustic walls YTONG
In this case, their use can be documented by the example of an apartment building in Kunovice near Uherský Brod. It is a five-storey apartment building designed by architect Radek Janska in a transverse wall system. All underground structures are made of prefabricated reinforced concrete. All above-ground structures are already made from YTONG blocks. In the two lowest floors, load-bearing walls made of P6-700 blocks with a compressive strength of 6.5 MPa are used. The remaining two residential floors are made from P4-500 blocks with a compressive strength of 4 MPa. The building thus also utilized load-bearing stressed walls made of YTONG blocks in higher strength classes P4 and P6, only some extremely stressed areas were addressed by the statics with piers made of lime-sand blocks. The internal apartment partitions and inter-apartment walls are also made of YTONG aerated concrete. Although, from a physical property perspective, it would be ideal to use a different type of aerated concrete for external walls, only one type of product with the same strength class was applied on each entire floor to prevent any undesirable material confusion. The project author did not hesitate a moment in choosing this system. “Long-term experiences with various masonry systems directly on the site clearly speak in favor of YTONG as the material least prone to masonry errors. The main criteria for the choice were high work productivity, speed, and accuracy of masonry,” states Radek Janska and adds: “Among designers, there is often a rooted idea that an aerated concrete wall will not meet the requirements for sound insulation of walls separating adjacent apartments. Yet walls with a thickness of 375 mm made of aerated concrete of classes P6-700 and P4-500 with a double-layer core plaster meet the standards."

YTONG and Silka blocks
Another example of a wall system in a multi-storey building is the combination of lime-sand Silka blocks for load-bearing and acoustic walls and external walls made of insulating YTONG blocks. Compared to buildings made from ceramic blocks, there are significant financial savings while achieving better parameters. A similar approach was implemented, for example, in a five-storey apartment building in Znojmo. The project initially considered the use of fired materials, but upon detailed financial analysis, the masonry system was changed. Ladislav Švach from the construction company Jelínek notes: “The newly used solution reduced the volume of mortar to approximately 1/6 (joint width 2 mm instead of 12 mm). Even with the higher price of adhesives, this meant significant savings already in the overall price for the materials consumed. The savings in terms of hundreds of thousands were also brought by the new solution concerning the labor, transportation, and handling of mortar on site. Significantly higher accuracy of masonry also resulted in considerable savings in the consumption of internal plasters and adhesives for the insulation system in the project. The total savings achieved at the residential building in Znojmo by using the aforementioned materials amount to around one million crowns, representing nearly 10% of the gross construction budget. Moreover, the investor did not achieve these savings at the expense of the parameters of the completed apartments; rather the opposite. A pleasant bonus was also the gain of several square meters of living space, which the developer successfully sold to satisfied clients.”

SUSPENDED FACADE WALLS

A technically quite unique construction solution is demonstrated by the Vienna Point administrative building in Brno. Its basis is made of aerated concrete wall panels suspended on a supporting steel skeleton. The project authors were offered a standard contemporary solution, which is the suspension of some lightweight aluminum facade systems commonly used for administrative buildings with a dominant share of glass facade areas. Instead, they ultimately applied a so far unique method of suspended wall structure in the Czech Republic. They hung precise reinforced YTONG panels with a thickness of 200 mm and a length of 6 meters on the supporting system of each floor. A series of horizontal panels 600 mm in height at the ceiling level of each of the five above-ground floors supports the remainder of the facade of the entire floor, including the podium and window pillars made of YTONG blocks of the same thickness, additional mineral insulation, and a final finish of polished granite. The panels have good thermal insulation parameters (lambda = 0.13 W/mK), so this load-bearing element also contributes to the thermal insulation of the facade. After additional insulation with just 12 cm of mineral insulation, the external shell achieves values recommended for the category of low-energy buildings. Given the large western and eastern facade, there would have been a high risk of overheating in the summer sunny days with the fully glazed area. Its wall structure, however, saves a significant amount of energy needed for summer cooling. The composition of the facade, along with tight windows, also exhibits above-standard acoustic parameters of the external shell, which are particularly important for the western side of the building, adjacent to the busy Vídeňská street. The project author, architect Tomáš Zlámal, assesses the solution as follows: “The appearance and properties of the facade emphasize the high standard of the entire building. I can also responsibly state that by using the system with YTONG panels we managed to save costs in the range of tens of millions of crowns compared to commonly used facade systems.”


Residential building in Znojmo (masonry system from aerated concrete)

Vienna Point in Brno (facade panels Hebel)

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