Germany’s first BIM settlement

The development currently under construction on the eastern outskirts of Borna, Germany, is probably the largest of its kind south of Leipzig. Construction on the 76,000-square-meter site is scheduled to commence before the end of the year. The official ground-breaking ceremony took place in mid-June. If everything goes according to plan, the first residents will be able to move in in spring 2020.

A flexible development plan offers the owners a great deal of leeway in the design of their future homes. Within the limits of the applicable building laws, owners are free to build single family houses, terraced houses, semi-detached houses or bungalows on the individual plots (130 building plots with sizes between 400 and 600 square meters). One of the specifications is an energy standard which optionally lies between the EnEV standard and KfW 55. The houses are heated by environmentally friendly heat pumps using energy from the outside air. All buildings will be prepared for subsequent installation of a PV system. The connection for an e-charging station is integrated into all houses. Additional comfort is provided by high-speed internet and a power grid designed for electromobility.

The exterior and interior walls of the houses will be built with autoclaved aerated concrete using solid construction methods. Construction is complemented by solid Ytong roof and ceiling panels. The homogeneous, solid construction method offers important advantages in terms of building biology and building physics and thus adds to the value of the property. The environmentally friendly building material, which is manufactured on the basis of natural raw materials, guarantees reliable noise protection and, thanks to its fine-pored structure, has very good thermal insulation properties. Wall structures measuring as little as 36.5 cm in thickness and built monolithically (i.e. without a composite thermal insulation system) using Ytong AAC even meet the KfW 55 standard. Thanks to its good thermal insulation properties, Ytong prevents undesirable temperature fluctuations and thus ensures a healthy, constant room climate throughout the year. Being a purely mineral building material, AAC corresponds to the highest building material class A1 according to DIN 4102 Part 4 and is non-combustible.

Digital Home Configurator

The concept is particularly aimed at young families. “This will obviously also be reflected in the price,” says project manager Silvio Weise, promising that “prices will be reasonable. There will be no high- priced construction such as in some of Leipzig’s new development areas.” Cost transparency is ensured by the Digital Home Configurator “Mr + Mrs Home”, which was developed by Pure Applikationen with the participation of Baywa and allows the owners to compose their own homes. They first select their desired plot on the site on which they can then plan their dream house. The configurator contains architectural plans and building regulations such as distance limits for the respective plots, so that homeowners can only plan what can actually be structurally implemented. Different models are available to suit every taste, e.g. a settlement house with a saddle roof, a town house or a Bauhaus-style cube. Clients can also choose between different styles, e.g. ‘modern’, ‘Scandinavian’ or ‘urban’. With- in a given framework – the building concept remains the same so that no static changes occur – the individual models can be personalized. It is possible, for instance, to change the external appearance, e.g. by changing the length or width of the house, by choosing a colored roof or by opting for floor-to-ceiling or corner windows. The floor plans can also be varied within the given static possibilities, e.g. by selecting an additional toilet or another shower. The Configurator then graphically displays the selection made in a 3D model, so that homeowners get an excellent idea of all the variants chosen.

What is special about the concept, however, is that the price is adjusted as soon as the model is changed, allowing clients to always keep an eye on the costs. The configurator shows the end price, which also includes the – usually quite considerable – additional building costs. This full cost transparency gives homeowners absolute certainty for budget-compliant planning without unpleasant surprises.

Multi-stage planning process

The Digital Home Configurator was not only used by homeowners to plan their dream house in accordance with their available budgets but was also a prerequisite for the multi-stage 3D-based planning and production process carried out in close cooperation between building materials manufacturer Xella, Florack Bauunternehmung GmbH and BayWa AG. “The customer gave us a building model of the basic type,” explains Dipl.-Ing. Andreas Radischewski, Digital Building Solutions and Transformation Manager (BIM) at Xella. “This serves as the starting point for all further planning.” In a first model check, the geometric, material-specific and non-geometric information for a building project is combined in a digital, three-dimensional building model based on BIM (Building Information Modeling). “This helps to identify optimization possibilities for a fast and smooth construction process,” Andreas Radischewski explains. “In the end, we can give the customer a recommendation for the best and most economical materials solution.”

In the present case, according to Radischewski, it quickly became clear that only a large-format solution could be considered given the sheer size of the building area and the tight construction schedule – after all, the first residents will move in as early as 2020. Three options were available: the large-format Silka XL construction system made of calcium silicate bricks, Ytong Jumbo double blocks with which 1.20 meters of masonry can be erected at layer heights of 499 mm or 624 mm with one crane lift, or Ytong System Wall Elements (SWE). The decision was finally made in favor of the large-format, solid AAC system known for its short construction times. It allows the time and effort to be reduced considerably without compromising the quality of the building shell.

Advantages of serial construction

The strengths of Ytong system wall elements are particularly evident in the serial construction of single and two-family homes. According to the manufacturer, the floor-to-ceiling format and the resulting rapid processing of the Ytong system wall elements allow the construction time to be cut to 10 minutes per square meter. Only two fitters and one crane operator are needed. And given that the price of a new building is determined not only by the cost of materials but that the working time is also an important cost factor, rapid construction progress means less working time and hence lower construction costs. This effect fully came to bear in the “Wohnen am Lerchenberg” development. “Depending on the size of the house, it is possible to complete a shell in between two-and-a-half and four days,” says Andreas Radischewski. “Experience shows that the workers get faster with every house.” The economical effect of the construction system is even more evident when it is combined with Ytong partition wall elements for non-load-bearing interior walls. By plan- ning in a grid of 7.5 cm, any floor plan can be realized without any problem whatsoever.

Project-specific production

Now that it has been decided that the houses in the Lerchenberg development will be built with large-format system wall elements, the wall plans of the basic model will be optimized for SWE implementation, taking into account all dependent details. Besides the technical properties of individual components, it is also possible to precisely define quantities, costs and processing times. “Using standard elements is the most economical solution, as it means that no cutting-to-size will be necessary on site;” emphasizes Andreas Radischewski. Any special elements that may still be required will be prefabricated at the factory.

After completion of these planning and optimization phases, project-specific walls will be available. The wall material will then be individually produced at the Xella factory and delivered to the construction site on a just-in-time basis. Processing will take place in accordance with the installation plan.

Conclusion

In a new development area for 130 single-family homes in Saxony, homeowners can plan their dream house using a Digital Home Configurator. The transfer to a three-dimensional BIM-based model and the use of large-format Ytong system wall elements (SWE) produced specifically for the project help optimize the entire construction process. The advantages for the contractor are fast assembly and short drying times. As no cutting-to-size is necessary, material is saved and waste is minimized. Due to the high thermal insulation of the building material, no material and labor costs are incurred for installation of an exterior insulation and finish system. What is more, the super-smooth surfaces form an excellent plaster base so that they can easily be filled with just a small amount of a thin-bed mortar. Homeowners benefit from a precise overview of the construction costs and can easily determine the maximum they are willing to spend. Compared to conventionally planned and realized projects, construction costs are lower as the standardization and optimization of the entire planning and construction process results in high cost efficiency.

Xella Deutschland GmbH Düsseldorfer Landstraße 395 47259 Duisburg, Germany www.xella.com