More often than not, the type of roof construction for apartment buildings is chosen without any discussions and the traditional construction of a flat roof is used. This is convenient if you do not think about the diversity and have no desire to improve the architectural style of the building. The company YIT LATVIJA, which is known as one of the largest builders of new, modern apartment buildings and contributors to the modern housing stock, prefers to think broader and implement fresher constructive solutions for buildings. For the new project on Anninmuiza Boulevard, it was decided not to choose the traditional flat roof but to implement a more attractive and functional solution and build a quadrilateral roof using timber trusses that were industrially manufactured by Freimans Timber Constructions.
Igors Vojevodins, the project manager of the company YIT, who was responsible for the implementation of the apartment building project on Anninmuiza Boulevard, shared his experience. Each YIT new apartment project is unique and different from the others, yet simultaneously it keeps the architectural qualities, style and mood of the neighborhood. With the construction of each new building, various technical solutions are improved to comply with laws and regulations, which are supplemented and changed rather rapidly and dynamically, affecting the entire construction industry.
Innovation will become a tradition
So far timber truss roof construction for apartment buildings has not been a traditional solution, however, one must admit that in the nearest future it will be used more and more often, replacing the simple construction of flat roofs. It must be noted that at the initial project stage of designing Anninmuiza boulevard, quadrilateral roofs were prevalent for the buildings.
Roof fire safety – solutions provided by Freimans Timber Constructions
Wood is an excellent material for the implementation in various solutions. The majority of manufacturers do not have enough competence to produce primary timber truss constructions in accordance with the high fire safety requirements set for apartment buildings though. As to this project, timber trusses were required to meet the fire resistance class R15, which means to maintain the designed load-bearing capacity in the event of a fire and not to change the geometry of the structure for 15 minutes. For many manufacturers, this requirement turned out to be a stumbling block because there were no finished standard products in the range supplied by manufacturers. Another, new solution had to be invented. Some manufacturers offered an option where the timber truss cross-section had to be increased significantly, still others made careless offers that had not been worked out enough, even ignoring the R15 fire resistance class.
Freimans Timber Constructions was the one and only supplier to take the problem seriously and develop a product that strictly meets fire safety requirements. The competent specialists of the company created their own vision of a product that is able to ensure compliance with legal requirements and does not need additional work on site. Another very important fact is that many manufacturers of timber trusses wanted the builder to bear the responsibility for the fire safety forcing them to organize compliance with fire safety requirements, covering the timber trusses with plaster coating, which is a time-consuming and quite expensive process.
R15 – technical requirements for timber trusses
In order to address the fire safety requirements and make it possible to use the roof trusses manufactured by Freimans Timber Constructions for the construction of a quadrilateral roof for apartment buildings, the weakest link to solve was the connection joints with metal parts. It is widely known that metal loses its resistance faster than wood under the influence of fire heat. To protect the metal connector plates, they were covered with 15 mm thick plywood, thus obtaining the resistance of the structure to fire required by the legislation. Now the structure guarantees durability for a period of 15 minutes under the influence of increased heat.
As to timber trusses as it has been noted by Freimans Timber Constructions designer Gatis Locans, the cross-sectional dimensions were boosted by applying a thicker material in order to increase the load-bearing capacity, calculating such dimensions that would strictly meet fire safety requirements.
Noteworthy is the fact that Freimans Timber Constructions is open to innovation and implementation of complex solutions. Each project is aimed to find the most efficient technology to balance the requirements and the costs. There are many concrete and metal structure designers in Latvia, but only few wooden structure designers, and not everyone of them is competent. We wish each customer to find their own designer who develops a unique and high-quality solution within the set the budget.
Time frame and quality
YIT Company has implemented thoughtful planning in its daily routine so that subcontractors and suppliers have time to prepare and develop a solution and then produce the final product. For Igor Vojevodin, this was his first experience with the installation of timber truss structures that are meant for an apartment building. The tender for the supply of timber roof trusses was announced in a timely manner and upon its completion, Freimans Timber Constructions was chosen as the supplier.
The harmonization of technical parameters took about a month, after which the manufacturing of the finished product took a bit less than two months. The assembly was performed extremely quickly, installing timber trusses for apartment buildings on Anninmuiza Boulevard within only two days. 26 timber trusses were installed for each apartment building, a total of 3 buildings were built, the fourth is still under construction. The timber trusses were delivered to the site by specialized cargo transport, but the assembly was performed using a crane.
Advantages of timber trusses
The buildings were made of silicate blocks using prefabricated reinforced concrete floors. The height of the roof timber truss in the middle reached 2.3 m, creating a small cold attic space, the truss span was more than 16 meters, and the trusses were based on only two points of the load-bearing walls, no structural supports in the middle were necessary. The timber trusses were covered with battens. For this purpose 32 mm thick boards, covered with steam insulation film were used. Profiled tin was used for the roof covering.
If a gable or quadrilateral roof is built for an apartment building, then the advantage compared to flat roofs is that it is possible to inspect the attic at any time and eliminate any problems in the operation of the roof in good time. For flat roofs, the detection of defects is much more complicated, which in turn leads to delaying of their elimination, and this can cause damage to the lower structural layers.
Assembly and experience
“In order to install large-sized roof timber trusses for apartment buildings qualitatively and safely, the experience of the workers is a crucial fact,” says Edgars Apinis, a foreman of Hoproof, who enriched his personal experience while working in Latvia, the USA and Norway. This broad geography allowed him getting to know different cultures and processes of work thus accumulating the most useful and valuable from each. Edgars Apinis and his team have installed timber trusses for apartment buildings manufactured by Freimans Timber Constructions in more than 10 structures so far. The process is successful, because they have relevant experience to work with such constructions. The trusses are delivered onto the roof by crane, which means that two specialists with knowledge of the correct fastening of the trusses to the crane cables must be engaged into the process. No mistakes are acceptable, as the cost can be high – slack fastening during lifting can do damage or result in loss of a truss.
Three or four workers with permission to work at height are supposed to work on the roof, so all safety requirements must be met. Specialists must be qualified to fasten trusses to the load-bearing structures of the building, perform the work in a certain order, and must be able to read the designer’s blueprints. Prompt and consistent communication between timber truss designers, manufacturers and assemblers is very important. That is the key to success. Edgars Apinis points out that having worked with Freimans Timber Constructions for a long time; he realized that it is the good level of communication that allows finding quick solutions in various situations during the truss assembly. Designers respond without hindrance, so there is no delay in work execution time. He admits that working with other manufacturers of timber trusses, it may turn out that it takes a whole day to solve a minor issue. Only observation of all the obvious and invisible technical nuances guarantees a good result.