What Is Brettstapel in Construction?
What Is Brettstapel in Construction?
Brettstapel is a green construction system made exclusively from softwood timber posts connected with hardwood timber dowels.
It employs a simple method wherein low-grade timber that would otherwise not be suitable for construction is utilized to form strong load-bearing solid wall, floor, and roof panels.
The hardwood dowels used in the system have a lower moisture content than the softwood posts, allowing them to expand over time and lock the posts together to create an effective structural load-bearing system.
Brettstapel foregoes the need for glues and nails, resulting in healthier indoor air quality while avoiding harmful toxins in other materials. Moreover, it locks up vast amounts of carbon dioxide, thus benefitting both users and the environment.
What Is The History Of Brettstapel?
Brettstapel was invented by German engineer Julius Natterer in the 1970s and is now commonly used across Austria, Switzerland, Germany, and increasingly in the UK.
Originally made up of low-grade timber posts continuously nailed together to form strong panels suitable for supporting mines and railways, in 1999, a German company developed a doweled system using varying moisture content to create solid structural panels before the glue was introduced for further strength.
In 2001 diagonal dowels replaced perpendicular ones to allow longer spans without separation issues.
Nowadays, most companies use this diagonal or perpendicular dowel system with no glue. In contrast, only one uses timber dowels-based CLT (cross-laminated timber made from rotating layers of boards).
Brettstapel is an advanced prefabrication technique that allows buildings to be erected in a matter of days with minimal on-site labour costs. Panels up to 12–15 metres in length can be produced and trusses made to span wider distances.
The tallest building so far achieved using Brettstapel is the E3 building in Germany at seven storeys tall, while four-storey buildings have also been built solely using this system.
Fire regulations currently limit timber building heights but these are being challenged and improved by large-scale timber systems as taller examples become realized.
Brettstapel is a type of prefabricated construction system which has a number of benefits over traditional timber frame construction. These benefits include:
- A lower energy demand, shorter and less labour-intensive construction period, and reduced lifecycle costs. The material cost of Brettstapel is approximately 20% higher than that of an equivalent area of timber frame construction; this cost is offset by the savings in other areas.
- Specifying untreated, exposed Brettstapel without glue and nails contributes to a healthy indoor environment free from potentially harmful compounds found in materials used in other systems. The hygroscopic nature of the panels further helps to create an excellent internal atmosphere.
- Brettstapel has many benefits environmentally and practically; it sequesters significantly more carbon dioxide than timber frame buildings, reducing our global footprint even further.
- It also has excellent thermal properties, with low U-values, airtight construction and high thermal mass reducing energy demands by up to 90%.
- It is prefabricated offsite and can be erected quickly with practical and economic advantages for the British construction industry despite the poor climate.
Brettstapel is a unique form of timber construction where posts and dowels are used to create load-bearing structures. Low-grade wood, like spruce or fir, is used for the posts, while beech is preferred for the dowels.
This approach of constructing with low-grade wood helps the optimum use of a renewable resource like timber and ensures that natural defects such as knots remain out of adjacent posts.
Moreover, this type of manufacture is particularly suitable for countries like the UK and Scotland which have an abundance of fast-growing timber resources.
Thus, Brettstapel manufacture is economical to build solid and efficient structures with quality materials and minimal wastage.