Brettstapel
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Brettstapel, also known as dowellam, is a massive
timber Lumber is wood that has been processed into uniform and useful sizes (dimensional lumber), including beams and planks or boards. Lumber is mainly used for construction framing, as well as finishing (floors, wall panels, window frames). ...
construction Construction are processes involved in delivering buildings, infrastructure, industrial facilities, and associated activities through to the end of their life. It typically starts with planning, financing, and design that continues until the a ...
system, fabricated exclusively from
softwood Scots pine, a typical and well-known softwood Softwood is wood from gymnosperm trees such as conifers. The term is opposed to hardwood, which is the wood from angiosperm trees. The main differences between hardwoods and softwoods is that the sof ...
timber posts connected with
hardwood Hardwood is wood from Flowering plant, angiosperm trees. These are usually found in broad-leaved temperate and tropical forests. In temperate and boreal ecosystem, boreal latitudes they are mostly deciduous, but in tropics and subtropics mostl ...
timber
dowel The dowel is a cylindrical shape made of wood, plastic, or metal. In its original manufactured form, a dowel is long and called a ''dowel rod'', which are often cut into shorter ''dowel pins''. Dowels are commonly used as structural reinforceme ...
s. It is a relatively simple method of construction that exploits low grade timber, not normally suitable for use in construction, to form load bearing solid timber wall, floor and roof panels. Brettstapel works by using hardwood dowels with a
moisture content Water content or moisture content is the quantity of water contained in a material, such as soil (called ''soil moisture''), rock, ceramics, crops, or wood. Water content is used in a wide range of scientific and technical areas, and is expressed ...
lower than that of softwood posts. Over time the dowels expand to achieve moisture equilibrium thus 'locking' the posts together and creating a structural load-bearing system. It is one of a few construction methods that can be entirely fabricated from timber. Although some variations do still use
glue Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. The use of adhesives offers certain advantage ...
and
nail Nail or Nails may refer to: In biology * Nail (anatomy), toughened protective protein-keratin (known as alpha-keratin, also found in hair) at the end of an animal or human digit, such as fingernail * Nail (beak), a plate of hard horny tissue a ...
s, these are not necessary and avoiding these means a healthier
indoor air quality Indoor air quality (IAQ) is the air quality within buildings and Nonbuilding structure, structures. Poor indoor air quality due to indoor air pollution is known to affect the health, comfort, and well-being of building occupants. It has also be ...
can be achieved. The timber itself locks in vast amounts of
carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
without emitting harmful
toxin A toxin is a naturally occurring poison produced by metabolic activities of living cells or organisms. They occur especially as proteins, often conjugated. The term was first used by organic chemist Ludwig Brieger (1849–1919), derived ...
s found in other materials, benefiting both the user and the environment.


History

Brettstapel was invented in the 1970s by the German engineer
Julius Natterer Julius Natterer, (December 5, 1938 – October 25, 2021), was a German engineer and professor of wood construction at the Swiss Federal Institute of Technology in Lausanne. Career Julius Natterer studied at the Technical University of Munic ...
. It is now commonly used across
Austria Austria, formally the Republic of Austria, is a landlocked country in Central Europe, lying in the Eastern Alps. It is a federation of nine Federal states of Austria, states, of which the capital Vienna is the List of largest cities in Aust ...
,
Switzerland Switzerland, officially the Swiss Confederation, is a landlocked country located in west-central Europe. It is bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. Switzerland ...
and
Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...
, whilst slowly emerging in the UK. Originally it consisted of low grade timber posts continuously nailed together to form panels strong enough to support mines and railways. In 1999 a German company developed a doweled system which relied on the varying moisture content to form solid structural panels however many companies introduced glue to the system to strengthen it. In 2001, a new variant of Brettstapel was developed where diagonal dowels replaced the perpendicular ones thus resolving separation issues and allowing for longer spans. Presently only one company uses the diagonal dowel system whilst all except for two (who still use nails) use perpendicular dowels, mostly without glue. There are now a range of companies producing CLT cross laminated timber (rotating layers of boards) using timber dowels based upon Brettstapel.


Manufacture

Throughout the development of Brettstapel, low grade wood (predominantly
spruce A spruce is a tree of the genus ''Picea'' ( ), a genus of about 40 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal ecosystem, boreal (taiga) regions of the Northern hemisphere. ''Picea'' ...
or
fir Firs are evergreen coniferous trees belonging to the genus ''Abies'' () in the family Pinaceae. There are approximately 48–65 extant species, found on mountains throughout much of North and Central America, Eurasia, and North Africa. The genu ...
) has remained the choice raw material for the posts where-as beech is more often used for the dowels. By ensuring natural defects, such as knots in the wooden posts are not adjacent to each other, poor quality timber can be utilised which makes for a highly economical way of using a fast-growing, underused resource, of which the UK and
Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...
in particular, has an abundance. Brettstapel is manufactured to three quality grades depending on how visible the final product will be: Industrial, Standard and Exposed. With this in mind, the most rudimentary solution is to use unfinished timber where the panels are to be covered. Alternatively, the posts can be planed,
chamfer A chamfer ( ) is a transitional edge between two faces of an object. Sometimes defined as a form of bevel, it is often created at a 45° angle between two adjoining right-angled faces. Chamfers are frequently used in machining, carpentry, fur ...
ed and profiled to give a highly aesthetic finish and further still, the posts can be altered with hollow voids along the edge to enhance the acoustic performance. Brettstapel can also be combined with
concrete Concrete is a composite material composed of aggregate bound together with a fluid cement that cures to a solid over time. It is the second-most-used substance (after water), the most–widely used building material, and the most-manufactur ...
and
steel Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...
to form composite structures for more demanding projects such as large spans, bridges and trusses.


Application

Brettstapel is commonly produced as part of a prefabricated wall, ceiling or roof panel. The
prefabrication Prefabrication is the practice of assembling components of a structure in a factory or other manufacturing site, and transporting complete assemblies or sub-assemblies to the construction site where the structure is to be located. Some research ...
takes place in dedicated factories using specialist
machinery A machine is a physical system that uses power to apply forces and control movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to natural biological macromolec ...
and an experienced team ensuring tight
quality control Quality control (QC) is a process by which entities review the quality of all factors involved in production. ISO 9000 defines quality control as "a part of quality management focused on fulfilling quality requirements". This approach plac ...
and fast construction. The structural panels are generally manufactured in 600mm wide sections, secured together using timber joints and further combined with sheathing board,
insulation Insulation may refer to: Thermal * Thermal insulation, use of materials to reduce rates of heat transfer ** List of insulation materials ** Building insulation, thermal insulation added to buildings for comfort and energy efficiency *** Insulated ...
, and a vapour barrier to form the completed panels. Structural openings are incorporated into the panels, and in some cases
plumbing Plumbing is any system that conveys fluids for a wide range of applications. Plumbing uses piping, pipes, valves, piping and plumbing fitting, plumbing fixtures, Storage tank, tanks, and other apparatuses to convey fluids. HVAC, Heating and co ...
and electrical fittings can be too, whilst the external finish commonly varies between render and timber cladding which is applied on-site. This high degree of prefabrication means buildings can be manufactured and erected extremely quickly and efficiently. It takes approximately five weeks from cutting dried timber to completing the fit-out of a house, whilst a house can be erected on site and made weather tight in a matter of days. Structurally,
manufacturer Manufacturing is the creation or Production (economics), production of goods with the help of equipment, Work (human activity), labor, machines, tools, and chemical or biological processing or formulation. It is the essence of the secondary se ...
s can produce panels up to 12–15 metres in length, although a 7metre span is more readily achievable with a 210-250mm deep panel. Brettstapel trusses can be made to span more demanding distances, such as those required in large industrial units and
bridge A bridge is a structure built to Span (engineering), span a physical obstacle (such as a body of water, valley, road, or railway) without blocking the path underneath. It is constructed for the purpose of providing passage over the obstacle, whi ...
s. The tallest building to use Brettstapel panels is currently the “E3” building in Germany at seven storeys tall. Although this incorporates other timber elements, four storey buildings have been erected solely using Brettstapel for the structure. Fire regulations currently limit the height of a timber building, however these are being challenged by the massive timber systems and taller examples are emerging; a typical 120mm panel has a 60 minute rating whilst complete structural panels can achieve 90 minute ratings which more than matches concrete and steel construction methods. Contemporary Brettstapel construction is also employed in th
IBA Soft House
in Hamburg, Germany. Whereas the timber skeleton of the E3 building is obscured by plaster, th
Brettstapel panels
in the Soft House are exposed on the interior floors, walls, and ceilings. The building was then clad in layers of mineral wool insulation, a water barrier, and a larch wood rainscreen to ensure stability against the elements.


Benefits

* Carbon dioxide is one of the biggest contributors to
global warming Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes ...
. Considering timber locks in 930 kilograms of carbon dioxide per cubic metre, (the equivalent to taking a car off the road for two months) a Brettstapel building sequesters significantly more carbon than a timber frame one. * Brettstapel has excellent thermal properties and if used efficiently could reduce energy demands by up to 90% due to its low U-values, airtight construction and high
thermal mass In building design, thermal mass is a property of the matter of a building that requires a flow of heat in order for it to change temperature. Not all writers agree on what physical property of matter "thermal mass" describes. Most writers use ...
, approximately five times higher than timber frame. Alone it has a
thermal conductivity The thermal conductivity of a material is a measure of its ability to heat conduction, conduct heat. It is commonly denoted by k, \lambda, or \kappa and is measured in W·m−1·K−1. Heat transfer occurs at a lower rate in materials of low ...
of 0.13 W/(m⋅K) and complete structural panels achieve U-values between 0.12 and 0.24 W/(m2⋅K). * The ability to prefabricate buildings offsite and erect them quickly has practical and economical advantages to the British
construction industry Construction are processes involved in delivering buildings, infrastructure, industrial facilities, and associated activities through to the end of their life. It typically starts with planning, financing, and design that continues until the ...
, especially considering the poor climate. * The reduced
energy demand World energy supply and consumption refers to the global supply of energy resources and its consumption. The system of global energy supply consists of the energy development, refinement, and trade of energy. Energy supplies may exist in vario ...
, along with the shorter and less labour-intensive construction period, contributes significantly towards lower lifecycle costs of a building. This offsets the higher material cost; Brettstapel is approximately 20% more expensive than an equivalent area of timber frame construction. * Specifying untreated, exposed Brettstapel, without glue and nails, helps to produce a healthy indoor environment that is free from potentially harmful compounds found in other materials; this is further enhanced by the
hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption (chemistry), absorption or adsorption from the surrounding Natural environment, environment, which is usually at normal or room temperature. If water mol ...
nature of the prefabricated panels.


British Industry

Brettstapel projects are starting to be realised in the UK, Acharacle Primary School in Scotland being the first and setting a fitting precedent for others to follow. Some private and public
housing project Public housing, also known as social housing, refers to Subsidized housing, subsidized or affordable housing provided in buildings that are usually owned and managed by local government, central government, nonprofit organizations or a ...
s are also being built in the Scottish borders and in
London London is the Capital city, capital and List of urban areas in the United Kingdom, largest city of both England and the United Kingdom, with a population of in . London metropolitan area, Its wider metropolitan area is the largest in Wester ...
. Plummerswood Active House in the Scottish Borders has received the Scottish Home Award for Architectural Excellence 2012. Currently Brettstapel is predominantly manufactured in Austria, Switzerland, Germany and
Norway Norway, officially the Kingdom of Norway, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. The remote Arctic island of Jan Mayen and the archipelago of Svalbard also form part of the Kingdom of ...
which has a negative effect on British users, due to increased
transportation Transport (in British English) or transportation (in American English) is the intentional Motion, movement of humans, animals, and cargo, goods from one location to another. Mode of transport, Modes of transport include aviation, air, land tr ...
costs and a subsequently a higher
embodied energy Embodied energy is the sum of all the energy required to produce any goods or services, considered as if that energy were incorporated or 'embodied' in the product itself. The concept can help determine the effectiveness of energy-producing or ...
. British
architect An architect is a person who plans, designs, and oversees the construction of buildings. To practice architecture means to provide services in connection with the design of buildings and the space within the site surrounding the buildings that h ...
s and clients are however slowly starting to use massive timber systems more frequently, but for all the benefits this brings, the British
timber industry Lumber is wood that has been processed into uniform and useful sizes (dimensional lumber), including beams and planks or boards. Lumber is mainly used for construction framing, as well as finishing (floors, wall panels, window frames). ...
has been missing out. However as of Spring 2013 In-Wood Developments in EastSussex is believed to be the first UK manufacturer of Brettstapel Panels in the UK, bringing this construction opportunity to the UK market on a more competitive basis. The first showing of these UK manufactured panels was made at Ecobuild 2013. Scotland produces the majority of UK timber, 65% of which is used for woodchips, fencing, packaging and sawdust, this is timber that could be used in Brettstapel construction. British grown
Sitka spruce ''Picea sitchensis'', the Sitka spruce, is a large, coniferous, evergreen tree growing to just over tall, with a trunk diameter at breast height that can exceed 5 m (16 ft). It is by far the largest species of spruce and the fifth- ...
is an ideal raw material to use for Brettstapel as it is a low coat timber that grows quickly and accounts for approximately third of all timber in the UK. If enough interest is generated, it is possible to conceive that the industry will soon have an incentive to produce more Brettstapel in the UK using Sitka spruce; this would be a highly profitable use of a resource that is currently predominantly used for cheaper products. Increasing the use of British timber will have huge ecological and economical benefits to the global environment and to British industries. Ultimately however, specifying Brettstapel within the UK will contribute towards a higher quality of construction; a higher standard of living; an improved
environment Environment most often refers to: __NOTOC__ * Natural environment, referring respectively to all living and non-living things occurring naturally and the physical and biological factors along with their chemical interactions that affect an organism ...
and towards the increased health and well-being of future occupants.


References


External links


Brettstapel
{{Webarchive, url=https://web.archive.org/web/20141218115353/http://brettstapel.org.uk/ , date=2014-12-18
Trada
information on timber construction
Scottish Ecological Design Association
development of ecological design

- IBA Soft House website
Merkle Gruppe
- IBA Soft House Brettstapel manufacturers Timber industry Engineered wood