Thatched roof
Reet (also Reeth , Reth , Reith , Ried , Riet and the like;., See Middle High German advised "reeds, rushes"), even tube called, refers to the growing on the banks or on swampy terrain reeds , which in many places in the dry state for roofing is used and served for many similar purposes in earlier times, such as embroidering new dikes with the dike needle . The thatched deckerei is one of the oldest craft techniques in home construction .
In addition to the name thatched rare and landscaped also names as are thatched roof or a thatched roof common. Thatch-roofed houses are also called Thatched or Reethus or thatched cottage called.
The thatched roofing trade was submitted by the state of Mecklenburg-Western Pomerania as an intangible cultural heritage to UNESCO and confirmed as such in 2014.
history
Thatch or reed was one of the first roofing materials for the settled people; this is mainly due to its properties as an aquatic plant and its local availability. The first thatched roofs were simple single-roof houses.
In the Middle Ages, due to the risk of fire in densely built-up areas, the thatched roof was replaced by hard roofs in the cities. In the country, however, the thatch has retained a certain importance to this day. The first proven thatched roofs (pile dwellings on Lake Constance) already existed around 4000 BC. It was reed that was lightly tied up and pressed onto the roof structure with hazelnut sticks as a shaft and soaked willow sticks.
distribution
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Thatched roofs are known in many landscapes in Europe , Asia and Africa . In many cases, however, these are particularly associated with the North and Baltic Sea coastal areas , where, for example, you can find fully thatched buildings in North Frisia or the thatched roofing of East Frisian Gulfhöfe . The Uthland Frisian house, which is typical for North Frisia, is also traditionally provided with a thatched roof. In some places, such as Kampen on Sylt , there are statutes that prescribe the exclusive use of thatch, i.e. the so-called "soft roofing". In the neighboring towns of Keitum and Wenningstedt there are districts or areas in which only thatched roofs may also be built. On the Eiderstedt peninsula, the striking, large farmhouses, the Haubarge , are traditionally thatched. Thatched or thatched roofing is a separate line of business, so that there are special thatched roofers in northern Germany who exclusively create and repair these roofs.
Thatched roofs are also common in the Midlands of England and Cornwall . Tradition is particularly artfully built ridge covers . One variant is the seaweed roof, which is traditional on the Danish island of Læsø .
construction
A thatched roof can traditionally be designed as a cold roof (with rear ventilation); in the past, the thatched or thatched roof was constructed as a warm roof without rear ventilation . The thatch is often said to have an excellent insulation effect, not least because of the thatched roof industry itself: Due to the low density of reeds, thatch provides good thermal insulation in summer and good thermal insulation in winter. In the thatched roof, however, any thermal insulation is “blown away” due to the strong ventilation due to the stalk structure. Anyone who has stayed in an undeveloped thatched roof even in a light wind (2 to 4 Bft) will feel how the air movements pass through the thatched cover almost unhindered. A manufacturer himself writes: “ If the air permeability of the thatched roof is also reduced by a too tight bond, the use of too fine stalks, or too wet thatch, a damp thatched roof can result in an ideal breeding ground for algae, bacteria and fungi ". The universally undisputed and required air permeability (in winter for cold air, in summer for warm air) logically excludes thermal insulation.
In the non-developed thatched roof, the wind permeability as a means of keeping dry is still out of the question, i. H. Nothing is added to the reed on the inside, you look inside against the stalks. In the course of modern construction techniques for loft extensions, however, the thatched roofs have adapted to their substructure and are nowadays built as a cold roof with rear ventilation (according to DIN 4108). The rear ventilation layer should - as with the non-dismantled roof - dissipate any moisture and thus ensure a longer service life of the thatched roof. However, a 4 to 6 cm thick rear ventilation layer on a developed thatched roof brings significantly less air exchange than a non-developed attic, and the effectiveness of the rear ventilation layer depends on how effectively the inlet and outlet openings for the rear ventilation function. In addition, the loft extension behind it represents an entry source of warm, humid air from the living space: the more penetrations, for example for electrical and sanitary cables and for the supporting structure, the higher the risk that individual penetrations will leak from the beginning or will leak over time, and then represent a permanent source of warm, humid air in the reeds.
After a series of damage to rebuilt thatched roofs, which was accused of fungal-contaminated reed material, experts who pointed out the inadequacies of a rear ventilation layer advocated direct flocking of the reed with blown cellulose insulation (without air layer) as a safer alternative, and can refer to reference roofs. The blown cellulose insulation can replace the air layer in its role as a dehumidifying medium due to its large moisture storage, buffer and drainage capacity. In addition, with compressed, blown-in cellulose insulation, you avoid the entry of warm, humid indoor air through the insulation layer into the thatch, because the cellulose insulation layer itself ("inherent to the material") has airtight properties that can only be achieved with mineral wool insulation by carefully gluing and masking with vapor barrier films. The direct reed flocking also prevents night air containing condensation from flowing in.
Correct execution must meet certain requirements and parameters. Thatched roofs should have a roof pitch of more than 45 °. The high pitch of the roof is necessary so that the individual drops of water can slide from stalk to stalk. With a functioning thatched roof, only the top layer of the roof covering is soaked through. Thatched roofs have a large roof overhang (eaves overhang ) of at least 50 cm as structural protection , since no rain gutter drains the water, it drips off at a sufficient distance from the masonry and seeps into a gravel bed or is drained through a gutter. According to the Firing Ordinance (FeuVO), the chimney outlet must be at least 0.8 m above the ridge.
The ridge of the thatched roof is made differently from region to region. In regions where heather grows, this is covered with heather . In the Netherlands , Flanders and France , clay cap ridges (burnt in natural red or steamed dove gray) are common. In Northern Friesland is grass sod ridge to find and in the Scandinavian countries and the region Kappeln / Flensburg , the slopes Holzer (oak tab) on a seaweed layer hanging.
processing
A thatched roof can be made in three different ways: as a screwed, sewn or tied roof. The thatch is delivered in tied bundles, distributed on the roof battens and then shifted so that the lower reed ends form a sloping, uniform, continuous surface. The roots of the reeds point towards the ground. The first layer, the so-called eaves layer, is held under tension by the bond on the roof. The tension is maintained by the fact that the support edge on the eaves (Kniep) is five to seven centimeters higher than the roof batten level. In the case of tied and screwed roofs, a retaining wire (shaft) is placed on the approximately one meter wide and 10–20 cm thick layers and pressed onto the layer with a screwed or tied wire. The layers are pounded up with the tapping board and brought into shape. This is continued layer by layer until the roof ridge is reached. By covering the individual layers, the bond is in the middle of the top layer. The sewn thatched roof does not require a retaining wire and is more complex to process.
Thatched roofing trade requires great technical skills. In December 2014, the handicrafts were therefore included as one of 27 forms of culture in the nationwide register of intangible cultural heritage by the Conference of Ministers of Education .
lifespan
dark brown (dormer): aged reed
pale brown: combed reed
brown-yellow: repair with new reed
A thatched roof lasts an average of 30 to 50 years, but roofs that were over 100 years old have also been documented. The service life of a thatched roof depends on different criteria:
- Shape and design details (e.g. roof pitch, number of dormers, stalk pitch)
- Ventilation of the thatched roof (ventilation habits of the residents)
- Construction of the roof (traditionally ventilated or non-ventilated)
- Quality of the roof thatch used (built-in moisture)
- Position of the thatched roof (position of the thatched roof in the area, in the region)
- Care and maintenance of the thatched roof (regular care and repair, e.g. through so-called combing )
Settlement cycle
The reed Phragmites australis is home to numerous other species. The population changes as the life of the roof increases. The following levels show the typical growth. This growth sequence can be disturbed by the weather and maintenance work. The composition of the species differs regionally and, even on a single roof, depends on the compass direction and shade.
- During the first years: Beginning of the colonization with air algae , green algae , diatoms and lichen .
- From the sixth year: Further colonization with leaf lichens and crustal lichens.
- From the 10th year: Now the fork-toothed pearl moss Dicranoweisia cirrata follows .
- From the 15th year: On the existing moss cushions different Epigee moss species settle , depending on the local humidity
- From the 20th year flowering plants (herbaceous and shrub species) begin to replace the moss.
Metals
There is currently a lively discussion among experts as to whether copper products , for example copper binding wires or quaternary ammonium compounds , can be used to maintain thatched roofs in order to extend the durability and thus the service life of a thatched roof.
Copper in the ridge region is said to be that the ions released by the rain reduce the moss and lichen growth on the roof surface. On the other hand, the reed has an impact on metals . If z. B. a rain gutter is constructed in the entrance area , it should be made of an acid-resistant material. Zinc will be eaten away in a few years. Aluminum and copper have proven to be more effective.
Thatch problem today
Reet is currently also being imported into Germany because the demand is higher than the domestic supply. Today about half of the reeds are imported from Romania , as well as from Ukraine and Hungary ; about ten percent come from Turkey and China (combined with other harvest times ). In this context, fears have been expressed that imports could introduce pests that have no natural enemies and that would reduce the durability or service life of the roofing.
Reports about mysterious mushroom species that have been stylized as "killer mushrooms" in the media have received a lot of attention. Such novel mushrooms, allegedly brought in by imports from Southeast Europe, and their effects have not been proven by any research, and some evidence suggests that the source of some of these theories is the manufacturer of an alleged remedy for the fungi.
Research at the University of Greifswald and other participating universities in northern Germany could not find any evidence of such a fungus or pest. The research showed that only lignin (wood) degrading fungi ( white rot fungi ) can be responsible for the premature aging of thatched roofs if they are provided with an appropriate environment due to permanent moisture. However, this milieu is only created through structural errors.
The Dutch guild Vakfederatie Rietdekkers similarly suspects that the cause of the rotting of many thatched roofs lies more in non-compliance with the basic principles of the roof structure (for example the roof pitch) and in the use of inferior thatch, which leads to increased moisture; However, the inferior thatch does not necessarily come to Germany from Southeastern Europe alone - reeds that are not used in the Netherlands due to poor quality are also imported into Germany.
Fire hazard
Thatched roofs are at risk of fire, especially in midsummer , if they have dried out from exposure to the sun. But the New Year's fireworks is also a danger, so that on the North Frisian Islands the burning of fireworks was generally prohibited. A fire usually spreads over a large area within half an hour; the tied bundles of thatch come loose and slide down burning from the roof surface, making it difficult to escape from the building. The fire services usually advise you to leave the building immediately in the event of a fire. This problem has been known for centuries, so that from the late 18th century, locally also earlier, so-called fire doors have spread (see also Uthlandfriesisches Haus ). These are located on the long sides of the house and have their own pointed gable so that they protect against the burning bundles of thatch when leaving the building. Due to the considerably higher risk of fire compared to a hard roof, the premiums for fire insurance are higher for traditionally thatched houses. A public real fire test at the Lübeck University of Applied Sciences has shown that the current binding technology with screwed V2A wires and without rear ventilation on a solid wood roof (regional house Lübeck Bay (R)) led to a burn on the roof surface. The reed does not slide down. The LBO-SH § 34 was changed accordingly in 2009.
literature
- Brigitta Seidel: Under the thatched roof. Husum, 2007, ISBN 978-3-89876-327-1 .
- Walter Schattke: The thatched roof. Instructions for correct construction and appropriate treatment of the soft roofing. Verlag Schleswiger Druck- und Verlagshaus, 1981, ISBN 3-88242-060-X .
- Walter Schattke: The thatched roof. Natural living under a soft roof - from prehistoric times to today. Verlag Christians, Hamburg 1996, ISBN 3-7672-1140-8 .
- Mila Schrader: Reet & straw as historical building material. Elsewhere , 1998, ISBN 3-931824-09-8 .
- Johann Garleff : How did thatch roofing work in Schleswig-Holstein? In: The home. Journal for Nature and Regional Studies of Schleswig-Holstein and Hamburg, Volume 75, No. 7, July 1968, ISSN 0017-9701 , pp. 188-194, ( uni-hamburg.de [accessed December 17, 2018]).
- Bernd Grützmacher: Thatched and thatched roofs. Old techniques revived. Callwey Verlag, Munich 1981, ISBN 3-7667-0554-7 .
- Rinus Spruit: The current that carries us. A family story . From the Dutch by Mirjam Pressler . dtv, Munich 2011, ISBN 978-3-423-24864-8 . (nl. Original: De rietdekker. Een familiegeschiedenis. Amsterdam 2009; Life story of an old thatched roofer from the Dutch province of Zealand.)
- Peter Thomas: House with a straw hat. In: FAZ , July 22, 2016. online
Documentation
- Dörte Petsch: From pipe to thatched roof NDR - How does it work? from August 9, 2017 (YouTube)
Web links
- Information page of the thatched roofing guilds
- Rotten roofs. Rotten thatch is a major problem for homeowners . Deutschlandradio , May 9, 2007
- Video: Thatched roofs in Fintel . Institute for Scientific Film (IWF) 1972, made available by the Technical Information Library (TIB), doi : 10.3203 / IWF / E-1540 .
Individual evidence
- ↑ UNESCO entry , accessed on February 19, 2018
- ↑ Thatched Roof: Origin & History of Thatched Roofers | Hoist thatch. Retrieved December 12, 2018 .
- ↑ See also the pages of the Reetdachdeckerinnung Reetdachcover.de ( Memento from February 3, 2014 in the Internet Archive )
- ↑ Ventilation of thatched roofs Website of the company Hiss Reet Schilfrohrhandel. Retrieved April 8, 2017.
- ↑ Andreas Sielaff: Thatched roof insulation - but how? Journal Der Holznagel , No. 5/2004, pages 38–39.
- ↑ Robert Heinicke: Insulate a thatched roof? Holzbau Quadriga trade journal , issue 05/2016, pages 28–32
- ↑ Robert Borsch Laaks: Can insulation seal? Holzbau Quadriga trade journal , issue 05/2016, pages 22–26
- ↑ Press release of the Standing Conference
- ↑ Communities on thatched roofs. In: Berndt Heydemann: New biological atlas. Ecology for Schleswig-Holstein and Hamburg. Verlag Wachholtz, Neumünster 1997, ISBN 3-529-05404-6 .
- ↑ a b c Dirk Asendorpf : Above is modert. Die Zeit , August 2, 2007, accessed October 29, 2011 .
- ↑ a b Thatched roof misinformation. January 12, 2010, accessed October 29, 2011 .
- ↑ Aggressive fungus causes roofs to rot. Süddeutsche Zeitung , January 12, 2009, accessed October 29, 2011 .
- ↑ Killer mushroom is causing the thatched roofs to rot. Stader Tageblatt, January 18, 2007, archived from the original on January 7, 2011 ; Retrieved October 29, 2011 .
- ↑ Frieder Schauer: Why do thatched roofs rot prematurely? (No longer available online.) Ernst Moritz Arndt University of Greifswald , December 21, 2010, archived from the original on August 3, 2011 ; Retrieved October 29, 2011 .