At first glance, Dorte Mandrup's design for the Wadden Sea Center seems to mimic the landscape. Its low height, its horizontal lines and, above all, its materiality make it a modern building in perfect harmony with the local nature. But its connection also encompasses the built heritage of the region, more specifically because of its covering with straw, harvested and dried close to the land. This is an extremely traditional and historic building technique, but which is rarely attributed to contemporary buildings. In this article we will rescue some of the history of this natural material, its constructive characteristics and some examples of use.
Researching the history of the use of thatched roofing is quite challenging. As it is a natural and biodegradable material, there are very few traces of its use in old constructions, unlike stone structures or even rudimentary cements, for example. However, researchers point out that the thatched structures date from the time when humans stopped being nomads and dedicated themselves to agriculture. There are indications of their use in the Aztec empires and in the first buildings of what we now call Europe, as well as research on its use in Europe, the UK and Mexico, among many others.
Thatched roofing is a traditional method that involves using dry fibers such as straw, reeds, palm trees and other natural fibers to create a roof covering. These are grouped and interwoven with a certain tension to form a surface, which through successive overlaps becomes impermeable and almost impenetrable to rodents and pests. The roof is mounted from the bottom up and the top is where more care must be taken and more maintenance must be done, as it is a weak point for water infiltration. Roofs with a steeper slope will make the water run faster, preventing potential infiltration problems. But this does not mean that the material restricts the designers' creativity. Because it is flexible, organic shapes can be easily achieved, as is the case with The Nest, by Porky Hefer Design, in which the material surrounds the roofs and most of the walls.
The material composition, due to the multiple voids and surface irregularities, provides excellent insulation when dry and compact. When applied correctly, straw also has very good wind resistance. Thatch is also relatively light, which means the roof support structure can be less robust. One issue that must be taken into account is its behavior in the event of a fire. As a dry and highly flammable material, precautions must be taken to prevent combustion and control flames as quickly as possible. Currently there are some companies that work with synthetic fibers with flame retardants, for example.
As it is an inexpensive and relatively simple construction, its application is usually concentrated in rural areas. In other words, we will hardly see thatched roofs in Manhattan or downtown São Paulo, since the incorporation of this constructive technique is especially interesting when materials and labor are available to do so. This is the case of Studio Anna Heringer's project for a kindergarten in Zimbabwe, which is part of a Permaculture Education Center in Zimbabwe and is designed within the philosophy of self-sufficiency, built in wood, straw and stone. As the project description points out, “With these local techniques, the project aims to build with a process that reinforces solidarity and team spirit, skills and knowledge, self-confidence and dignity. Due to climatic contexts and local conditions, buildings, unless constructed of glass and steel, will not last forever, but it is essential that the know-how to maintain and rebuild them is kept alive and passed on to succeeding generations. (...) That's why we see this project primarily as training in advanced building techniques with existing materials that can then become compost from the kindergarten's fields.”
At Studio Morison's Mother Pavilion, the approach was similar. “The shape is an interpretation of the remarkable hayricks that dotted this countryside. (...) The walls and roof are made of local straw, the roofing of which was made in the traditional style by a master craftsman, whose first job as an apprentice was to harvest a haystack on this very spot.”
In this house in India, the traditional technique was incorporated with more dynamic forms, to bring a primary function to the roof, which is to collect rainwater. "The thatched roof is shaped like an inverted pyramid that descends inwards towards the courtyard. Not only focused as the central concentration, the courtyard also doubles as a rainwater catchment."
As previously mentioned, the ridge is the most worrying point of a straw roof (in fact, these are important parts of all roofs ). In the Facts Tåkern Visitor Center project, Wingårdh Arkitektkontor AB solved this by incorporating a skylight. As the architects point out: “The building is clad in straw, camouflaged like a birdwatcher's curtain, hiding its contents from the natural world around it. The steep tone gives them longevity. The gable, where a thatched roof is most vulnerable, is transformed into a glazed skylight.”
Straw can also work to create a contrast between modernity and tradition. At Sandellsandberg's Synvillan Eriksberg Hotel & Nature Reserve, the thatched roof contrasts with the straight shapes and polished metallic cladding, whose reflective properties aim to give the illusion of a house dissolved into the landscape.
Find more examples of projects that use thatched roofs in this My ArchDaily folder.
