Thatching, a Modern Durable Roofing Material
This information is from Thatching, A Handbook by Nicolas Hall and my own experiences – Deanne Bednar)
Definition: dead plant material other than wood. Usually palm or grasses, can be sea weed, herbaceous fibers, large leaves, etc.
Traditional Thatch: In conjunction with rough pole timber, the original building material. Still in use in rural areas of Asia, Africa, where it is associated with poverty and not thought of as permanent. Also used in NW Europe, as a pleasing, weather-tight, durable covering. Some thatched roofs do have very real shortcomings: leaks, insects, tend to catch fire, and don’t last long. Palm leaf thatch can be improved, but can only last about 15 years. But in contrast, some species of grass with tall, rigid stems can last 50 years or more.
Advantages of Thatch:
- Locally economy and independence, saves on transportation.
- Low tech: doesn’t need sophisticated machinery, saves other resources (slate, metal,etc)
- Abundant: grows back every year and can provide abundant material.
- Creative and satisfying craft that is easily learned/integrated into the community.
- Ecological, non-toxic, bio-degradable, non-manufactured, useful, beautiful to look at.
- Insulative: 300mm (10” ) of thatch equals about 200 mm (7 “) of fiberglass insulation under a metal roof.
- Versatile: keeps a house cool in summer, warm in winter
- Long-lasting if made from suitable plants and applied with skill.
- Fire: Not suitable in dense urban areas (although much can be done to reduce the fire risk)
• Transportation expense. Materials are bulky, and transportation can be expensive
• Labor-intensive work
• Poor rain water collection, cannot easily be used due to gutter construction and
2) Thatching Materials
Primarily Materials: palm, soft stem grasses and stiff stem reed-like grasses.
Sources: Indigenous vegetation, by-product of food crops, and by cultivation.
Grasses, with some 9,000 species. Cereal straw as a crop by-product is widely used ~ wheat and rye in Europe, rice in Asia and millet and sorghum in Africa.
Uncultivated wild grasses, primary economic value as thatch, most durable is Phragmites australis (water reed) which can last up to a hundred years. Grown in controlled wetlands in Europe, or can be harvest from wild stands in Asia, Africa and North America. Our US reed is usually not native, but a more recently evolved sub-species.
4) Harvesting and Processing.
Water reed (Phragmites australis) dense stands, marshy areas, fertilizer not desired, annual or biennial farvesting during winter after frosts have loosened the leaves. Done by maching and stems cleaned with a hand-held side rake before being bundled.
Winter wheat. Tall straw varieties, grows best with less artificial fertilizers and weeding is needed. Cut with reciprocating blade madhine, cleaned with a revolving drum (same machine which separates grain from the ears.
Tying into bundles: 550mm circumference at the binding, 300 mm from the cut end. A higher second tie is used if reed is longer, or is moved several times. Keep in dry well-ventilated condition until used (indoors in alternating orientation piles like cordwood ends, or outdoors in teepee style cones).
Thatch decay: lasts best if kept dry and out of the sun (in storage and on roof). Decays through physical and biological erosion, when stem is physically damaged by wind, rain, swelling and shrinking through temperature change, or exposed to sunlight. Ultra violet light reacts with the lignin in the surface cells (epidermis), causing stems to split and exposing internal cells that are less strongly bonded. (parenchyma). Then fungal attack can cause significant damage when moisture content exceeds 20 percent and temperature is 20 to 30 degrees (warm, wet conditions). Therefore, minimize area of stem exposed to the weather, have a sttp room, tightly packed so water runs from tip to tip rather than pentration. After 50 or more years a 300mm thick roof of tough water reed, skillfully laid and exposed to damptemperate climate of northen Europe, for example, will have eroded to about 180mm, and should still be weather-tight.
3) Building Types and Roof Structures
Roof slope and Thatch Load:
Roof pitch of at least 45 degrees, preferably 50. best suited to small and medium span buildings. Water Reed is 40kg/m2 when dry, 50 when wet. This is about 500 lbs per 10 by 10 foot square. Rafters should be 100 by 50mm spaces at 750mm centers with horizontal battens cut from 50 x25mm timber fixed at aprox. 300mm intervals. Round pole timber can be used, thus being unprocessed.
Attachment details: Grass is overlapped in ascending courses from the eaves up to the ridge and attached about half way up the reed. The butt ends of the reed are exposed and the tips are covered by the next applied layer of reed. A wider batten spacing (350mm) can be used with long grass over 1.5m which covers more roof area with each layer, while a shorter spacing (250mm) can be used for a thick layer of short grass under 1.5mm. When using 25mm screws, sawn softwood battens of sufficient strength should be used.
- The foundation course of reed begins at the bottom right hand corner of the roof and is fixed securely in visible compression. Tie the first row to the battens. Gable roofs have additional considerations.
- Surface layers. The subsequent surface courses are laid on top and tied, or attached with sways, then straight poles. The first row has two layers: the base, and surface layer, while the other rows have a single surface layer.
- Tools: Pegs, sharpened 15” poles hold the bundles temporarily in place. Leggat, 18” needles or battery drill.
Eave and Ceiling Detail: A tilt board(or pole) of about 40mm thicker than the subsequent battening puts the ends of the reed into compression. For a gable roof, a fascia board shold be 25mm higher than the ends of the battens. A ceiling may be attached directly to the rafters and serves as a fire-check liner.
Lightening rods, Roof Windows, Valleys: see books for details.
Where to order TOOLS:
Sickle for hand-harvesting reed. Select a blade at least 6 1/2 inches long. Serrated works well, or carbon steel. Cost,$5.
Thatch Living Magazine http://www.thatchedliving.co.uk/magazine/magazine.html
Rödler, drill apparatusThe Rödler is an about 30 cm long apparatus with a plastic handle in which a milled spindle is placed with an automatic return pipe. There is a bent top at the end of the apparatus. For the screwed thatched roof the attachment is tightened by this apparatus.
Traditional Thatching tools . See online page “Thatching Outline” for live links.
Wire Twister .
Stainless Steel Wire .040 .
Rachet & Tie Wire Twisters .
Reeper Binder info for harvesting reed mechanically
Master Thatchers in the United States:
William Cahill, Master Thatcher, USA www.roofthatch.com
Colin McGhee Master Thatcher, USA www.thatching.com
Erin Collins, Irish Thatcher living in Wisconsin.
Frame construction & thatching links:
Graves Bushcraft: huts and thatching http://chrismolloy.com/www/p133
The Way we used to live. http://www.facebook.com/media/set/?set=a.171429079576831.48530.147479555305117&type=3
Poland House, round stone/gravel foundation. thatched. http://earthhandsandhouses.org/projecthancza.htm
Outside Educators: http://www.primitiveways.com/pt-tule_shelter.html