Thatching Roofs
A silent revolution towards Sustainability
Crafting modern architecture
Using natural materials in construction of structures thus by becoming one with the nature was evidently followed by people in the history. One of the widely used construction methods in ancient period was thatching. It is almost certainly the oldest roofing material in the world.
Thatching is the craft of building a roof with dry vegetation such as straw, water reed, sedge (Cladium mariscus), rushes, or heather, layering the vegetation so as to shed water away from the inner roof. One of the most widely referenced definitions of thatch is provided by one of the turf grass industry’s foremost leaders, James B. Beard. He describes thatch as “an intermingled organic layer of dead and living shoots, stems and roots that develops between the zone of green vegetation and the soil surface”
This roofing method has been used in both tropical and temperate climates. Thatch is still employed by builders in developing countries, usually with low-cost, local vegetation. By contrast in some developed countries it is now the choice of affluent people who desire a rustic look for their home, would like a more ecologically friendly roof, or who have purchased an originally thatched abode.
Techniques in thatching
With renewed interest in our historic architecture, thatching is now, once again, in the ascendancy. There are quite different traditions of thatching all over the world. The Chol Indians of Mexico use palm foliage, while the nike palm is used in Indonesia and Malaysia. Different parts of the world use materials depending upon the vegetation grown in those specific geographic locations. The three main thatching materials in use today are water reed (often known as Norfolk Reed although a large amount is imported from Eastern European countries), long straw and combed wheat reed. Sedge, a grass-like plant which grows in wetland areas, is also used extensively in ridging.
Thatching methods have traditionally been passed down from generation to generation, and numerous descriptions of the materials and methods used in Europe over the past three centuries survive in archives and early publications. In most parts of the world the thatching material was tied in bundles and these were then tied to the roof battens.
In equatorial countries thatch is the prevalent local material for roofs, and often walls. There are diverse building techniques from the ancient Hawaiian hale shelter made from the local ti leaves, lauhala or pili grass of fan palms to the Na Bure Fijian home with layered reed walls and sugar cane leaf roofs and the Kikuyu tribal homes in Kenya.
Wild vegetation such as water reed (Phragmites australis), bulrush/cat tail (Typha spp.), broom (Cytisus scoparius), heather (Calluna vulgaris), and rushes (Juncus spp. and Schoenoplectus lacustris) was probably used to cover shelters and primitive dwellings in Europe in the late Palaeolithic period. Straw probably began to be used in the Neolithic period when people first began to grow cereals, but once again no direct archaeological evidence of the use of straw for thatching survives in Europe prior to the early medieval period.
The Life Expectancy
Ling - Heather Thatch
The life span of a thatched roof depends on numerous factors. The shape of the roof and details of production, proper ventilation, the design of the roof, the combination of old and new materials and structures, the quality of the reed, the location, the infestation with algae and moss, fungal decay and the maintenance of the thatched roof affect its durability.
Scores of potentials
Housing in Germany Constructing
With greater awareness of the vernacular materials and style of particular regions, conservationists have realised the importance of maintaining (and even returning to) the historically correct thatching style and material pertinent to the area. A common misconception with thatch is the idea that it absorbs large amounts of water. This is not the case at all. Water is transferred down the roof from stem to stem until it drops from the eave. The steep pitches associated with thatched roofs allow for water to be shed at a very fast rate. When designing for thatch, ample allowance should be made for the projection of the eaves and gables to project water clear of the building, and the ground should be well drained.
Los santos thatch roof install panama post and beam dex witt
The performance of thatch depends on roof shape and design, pitch of roof, position - its geography and topography - the quality of material and the expertise of the thatcher. Thatch has some natural properties that are advantageous to its performance. It is naturally weather-resistant and when properly maintained does not absorb a lot of water. There should not be a significant increase to roof weight due to water retention. A roof pitch of at least 50 degrees allows precipitation to travel quickly down slope so that it runs off the roof before it can penetrate the structure. Thatch is also a natural insulator, and air pockets within straw thatch insulate a building in both warm and cold weather. A thatched roof will ensure that a building will be cool in summer and warm in winter.
Thatch also has very good resistance to wind damage when applied correctly. A greater cause for concern is the risk of fire in a thatched properly, although the risk however is probably overstated. Evidence shows that thatch fires are usually caused by the same kinds of hazards affecting all housing and that genuine thatch fires are extremely rare. Figures from the Dorset Fire Brigade indicate that of 3,000 fires each year, only 8-10 of these involve thatched buildings and in the majority of these incidents, the fire will have started within the building itself. The reality is that all thatched building owners tend to be more careful about the dangers and employ a number of fire prevention measures. Nevertheless, many thatchers now recommend the installation of a fireboard which is fitted to the rafters and gives at least a half hour's fire resistance. Depending on the material and position of the building, this might then be counter battened to provide air movement between the material and fire retardant.
Pros and cons of thatching
Thatching materials range from plains grasses to waterproof leaves found in equatorial regions. It is the most common roofing material in the world, because the materials are readily available. The combination of thatch and roof tiles is quite common in that area. Because thatch is lighter, less timber is required in the roof that supports it. Thatch is a versatile material when it comes to covering irregular roof structures. This fact lends itself to the use of second-hand, recycled and natural materials that are not only more sustainable, but need not fit exact standard dimensions to perform well.
Thatched houses are harder to insure because of the perceived fire risk, and because thatching is labour intensive, it is much more expensive to thatch a roof than to cover it with slate or tiles. Birds can damage a roof while they are foraging for grubs, and rodents are attracted by residual grain in straw.
Thatch has fallen out of favour in much of the industrialised world not because of fire, but because thatching has become very expensive and alternative 'hard' materials are cheaper — but this situation is slowly changing.
It is claimed that thatch cannot cope with regular snowfall but, as with all roofing materials, this depends on the strength of the underlying roof structure and the pitch of the surface. A law passed in 1640 in Massachusetts outlawed the use of thatched roofs in the colony for this reason. Thatch is lighter than most other roofing materials, typically around 7 lb per square foot, so the roof supporting it does not need to be so heavily constructed, but if snow is allowed to accumulate on a lightly constructed thatched roof it could collapse. A thatched roof is usually pitched between 45–55 degrees and under normal circumstances this is sufficient to shed snow and water. In areas of extreme snowfall, such as parts of Japan, the pitch is increased further.
Maintenance of thatched roofing
A thatched roof needs consistent maintenance to prolong the life of the roof. As well as general degredation of the thatch which happens over time, common problems in thatched roofs which require maintenance include damage caused by monkeys, birds and overhanging trees as well as leaks and rotting often caused because the roof was improperly thatched and built in the first place.
A long term maintenance plan can also be put together to prevent future problems in a thatched roof and ensure that regular maintenance is carried out.
Brushing
This is the most regular maintenance a thatched roof usually requires. The top layer of thatch on any thatched roof rots over time. This layer of rotten thatch needs to be brushed off every 5-8yrs to ensure no deeper rotting and thatch degeneration. When a thatched roof is originally built the thickness of the thatch should always allow for this maintenance. After years of brushing, a thatched roof will reach a minimum thickness and wires will be exposed - this indicates that no more brushing maintenance can be done and it is time to re-thatch.
Valleys & Drainage Systems
A common maintenance problem in thatched roofs is lack of drainage which leads to premature rotting and leaks. Often these problem areas appear where thatch meets from several directions (in a corner for example) or if there is an overhang (one thatched roof above another). In some cases no allowance for drainage was made in the original build or the thatched roof valleys were not fitted adequately.
Parapet Wall Drainage
Drainage of parapet walls is a common problem in thatch roofs and if not addressed properly there are often leaks where the thatch meets to wall. Read our article "A Solution to Parapet Wall Drainage on Thatch Roofs" for more information on the problem and the best solution.
Re-Thatching & Patching
In some cases when carrying out maintenance on a thatched roof extra thatch needs to be added to patch thin spots. In extreme cases or on an old and thin roof, brushing and patching is not enough and the roof must be re-thatched.
Thatched Roof Capping
The capping (or ridging) on a thatched roof can be a problem area. Sometimes the concrete mixture is not made to the correct specifications originally and the capping can crack and cause endless maintenance problems.
Thatching Proficiency
Thatching is an art which requires a good deal of skill and experience; and the difference between a well-made roof and one that has been put together by an unskillful hand is very great, both as regards efficiency and durability. In many parts of Europe thatching is a regular trade, to which the beginner serves an apprenticeship, as to any of the ordinary trades.
The following directions, however, if carefully followed, will enable the amateur to cover a small building in a manner that is at least respectable: -
Rye or wheat straw only should be used, and must be carefully threshed with a flail to leave the straws unbroken. Bind in bundles, distributing the straws equally to each end of the bundle. A good roof cannot be made if the straws all lie one way. It was always customary to make the band three feet long, as this gave a bundle of convenient size for handling. The rafters are placed in the usual way, and crossed by slats two by two, nailed 14 inches apart, though 12 inches will do equally well.
Begin at the eaves and lay a row of bundles across. Have an iron needle 18 inches long prepared and threaded with oakum 8 feet long. Fasten the thread to the slat and pass the needle through the bundle to a boy stationed under the rafters, making three to four stitches to the bundle. The boy draws the cord up tight, and passes the needle up through again, but on the other side of the slat. By this means the first course is sewed on. Succeeding courses are treated in the same way, being laid so as to overlap the stitching. Lay the heaviest row of straw at the eaves to make it look well. When you come to the ridge, fold the tops of the straw over until you bring up the other side, then get some thin sods, 10 by 14 inches, and 11/2 inches thick, and lay them neatly upon the top, using a small piece of board to clap them all slick and smooth. Boards put on like ordinary ridge-boards will do instead of sods, if preferred.
Get the point of an old scythe, about 18 inches long; attach a handle, so that it will be like a long knife, and with it "switch down" the roof all over, to carry off all the loose straws, and trim the others off smooth. If well done, the roof will be as smooth as a board. Stretch a cord along the eaves the whole length of the building, and trim off straight by it, leaving the outside a little lower than the inside, which will prevent its looking thick and heavy.
A roof made in this way will not be injured by wind and rain, and it ought to last from 25 to 30 years.
QUOTES
- Thatch is “an intermingled organic layer of dead and living shoots, stems and roots that develops between the zone of green vegetation and the soil surface”
- In some developed countries it is now the choice of affluent people who desire a rustic look for their home, would like a more ecologically friendly roof, or who have purchased an originally thatched abode.
- A common misconception with thatch is the idea that it absorbs large amounts of water. This is not the case at all. Water is transferred down the roof from stem to stem until it drops from the eave. The steep pitches associated with thatched roofs allow for water to be shed at a very fast rate.
- The performance of thatch depends on roof shape and design, pitch of roof, position — its geography and topography — the quality of material and the expertise of the thatcher.
- Thatch is a versatile material when it comes to covering irregular roof structures. This fact lends itself to the use of second-hand, recycled and natural materials that are not only more sustainable, but need not fit exact standard dimensions to perform well.