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CLOSE THIS BOOKThe Basic of Biomass Roofing (GTZ - ITDG - SKAT - CRATerre-EAG, 1997, 36 p.)
VIEW THE DOCUMENT(introduction...)
VIEW THE DOCUMENTIntroduction
VIEW THE DOCUMENTGrass thatch
VIEW THE DOCUMENTPalm thatch
VIEW THE DOCUMENTWood tiles (shingles and shakes)
VIEW THE DOCUMENTRoof sheets with organic fibres
VIEW THE DOCUMENTTreatment of biomass materials: preservation
VIEW THE DOCUMENTFire protection
VIEW THE DOCUMENTSources of further information
VIEW THE DOCUMENTKey questions
VIEW THE DOCUMENTRecommendations
VIEW THE DOCUMENTBASIN
VIEW THE DOCUMENTBack cover

Roof sheets with organic fibres

Fundamental information

Fibre reinforced roof sheets made primarily of organic materials, or reinforced with grass stems, fibres or wood chips offer considerable potential for low-cost roofing. They are light in weight, can utilise waste materials and, in principle, should be an attractive alternative to thatch, corrugated iron or asbestos cement sheets. Research in many countries has shown that a wide variety of fibrous organic materials are suitable.

However, this product has had very limited commercial success in the domestic roofing market in developing countries. They are more evident in use for industrial buildings and emergency, post-disaster housing. The best quality sheets can last for up to 15 years, but standard quality sheets in a tropical climate are rarely functional for more than 6 years.

Basic techniques for processing and use

There are two types of sheet.

The first is a corrugated sheet made of fine fibres which are bonded together and waterproofed with asphalt.

The second type are flat sheets which use larger fibres, such as wood chips. They are bonded with cement and then coated with a sealer.

Corrugated asphalt roofing sheets (ARS)

Suitable fibres are obtained from a wide range of materials including bagasse, sisal, coir, coconut, cotton and waste paper. They are pulped and washed to remove sugars and starches. The wet mixture is then spun in a centrifuge. The resulting mat is dried, trimmed to the desired size and then pressed between corrugated dies before being pressure impregnated or dip coated with hot paving-grade asphalt. Finally the sheet can be painted with asphalt, aluminium or acrylic sealer for further weather protection. Asphalt is approximately 50% of the product weight.


The final coat on asphalt roof sheets (Colombia)

Dimensions

Sheets are 6mm to 8mm thick, between 500mm and 900mm wide and between 900 and 1830mm long. Most manufacturers sell a variety of sizes to suit different applications.

Weight

Depending on the thickness, between 3 and 5kg/m2.

Uses of ARS sheets

ARS sheets are similar to corrugated iron and asbestos cement sheets and are suitable for all types of building. They are particularly useful for temporary structures such as emergency housing.

Roof structure

Minimum roof angle is 22°. Sheets need supporting on horizontal battens fixed to rafters at maximum spacing of 500mm.

Fixing method

Sheets are nailed top and bottom, starting at the bottom of the roof and overlapping both side and top. Special shaped ridge pieces are used to protect the apex.

Cost

Varies with thickness and size. In India (1994) sheets cost approximately one-third the price of asbestos-cement sheets and half that of corrugated iron sheets, but lower durability means that ARS may be a poor investment.

Durability

Varies with quality up to a maximum of 15 years.

The quantity of asphalt and the uniformity of impregnation is vital to avoid deformation or de-lamination of sheets. Research shows considerable variation in quality and therefore durability between manufacturers in developing countries suggesting a need for better quality control.

Fire proofing chemicals can be incorporated during manufacture, at additional cost. The sheets reach class B - moderate - (US standard) fire rating without additional treatment.

Production and economics

ARS sheets are manufactured in many countries around the world. Production equipment varies in output. Typical labour intensive processing, using Indian equipment (source MAS, Kerala) with 100 employees produces a maximum of 1 million sheets (2m x 1m) per annum. Machinery (inc. spares and laboratory) costs approximately US$ 1.1 million (1993) and would be sited in a 1500m2 building within a 15,000m2 factory site with 400 to 500 workers.

An ARS factory should be sited near a river, close to raw materials sources and away from residential areas due to petroleum/asphalt odours. If sheets are to be sun-dried a large yard and 200 sunny days per year are necessary.

Standards

Many countries have standard specifications for this type of sheet, but there is no internationally accepted standard. Indian Standard No. 12583.1988 is typical; it details: asphalt content, water absorption, weight bearing strength, behaviour at high temperature, and dimensional stability in varying conditions.

Particle board

Sheets are formed from wood chips, other small size ligno-cellulose chips or fibrous materials. A very extensive range of crop residues, wood chips and agricultural waste materials were tested for suitability with different binders during the 1970s in many countries. The material is thoroughly washed and then blended with a binder before being either hot pressed or extrusion pressed to form sheets. These may be corrugated or flat. The sheets should be coated with a weather-proof paint for external use - this is usually done in the factory. The price and durability will depend on the type of binder used.

Common binders are cement, magnesium oxychloride or phenol-formaldehyde resin. Cement bonded sheets contain 62% cement, 28% organic fibre with optional additives such as sodium silicate to improve dimensional stability. A water-proof coating has to be applied if sheets are used for roof cladding.

Dimensions

Thickness - 4mm to 40mm, for roof cladding. 15mm is recommended, Cement bonded sheets are produced in India in two sizes - 2240 x 1220mm or 3050 x 1220mm. Exact sizes will depend on the manufacturing equipment being used, and sheets can be cut to the desired size with a hand-saw. Most boards are flat, but corrugated panels can be made.

Weight

Varies with thickness up to 15kg/m2 for roofing grade sheets.

Roof structure

Similar requirements as for asphalt sheets. Minimum roof angle is 22°, steeper angle will be more durable. Sheets need supporting on horizontal battens which are nailed to rafters at maximum spacing of 500mm.

Resistance to termites and fungi

The fibres are mineralised within the binder and are thus not susceptible to insect or fungi attack.

Uses

Suitable for all types of building, but roof must be accessible for periodic re-sealing and maintenance.

Fixing method

Sheets are nailed or preferably screwed to the battens. If flat (rather than corrugated) sheets are used the vertical joints between sheets must be filled with a flexible sealing compound, and screw heads must also be similarly protected.

Durability

Depends on the roof slope, the quality of the waterproof coating and on climatic exposure. 10 years is maximum expected life for a regularly maintained roof on a 35° slope in tropical conditions.

Cost

Commercial products in India, per m2 of roofing, cost approximately the same as asphalt corrugated sheets. Prices vary according to the cost of the binder, price of the organic material and the scale of technology.

Production and economics

Equipment is available from a number of manufacturers to suit widely varying production conditions. The largest scale mechanised factories operating on a continuous basis with a minimum of manual handling may produce up to 800,000 roof sheets (2m x 1m) per year. The equipment cost would be at least US$2 million (1992), excluding land, building and staff costs. The smallest-scale plant, such as that developed by the Natural Resources Institute (NRI) in the UK, has an output of about 250,000 sheets per year output.


Asphalt impregnated sheets tend to warp and de-laminate in tropical conditions

Further information:

Bryant B.S.; Corrugated Roofing Panels from Agricultural Residues; Appropriate Technology. Vol. 4 No. 4, 1978, London.

Composite Roofing and Panelling Materials from Wood waste and Agricultural Fibrous Residues for Low-cost Housing; Construction Industry Authority of the Philippines, Manila, 1986.

Flynn G.; An Industrial Profile of Fibreboard Panel Processing; Tropical Products Institute, London, 1980.

Indian Bureau of Standards, Delhi.

LightRoofings Ltd. Hardiyan Sing Road, Karol Bagh, New Delhi - 110 0056.

NCL Industries, B - 87 Defence Colony, New Delhi 110024.

Mechanical Assembly Systems, Mayithara Market, PO Alleppy District, Kerala 688539, India. (for ARS equipment)

Natural Resources Institute, Central Ave., Chatham, ME4 4TB, UK (for particle board information.)

Checklist of benefits and problems for roof sheets with organic fibres

Potentials

Limits



· Light weight - easy to transport and requires light roof structure.

· Low durability.

· High strength/stiffness to weight ratio.

· Must be manufactured in centralised factories requiring high level of management skill and quality control.

· Suits all type of buildings, especially low-cost housing and temporary buildings.

· Binder, fire-retardants and water-proof coatings may have to be imported and may be expensive.

· Can be made fire-proof so may be used in urban areas.

· Low customer/house-owner appeal because of poor durability, variable quality and usually unattractive colour.

· Utilises organic materials that may otherwise be wasted - eg wood chips, bagasse, coir.


· Roofs can be used to collect water if weatherproof coating is non-toxic.


· Fairly low skill needed to fix the sheets.


· Low maintenance.


· Can be made in either small or very large factories.


· Low cost compared to other metal or asbestos cement sheets.


· Asphalt impregnated sheets are naturally more weatherproof and dimensionally stable than flat particle board.


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