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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

Wood tiles (shingles and shakes)

Fundamental information

Shingles and shakes are wood tiles which are either split or sawn from blocks of unseasoned timber and laid in overlapping layers on a sloping roof. Many different timber species are suitable and they can be made either with simple hand tools or in sophisticated mechanised factories. The resulting roof can last 70 or more years, depending on species, preservative treatment and on exposure conditions.

Bamboo can also be split to make roof tiles.

Split wood shakes have a very long history. In Europe oak shakes were used for medieval building, in North America records show that cedar shakes were used by the first old world settlers. In Canada untreated western red cedar shake roofs have been known to last over a 100 years. Today wood tiles are used throughout the world. The economy offered by modern timber processing and preserving methods means that sawn shingles are now more widely used than split shakes.


Wood tiles are split to make shakes


Shingles are sawn wood tiles


Shake makers tools - the wedge shape of the froe is important as it splits the wood whilst the handle provides leverage


Shakes are split from blocks of timber

Basic techniques - processing and use

Materials

Straight grained timber, preferably from a mature hardwood tree makes the best wood tiles. Red cedar and oak, traditionally used in Europe and America, are very durable but many other species are suitable. Choice depends primarily on what is locally available. Softer woods should be treated with preservatives.

For economy and less waste the tree should be minimum 400mm diameter and without branches for first 5m. Wood tiles should be made when the timber is freshly cut, before it dries.

Processing

Tree trunks are sawn into logs at least 450mm long.

Shakes are split using a froe and wedges. The process of splitting leaves a slightly rough surface which gives shake roofs a distinctive and aesthetically attractive appearance. The work is labour intensive - a positive advantage wherever unemployment rates are high.

Shingles are cut using a saw. Sawing cuts across the natural fibres of the timber, so water penetrates shingles more readily than shakes.


A modern wood shingle roof in Germany

Both shakes and shingles are wedge shaped - slightly thicker at one end.

Many sawmills have equipment that can produce small sawn boards from off-cuts which may otherwise be wasted. This may be a low cost source as shingles. For example, in Myanmar (Burma) plywood off-cuts sealed with old engine oil are the cheapest roofing material. They last about 6 years. A band-saw or a veneer lathe can be used.

A purpose made circular blade shingle saw set within a flat-bed steel frame is most productive. This is not worth the investment unless a substantial market can be served. An efficient operation will require a small factory able to manage handling, processing, preservative treatment, storage and transport of raw materials and products.

If preservative treatment is desirable this is done by dipping or by pressure or vacuum impregnation (see page 23 for details).

Dimensions of wood tiles

Minimum: 150mm wide x 450mm long x 10mm thick
Maximum: 250mm wide x 600mm long x 25mm thick

Quantity required for roofing

The number of tiles needed varies with species, roof slope and the exposure (the amount of each of tile exposed to the elements on the roof surface). On average 33 shingles are needed for each square meter of roof area. These will weigh between 30 and 40kg, depending on species. A medium size house (150m2 floor area) would use about 3,300 tiles.

Roof structures

Shingles and shakes must be laid on a roof with a minimum slope of 30°, preferably 45° for better durability. Below 30° rainwater will not discharge rapidly so tiles will be liable to rapid decay.

The roof must be designed to support weight of 30-40kg/m2 Rafter spacing: 600 to 1500mm, Batten size: 75mm x 20mm for 1500mm rafter spacing, less for closer rafters.

Batten spacing: 180mm - 210mm centres, depending on roof slope and exposure of shingles.

A general principle is that the roof design, as for thatch, should preferably be simple without changes of slope. But wood tiles are a flexible covering so will accommodate irregular shaped and curved roofs.

Fire risk means that untreated tiles should not be used on public buildings, And building laws may prohibit their use in urban areas.


A wood tile roof showing key features of best practice

Roofing work

Tiles are laid in ascending layers starting with a double thick layer at eaves and verges. Each tile is secured to battens with two non-rusting nails (copper, aluminium or galvanized steel) half way up each tile. Work is completed layer by layer to the ridge, overlapping to cover nailing and to create desired exposure of tile on the surface (see table). Avoid vertical joint overlaps and allow 5mm gap between each tile for expansion and movement. At the ridge, hips and valleys, provide protective underlay of tar paper or thin sheet metal. The ridge may be made of tiles, or a metal capping wide enough to cover the nailed fixing of the uppermost layer of tiles on each side of the roof.

Performance

Durability depends on species, roof angle, length of tile exposed and climate. Up to 70 years in temperate zone on 45% roof slope, 30 years in humid tropics.

Cost

Varies with labour rate and cost of material. A team of two skilled tilers can lay up to 20m2 per day. In Europe, finished roof price per m2 is comparable with a clay tile roof, but more expensive than corrugated iron.

Maintenance

A steeply pitched roof should require less maintenance than a flatter one; rainwater will run off quickly as decay should be slower. Whenever necessary, moss, fallen leaves and fungi should be removed from the roof by brushing, but avoid climbing on an old roof.

A copper strip or thin cable, fixed along the ridge should improve durability. Copper sulphate solution created by rain reacting with the copper acts as an effective fungicide/herbicide.

If a leak occurs - this may happen if a tile splits or is damaged, a tar paper 'tile' should be inserted between shingles.

Bamboo tiles and planks

Where bamboo is plentiful and knowledge of bamboo building exists, tiles or long planks can be used for very low-cost roof covering.


Inside view of a split bamboo tile roof


Red cedar shingles

Flat tiles are made from 300mm long lengths of bamboo. The culm should have a minimum diameter of 130mm. The tiles are made by hand by scoring grooves around the circumference of a bamboo culm with a sharp chisel and then flattening the culm with a mallet. The inner part of the culm internode diaphragm acts as a tile nib which can be used to hang the tile from battens. Battens may also be made from lengths of split bamboo. A tile roof made with flattened sections of bamboo is laid in the same way as any other flat tile or shingle roof.

An alternative way of using bamboo for tiling is to split bamboo culms into two equal half-cylinder sections. These are then laid on split-bamboo battens like interlocking Spanish tiles to create a roof 3 layers thick and weighing about 25kg/m2.

Bamboo planks are made by splitting lengths of bamboo into two sections. The length may be as long at the roof's ridge to eave length. The half-round sections interlock and overlap each other, like Spanish tiles. Bamboo plank roofing will be lighter and more durable than bamboo tiles.

The durability of these tiles and planks is low as bamboo rots quickly when wet, but may reach a maximum of ten years in a dry climate on a steeply angled roof. Preservative treatment by dipping in chemicals will increase the cost but ensure a minimum life even in a warm humid climate to at least 7 years. Bamboo roofs, in common with other biomass roofing materials, are very combustible.

Optimum exposure for different shingle and shakes sizes on different roof slopes

Shingles

Tile length

1:4 slope

1:3 slope

400mm

90mm

130mm

450mm

105mm

135mm

650mm

140mm

185mm

Shakes

Tile length

1:4 slope

>1:3 slope

450mm

185mm

185mm

600mm

250mm

250mm


Shake roof and timber-clad walls

Further Information:

Powter A.; Papua New Guinea Shingle and Shake Manual; Forest Products Research Centre, Port Moresby, PNG, 1976.

Trelaun B.; Tuiles de Bois - USA and Canada; GRET, Paris, 1984.

Janssen J.; Building with Bamboo; IT Publications, London, 1995

Checklist of benefits and problems

Potentials

Limits



Shingles (sawn wood tiles)

Shingles

· Can use any species, both softwood and hardwood, but avoid knotty or twisted timber.

· must use straight grained hardwood species which split easily.

· Mechanisation gives possibility for high output.

· produced manually so output rates are lower than sawn shakes.

· Standardised product may be less pleasing aesthetically than shakes.

· are dimensionally stable because they are split radially leaving natural grain intact.

· Must be treated with preservatives, preferably by pressure impregnation - but this prevents water collection from the roof.

· each shingle is slightly different size and appearance - roofing work may take longer but the finished roof may be more attractive than shakes.

· Shingles are thinner than shakes, so roof structure may be lighter.

· shingles are thicker than shakes so roof structure must be stronger.



Shakes (split wood tiles)

Shakes

· Need not be treated with preservatives - rainwater can be collected.

· needs expensive mechanical saws (band saw or circular saw) and rigorous management of processing plant.

· Needs simple hand tools to split and trim to size - variable production rate depends on skill and labour availability.

· more waste than shingles.

· Can be produced close to timber resource or building site, avoiding expensive transport.

· central processing may mean expensive transport to building site.

· Produces less waste than shingles.

· dimensionally unstable - tend to warp, crack and cup when wet due to exposure of sawn timber fibres - shakes are often less durable.

· Hardwood shakes are naturally more durable than shingles.

· standardised product allows more rapid roofing work.