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Earth reel roofs1.The main component is a reel,made by rolling long vegetablefibrous material (generally straw)and a wet clayey soil around awooden spindle (3 - 5 cm 0, 80 -100 cm long).2.The reels are laid between thetimber purlins when still moist andpressed against each other, thespace between them being filledwith a fibre-soil mix.3.After drying, the cracks arefilled with a mud slurry, on top ofwhich a 2 cm layer of soil,stabilized with finely choppedfibres and lime is applied.Finally, the roof is covered witha bitumen roofing felt and alayer of sand or fine gravel.4.On account of the largeproportion of vegetable fibres andtimber, the risk of termite attack isgreat.
Clay tile roofs 1.Burnt clay tile roofs are only used for sloping roofs between about 20° and 50° inclination of rafter, and the tile shapes differ for each range of slope. It should be remembered that the rafter pitch is always steeper than the tile pitch 2. Depending on the clay type and production method, a major problem of clay tiles is the immense loss (in India about 35 %) due to cracking and breakage. A good remedy has been found in the use of ammonium chloride as an admixture varying between 0.1 and 1.0 %, depending on the type of soil . 3.Clay tiles are heavy, requiring a strong substructure and closely spaced battens. Therefore, tile designs (eg Mangalore tiles), which require wider spacing of battens, are lighter and more economical. But generally, the weight of the roof and loose connection of tiles, make them susceptible to destruction in earthquakes.
Gypsum-sisal conoid 1.The conoid unit has a shape which makes it suitable for use as roofing as well as wall components.• The aim was to produce a strong, versatile component from gypsum and sisal (which are abundantly available in some regions), using simple formwork and equipment 2.Preparing the formwork: the timber frame is filled with broken bricks and stone, first large pieces, then small pieces and finally a fine sand, which is smoothed to the desired shape, and covered with a polythene sheet. On this the gypsum-sisal mortar is spread to form the conoid. 3.Laboratory tests showed a good strength to weight performance, since the fibres have high tensile strength and bond well with the gypsum. Furthermore, resistance to fire and biological attack is Potential assembly of the modules good.
Precast concrete channel roof 1.The assembly of the roof is done manually. After placing the boughs side by side, the gaps between them and the top of the walls are closed by inserting precast filler blocks and sealed around the edges. A polythene sheet is laid over the troughs, which are covered with a 20 mm layer of loose gravel, for improved thermal performance and to protect the sheet. The gravel is kept in place by precast, shaped, no-fines concrete blocks placed dry at the ends of the troughs. Rainwater that collects in the troughs percolates through the no-fines concrete and can be collected. Hence, a 5 % slope is suitable.
Ferrocement roofsFerrocement components are extremelythin (15 to 25 mm), but have a higherpercentage of reinforcement thanreinforced concrete, thus achieving ahigher tensile-strength-to-weight ratio.Further strength and rigidity isachieved by curvature or folds.• Ferrocement roofs can be made insitu or with precast components, theformer being useful for free forms, thelatter being appropriate for modularand repetitive constructions.• Depending on the design,ferrocement roofs can be made to span .large areas without supportingstructures, thus saving costs andproviding unobstructed covered areas.If the ferrocement surface is properlyexecuted (complete cover of wire mesh,dense and smooth finish, cracks sealed)no surface protection is needed, thussaving further costs. However, it isadvantageous to apply a reflective coaton the outer surface to reduce solarheat absorption
Corrugated metal sheet roofing• The metal sheets are either galvanized iron or aluminium, whereby gi issusceptible to rapid corrosion if the zinc coating is not sufficientlythick (a common problem with cheaper varieties). Aluminium is lighter,more durable and reflects heat more efficiently, but is more expensive and produced with an extremely high energy input.
1 Once the walls are erected, noreinforced concrete ring beam isrequired, as the roof is designed toclamp the walls together.• Around the top, outer edge of thewalls, a timber frame (6 x 6 cm) is fixed,as well as two tripod frames above thefloor area. The surfaces described bythese frames are hyperbolicparaboloids (hypars), which are madeup of straight lines. This simplifies thefixing of the wire mesh 2.The mesh (2 or 3 layers) is stretched over the frame and nailed or stapled onto it. The frame is only needed to hold the mesh during construction, as the structure will be self-supporting once plastered. 3. Reinforcing bars are fixed around the wall and along the folds of the roof. 4. The roof is plastered by a team on top forcing the mortar through the mesh, while another team below recovers the falling mortar to plaster the inside.
Ferro cement roofing channels have a uniform segmental profile; they are 2.5 cm thick and 83 cm. wide.Maximum length of mechanically produced channels can be 6 meters. Longer spans for roofing can be builtwith intermediate supports. Ferro cement roofing channels are manufactured using a fixed proportion of cement, sand and water to givehigh strength mortar that is reinforced with a layer of galvanized iron chicken wire mesh of 22 gauge and Torsteel bars of 8-12 mm diameter provided in the bottom nibs of the channel. Ferro cement roofing channelscan be safely transported after a curing period of 14 days,.
Corrugated fibre concrete roofing sheets 1.require fairly simple, locally made equipment and a very well coordinated working team of at least two workers; 2. consume about the same amount of cement es asbestos cements sheets (15 kg per m2), on account of their greater thickness and production method by manual tamping, but require no electricity; 3.are difficult to handle when fresh and to cure in water tanks, because of their large size;4. are difficult to transport and install without breakage, and do not tolerate inaccurately constructed and flexing supporting structures; 4. withstand strong wind forces because they are heavy and have few overlaps.6.In most cases FC/MC tiles are easier to produce and install than FC sheets and therefore represent the more appropriate solution. 5.The corrugated FC sheets are laid on timber roof structures in much the same way as gci and ac sheets. However, FC sheets are less flexible and can be damaged if the loads are not evenly distributed.
Fibre and micro concrete tiles1.were developed to overcome most of the problems encountered in producing andinstalling corrugated FC sheets (previous example);2, are made most efficiently on a small vibrating table (hand powered or run by electricity,ea. a car battery), which can be operated by a single trained worker;3.can be made thinner (6 mm) than FC sheets (10 mm), and their cement: sand ratio(between 1: 2 and 1: 3) is less than for FC sheets (1: 1), so that the cement used formaking tiles is only between 5 and 7 kg per m 2 of roofing;4.are easy to handle when fresh and to cure in water tanks; do not tend to break as easilyas sheets during transport and installation, and minor inaccuracies in the supportingstructure have no negative effects; are easily torn off by strong wind forces, if they arenot well fixed to the substructure.
Installation of FC/MC Roofing1.The FC/MC tiles are laid on timber laths (spaced at 40cm centres) in the same way as clay roof materials. Slightinaccuracies do not cause major problems especially in thecase of pantile. The tiles are fixed with wire loops, nailed ortied onto the timber laths.2.Two types of tiles are common:• The pantile : is of a sinouscourve like shape and can easily beplaced on a slightly uneven roof.• The Roman tile: gives a neater roof surface but requires an evenroof structure.
Durable thatch with stiff-stem grasses 1.Thatch is the most commonly used roof covering in the world, although it is barely recognized by construction experts. In India, for example, some 40 million houses are thatched. 2.Almost any vegetable material, from the bark of trees to finely-tapering water reeds, can be used, though grasses, reeds and palms are most common. 3.Traditional types of thatch have short durability and performance, but in certain regions (N.W. Europe, Southern Africa, Japan) skilled workmanship produces good quality functional roofing, with life expectancies between 25 and 70 years. 4.Thatch uses renewable, local materials requiring minimal or zero artificial energy input in production, and costing less than most other types of roofing. Their application is labour-intensive - an important advantage in terms of employment generation. At the end of their useful life, thatching materials can be composted or compacted for use as fuel.
1.Almost any shape of roof with a minimum pitch of 45° can be thatched. Thatch will mould itself toany curve except a convex-shaped roof.2. Pole timbers and split battens may be used, and simple configurations work best, that is, valleysand other changes of roof pitch are not recommended.3 The structure should be capable of supporting up to 40 kg/m2, which is the weight of theheaviest material - reed.4. A tilting board, 35 mm thicker than subsequent battens, fixed along all the eaves and barges ateave level, is essential to force the first course into tension, making the rest of the thatch moretightly compacted.
Bamboo roof structure1.On the principle of masonry barrel vaults,full-section bamboo culms are laidhorizontally, one on top of the otherfollowing a curve, defined by an invertedcatenary. (This is a curve formed by hanginga uniform chain freely between two points.The tensile forces induced by gravitation runalong the line connecting the points ofcontact of each chain link.2.Since the curve remains stable whenreversing the direction of forces, an invertedcatenary is the ideal shape of a barrel vault.)3. Split bamboo strips of equal length arehung such that their ends are exactly thesame distance apart as the ultimate roofspan. The full-section bamboo culms are laidhorizontally forming an inverted vault. 4.Splitbamboo strips are then laid on the inside,exactly opposite the outer ones. Holes aredrilled through the split and whole bamboo It is a traditional technology, which is well understood by localand fixed by bolts or rivets. artisans. No special tools are required. 1. The large-scale utilization of bamboo has no disastrous5. The whole structure is then turned over environmental consequences (as in the case of timber), onand fixed on the top of the walls, which account of its quick replacement within 4 or 5 years.preferably should have a timber or concrete 2. The physical properties of bamboo make it an idealring beam, onto which the roof is connected. construction material for seismic areas. 3.Compared with most other building materials, bamboo is cheap to buy, process and maintain.
1.Corresponding to the chain net,the grid is assembled on the groundand tied at each cross point. Forirregular base plans, each bar willhave a different length, which ismeasured off the suspended model.Since the split bamboo gets moretwisted, the steeper the slope of thegrid shell, dowel joints cannot beused, while rope tie joints maintain aharmonious curvature of thestructure.2.In order to construct spatiallycurved load-bearing structures usingrelatively thin bars, the same principleof inverting catenary lines, asdescribed under "Barrel Vault", isapplied. The shape of such gridshells is, therefore, not designed, butdetermined by using suspendedmodels (eg with chain nets). Severalsuch structures using split bamboohave been developed and erected ona joint project of the Institute ofLightweight Structures
Pole timber roof structures1.Unprocessed roundwood is cheaper and more easilyavailable than sawn timber, and is mainly used for framestructures, ie skeleton wall and roof structures, trussesand the like.2. The advantages of using pole timber from young trees(5 - 7 years old) as compared to those of using sawntimber are numerous. The main ones are:3. The cost and wastage of sawing are eliminated.4. 100 % of the harvested timbers strength is utilized,while the immense original strength of large tree trunks isforfeited by sub-division or lost in the sawing wastes.5.A timber pole is stronger than sawn timber of equalcross-sectional area, because the fibres flow smoothlyaround natural defects and do not end as sloping grain atcut surfaces.6.Hence, from the points of view of economy, strengthcharacteristics and environmental acceptability, the useof pole timber (eg from mangrove swamps, thinnings fromeucalyptus or softwood plantations, etc.) can be far moreappropriate for a range of building constructions than theuse of sawn timber.
1.Where strong connections are vital, steel bolts and nutsare most suitable, but also very expensive, costing three tofour times that of the mild steel rods from which they aremade. Using the rods straight away as dowels is cheaperand equally effective. To prevent them from slipping outof the timber, 10- 12mm deep holes should be drilled intothe ends of the dowels, as described above in the case ofwooden dowels. With a cross saw cut, the end pieces canbe bent back like flower petals, holding down a steelwasher..2. Space Frame Connections (Bibl. 23.10)1.A method of using short length, local pole timber toconstruct space frames for large covered areas (such asmeeting halls, workshops, markets, etc.) was developed inSweden by Habitropic. The system is based on specialspace frame connectors, comprising a cros-scomponent ofwelded steel, and tail end connectors with screws, washersand nuts2.The poles are all cut to the same length, say 1.5 m, andcut lengthwise at both ends with a saw. Holes for bolts aredrilled at each end, the steel tail-end connectors insertedin the saw cut and fixed with bolt, washer and nut. Afterprefabricating all the required pores, they are assembledon the ground, directly below their final position and liftedinto place by a pulley system.
Hogan Roof ConstructionThe North American Navajo Indians traditionally 1.A well designed roof with accurately cut andbuild their homes (hogans) with this simple method. assembled poles should in theory be stable with onlyA hogan is usually an octagonal house covered by a few bolt or dowel connections at certain strategicseveral layers of timber poles, which are laid across points. However, it is advisable to fix each polethe corners of the layer below, thus reducing the firmly to the one below to avoid excessive lateralvoid with each new layer. The same system can be movement, especially in earthquake or hurricaneused to cover triangular, square or other polygonal prone regions.structures, without the need for supports otherthan at the periphery of the roof. 2.Traditionally, the hogan roof is covered with earth to provide a high thermal capacity, which is advantageous in climates with large diurnal temperature fluctuations. Lighter roofs with low thermal capacity are also possible by merely constructing a framework and bridging the gaps with a waterproof membrane and light roof cover (eg wooden lathing and shingles, mats, thatch).
Bamboo and wood shingles1.Shingles are used to cover pitched roofs (and quiteoften walls) on a supporting grid of bamboo orwooden laths. The appearance is typically a fish-scalestructure, but some types of bamboo shingles ratherresemble Spanish tiles.2, Appropriate lengths of bamboo culms or timberlogs are cut and the shingles are split off thesevertically, whereby bamboo culms are split into quarteror half sections, and wood shingles are flat tiles cutwith a special knife and hammer. .3. For fixing bamboo shingles, pre-drilled holes areneeded for nailing or tying with a tough string.Quarter-cut bamboo shingles can also be made withsplints which are hooked onto the lathing.4.Timber shingles are nailed onto the battens,whereby the curvature of the shingles after dryingmust be taken into consideration. Bamboo Shingles with Splint or String Fixing
Corrugated metal sheet roofing1.The corrugations make the thin sheets stiffenough to span between two purlins withoutsagging. Thus large areas can be roofed with aminimum of supporting construction, making the rooflight (good in earthquake zones) and cheaper (lesstimber or steel framework).2. Thin gauge sheets are often too weak to walk on,can be dented, punctured or torn off by strongwinds.3. Major problems of metal sheet roofing are theimmense heat transmission to the interior (lesssevere with aluminium) during sunshine, and watercondensation on the underside .4.The metal sheets are either galvanized iron oraluminium, whereby gi is susceptible to rapidcorrosion if the zinc coating is not sufficiently thick(a common problem with cheaper varieties).Aluminium is lighter, more durable and reflects heatmore efficiently, but is more expensive andproduced with an extremely high energy input.5.The corrugations make the thin sheets stiffenough to span between two purlins withoutsagging. Thus large areas can be roofed with aminimum of supporting construction, making the rooflight (good in earthquake zones) and cheaper (lesstimber or steel framework).
Concrete block constructionConcrete block construction is gaining importance in developing countries, even in low-cost housing, and has become a valid alternative to fired clay bricks, stabilized soil,stone, timber and other common constructions, providing the ingredients are availablelocally, are of good qualityThe essential ingredients of concrete are cement, aggregate (sand, gravel) and water,but the physical characteristics of the material can be extremely diverse, depending onthe type and relative proportions of these ingredients, the addition of other ingredientsand components, and also the production method. and economically blocks are produced in a 3.Concrete viable. large variety of shapes and sizes, either solid, cellular or hollow, dense or lightweight, air-cured or steam- cured, loadbearing or non- loadbearing, and can be produced manually or with the help of machines. 4.Block sizes are usually referred to by their nominal dimensions, which are the actual block length, width and height plus 10 mm of mortar bed thickness added to each dimension. These are normally based on the modular coordination of design with the 10cm module as its basic unit.
This style of earth dome and vaultconstruction was used in a reconstructionprogram at New Gourna, Egypt. wall section for adobe walls
The various shapes of blocks produced byThis typical wall section for adobe the Land-crete block making machine allow rigid construction of corners and tees