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SheetingIts use for emergency shelterand other purposes

AN OXFAM TECHNI


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revision February 1981Third revision May 1989

xfam 1989Library Cataloguing in Publication Da

Howard, Jim 1926-Plastic sheeting: its use for emergency houand other purposes - 2nd ed.1.Developing Countries. Residences. Build1materials. Plastic sheeting.Ie 11 . Spice, Ron

.92

Oxfam is a partnership ofpeople committed to therelief of poverty, distressand suffering in any part ofthe world.We believe In the essentialdignity of people and Intheir capacity to overcomethe problems they facewhether they stem fromnatural, social, poiltical oreconomic conditions. 851~~189


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Contents 1 Introduction 12 Types of flexible plastic sheeting available 33 Properties of polythene sheeting 53.1 General properties3.2 Mechanical properties3.3 Thicknesses3.4 Colours3.5 Sunshine degradation or weakening 83.6 Thermal properties of film-coveredstructures 93.7 Condensation in film-covered structures 114 Structures covered with plastic films 134.1 General points 134.2 Semi-cylindrical structure 144.3 Ridge tent structure 164.4 The Oxfam temporary shelter 22

6 Details of manufacturers

lIIIllIV

AppendicesUseful data for water SPrecipitation dataOther useful dataA guide to pricesand accessories

iii


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Introduction This technical guide arises from Oxfam'sxperience of using considerable quantitieslastic sheeting in disaster situations. It haeen prepared to help field s taf f and othe

of structures, with a

be seen in the UK and elsewhere, and the greatnumber of semi-permanent plastic-clad farmbuildings used for farm stocand storage.Polythene or, more correctlysheeting is now readily availthe world in large quantitiesand qualities. In addition to its use for shelter,can be used for storage, tank linings, tarpaulintype covers, groundsheets, food containers, cprotection, inflated-walled houses, irrigation ansoil mulching.

can also be a m ajor form of trash and litter

isintegrate. It is essential tha t every e ffo rt

anner in the given cond ition


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Description

Black rolls

Black rolls

Greentarpaulins

Dark greertarpaulinrolls

Greentarpaulinrolls

No

No

Yes

Yes

Yes

Yes

Eyelets

None

None

At475mmcentres311 rounc

II

At950mmcentresdownlongsidesII

Aream x m

Unit *,kg Unit size as storedm x m x m


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Types of Most plastic materials such as polythene,flexible polyvinyl chloride (PVC), nylon, terylene,polypropylene, etc. can be produced in the formP of thin , flexible sheeting. Also available asheeting several kinds of flexible sheeting reinfavailable a square m esh of natural or syntheticgive greater strength and resistance tSuch reinforcement increases the cos tweight per un it area. The maximum seamwidths of 1 0 0 0 gauge (2 5 0 micron or 0.25 mm)sheeting available are 4 metres reinforced and 8metres with no reinforcing. Wider sheets have tobe fabricated by stitching or heat sealing. Thereinforced sheeting is available with ready-fixedeyelets in various spacings and configurations.M os t of this guide relates to polythene sheeting.However, all the techniques discussed w ill workequally well with any flexible plastic she eting thatis available on site.


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of Polythene sheeting has many advantages whenpolythene compared to other flexible materials that can besheeting used as waterproof membranes. The chieadvantages are its low cost and weight pearea. It is available from the manufacturers instandard seamless sheeting up to 8 metres widein 1000 gauge or 1500 gauge (250 and 375microns). Its properties are as follows:

a. Resistance to water. It is completelywaterproof and has a very low moisturevapour permeability.b. Chemical resistance. It is unaffected bvsalts, dung- urine and most agriculturalchemicals. Petrol and lubricating oils maycause swelling by absorption and should notbe stored in contact with the sheetinc. Ageing and weathering. Polytcannot mildew or rot in store and itunaffected by moisture. Clear sheedeteriorates slowly in sunshine and theprogressive loss of strength and flexibilbecome apparent after a period of fro15 months. Black sheeting, however,resistant to sunlight and is recommenmost outdoor uses where light trnot essential.

S. The sheeting isflexible down to temperatures well belowfreezing point. It melts at 115'C (239' F), i.e.above the boiling point of water, but starts tosoften and lose tensile strength at above80' C (175' F)


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, he main propertiesstic material can be listed a!

a. Flexibility, for ease of insta llation and to

b. Toughness, to remain undamaged duringnstallation process and subsequentackfilling' operation.etain its physical propertie

ck by soil fauna.ernes of temperature.

3.3 ThicknessesPolythene films are made in thicknesses rangi~rom 1 2 m icrons (5 0 gauge) to 1 0 0 0 m icrons0 0 0 gauge). Cost per unit area is proportiorthickness.Polythene sheeting i s available from UK,Continental and American manufacturers inseamless widths o f up to 8 metres in 1 0 0 0gauge and in seam less widths of 1 7 metres in500 gauge. For ease of transport th is wide


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ting is normally folded twice at the factoryat it can be rolled on to a cardboard core.Thus, 8 metre wide seaon a 2 metre wide core. The weigauge sheeting is approximatelysquare metre.Polythene films are mamachine direction (alongthan in the transverse diUnreinforced polythene film of 1 0 0 0 gauge istough enough to withstand wind stressesadequately if correctly fixed to structures. (Mostof the greenhouse acreage already mentioned iscovered with film of 5 0 0 gauge. The 5 0 kg sacksused to trans port fertilisers and other chemicalsare usually made from 8 0 0 gauge sheeting andsome farmers use cut open plastic sacks forsimple farm buldings such as calf housing.)

7


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3.5 Sunshine degradation or weakeningClear plastic deteriorates fairly quickly in stronsunlight, although coloured polythenes are faless susceptible to degradation due to sunshwith darker colours being more res istant andblack extremely resistant.

by continuous exposure to suns hine . Thedurability of clear films intended for use oucan be considerably increased by addingchem icals called 'ultra-violet light absorbers'during manufacture. Such 'ultra-violet lighinhibited' film s currently commercially availas t for a t least two years when continuexposed to sunshine on greenhouse strin the UK and it would be reasonable toleast a one-year life from them even in coun tr~like India. Ultra-violet light inhibited films oftehave a sligh t yellow or green colour which is dto the nature of the absorbing chemical use

long sunshine periods, at high temperatures tdegradation of reinforced plastic sheaccelerated when such sheetings areexposed to sun light. The reinforcingwhether this be metal wire, nylon or somesubstance, can cause 'hot spo ts' within tsheeting and these temperature different!cause local damage - brittleness or laminatiwhich reduces the structural strength of thesheeting materialTo a lesser degree th is sam e 'hot sparises where polythene film is stressstruc ture which will absorb and ho ld heat, sueas metal tubing. Film in contact with th is ho tstruc ture will weaken more quickly for any givamount of ultra-violet light rad iation than film


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air temperature. Ways of providing thenecessary protection are:a. Using a black polythene adhesive tape onthe outside o f the polythene cover, so tha t itprotects the sheet itself from sunshine in thiscritical area (black polythene film is acompletely resistant to ultra-violet lighdegradatiob. Painting the film with aluminium orbitumastic paint at those points where it is incontact with the structure.c. Using anti-hot spot foam tape.

3.6 Thermal properties of film-coveredstructuresBlack films expand when the sun shines andcontract a t night. The actual expansion factor is1%er 38- (100' F) temperature change.Thus, a black plastic skin fitted to a strwhen the sun is sh ining will become drafter n ightfall; allowance should be m aconstruction for this expansion and contract!Clear films do no t absorb heat energy from tsun and stay at ambient temperature;consequently the expansion/contraction rate cangenerally be ignored.The thermal insulation properties ('U' factor) ofpolythene films are poor. However, well-insulatedbuildings can be made by using two sheets ofplastic between which is sandwiched aninsulating material. In the UK some verysatisfactory mushroom-growinghouses havebeen made in this way, using fibreglass ormineral wool as an insu lant. In Italy, farmbuildings have been made in the same manner,using two layers of p lastic with straw as an


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insulant. Any lightweight, dry material whichcontains a lo t of air spaces would be su itable. lanic material like straw or hay is so usedbe desirable to pre-treat it with an

If the temperature within any plastic-cladstructure becom es too high in sunshine it can I:reduced by spraying the outer su rface withaluminium or light-coloured paint. Even a lime-wash or thin mud slurry might give temporaryprotection in extreme circumstances. Somepaints do not adhere very well to polythenesurfaces, and may need to be replaced after aperiod of time .Alternatively, a special polythene netting can beused over the sheeting to provide partial shadeNetting can also be used on its own to providesome protection against wind and sun insituations where som e air movement andsubdued light is desirable.Living conditions in an emergency sheltercovered with white, green or blue film might bere agreeable than in structures clad with clefilm; day temperatures would certainlyequable as emergency housing sheltetplastic film will tend to be hot when thsun shines and cold at night.The fire hazards to the occupants of a structurecovered with a single skin of polythene areminimal; the film melts at temperatures inexcess of 100'C (212' ).However, th is is not true where two layers ofplastic are used with a straw or hay inner fillingClearly, the risk of ignition from cooking, lightingor cigarettes is much higher. It is essential thatthe f ire risks and danger are appreciated by theusers of the structures.


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3.7 Condensation in film-covered structuresWhen the temperature inside the shelter i sgreater than that outside, condensation mayform on the inner surface. This may be causedby dampness in the soil and in this case tamount of condensation forming can be reby using a polythene film 'carpet' on th e floor othe shelter to help prevent evaporation from thesoil. Condensation can also be caused bycooking or by the drying of wet clothes inside astructure. Increased ventilation can help toreduce condensation caused in these ways.


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Structures 4.1General pointstended for emergency

film a. offer shelter from the weat

c. no t be unbearably ho t in daytime.Choice between different films as a coveringwill depend on:a. availability;b. expected life of the shelter;c. prevailing climatic conditions.

The circumstances in which any emergency andcally available structural materials are used willbviously vary greatly. It would therefore beunhelpful to be dogmatic in these notes, whare intended for general guidance only.There are three problstructures, namely:

a. erection of the framework;b. securing the plastic to the framework;c. securing the plastic to the ground.

An obvious bu t extremely importan t rule withpolythene structures is to prevent the polythenepressing against sharp or rough points whichcould initiate tearing. Thus, contact areasn sheeting and other materials should be


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4.2 Semi-cyllndrlcal structureA semi-cylindrical structufilm is commonly usedUK. The basic structurBecause the p lastic iscurved surface no streflapping should occur in the wind.dimensions of the frato suit the plastic film available and to thmethod used for securing the film to the

Figure 1.Framework for plastic greenhouse

One poss ibility is that rolls of 8m width blapolythene without eyelets or reinforcing migavailable (see Table 1). n this case it might bmost appropriate to secure the sheeting byburying its edges in the ground. Methods of


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doing this are described later, but about 800 m mshould be allowed for this purpose on each s ide(Figure 2). The remaining width will be sufficien tto cover a semi-circle of 4.3m diameter (D) and2.15m height (H). The length of curved polerequired for each arch, allowing for 300m in theground on bo th sides, is 7.35m.

Figure 2. Cross section of plastic greenhousePolythene sheeting

Trench backfilled trench at either

Supports n ground

Another possibility is that rolls of 4 m width greenreinforced tarpaulins and tentpegs are available.In this case two 4m rolls could be joined at thehighest point of the structure using the built-ineyelets. Securing the sheeting to the groundwith te nt pegs through the o ther eyelets will allowthe fu ll 8 m width to be used for cover.In the UK, suitably curved steel tub ing i s used forthe framework. If this is not available quickly in adisaster area, PVC rigid tube can be utilized.PVC rigid tube arches smoothly, returns to itsoriginal straightness, is relatively cheap,lightweight and easy to transport. The ridge of astructure made of PVC tubing could be joined t o


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Figure4. Basic shelter using rope as a ridge

Wooden or metal

buriedand coveredwith stones

A more durable ridge tent can be constructed byspanning the upright posts with a metal orwooden ridge pole. If the materials available tomake ridge poles are not sufficiently strong tospan the entire length of the tent,intermediate uprights can be usedThe stability of this type of structure wiupon the rigidity of the ridge and the anchoringFigure5 .Simple plastic covered shelter with intermediate uprig


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The ridge poles should be as free of protrusionsor irregularities as possible to avoid tearing theplastic and are m ost simply fixed to th e uprightsby means of nails. Rather than having tpierce the p lastic directly, it is preferablsandwich the film between the ridge pole ashort upper piece of sawn timber which wilresist tearing better. If sufficient sawn timavailable, a piece the full length of the ridgecould be used and na iled a t several points.Obviously, sharp edges or rubbing poin ts onthese lengths of sawn timber should be avoided.The simplest method of anchoring the sheetingto the ground is to dig a shallow trench and burythe length of sheeting. However, in areas withstrong winds or with sandy soils which do noteasily grip polythene, this is unlikely to proveadequate. Figures 9, 1 0 and 11show methodsof improving the anchorage between thepolythene and the soil. The techn iquesillustra ted in Figures 9 and 1 0 have thedisadvantage of burying quite long lengths ofsheeting, with the resu lt of reducing the effectivcoverage of the tent.

Figure 9.


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Figure10.Using timber to secure plastic at ground level /film

-

Figure11.Securing plastic at ground level using sawn timberT /

Batten or similar25mm X 20mmtimber - dge of polytheneis wrapped around battenand nailed to timberfixed at soil levelTimber rail fixed at+round level50mm X 50mm75mm X 50mm

Alternatively, where available, tent pegs can beused; however, they will require specialreinforcing eyelets to prevent the sheet tearing.ome plastic sheetings are manufactured withyelets built in at various centres (see Table 1).hen sheeting materials need to be fitted witheyelets in the field, these can be suppliedseparately. They come in two pieces and arefixed through sheeting materials either by using amandrel and die, or, for the snapand-fix 'ARRO'eyelets, simply by hammering.


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Sheet materials should be double thickness, ifpossible, at eyeletting points. The material

shown in Figure 12.Figure12. Use of knot for securing plastic

Corner of polythene sheet

a. The use of guy ropes, good practice in allcircumstances, is essential in areas withb. Any available netting material placed overthe plastic sheeting will help to reduce winddamage.c. Where available, reinforced polythensheeting shoufd be used for the mainthe tent as its far greater resistance tmakes the additional expenditure wor

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pecial polythene mesh can be used as abreak, normally as a free standing barriern t of a line of tents. (Thin polythene meshmaterial is commonly used in Europe to protectcrops or prevent snow drifting on exposedhillsides.)Where very cold conditions are experiencedpeople using emergency shelters sometimesexcavate par t of the floor area within the ten t toprovide a sleep ing space free from draughts.

4.4 The Oxfam temporary shelterThe Oxfam Technical Unit have designed a simpleridge tent, in kit form, based on polythenesheeting and tubular steel, to allow a rapidthe need for durable temporarymergency situations (Figure 13) .

Figure 13.The Oxfam Temporary Shelter

The advantages of the kit are it s ease ofhandling and transportation, simple erection,durability and low cost (6 n 19 88 in the UK).


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he te nt 's framework consists of a 4m stedge pole supported at i ts ends and mid-pm high steel ten t poles and secured bypes. One shee t of reinforced plas tic ge ridge pole and is pierced by the ten t poh reinforced eyelets. A second squarof reinforced plastic i s cut diagonallyalf used t o make doorways to close thends of the tent. The item s making up this kilisted in Table 2.

I l lreinforced

Wooden guy 6adjustment block


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The tent is large in size, with a floor area of 1 6square metres, and can in an emergency sleep1 6 adults, although it is more suited to a familyunit of 6 to 1 0 persons plus belongings. The unitweight of the kit is 25kg.


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The Oxfam Temporary Shelter


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Use of Plastic sheeting can be used in combination withplastic traditional cons truction materials to great effect.Plastic sheeting will considerably improve thesheeti"g resistance to wind and rain of traditionalconstruction methods while traditional materialscombin- such as grasses and ea rth can help overcomeation with the poor insulation properties associated withpolythene structures. In th is way semi-traditionalermanent, as opposed to temporary, sheltersmaterials can be constructed. A fine example is inSouthern Sudan, where traditional racubas(hemispherical structures made from a timberframework covered with reed or grass m atting orany other suitable material available) have beenconsiderably improved by the use of plasticsheeting sandwiched between the inner timberframework and an outer layer of empty sacks andcardboard. The use of sheeting was of particularimportance in th is instance as the grass andreeds, traditiona lly used, were in sh or t supply.

In Bangladesh and India plastic sheeting hasbeen used in conjunction with bamboo matting ina very successful way. Several thousand houseshave been built using plastic sheeting as awaterproof and windproof membrane sandwichedbetween an inner and outer woven bamboo mat(Figure 14).

Figure 14. Plastic and bamboo m atting house, Bangladesh


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St AlbansHerts AL4 OLQAnaplast LtdLundholm Road

Calnay LtdMaerdy Industrial EstateRhymneyGwent NP2 5XQBritish Visqueen Ltdrm Roadockton-on-TeesCleveland TS18 3RDZedcor Marketing LtdBridge Street MillBridge StreetWitneyOxon OX8 6U

Suppliersof reinforced polythene tarpaulins


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Suppliers of polythene lay-flat tubing andpolythene bagsZedcor Marketing LtdBridge Street M illBridge StreetWitneyOxon OX8 6 U

Suppliers of polypropylene ropeMonarflex LtdLyon WayHatfield RoadSt AlbansHer ts AL4 OLQ

Makers and suppliers of eyelets and woodentent rope runnersThe North Face (Scotland) LtdPO Box 1 6Industrial EstatePort GlasgowScotland PA14 5XL

Makers and suppliers of tent poles and pegsAllvic Engineering COElm CrescentKingston-upon-ThamesSurrey KT2 6HL


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ppendices Appen eful data for water storage1 allon of water = 1 0 1b1 ubic foot of water = 6.25 gallons1 ubic metre = 1000 litres = 220 gallons1 allon = 4,546 litres1 itre of water =1 ilogram1 ubic metre of water = 1000 kilograms1 ubic yard of water = 764.6 kilograms1 ubic yard = 0.7646 cubic metres1 ubic metre = 1.308 cubic yards1 quare metre = 1.196 square yards1 ectare = 2.47 acres

Appendix II Precipitation data1mm of water = 10,000 litre of water/hectare1 nch of water = 22,610 gallons/acre1 nch of water1 cre - inch1 cre - foot1mm of water1 cre - 100 mm1 ectare - 100 m

1,000 microns =1 illimetre = 0.039inches1metre = 1,000 millimetres = 3.28 feet

1,000 gauge = 0.25 millimetres = 0.01 inches1US gallon = 0.83 Imperial gallons = 3.76

litres1 ilogram = 2.2 pound Avoirdupois


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