Roof and roof covering

This presentation includes the types of roofs and roof covering materials. this presentation explained briefly about the pitched roofs, curved roofs and flat roofs.

1. ALLPPT.com _ Free PowerPoint Templates, Diagrams and Charts
BUILDING MATERIALS
& CONSTRUCTIONS
POORNIMA COLLEGE OF ENGINEERING, JAIPUR
DEPARTMENT OF CIVIL ENGINEERING
Roof and Roof Covering
DIVYA VISHNOI
ASSISTANT PROFESSOR

2. ROOF
•Roofisthecoveringontheuppermostpartof
abuildingorshelterwhichprovidesprotectionfromanimalsand
weatheraswellasrainorsnow,heat,windandsunlight.
•Thewordalsodenotestheframingorstructurewhichsupportsthat
covering.
•Thecharacteristicsofaroofaredependentuponthepurposeofthe
building.

3. Requirements of a good Roof
Following are the requirements of a well planned roof;
1.It should be durable against the adverse effects of
various agencies such as wind, rain, sun, etc.
2.It should grant the desirable insulation against sound
and heat.
3.It should be structurally stable and sound and it should
be capable of taking the loads likely to come over it.
4.It should be well-drained.
5.It should have efficient water-proofing arrangements.
6.It should be fire resistance.

4. TYPES OF ROOF
Flat roof or terraced roof
•Flat roofs are used in plains where rainfall is less and
climate is moderate.
Pitched or sloping roof
•Pitched roofs are preferred wherever rainfall is more.
Curved roof
•Shells and folded plate roofs are used to cover large column
free areas required for auditoriums, factories etc.
•The choice of the type of roof will depend on the climatic
conditions, shape of building, availability of materials,
importance of building, etc.

5. PITCHEDROOFS:BASICELEMENTS
•Aroofwithslopingsurfaceisknownasapitchedroof.
Pitchedroofsarebasicallyofthefollowingforms:
1.Lean-to-roof 2. Gableroof
3.Hiproof 4. Gambrelroof
5.Mansardorcurbroof6. Deckroof.
•Lean-to-roof:Thisisthesimplesttypeofslopingroof,providedeitherfora
roomofsmallspan,orfortheverandah.Ithasslopeonlyoneside.
•Gableroof:Thisisthecommontypeofslopingroofwhichslopesintwo
directions.Thetwoslopesmeetattheridge.Attheendface,avertical
triangleifformed.
•Hiproof:Thisroofisformedbyfourslopingsurfacesinfourdirections.At
theendfaces,slopedtrianglesareformed.
•Gambrelroof:Thisroof,likegableroof,slopesintwodirections,butthere
isabreakineachslope.Ateachend,verticalfaceisformed.
•Mansardroof:Mansardroof,likeahiproof,slopesinthefourdirections,
buteachslopehasabreakThus,slopingendsareobtained.
•Deckroof:Adeckroofhasslopesinallthefourdirectionanddeckorplane
surfaceisformatthetop.

7. Elementsofpitchedroof:
•Ridge:Thisisthehighestpointorpeakoftheroof.
•Hip:Thisisthehighpointwheretwoadjoiningroofsectionsmeet.
•Valley:Whentwosectionsoftheroofslopedownwardandmeet,theycreate
thisthirdelementcalledavalley.
•Pitch:Thisreferstotheslopeorsteepnessoftheroof.
•Eaves:Thisreferstothepartoftheroofthathangsovertherestofthehome.
•Gables:Thesearethetriangularportionsoftheendsofthehome,whichextend
fromtheeavestothepeakoftheroof.
•Dormer:Thesearethesectionsofthehomethatextrudefromtheroof.They
areusuallyaddedasawaytobringlightintotheupperlevelofyourhome.
•rafter:Arafterisoneofaseriesofslopedstructuralmembers(beams)that
extendfromtheridgeorhiptothewallplate,downslopeperimeteroreave,
andthataredesignedtosupporttheroofdeckanditsassociatedloads.
•Purlins:thesearehorizontalwoodenorsteelmemberusedtosupportcommon
rafterofaroofwhenspanislarge.

10. TYPESOFPITCHEDROOFS
Pitchedroofsmaybebroadlyclassifiedintothefollowing
(а)Singleroofs
1.Lean-to-roof(verandahroof)2.Coupleroof.
3.Couple-closeroof. 4.Collarbeamrooforcollartieroof.
(b)Doubleorpurlinroofs
(c)Triple-memberedorframedortrussedroofs
•King-postrooftruss.
•Queen-postrooftruss.
•Combinationofking-postandqueen-posttrusses,
•Mansardrooftruss.
•Truncatedrooftruss.
•Bel-fastrooftrussorlatticedrooftruss.
•Compositerooftrusses.
•Steelslopingrooftrusses.

11. (а) Single roofs
•Singleroofsconsistofonlycommonrafterswhicharesecuredatthe
ridgeandwallplate.
•Theseareusedwhenspanislesssothatnointermediatesupportis
requiredfortherafters.

12. Lean-to-roof
•Thisisthesimplesttypeofslopingroofinwhichraftersslopetoone
sideonly.
•Awoodenwallplateissupportedeitheronasteelcorbelorastone
corbel,whichareprovidedat1mcentretocentre.
•Thewallplateisembeddedontheotherside,tothewallorpillars.
•Thedifferenceinelevationbetweenthetwowallplatesissokept
thatthedesiredslopeisobtained.Usualslopeis30°.
•Thecommonraftersarenailedtowoodenwallplateattheirupper
end.
•Thistypeofroofissuitableformaximumspanof2.5m.
•Theseareprovidedforshed,out-housesattachedtomainbuilding,
verandahs,etc.

14. Couple roof
•Thistypeofroofisformedbycoupleorpairofrafterswhich
slopetoboththesidesoftheridgeoftheroof.
•Theupperendsofeachpairofrafterisnailedtoacommon
ridgepieceandtheirlowerendsarenotchedandnailedtothe
woodenwallplatesembeddedinthemasonryonthetopofthe
outerwalls.
•thecoupleroofisusedwhenthespanislimitedto3.6meters.

16. Couplecloseroof
•Acouplecloseroofissimilartothecoupleroof,exceptthatthe
endsofthecoupleofcommonraftersisconnectedbyhorizontal
member,calledtiebeam,topreventtheraftersfromspreading
andthrustingoutofthewall.
•Thetiebeammaybeawoodenmemberorasteelrod.
•Theconnectionbetweenwoodentieandfeetofraftersis
obtainedbydovetailhalvedjoint.
•Acouple-closeroofiseconomicallysuitableforspanupto
4.20m.

18. Collarbeamroof
•Whenthespanincreases,orwhentheloadismore,theraftersof
thecouplecloseroofhavethetendencytobend.
•Thisisavoidedbyraisingthetiebeamandfixingitatone-thirdto
one-halfoftheverticalheightfromwallplatetotheridge.
•Thisraisedbeamisknownasthecollarbeam(orcollartie).
•Thisroofissuitableforspanupto5m.

20. Collarandscissorsroof
•Itissimilartothecollarroof,exceptthattwocollarbeamcrossingeach
othertohaveanappearanceofscissorsisprovided.

21. Doubleorpurlinroof
•Adoubleroofistheoneinwhichpurlinsareintroducedto
supportthecommonraftersatintermediatepoint.
•Suchroofsareusedwhenthespanexceeds5metres.
•Thefunctionofapurlinistotietherafterstogether,andto
actasanintermediatesupporttotherafters.
•Theseroofshavetwobasicelements:(i)rafters,and(ii)
purlins.
•Theintermediatesupportssoprovidedintheformof
purlins,reducethesizeoftherafterstotheeconomical
range.
•Eachrafteristhussupportedatthreepoints:(i)atthe
bottom;onthewallthroughwallplate,(ii)atthetop,bythe
ridgebeam,and(iii)atthecentrebyapurlin.

23. TRUSSED ROOFS
•Whenthespanoftheroofexceeds5mandwherethereareno
insidewallstosupportthepurlins,thentrussesareprovidedat
suitableintervalalongthelengthoftheroom.
•Spacingisgenerallylimitedto3metresforwoodentrusses.
•Atriplememberortrussedroofconsistsofthreesetsof
members:(i)commonrafters,(ii)purlins,and(iii)trusses.
•Thepurlins,whichgiveanintermediatesupporttotherafters,
arethemselvessupportedontrusseswhicharesuitablyspaced
alongthelengthofaroom.
•Atrussedroofisprovidedwhenthelengthoftheroomislarge.

24. Thevarioustypesoftrussesinuseare:
•King-post,truss
•Queenposttruss
•Combinationofking-postandQueenposttruss
•Mansardtruss.
•Truncatedtruss
•Bel-fasttruss.
•Steeltruss
•Compositetrusses.
•Thefirstsixtypesareessentiallywoodentrusses.

25. King-posttruss
•Aking-posttrussconsistsofthefollowingcomponents:
(i)lowertiebeam,
(ii)twoinclinedprincipalrafters,
(iii)twostruts,and
(iv)akingpost.
•Theprincipalrafterssupportthepurlins.
•Thepurlinssupporttheclosely-spacedcommonrafterswhichhavethesameslopeas
theprincipalrafters.
•Thecommonrafterssupporttheroofcoveringasusual.
•Thespacingofthekingposttrussislimitedto3mcentretocentre.
•Thetrussissuitableforspansvaryingfrom5to8metres.
•Theprincipalrafterisjointedtothetiebeambyasingleabutmentand‘tenonjoint’or
bya‘bridlejoint’.
•Thejointisfurtherstrengthenedbyawroughtironheelstrap,wouldroundthejoint.
•Theking-postisprovidedwithsplayedshouldersandfeet,andistenonedintothe
upperedgeofthetiebeamforasufficientdistance.

28. Queen-posttruss
•Aqueen-posttrussdiffersfromaking-posttrussinhavingtwoverticalposts,rather
thanone.
•Theverticalpostsareknownasqueen-posts,thetopsofwhichareconnectedbya
horizontalpiece,knownasstrainingbeam.
•Twostrutsareprovidedtojointhefeetofeachqueen-posttotheprincipalrafter,The
queen-postsarethetensionmembers.
•Thestrainingbeamsreceivesthethrustfromtheprincipalrafters,andkeepsthe
junctioninstableposition.
•Astrainingsillisintroducedonthetiebeambetweenthequeen-poststocounteractthe
thrustfrominclinedstrutswhichareincompression.
•Inabsenceofthestrainingsill,thethrustfromthestrutwouldtendtoforcethefootof
thequeen-postinwards.
•Thesetrussesaresuitableforspansbetween8to12metres.
•Thejointattheheadofqueen-post-isformedduetothejunctionoftwocompression
members(principalrafterandstrainingbeam)andatensionmember(queen-post).

31. Combinationofking-postandqueenposttruss
•KingpostandQueen-posttrussesaresuitableforspansupto
12meters.
•Forgreaterspans,thequeen-posttrusscanstrengthenedby
onemoreuprightmember,calledprincess-posttoeachside.
•Fig.showtheresultingcombinationofking-postandqueen-
posttrusses,whicharesuitableupto18mspan.

33. Mansardrooftruss
•Thisrooftruss,namedgivenbyitsdesignerFrancoisMansard,a
Frencharchitect.
•Mansardrooftrussisacombinationofking-postandqueen-post
trusses.
•Itisatwo-storeytruss,withupperportionconsistingofking-post
trussandthelowerportionofqueen-posttruss.
•Theentiretrusshastwopitches.Theupperpitch(king-posttruss)
variesfrom30°to40°whiletwolowerpitch(queen-truss)varries
from60°to70°.
•Theuseofthistrussresultsineconomyinspace.

35. Truncatedtruss
•AtruncatedtrussissimilartoMansardtruss,except
thatitstopisformedflat,withagentleslopetoone
side.
•Thistypeoftrussisusedwhenitisrequiredtoprovide
aroomintheroof,betweenthetwoqueen-postsofthe
truss,asshowninFig.

37. Bel-fastrooftruss(Bowstringtruss)
•Thistruss,intheformofabow,consistsofthin
sectionsoftimber,withitstopchordcurved.
•Iftheroofcoveringislight,thisrooftrusscanbeused
upto30m.

39. Compositerooftrusses
•Rooftrussesmadeoftwomaterials,suchastimberand
steel,areknownascompositerooftrusses.
•Inacompositetruss,thetensionmembersaremadeof
steel,whilecompressionmembersaremadeoftimber.
•Iftensionmembersaremadeoftimber,theirsection
becomesveryheavybecauseofreductionofsectionat
thejoints.
•Specialfittingsarerequiredatthejunctionofsteeland
timbermembers.

41. STEELROOFTRUSSES
•Whenthespanexceeds10m,timbertrussesbecomeheavyand
uneconomical.
•Steeltrussesaremoreeconomicalforlargerspans.
•However,steeltrussesaremorecommonlyusedthesedays,forallspans-
smallorlarge.
•Theyare:(i)moreeconomical,(ii)easytoconstructorfabricate,
(iii)fire-proof, (iv)morerigid,and(v)permanent.
•Steeltrussesarefabricatedfromrolledsteelstructuralmemberssuchas
channels,angles,T-sectionsandplates.
•Mostoftherooftrussesarefabricatedfromangle-sectionsbecausetheycan
resisteffectivelybothtensionaswellascompression,andtheirjointingis
easy.
•Steeltrussesmaybegroupedinthefollowingcategories:
(а)Opentrusses
(b)Northlighttrusses
(c)Bowstringtrusses
(d)Archedribtrussesandsolidarchedribs.

45. Steeltrusseshavethefollowingadvantagesovertimbertrusses:
•Thesectionscomprisingofasteeltrussarereadilyavailableintherequired
dimensions,resultinginminimumwastageofmaterial.
•Steeltrussesarelightinweight,andcanbefabricatedinanyshape
dependinguponstructuralandarchitecturalrequirements.
•Steeltrussesarestrongerandmorerigidincomparisontotimbertrusses.
•ThemembersinSteeltrussesareequallystrongintensionaswellas
compression.
•Steeltrussescanbeusedoveranyspan,whiletimbertrussesaresuitableonly
upto15mspan.
•Steeltrussarefireproof.
•Steeltrussaretermiteproof.
•Steeltrusshavelongerlife.

46. ROOFCOVERINGSFORPITCHEDROOFS
•Roofcoveringisanessentialcomponentofpitchedroof,tobeplacedoverthe
roofframeworktoprotectitfromrain,snow,sun,windandother
atmosphericagency.
Varioustypesofroofingmaterialsareavailable,andtheirselectiondependsupon
1)Typeofbuilding,(2)Typeofroofframework,(3)Initialcost,(4)
Maintenancerequirements(5)fabricationfacilities,(6)Appearanceand
specialfeaturesofthelocality,(7)Durability(8)Availabilityofthematerial
itself,and(9)Climateofthelocality.
Thefollowingaretheroof-coveringmaterialscommonlyusedforpitchedroofs:
1.Thatchcovering
2.Woodshingles
3.Tiles
4.Asbestoscementsheets
5.Galvanizedcorrugatedironsheets
6.Eternitslates.
7.Lightweightroofing.

47. Thatchcovering
•Thisisthecheapestroof-covering,commonlyusedinvillages.
•Itsverylight,butishighlycombustible.
•Itisunstableagainsthighwinds.
•Itabsorbsmoistureandisliabletodecay.
•Thatchroof-coveringconsistsofbundlesofreedsorstraw.
•Theframeworktosupportthatchconsistsofroundbamboo
raftersspaced20to30cmapartandtiedwithsplitbamboos
laidatrightanglestotherafters.
•Thethatchistightlysecuredtotheframeworkwiththehelpof
ropesortwines.
•Inordertodraintheroofeffectively,aminimumslopeof45°is
kept.
•Thethicknessofthatchcoveringshouldatleastbe15cm.

49. Woodshingleroofing
•Shinglesarethinslabsofwoodusedtocoverroofs.
•Theuseofshinglesisrestrictedtohillyareaswherelocaltimber
iseasilyavailableatlowcost.
•Thoughshingleroofingislightweight,itisnotfireandtermite
resistant.
•Woodshinglesareobtainedfromwellseasonedtimber,by
eithersawingorsplitting.
•Sawnshinglesareusedchiefly,Theyareobtainedinlengths
varyingfrom30to40cmandwidthsvaryingfrom6cmto25
cm.
•Theyareapproximately10mmthickatthetail.
•Theyarelaidinasimilarfashionastilesandslates.

51. Tileroofing
•Useoftilesforroofingisoneoftheoldest,andisstillpreferred
forresidentialbuildingsandcountryhouses.
•Thisisbecausecountrytilesaremanufacturedfromlocally
availableearth.
•Tilesarenamedaccordingtotheirshapeandpattern,andthey
aremanufacturedbyaprocesssimilartotheoneusedforthe
manufactureofbricks.
•Thevarioustypesoftilesgenerallyusedare:
1.Plainorflatfiles.
2.Curvedorpan-tiles.
3.Pottilesorhalf-roundcountrytiles.
4.Spanishtiles.
5.ItalianorAllahabadtiles.
6.Inter-lockingtiles.

53. Asbestoscementsheets(A.C.sheets)
•Asbestoscementsheetsarenowincreasinglybecomingpopularfor
industrialbuildings,factories,sheds,cinemahouses,auditoriumandeven
residentialbuildings,sincetheyarecheap,lightweight,tough,durable,
watertight,fire-resisting.
•Thebiggestadvantageisthattheyareavailableinbiggerunitsunliketiles,
andhencesupportingframework(groundwork)isalsocheaper,easierand
lighter.
•Thesesheetsdonotrequireanyprotectivepaint,andnoelaborate
maintenanceisrequired.
•Also,theconstructionwithA.C.sheetsisveryfast.A.C.sheetsare
manufacturedfromasbestos,fiber(about15%)andPortlandcement.
•Asbestosisasilkyfibrousmineralmadeupofmetamorphosedvolcanicrocks.
•Itisfoundinseveralvarietiesbutwhiteasbestos,whichisacompoundof
magnesiaandsilica,isprincipallyused.
•InIndia,asbestoscementroofcoveringsareavailableinfollowingforms:
Everestbig-sixcorrugatedA.C.sheets.
EvereststandardcorrugatedA.C.sheets.
EverestTraffordA.C.tiles(orsheets).
•Thesesheetshavelengthof1.25to3metersinincrementsof15cm.

55. GalvanizedIroncorrugatedsheets(G.I.sheets)
•G.I.sheetsarealsowidelyused.
•TheyarestrongerthanA.C.sheets.However,becauseoftheir
highercost,theyarenowgraduallyreplacedbyA.C.sheets.
•Theyarenotusedforslopesflatterthan1in4.
•G.I.sheetsaremadeofironsheetswhicharegalvanizedwith
zinctoprotectthemfromrustingactionofwaterandwet
weather.
•ThesesheetsarefixedinamannersimilartotheA.C.sheets.
Endlapshouldnotbelessthan15cmandTheholesareeither
drilledorpunchedinthesheetcrowns.
•ThesheetsaresecuredtopurlinsbymeansofG.I.hookbolts,
screwsandnailsetc.,withcurvedwashers.
•Thesheetsshouldbefixedtoeavesbymeansofflatironwind
ties.

57. LightWeightroofing
•Forwide-spanindustrialstructures,itisdesirabletoreducethe
weightofroof,sothatstructuralframingcanbeeconomized.
•Conventionalroofingmaterials(suchastiles,slatesetc.)are
heavyandrequireheavyframingtosupportthem.
•Thelightweightroofingmaterialsareoftwotypes:
(а)Sheeting
(i)Aluminumsheets
(ii)Asbestoscementsheets.
(b)Decking
(i)Woodwool
(ii)Strawboard
(iii)Aluminumandsteeldecking.

59. FLAT ROOF
•FlatRoofsTheseroofsarenearlyflat.Howeverslightslope
(notmorethan10°)isgiventodrainouttherainwater.
Theadvantagesofflatroofsare:
a)Theroofcanbeusedasaterraceforplayingandcelebrating
functions.
b)Atanylatterstagetheroofcanbeconvertedasafloorby
addinganotherstorey.
c)Theycansuittoanyshapeofthebuilding.
d)Over-headwatertanksandotherservicescanbelocated
easily.
e)Theycanbemadefireproofeasilycomparedtopitched
roof.

60. FLAT ROOF
Thedisadvantagesofflatroofsare:
a)Theycannotcoverlargecolumnfreeareas.
b)Leakageproblemmayoccuratlatterdatealsodueto
developmentofcracks.Onceleakageproblemstarts,itneeds
costlytreatments.
c)Thedeadweightofflatroofsismore.
d)Inplacesofsnowfallflatroofsaretobeavoidedtoreduce
snowload.
e)Theinitialcostofconstructionismore.
f)Speedofconstructionofflatroofsisless.

61. CURVED ROOF
ShellsandFoldedPlateRoofsShell
roofmaybedefinedasacurved
surface,thethicknessofwhichissmall
comparedtotheotherdimensions.In
theseroofslotofloadistransferredby
membranecompressioninsteadofby
bendingasinthecaseofconventional
slabandbeamconstructions.Cavesare
havingnaturalshellroofs.

62. CURVED ROOF
Advantages of shell roofs are:
a)Good from aesthetic point of view
b)Material consumption is quite less
c)Form work can be removed early
d)Large column free areas can be covered.
Disadvantages of shell roofs are:
a)Top surface is curved and hence advantage of terrace is lost.
b)Form work is costly.

63. References
1)“Building Construction” authored by S.C. Rangwala,
Charotarpublishing house Pvt. Ltd.
2)“Building Construction” authored by Bindraand Arora,
DhanpatRaipublication.
3)“Building Construction” authored by M.L. Gambhir, Tata
MeghrawHills publication.