A sloping roof is known as a pitched roof. It is the most common form of roof and is generally regarded as the cheapest alternative for covering a structure. These are suitable in those areas where rainfall/snowfall is very heavy. Broadly, buildings with limited width and simple shape can generally be covered satisfactorily by pitched roofs. Buildings those are irregular in plan or with long spans, present awkward problems in the designs of pitched roof, involving numerous valleys, gutters and hips. Buildings of large area, such as factories, when covered by a series of parallel pitched roofs, require internal guttering in the valleys.
Pitched roofs are almost constructed in steel or wood. Pitched roofs are basically of the following forms.
Roof covering is an essential component of pitched roof, to be placed over the roof frame work, to protect it from rain, snow, sun, wind and other atmospheric agencies. Various types of roofing materials are available and their selection depends upon (i) type of building (ii) Type of roof framework (iii) Initial cost (iv) Maintenance requirements (v) Fabrication facilities (vi) Appearance and special features of the locality (vii) Durability (viii) Availability of the material (ix) Climate of the locality
Following are common roof coverings for pitched roofs
Thatch
This is a very light roof covering. But it is combustible, absorbs moisture rapidly and is easily liable to decay. A bed of matting is prepared to receive the thatch and in order to drain the roof easily a pitch of 45 degrees is kept. Thatch is used in rural areas because it is the cheapest form of roof covering and it is simple in construction.
Ordinary half-round country tiles
These are used for cheap buildings. If tiles are laid in two layers, the roof is known as a double-tiled roof. An overlap of at least 80 mm should be provided when these tiles are used. These tiles are liable to break easily and hence, they require frequent replacement.
Shingles
Wood shingles are obtained from well seasoned timber with lengths varying from 30 cm to 38 cm and widths varying from 60 mm to 250 mm. They are laid in a similar fashion as tiles and slates and this roof covering is found to be useful especially in hilly areas where wood is easily and cheaply available.
Patent tiles
Various patent tiles are variable which can be used as roof covering. Magalore tiles are one of such patent tiles. They are red in colour and made of double channeled Basel Mission Mangalore pattern. Special Mangalore tiles are available for ridge. It is found that about fifteen Mangalore tiles are required for covering one square meter of roof area.
These are made of cement and asbestos. They posses less corrugations and are laid with laps of 15 cm and 10 cm at the ends and at the sides respectively.
Eternit slates
These are fire-resisting, light and cool. They are not easily affected by weather. About eight slates are required for covering one square meter of roof area. Eternit slates are generally available in three colours – grey, black and red.
Corrugated galvanized iron sheets
These are used as roof covering for factories, sheds, cheap buildings etc. They are sometimes covered with ordinary half round country tiles so as to cool the inside of the building. The sheets are laid with the corrugations running down the slope of the roof. Laps of 15 cm at the ends and of two corrugations at the sides are to be provided. These sheets are light in weight and easy to fix.
These are similar to Trafford tiles. But they have continuous corrugations. Pitch of the corrugations depends on the width of the sheet. Laps of 15cm at the end and 1 to 1 ½ corrugations at the sides are to be provided. These sheets can be cut, nailed, swan or screwed and they are light, non-absorptive, strong and tough. These sheets stand extreme variation of temperature and they are fast replacing other roofing materials for the pitched roofs.
Ruberoid
Ruberoid is a light, flexible and water-proof material. This material is not affected by extreme heat or cold and it is not attached by white ants.. This material is available in two colours – red and slate. The weight of the material varies from 1 to 2 kg / m2. This material is available in rolls.
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