Steel sloping roofs? Types Steel sloping roofs 2023
For greater spans timber trusses become heavy and it is economical use steel trusses. Even for short spans of about 8 mtrs, steel trusses can be economically used to instead of timber trusses, Steel trusses are much, stronger than timber trusses.
They are more fire resisting and durable as cannot be attacked by white ants and are not subjected to dry rot. Joints in these trusses are more simple and satisfactory.
Members of steel sloping roofs truss are constructed of mild steel and most of them are consisting of angles because the angle sections can effectively resist both compressive and tensile stresses.
Angles can be manufactured economically and connected conveniently. Instead of using t-sections for rafters, either one of two angles, placed back to back can be employed.
Struts consist generally of either single or double lanes. One or two angles, back to back, can be used as the beam.
The members of trusses are usually connected together by means of rivetting or bolting them over thin plates, called gusset plates.
Now-a-days, welding is generally done for connecting the members either with or without gusset plates.
A steel roof truss should be properly triangulated I.e. all the members of the truss should be arranged to form triangles in order to make it a perfect or efficient truss.
The following points should be considered while constructing steel trusses:
1. Principal rafters should not be longer than 3mtrs between the struts.
2. All the purlins should be fixed at joints.
3. The struts should be as short as possible.
4. In case of horizontal tie, a camber of 1/480 of the span is given to avoid appearance of sagging.
5. Spacing of the trusses is kept 3mtrs upto 15mtrs span and 1/5th of the span beyond 15m span.
6. Provision for expansion and contraction of the steel trusses due to variation of temperature should be made.
Types of steel roof trusses
Usual types of steel trusses for roofs of different spans are as follows:
These roof trusses are called open trusses. For small spans, the bottom member is level and is in one piece for the whole span.
But for longer spans, camber is introduced to reduce the effective length of the struts and to avoid appearance of sagging.
The tie member of such a truss is built up. Three special forms of steel trusses are arched truss, bow string truss and north light truss.
Arched trusses are usually designed with stanchions which support them. Bow string trusses are used for large spans but they are more expensive.
North light trusses are usually built for factories and workshops. They are not commonly used over a span larger than 12mtrs.
The glazed slope always faces North to avoid direct sunlight shining into the building.
How to use steel on sloping roof
Different roof covering materials?
The following roof covering materials are as follows:
d) Asbestos coment sheets
e) G.I sheets
a) Thatch: This is one of the cheapest and lightest roof covering material. It consists of reeds of straw, secured to battens made of bamboo made with help of ropes.
It is easily combustible, absorbs moisture and gives out a foul odour. It has to be renewed frequently. dithe slope of the roof is kept about 45°.
It is desirable to make thatch worm-proof so that it may not be attacked by insect, and birds do not make nest inside it.
b) Siates: Slate is a stratified metamorphic rock and it is obtained from open quarties. It is normally blue or grey in colour and is available in thin sheets.
It is normally blue or grey in color and is available in thin sheets. A good slate should be free from white patches, hand, tough, durable and gives a sharp metallic ringing sound when struck with each other.
A good slets should be holed. It should not spilt and should absorb water upto 2% of its weight when soaked in water for 24 hours. Common sizes of states are: 600 x 300mm, 500 x 250mm and 450 x 200mm. These are further of two types based on the style of laying L
By nalling near the head, L.e. head-nailed sheets
By nalling near the middle, Le. centre nailed states
c) Tiles: These are largely used as roof coverings. If properly selected and laid, tiles are impervious, fire-resisting, non-conductor of heat and also strong durable and economical Clay tiles are mostly used after they have been burnt thoroughly.
For foing tiles common rafters are laid at 320 to 450mm centre to centre and bettens are nalled across them. Spacing of battens depends upon the type of tiles used.
Different types of tiles used are as follows:
d) Asbestos cement sheets: These sheets consist of a mix of asbestos and Portland cement. These sheets are cheap, tough, durable, quite impervious and perfectly fire and vermin proof.
These sheets do not rust and need no protective coating of any other material.
The main disadvantage of these sheets is that in cold climate, condensation is introduced on the underside of the roof. These sheets may be plain or corrugated and available in various size.
In case of corrugated sheets the pitch is generally 140mm. Different types of asbestos sheets are as follows:
1. Everite big six corrugated asbestos cement sheets
2. Everite standard corrugated asbestos cement sheets
3. Turnall Trafford asbestos cement sheets
e) Galvanized iron sheets: Corrugated galvanized Iron sheets are commonly used as roofing material. These are light in weight, easy to use and fixing.
These are also very durable and fire proof. The iron sheets are galvanized with zinc to protect them from rusting.
The main advantage of this type of sheets is that it transmits heat and cold easily. It also creates condensation problem on the inner side in cold climates.
These are available in 660mm (generally 600 to 1250mm) in width, having 8 corrugations, each of pitch 76mm. The length of these sheets varies from 1.5m to 3.5m and their thickness varies from 1.6mm to 6.56mm (16 to 24 gauge).