HOW TO DO ROOFING
Roofing is the process of constructing a roof over a structure.it is usually a delicate task that requires to be approached with due knowledge.
Modern timber roofs are mostly framed with pairs of common rafters or prefabricated wooden trusses fastened together with truss connector plates. Roofs are also designated as either warm or cold roofs in regard to thermal temperatures of the building, insulation and ventilation. The roof covering material and aesthetic design is what determines the steepness (roof pitch) of a sloped roof. Flat roofs (mostly constructed in arid regions) actually slope up to approximately ten degrees for purposes of shedding water.
Fig.1. Section view through a house roof drawing showing names for parts of the structure
In high wind regions, where hurricanes frequent, the chief engineering deliberation is to hold the roof intact during severe storms. Thus all components of the roof have to withstand the hoist forces of high wind speeds. This is accomplished by using metal ties fastened to each rafter or truss.
The roof framing may be broken up for openings such as a chimney or skylight. Chimneys are typically built with a water diverter known as a cricket or saddle above the chimney. Flashing is used to seal the gap between the chimney and roofing material.
Also when roofing the following should be taken into consideration:
a)The roof framing must be designed to hold up a structural load that includes dead load, its own weight and the weight of the roof covering, and additional loading called the environmental load like as snow and wind.
b)The ventilation of the roof deck speeds the evaporation of water from leakage or condensation and removes heat which helps prevent ice dams and helps asphalt shingles last longer.
Below are expiations of how different types of roofs are constructed:
1)The Rafter roof
Rafter roof consists of rafters where the rafters’ foot rest on horizontal wall plates on top of each wall. The top ends of the rafters can meet at a ridge beam, or butt directly to another rafter to form a pair of rafters referred to as a couple. Horizontal laths, battens, or purlins are fixed to the rafters, depending on the roof covering material used. Heavier under purlins or purlin plates are used to support longer rafter spans. Tie beams, which may also serve as ceiling joists, are typically connected between the lower ends of opposite rafters to prevent them from spreading and forcing the walls apart. Collar beams or collar ties may be fixed higher up between opposite rafters for extra strength. The rafters, tie beams and plates serve to transmit the weight of the roof to the walls of the building
2)The Truss roof
Fig.2.A truss roof with tongue and groove sheathing.
Trusses (may be made of wood or metal) are the structure upon which the roof covering like iron sheet is placed and attached on. Timber trusses also are built in a variety of styles using wood or metal joints.