Without much ado or taking for granted anything, let me start by saying that the roof is the upper-most part of a building structure. Erecting a roof is a specialist work done by trades personnel called roofers and is as complex as it is delicate. This explains why most contractors avoid it by subcontracting it out. Roofing requires greater skill and workmanship ,especially because a roof is the most visible part of a building . And your guess is as good as mine ,that most customers will not tolerate second rate skills that may compromise the bold statement the roof is supposed to make ;people want the heads of all and sundry to keep turning . Indeed homes are built on foundation of wisdom, but a roofs makes a house. If the roof is not good, the building will be shed not a house.
In designing a roof, the builder must consider the need for shelter from the elements as well as the need to conserve heat and fuel. Where a roof type chosen is the kind that sheds heat to the night air faster, then insulation measure must be built into the roof.
There are three main types of roofs, classified on the basis of their steepness or pitch:
- Others-Dome, Barrel, and Hyperbolic.
The pitch of a roof is the angle it makes or the roof Rafter makes with horizontal line parallel to the ground. Anything less than 10◦ is considered a flat roof, and anything greater than 80◦is considered a wall. A steep roof of more than 40◦ uses more material and has more dead weight than less steep roof.
Softwood is used to construct the structure of most roofs, which is then covered by iron sheets, clay tiles, stones, cedar wood shingles , asphalt shingles, reeds, straw or even need grass depending building specifications and how prepared the owner is ,to dig deeper into his pockets.
Generally speaking , roofs protect us from the elements, provide stability to the walls(without it the top of the wall will be weak) and insulate us from heat and sound.
Pitched roofs can be cut at the site or be prefabricated. Prefabricated roofs are factory made and delivered to the site, in assembly sections ready for erection.Wastage is minimized with prefabricated roofs because ,off-cuts can be finger jointed together to form longer lengths and used. Pitched roofs must be ventilated to remove water vapour and eliminate the risk of condensation. This ventilation can be through soffit board with either holes backed with insect mesh to prevent wasps and bees from entering the roof space between the cover and ceiling board. The other approach is to have the fascia board ventilated .To ensure efficient ventilation, high level vent can be installed at the ridge or ventilation tile should be used.
Parts of a Pitched roof
1.Rafter-A long and strong piece of timber that runs from the ridge to the wall plate on slopping roof.
2.Strut- A piece of wood that support the roof and run between rafter and ceiling joist.
3.Ceiling Joist-A long piece of timber put below the ceiling and fixed on the wall plate to support both the rafter (erected above it) and ceiling board( below it).
4.Ridge-A raise top or a line formed between the two sloping sides of a roof.
5.Wall plate- A piece of metal used to cover and protect to topmost course of a wall from the drown thrust of the ceiling joist.
6.Collar-a short piece of timber that run parallel and above the ceiling joist, but hold together two, sloping rafters.
7.Fascia board- A board that fixed round a roof cover overhanging the external walls and used to protect the roof void from elements.
8.Soffit board-board that lies horizontal and fixed between the fascia board and the external walls.
9.Valley- A low line formed at the intersection of two sloping sides of a roof.
9.Truss-A wooden frame made up of two sloping Rafters, Struts and Ceiling joist. Several trusses are need to erect a roof. They are also called Trussed rafters.(see image above).
Sources: Building in the 21 Century by Robert Cooke.