VARIOUS TYPES OF CHALLENGING ROOFS.

1. NORTH LIGHT ROOF.

This is a pitched roof with unequal slopes, of which the steeper is glazed and arranged in such a way as to receive light from the north. They can be fabricated in steel, aluminum alloy, timber, reinforced concrete and prestressed concrete. North light roofs can be used for buildings such as factories, large public halls and gymnasiums. The primary function of this kind of roof is to provide protection to weather and to bring means of natural daylight.






                                      A BUILDING WITH NORTH LIGHT ROOF.

The roof contain two sloped sides which consist of two different characteristics. The first side is covered by roof coverings such as sheets or tiles and the other side is covered by glazing material in order to provide daylight.


2. SHELL ROOF.

A shell roof is a type of roof which is characterized by its geometry, being a three-dimensional solid whose thickness is very small when compared with other dimensions, and in structural terms. Essentially, a shell can be derived from a plate by two means by initially forming the middle surface as a curved surface and by applying loads which are coplanar to a plate's plane which generate significant stresses. The roof is curved and used to cover large buildings such as one or two story buildings. It is usually aesthetically pleasing, a shell roof is commonly used in public buildings. Shell roofs are useful when the inside of the building is open and does not contain walls or pillars that could support a flat or pitched roof.

The floor space beneath a shell roof can be made much larger than the floor space below another type of roof. This is because the curve in the roof adds additional structural support, allowing the roof to be heavier and larger while remaining intact. It is an ideal roof structure for office buildings and public buildings, such as libraries, theaters and recreation centers, where large groups of people need to meet in an unobstructed area.



TYPES OF SHELL ROOF.



There are three main types of shell roof: the barrel shell, which can be either single barrel shell, multi barrel shell or continuous barrel, also there are domes, conoids and hyperbolic paraboloids.



· BARREL SHELL ROOF.

These are curvature shells which are essentially a cut cylinder which must be restrained at both ends to overcome the tendency to flatten.

A single barrel shell looks like a long arch and is used in long, rectangular structures, such as airplane hangars. Multi-barrel shells often contain arrangements of different-sized arches, and are often used in public works buildings. Continuous barrel roofs are used on large structures, such as airports, that require multiple shells to cover the floor space. These roofs appear to roll up and down like waves. 

· DOMES.

These are structures which formed by assembling the hollow upper surface of the sphere which can be rotationally formed by any curved geometrical plane figure rotating about a central vertical axis. They are formed by a curved line moving over another curved line. Domes can be either rotational domes, which contain the round base and pendentive dome and translational dome. Translation domes are formed by a curved line moving over another curved line whereas pendentive domes are formed by inscribing within the base circle a regular polygon and vertical planes through the true hemispherical dome. 






 NKURUMAH HALL AT UNIVERSITY OF DAR ES SALAAM

· CONOIDS.

These are like barrel vaults, but they have double curvative shell roofs which can be considered as an alternative to barrel vaults. It can be described as a warped plane curvature like the side of the cone. 



                                         A BUILDING WITH BARREL VAULT ROOF.


· HYPERBOLIC PARABOLOIDS.

This is the one which follows a convex curve about one axis and concave curve about the other. The two vertical parabolas i.e. the generator and the directrix are set at right angles to the moving parabola. This forms a saddle shape where horizontal sections taken through the roof are hyperbolic in format and vertical sections are parabolic. Always these roof result in a very strange outlook. 
 

                              A BUILDING WITH SADDLE ROOF.

3. FOLDED PLATE ROOF.

A folded plate roof is a roof constructed of flat plates, often of reinforced concrete, joined at various angles. They are best defined as assemblies of flat plates or slabs which inclined in different directions and joined along their longitudinal edges. Sometimes folded plates can be connected and looks like shell. Other names which used to describe the folded plate roofs are hippedplate.

            A BUILDING WITH FOLDE PLATE ROOF.