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Traditional roof structures.
2.1 Characterises of traditional roof
Traditional roof structures are prevailing from long ago where the structures had a shelter. Roof structure is the most aesthetic thing from the past. In the world wide there are a lot of roof structures with difference forms and difference shapes. We can divided roof structures into own qualities of countries tradition. It can be explain with own traditional qualities of each countries. As an example we can get Dutch roof, British roof and Spanish roof structures. In Dutch roof structures there are difference shape because of climate condition. Dutch roof are normal gable roof but in tropical countries they have some update with solar geometrical. An also we can divided into the cultural and climate responds. In the North Pole and South Pole structures they have vaulted roof or dome roof. Islamic and Hindu’s structures have decorated dome roof. And also catholic chambers have decorated trussed roof structures with large holly space. And also those roof’s decorated with difference colours, tiles, glass panels, etc. Then roof can be divided into the category of Design in roof structures. In the tropical countries like as Sri Lanka they have traditional roof structure can be explain as a gable roof.
2.2 Type of traditional roof structure
The roof structures of tropical countries they are prevailing from ancient people who lived in colonial and pre historic era. After the some of moderation from cultural and weather condition then traditional roof structures can be divided in to three types of structure.
Those roof types are can be explained as a traditional roof. Because of these types prevailing from traditional structures from past. And modern types of roof moderated and developed from those types.
2.2.1 Single roof
Rafters of single roof they won’t any intermediate support. Those type of roof has a limitation. Because of it can only use for small spans. If large spans are need then it should have to large roof section. If the bottom of the rafters are not tied of not in great bond then this type of roof will have a tendency, underweight, to push the supporting walls outwards at the top causing structural failure of the walls. Then single roof can be divided into the three categorised of structural strength from additional support. They are,
- Couple roof
- Collar roof
- Close couple roof
22.214.171.124 Couple roof
This type also rare type in it use. The bottom of common rafters fixed at the ridge and at the wall plate. When subjected to any type of load or force acting vertically downwards the rafters will move outwards at their feet thus exerting thrust to the wall forcing them outwards and causing possible failure of the wall structure. Because of that wall had to tendency or failure of the wall. Then single roof have to update to prevent that cause so it joined additional support to common rafters.
Then couple roof in under pressure when load exerted walls have a tendency to spread. Because of that common rafters get another membered support.
126.96.36.199 Collar roof
A collar roof have a horizontal roof member positioned approximately one third of the distance from the ridge to the wall plate line. This extra member support prevent the rafters from spreading under load. This type of roof structures have better roof span than couple roof. And also this type of roof structure can get greater ceiling height from use of member support.
188.8.131.52 Close couple roof
This roof incorporates main tie which is secured to the feet of each rafter and spans the width of the building. This added member forms a triangle which introduces the triangulation of forces within the structure. To stop the ceiling joist from sagging, a hanger is fixed to the top and the ceiling joist at the bottom. To increase the strength of this structure, a binder is fixed to each ceiling joist and hanger. This binder runs parallel with the main wall and at right angles to the ceiling joist. This type of structure ensures that this type of roof can be used for great spans without the fear of the roof spreading under loads.
Close couple are used to get greater span than other single roof from vertical and horizontal members.
2.2.2 Double roof
A double roof is a roof whose rafters are of such a length that they require an intermediate support. This support is a usually a beam which is secured under the rafters at a point half way between the ridge and wall plate. This beam called a purling. In gable roof the purling is fixed into the gable wall to provide additional support. In double pitched roof the purling is fixed to the rafters in a continues length, jointed at all the internal and external corners of the roof. In traditional constructed roof the roof may also require added support in the form of roof trusses. This will depend upon the size of the roof and the type of roof covering the roof has to support. There are many design and combination of double roof. The design of the roof will depend upon the size and shape of the ground floor plan of the building.
The drawing of above shows a partly hipped roof with one hipped end and one gable end. A fully hipped roof has no gables, and the eaves run around the around of the roof. The eaves are usually of the box type. Double roof is the most common type of roof in the world. Because of purling can get more span than single roof type. The double roof can be used rafters as a hipped. Then it called a hipped roof and also it can be used as a joined of different angle roof.
2.2.3 Trussed roof
Trussed rafters are individually designed components made from strength graded timber with steel or timber nail plates. They provide a structural framework to support the roof fabric and ceiling. Trussed rafters can be used on a wide range of building types including timber frame, masonry and steel frame. Trussed roof have difference design.
They are W truss, M truss, scissor truss and gable truss. In traditional roof structure commonly used W truss and M truss. There are some another type of truss system. They are king post truss and queen post truss .They are commonly used in traditional roof structure. The king post is normally under tension and requires quite sophisticated joints with the tie beam and principal rafters. The queen post truss has two principal rafters and two vertical queen posts. The queen post truss extends the span, and combined with spliced joints in the longer members extends the useful span for trusses of these types. As with a king post, the queen posts may be replaced with iron rods and thus called a queen rod truss.
2.3 Traditional roof structures in Sri Lanka
In Sri Lanka traditional roof structures can be describe in the structural form, roof design and decoration and impact of roof structures to appearance of building. In history of Sri Lankan roof structure can be began from pre historic era with stone shelter and it moderated with cultural and climatic aspects. It’s began with the structural knowledge from abroad then there are some moderation of roof structures. The arrival of Arahath Mahinda thero in Sri Lanka there was some aspects in difference kind of form in roof structure. They are,
- Socio cultural
2.3.1 Socio cultural aspect of dewala in Sri Lanka
Every society has an identity and it is the socio cultural values of the people that make up this identity. The society is often described base on its identity and the creation of those roof structure. Socio cultural is the major part of the developing of roof structure. The relationship of these socio cultural factors to roof structure is that it helps the creator to determine the roof form and composition, size and appearances. In Sri Lanka there are some kind of socio cultural aspect to roof structures. They are religious, cultural and social aspect.
The religious aspect is mostly have to see on Dewala, temple, church, kovila and other sacred places. The cultural aspect is how people join with roof structure with their opinion and behave of them. In roof structure of Dewala can be describe with how people pray their deity and qualities of deity. Roof structure is significant structure of the dewala building. Then roof of the dewalaya had to contrast from other building.
2.3.2 Economical aspect of Dewala in Sri Lanka
In society has a difference about economical level through the society. Then building can describe that point with economical level of society. According to economical aspect of society it can be divided to poor and rich, and also it can be divided to empire state and villages. The dewala which located in dewala village they had honour of village peoples. The village people always had to serve dewala. And also during the construction period all construction works are done by village peoples. As an example timber work, masonry wall, timber details, roof tiles, roof decoration all are done under the village people’s knowledge. Then roof structures are normally get gable or pitch roof. But when consider about Embekke dewalaya, it had honour service from palace. Then it had a great roof structures better than law countries roof structure.
2.3.3 Political aspect of dewala in Sri Lanka
The political aspect is under control by who had a hand of city or country. In Sri Lanka as historic evidences king is the major handler of the all economic, political and all valuable things in the city or country. The king and his palace is the central place of the country. The palace and city centre develop around the king’s facilities. But Dewala village was the under the village peoples. Then rural people haven’t any facilities to build Dewala to great structure. But after the arrival of Hindu culture Dewala became a beside place of the king. Because of king had a prevent of Tamil and Hinduism. Then dewala became a centre of the city.
These all gathered information have about what are the aspect to the traditional roof structures in past Sri Lanka. Socio cultural, Economical, and Political aspects closely related to the country development. In past Sri Lanka development of country done by under the King. What were the factors which related to the King’s power then it became the greatest service centre of the country. After the Hinduism and Tamil aspects then dewala became a major centre of the country. After that peoples who lived around the dewala they got a lot of knowledge and development around their living styles. Then there was a development in dewala village. Sri Lankan traditional roof structure is not look like a compressed roof. It such a gable and pitch roof structure. But when consider with temple roof and traditional house roof then there was an absolutely own style of dewala roof structure.
Roof of Boltumbe dewalaya
When consider with those above figures there was a difference with traditional house and royal temple of Sri Daladha Maligawa. Then consider with dewlaya and both of that dewala roof is so difference with other roof roof structures. Because of dewala have own qualities of roof structure from socio cultural, economic, and politic aspects, and also there was another thing that not happening on the temple and houses it was the respect of god who owner of the dewalaya. The people who live in the dewala village they had respect and fear to the god. Then dewala building got difference from other buildings. In dewala building roof is the main structure of the building get to the respectful and proud.