Pitched Clay Tile Roofs in Coastal Saurashtra, Gujarat

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Title

Pitched Clay Tile Roofs in Coastal Saurashtra, Gujarat

Summary

Gable and hipped roofs are found commonly in buildings of coastal Saurashtra. Construction of sloping roofs, especially gable roof is very easy and can be done in a relatively short period of time. The masonry walls for these roofs can remain low height while the central space can have enough height. These roofs require a few key structural pieces of wood and can be covered with locally produced clay tiles and thus prove to be cheaper than concrete roofs. If secured properly, these roofs can withstand high winds and the light roof structures also are less problematic in earthquake situations.

Location

Pitched clay tile roofs are found in all parts of Saurashtra, including its coastal areas.

Fig 1: Map Showing Location of Saurashtra

Present studies were mainly found in Khambhalia and Dwarka region.

Context

Materials:
Teak was available more easily for construction of under structure of the pitched roofs. Nowadays, teak is only used for the key structural members like the ridge, but locally available inexpensive wood from Babul (Desi Bawal) tree is used for most structural members of the roof. Bamboos from Gir forest and south Gujarat are also used. In areas close to the ports, found logs from ships are also used for the construction of the roof structure. Country tiles and Manglore tiles are produced in many parts of the region and are used for roofing¹.

Risk of Disasters²:

1. Most of the coastal Saurashtra region falls under seismic zones MSK VII (Moderate risk zone for earthquakes) and some parts including the coastline of Jamnagar district fall under MSK VIII (High risk zone for earthquakes) (Fig. 4). These zones relates to Richter scale magnitude range of 6.0 to 6.9.³
2. The wind currents are strong, with the average velocity of 50 metres/second (180km/h) throughout the year making this region very high damage risk zone B for wind and cyclone hazards (refer fig. 5 below).

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Fig 4: Gujarat Earthquake Hazard Map (Source: Vulnerability Atlas of India: Gujarat, 1997, BMTPC and MUD)
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Fig 5: Gujarat Wind and Cyclone Hazard Map (Source: Vulnerability Atlas of India: Gujarat, 1997, BMTPC and MUD)

Housing/ Settlement Typology

Traditional buildings with pitched clay tile roofs are found in most part of Saurashtra. The building typology varies depending on local context and region. Pitched roofs of both types, gable and hipped are sometimes also used in combination with flat roofs. Hipped roofs are generally found on buildings of importance like institutions etc and these can cover bigger areas than gable roofs.

Knowledge System/ Innovation

There are mainly two types of pitched roofs found in traditional buildings of coastal Saurashtra region: gable roofs and hipped roofs.

Gable Roof:
A gable roof is a roof having a single slope on each side of a central ridge, usually with gable. The range of spans found in the region is x m to x m. These would also depend on the length of the timber structural elements available. When the spans are larger a special system of joining the beams was developed. Refer to section x for details.

Hipped Roof:
A hipped roof is a roof which rises by inclined planes from all four sides of a building. The line where two adjacent sloping sides of a roof meet is called the hip. The range of spans found in the region is x m to x m. These would also depend on the length of the timber structural elements available. A hipped roof can cover relatively larger span than other timber roofs due to its structural arrangement.

Disaster Resistance/ Structural System

Timber roofs are relatively light weight roofs and thus keep the centre of gravity of the buildings lower and make the structures stable in earthquake situations, but if light weight roofs are not properly secured to the structure below, they are more likely to be damaged in cylcones. When the walls and roof are not properly connected, they tend to separate during the sway due to their independent movement. If secured properly, steep roofs on low height walls have better performance in the cyclone than low slope roofs on high walls. Flat roofs or shallow pitched roofs are more susceptible to uplift in high wind situation. In order to lessen the effect of the uplifting forces on the roof, the roof Pitch should not be less than 22º.⁴ Gable roofs with wind ties/trusses perform better in disasters but absence of ties/trusses can make these roofs vulnerable. Hipped Roof is one of the most stable roof structures due to its equal slopes on 4 sides. This roof faces less upward pressure due to its shape, because its four slopes offer bracing in each direction. However, it was noted that these roofs were not very commonly found in coastal Saurashtra and were possibly brought to this region by the merchants involved in international trade. For example, in Beyt Dwarka, these roofs were mostly constructed by the builders brought from Sindh and no special details were derived to counter the cyclonic winds and rains prevalent in the region.

• Gable roofs with timber structures usually do not span large distances due to the limited length of logs available. When the spans are larger, and a joint required for the main beam, an ‘inverted-V’ (Fig ) or an ‘I-shaped’ (Fig ) supporting system is worked out, that transfers the load onto a perpendicular beam underneath. In a gable roof, if the ridge beam is not properly secured, it can move by horizontal force in earthquake situation and can result in collapse of the roof. These inverted 'V' and 'I' sections may also help in keeping the ridge beam secured in its position.

Inverted 'V' Supports for Gable Roof	Inverted 'V' Supporting Joint in the Structural Member	Joint in the Structural Member

'I' Support	'I' Support (Seen in Kutchh)

• In gable roofs, the gable wall extending over the roof edge also helps in anchoring the roof members and the tiles, and prevents damage from the strong wind currents.

Gable Wall Extending Above the Roof Level	Gable Wall Extending Above the Roof Level	Absence Gable Wall Above Roof Level

• Roof projections at eave levels and window projections are subjected to uplift pressures. In coastal Saurashtra buildings, the overhangs are generally short avoiding damage from wind (Fig ). If there is any overhang provided, the rafters end in a continuous solid wooden plate thus preventing them from rotating or displacing laterally from their position (Fig ). Overhangs of some of the roofs made out of stone slabs also protect the edges of the roof from the wind damage (Fig ).

Stone Overhang	Detail of Overhang End	Rafters Attached in the Wooden Plate	Long Overhangs Damaged in High Wind

• Structural elements like rafters need to be properly anchored and supported on the wall. If not anchored, these can fly away in cyclones. They can also cause cracks on the walls if there is no proper support. Addition of wall plate can also help in attaching the rafters and distributing the load of the roof evenly on the wall.

Damage to Roof	Lack of Proper Details of Rafter and Wall

• In most of the hipped roofs, a wooden member is found nailed onto the beam which acts as a stopper to prevent the purlins from sliding away from their positions.

Members Stopping the Purlins from Displacement	Detail

• In some of the hipped roofs, various members of the truss are connected by metal clamps, which provided additional stability to the structure.

Clamps Securing the Truss Members

• Presence of bed blocks under the horizontal members of trusses help distribute the load more evenly.

cell-content
cell-content	Bed Block Under the Horizontal Member of the Truss

• At the ridge positions of the hipped roofs, wooden boards are placed under the roofing to prevent rain water from entering and to cover the gaps in the roofing that might occur at the ends. This detail can also be useful in preventing the leakage in valley situations. Closely placed batons also help in reducing potential water leakage (Fig ).

Gaps in the Roofing at the Ridge	Wooden Board at the Ridge	Detail	Closely Placed Bamboo Batons

Climate response

Due to the sloping shape of these roofs, the centre is high while the walls can remain low. This works well in ventilating the spaces as the hot air raises up and is ventilated through clay tiled roof keeping the lower part of the room relatively cool.

Key Issues with the Building Practice

1. Increased prices and lack of availability of wood impacts on use of wood for construction of the under structure of roofs.
2. Country tiles production is becoming expensive and other cheaper roofing materials like AC sheets are replacing these tiles.
3. Attachment details of walls to the roofs are not properly worked out.
4. Alignment of all the members of the roof structure is sometimes lacking, resulting in a poor performance during disasters.
5. In many cases, joinery details between different wooden elements are not worked out.

Artisans

• Godadbha Virabha

Address: Baradiya, Chandrabhaga Area, Taluko Dwarka

Godadbha is an artisan who specialises in construction of gable roofs with timber structure. He has experience in making wooden structures and roofing of gable roofs.

Special Tools/ Equipments

Construction Methodology

Gable Roof Construction Method by Godadbha Virabha from Dwarka Region:⁵

When the side walls are constructed till desired height, the construction of gable end walls is started. At this point, it is important to determine the slope of the roof and the top of the gable walls are constructed with the desired angle. To arrive at the angle of the gable walls, a log of wood (generally bamboo) and rope/strings are used. The slope is decided visually, generally for every 6 feet of span the height of gable wall is raised approximately to 1.5 feet. Bamboo is positioned at the ridge location indicating the height and then another bamboo or a stone is placed on the lower point of the slope. A rope is tied between the bamboo at ridge level and bamboo or stone at the lower level. This rope gives the angle of the gable wall. Gable walls are then constructed following the angle given by the rope. After the gable walls are finished, the ridge beam (aadsar) of approximately 1.5 ft by 1.75 ft. is positioned on top corners of these walls. The length of the ridge beam needs to be a bit more than the length of the room. Rafters (bambooda) are placed on the ridge beam at approx 1.5 ft distance. These are nailed or tied to the ridge beam. Batons (vajji) are placed on the rafters at the distance of 2-3 inch. When Manglore tiles are used for roofing, the distance of batons should be adjusted according to the size of the tiles. For the country tiles, the denser the batons are placed, the better it is, since there will be less problems of leakage and falling of tiles etc. Batons are normally made out of halved/split bamboos. Purlins if needed are placed and supported directly on the wall. Laying of the roofing tiles starts from the lower end of the roof. A certain area is taken and roofing is done till the ridge. Then it starts again from the lower part of the roof, reaching up. At the ridge, ridge tiles (mobhiya) are placed. To keep the ridge tiles in place and to prevent them from flying away, a rope tied with two stones on sides is placed on the top end ridge tile, which will add the weight on the tiles and keep them in position.

Bibliography

Credits and Acknowledgements

Documentation

• Rushank Mehta ('People in Centre' Consulting)
• Chintan Gohil ('People in Centre' Consulting)
• Ashish Parmar (CEPT University)
• Shakeel Khimani (CEPT University)

Information

• Babubhai Vadgama for telling the history of Beyt Dwarka and the use of construction materials and for the help in getting permissions for measuring the case study.
• Hemubha Vadher for the help in collection of information about the buildings and building materials. He was born on the Island and has lived all his life there, so he had some information on where the materials were imported from in earlier days.
• Mihir Parmar for the help in measuring the case studies.
• Mr. Ker from Gram Vikas Trust, Dwarka for useful information about villages of Dwarka region and contacts of artisans.
• Sadurbha from Dwarka (Mobile: [phone]) for providing us information on Tanks as well as contacts of artisans in Dwarka region.
• Varsing Mala from Rabari Vaas, Beyt Dwarka for information on Beyt Dwarka’s history.

Comments

Footnotes

1. Information on availability of clay required.

2. Information on history of disasters e.g. magnitudes of particular places in Saurashtra during last few major earthquakes, wind speeds in cyclones etc would be useful.

3. The relationship between the earthquake magnitude and the maximum intensity caused is not a precise one. This approximation of magnitude is based on Earthquakes. (Reference: Don de Nevi, Celestial Arts, Calif., 1977, P.102)

4. Reference: Cyclone resistant building architecture, Ankush Agarwal, Technical Officer (Hazard Vulnerability Reduction) GoI – UNDP, Disaster Risk management Programme, March, 2007

5. Based on Discussions with Godadbha on 21.08.09. His contact details are mentioned in the section of artisans.