Roof

A roof is defined as the uppermost part of a building which is constructed in the form of a frame work to given protection to the building against rain, heat, snow, wind etc. A roof basically consists of structural elements provided at the top of building for the support of roof coverings.

Following are the requirements of well-planned roof:
  • It should be durable against the adverse effects of various agencies such as wind, rain, sun etc.
  • It should grant the desirable insulation against sound and heat.
  • It should be structurally stable and sound, it should be capable of taking the loads likely to come over it.
  • It should be well-drained
  • It should have efficient water-proofing arrangement

Types of roof – advantages and disadvantages of each type of roof (mainly materials used in north paravur context)

The roofs classified into the following three categories according to method of construction;

Pitched roofs: A sloping roof is known as pitched roof. Pitched/Sloping roof can be constructed by

  1. Mangalore pattern Roof tiles over Anjali or Teak wood truss work (Rafters & Purlins)
  2. Managalore pattern Roof tiles over Truss made with14gauge /16gauge GI Tube sections (Rafters & Purlins)
  3. 0.36mm Aluminium or GI Troughed sheet over Truss made with 14gauge/16gauge GI Tube sections (Rafters & Purlins)
  4. Sloping Roof can also be made with RCC Slab. The normal thickness up to 3.3m span can be 10cm.
Advantages of pitched roofs:
  • Shaped like a triangle, they are stable and far more effective when dealing with excessive weather, including heavy rain and snowfall. The roof design helps to direct the water away from the home and leaves little chance of water logging.
  • The natural ventilation underneath the top roof layer significantly improves the thermal efficiency of a building. This ensures optimal indoor comfort both in winter and summer.
  • The building envelope is responsible for around 25-35% loss of energy within a building. Pitched roofs are built to allow natural ventilation between the outer layer and the building, preserving energy.
  • Some roofing tiles have sustainable credentials to integrate solar panels within the structure of pitched roofs.
  • Flat roofs require constant maintenance of their drainage systems to avoid leaking. While pitched roofs are more expensive, cheaper and less frequent repairs compensates for this. This is especially true is the roof is covered in high-quality natural slate, with a lifespan of over 100 years and no need for any maintenance.
  • The pitched roof makes it easier to reuse rainwater than flat roofs. The external drainage system is easier to modify and maintain.
  • Pitched roofs can be converted to house substantial extra living space inside.
Disadvantages of pitched roofs:
  • Pitched roofs place a greater burden on the foundations of the building and demand a greater depth of the footings.
  • Replacing a flat roof with a pitched roof on an existing structure is not always feasible Not feasible for buildings with multiple levels or complex plans.
  • Cannot be done as much with a pitched roof regarding architecture.
  • More expensive to install and maintain.

Flat Roofs: A roof which is nearly flat is known as flat roof. It should be noted that no roof can be laid perfectly level. The roof must slope in one direction or the other to cause rain water to flow off rapidly and easily. The construction of flat roof is same as that of floors except that the top surface is made slightly sloping in case of flat roofs. The types of flat roofs commonly used are

  1. Madras terrace roof
  2. Bengal terrace roof
Advantages of flat roofs:
  • The construction of roof is simplified.
  • It is easier to make a flat roof fire-proof than a sloping roof.
  • The roof are can be utilized as roof garden, dry ling yards and conveniently be used for sleeping in hot season.
  • The construction of work of upper floors can be easily started whereas pitched roof, the entire roof is to be removed and is to be replaced by a new floor under such circumstances.
  • Flat roofs is found to be economical than pitched roof.
Disadvantages of flat roofs:
  • Flat roofs cannot be used for long spans without introduction of intermediate pillars and beams.
  • Cracks are developed on the surface of the roof due to the variation in temperature.
  • Pockets of water are formed on the surface of the roof if slope is not sufficient and leads to leakage of roof.
  • Flat roofs are not suitable, where rainfall is heavy.
  • The dead weight of flat roof is considered and hence it proves to be more expensive, Initial cost is higher than pitched roof.

Curved roofs: These are the just the modifications of pitched roofs and are frequently employed in modern age to cover large areas shed/roofs and domes are the varieties of curved roofs. They are useful for big structures such as factories, monumental works etc. curved roofs may be constructed of timber or R.C.C. the latter material being very common now-a-days. They are two common forms of a shell roof

  • A north-light shell roof
  • A barrel vault shell roof
Advantages of curved roofs:
  • It can be constructed in short time
  • It does not require skilled supervision
  • It is cheap in construction
  • It requires less frame work

Specification of a rcc flat roof construction

  1. The proportion of concrete used shall be 1 part cement, 1.5 parts sand and 3 parts coarse aggregate (1:1.5:3, M20) or 1 part cement, 2 parts sand and 4 parts coarse aggregate (1:2:4, M15) depending upon the load. 1:1.5:3 mixes shall be preferred.
  2. The cement shall be used in this work shall comply with the standard requirements. 53 grade cement shall be used for the concrete mix. The preferred cement would include Ramco, Ambuja, Chettinad, Penna, JSW, Daimler etc.
  3. The sand to be used shall be clean and coarse and shall be free from any organic or vegetable matter. Nowadays as sand is not available, Manufactured sand (M-Sand) is being used widely
  4. Coarse aggregate used shall be of size 20mm and shall be clean and free from impurities such as earth, coal dust and other organic materials
  5. In general 12mm, 10mm and 8mm diameter MS/TMT steel bars are used in RCC slab according to the length of span of the slab and similarly spacing is from 4.5’’ to 6’’ in the main bars and 6’’ to 8’’ in distribution bars. 8mm bars are used as distributers and not as main bars.
  6. Choosing between two way slab and one way slab should be decided on the basis of the length of the roof slab. For smaller area, one way slab can be adopted.
  7. After steel bar bending and binding, lay the conduit pipe for electricity and fan hook etc as per requirement.
  8. The thickness of the roof slab shall not be less than 10cm.
  9. Sheets, Jacky and spans are preferred nowadays instead of timber shuttering for easy installation and less time consumption. The gaps in the formwork should be filled before laying the concrete.
  10. The mixing of concrete shall be done in a mechanical mixer (preferred more) or by hand operations depending on the quantity of the concrete which shall be decided by the engineer. In the former case, the mixing drum shall be turned at least for 1.5 minutes after all the ingredients are added and the drum shall be completely emptied every time.
  11. Cement Cover blocks should be provided under the steel reinforcement to ensure proper cover for RCC. Stones or any other materials shall not be used.
  12. Compacting of concrete should be done with a mechanical vibrator to avoid the formation of honeycombing. No other means of compaction such as use of steel rods should be adopted
  13. All exposed surfaces of the concrete work shall be finished with 12mm thick cement plaster finish and three coats of white or colour shall be applied on these exposed surfaces of concrete.
  14. While plastering the roof slab, it is necessary to provide slope to one direction to allow the drainage of the rain water. Stagnation of rain water should not allow on a roof slab.

Methods of roof waterproofing

A place like Kerala receives the heaviest rainfall during monsoon season which lasts for nearly six months which in turn points to the fact that the houses constructed in Kerala are subjected to heavy rain and winds. These weather conditions is considered as the biggest threats to a roof system as it can break roofing material, allowing water to trickle down to the roof’s substructure causing leaks. A significant damage can be caused to the roof as wet roof surfaces run the risk of vegetation and other biological growth, like mould. Additionally, water damage can spread from the roof to the ceiling and walls, causing the structure to become unstable over time if the problem isn’t resolved.

The most important step in the roof installation process is water proofing as it protects the material with which the house was built, as well as all the things you keep inside. Due to certain reasons, the concrete can lose its permeability and will not be watertight on its own which makes it necessary to water proof the roof. Roof waterproofing is the layer of extra protection added to your roof that guarantees no water gets inside your home or starts causing the walls or support beams to rot. There are many causes of roof leaks, with inadequate roof waterproofing at the top of that list. Simply, waterproofing seals cracks, will stop leaks, protect smooth surfaces, and keep the roof structurally strong.

Few decades before, in North Paravur, as the roof of the houses were thatched roofs which in turn was replaced by tiled roofs, waterproofing did not have much of a popularity. Prior to the onset of monsoon, the homeowners would carry out maintenance in their roof by adding more thatches on top of it or fill the gaps in the tiled roof. As homeowners began relying on RCC roof, the necessity of The most commonly adopted method of waterproofing in

  • Liquid/Paint water proofing

    Brush applied water proofing compounds can be applied on top of the screed over RCC slab which costs Rs. 35/sqft. e.g.:- Pidilite, BASF etc. Dr. Fixit Pidifin 2K is a high performance flexible waterproofing membrane, which gives a waterproof coating for all bathrooms, kitchen, small roofs, balconies, terraces, wet areas, chajjas, sloping RCC roofs, and basements. It’s a two-component acrylic cementous waterproof coating for water tanks.

  • Workability agents or Super plasticizers

    Workability agents can be added to concrete during batching, to reduce the water content so that a more durable and non-perforated concrete can be obtained. Other substances include calcium chloride, lime, fly ash, and other pozzolans. Calcium chloride is also an accelerator. Lime increases the cementing properties of cement, as do pozzolans combined with lime. Fly ash is inexpensive compared to cement and is used as a partial replacement (up to as much as 50 percent) of the cement. It changes both the plastic and the hardened properties of concrete. Fly ash improves workability and reduces segregation, bleeding, and the heat of hydration.

  • Membrane

    A waterproofing membrane is a thin layer of water-tight material that is laid over a surface. This layer is continuous and does not allow water to pass through it. For example, on a flat terrace, a waterproofing membrane could be laid above the structural slab and below the finish tiles. Heat applied or self-adhesive water proof membranes are available in the market. Dr. Fixit Torchshield AP range of polymer modified membranes are modified bitumen waterproofing membranes manufactured by saturating and coating a polyester carrier with a waterproofing compound made of a special grade of modified bitumen with APP polymers. The upper and lower surfaces are laminated with polyethylene film.