Cool Roofs is a green building technology that is especially suited to the climate of the India. It is a relatively cheap option with substantial benefits. Yet you may not be familiar with what exactly the term means :) So let’s give you a quick primer on Cool Roof Technology with a special emphasis on its suitability in the Indian context.
How does a Cool Roof work?
The term itself provides a big clue to its meaning. Cool Roof is a roofing system that helps keep a building cool. It manages to do this via two methods
- reflect away a percentage of the visible, infrared and ultraviolet radiation from the sun. This reduces the heat gained by the building itself and is called high solar reflectance.
- emit away the heat retained by the building. This helps in the building down quicker as compared to traditional materials and is called high thermal emittance.
A traditional, dark material roof can reach temperatures of 65oC. Installing an appropriate cool roof technology can bring this down to under 40oC. This is a big difference and results in energy and money savings by using lesser air conditioning.
Great! Tell me more about these benefits.
The obvious benefits to the occupants of a building utilising cool roof technology would be
- Reduction in electricity bills due to lesser cooling requirement and AC loads.
- Better indoor comfort for non air conditioned spaces, such as garages, covered patios, garden sheds etc.
- A possible increase in roof life due to it being subjected to lower than average temperatures.
Additionally, when a high percentage of buildings in an area utilise cool roofs, there are synergistic benefits
- Reduction in local air temperatures. It can be thought of as the reverse of the urban heat island effect (maybe call it the urban cool island effect :P)
- Lower peak electricity demand, which can help prevent power outages
- Reduce power plant emissions, including carbon dioxide, sulfur dioxide, nitrous oxides, and mercury, by reducing energy demand.
Roofing solutions for India
Cool Roof Coatings
These can range from a simple limestone whitewash on the cheapest end to good quality reflective coatings. The price ranges from under Rs 20 per sq ft (for whitewash) to Rs 80 per sq ft (for a good quality reflective coating)
In addition to high reflectivity, certain coatings also provide better UV protection and some protection from water and chemical damage. These additional protections may prove useful if the climate is humid as well as sunny.
Flat roofs can be covered with white or light coloured glazed tiles. Other tiling solutions also exist for sloped roofs for ex cool shingle tiles, slate tiles etc. These material may either be naturally reflective enough to meet cool roof standards or may have coatings pre-applied to them to increase their reflectivity.
Metal roofs usually have high reflectivity but are very poor in terms of thermal emittance. This can be improved by applying cool roof paints and coatings on these.
Earthen pots Insulation system
This is a traditional method used in India where the roofs (and sometimes even walls) are covered with upside down earthen pots and then cemented in place. This traps air between the original roof and the final surface thus providing insulation. This method helps keep the building cool in summers and warm in winters.
You may choose to install a green roof for your building as an alternative to cool roof. However the following should be kept in mind
- They are suitable for urban building with flat roof surface.
- They can be designed to have basic plant cover to a garden.
- They are more expensive to implement (as compared to a cool roof solution) and require ongoing maintenance in most climates.
- They do lower the need for heating and cooling since they provide good insulation and also reduce urban heat island effect.
- However they are more successful in climates where the heat is not intense enough to wilt the plant cover or otherwise require additional protection from heat.
- Water requirements and drainage is a concern as well and green roofs may be more suitable in climates with frequent rains and storms.
- Consulting a professional is highly recommended to get a better idea of how suitable the building is for such a roofing solution.
If the conditions on the rooftop are suitable to the installation of solar panels, this may be considered as an option. However the cost to install this is 10 to 50 times higher as compared to a cool roof solution so it is usually only considered by institutions and industries if at all.
Should I install a cool roof for my building?
The honest answer is that it depends on a number of factors. However as a rough guide, given the long and very hot summers in the Indian subcontinent, there is a good chance that you’ll benefit from a cool roof installation. Some of the factors that you should still consider are
- What is the climate like? How much sun does the roof get? The greatest savings are seen in hot climates while cold climates might see an increase in their heating bill.
- Humidity. In warm climates with a higher humidity, cool roofs are more prone to mold and fungal growth due to lower temperatures. Thus coating that protect against moisture and include microbial protection should be selected. In cooler climates with high humidity, cool roofs are more prone to condensation and thus proper care must be taken with the roof design to mitigate these issues.
- Is the building still in the planning phase or has already been constructed? There is more leeway in choosing a roofing solution if the building is still in the planning phase. The solutions available for existing buildings are somewhat restricted in comparison.
- Condition of the roof. It makes less sense to go for a cool roof solution if the existing roof is relatively new and in good condition. This is because a big chunk of the cost comes from the specialised material and labour involved in the installation. It may be better to pick solution requiring more specialised labour and materials if the roof requires repairs anyway so that the investment can be defrayed against regular maintenenance.