THE COOL ROOF AND THE GREEN ROOF
There are two main types of environmentally friendly roof treatments i.e the cool roof and the green roof.
Cool roofing is an easy and cost-efficient, environmentally friendly finishing technique that can be considered by all prospective home and building owners in order to minimise energy use. It calls for either the cladding of rooftop surfaces in high solar reflective materials or the painting of this in light, bright colours, such as white which means of cutting energy consumption.
BENEFITS OF COOL ROOFING
The concept is as simple as wearing a white shirt on a hot day. Your roof can get up to 50 degrees hotter than external temperatures. Light, or reflective surfaces, absorb less heat and therefore minimise heat transfer to the underlying slab of the roof and subsequently into the building’s interior.
Achieving this means:
- decreased necessity for artificial cooling which can save up to 10 percent on energy costs
- increased indoor comfort through creating a cooler environment
- decreased roof maintenance costs due to longer roof lifespan
- inexpensive material and installation costs
ENVIRONMENTAL BENEFITS OF COOL ROOFING
Aside from user-specific benefits, cool roofing can also play a role in improving overall environmental conditions in more urban areas. Dark pavements and roof surfaces in more developed areas can contribute to air pollution and greenhouse gas emissions through creating an increased platform for heat absorption and subsequently energy consumption, leading to greenhouse gas emissions from power plants. This phenomenon is referred to as the ’heat island effect’, which causes these areas to release accumulated heat back into the atmosphere and cause up to a 5-degree temperature rise in comparison to less urban areas.
Extensive use of cool roofing city/island wide could manifest environmental benefits such as:
- improved air quality
- a cooler urban environment
- reduced greenhouse gas emissions
GREEN ROOFS IN TROPICAL CLIMATES
A green roof or living roof involves completely covering the top exterior level of a building with vegetation and growing medium. Traditionally, these are known for their ability to better insulate homes in temperate climates, providing a warmer indoor environment. However, these can also be utilised to serve various purposes in tropical climates.
The average underlying system consists of:
- roofing waterproofing membrane
- root barrier
- air barrier
- water retention mat
- drainage/water storage/ aeration
- filter fabric
GREEN ROOF BENEFITS
Green roofs help minimise heat transfer into building interiors through the shading provided by its plants and associated growing medium which helps block sunlight from reaching underlying roof membranes. This occurs alongside a cooling effect achieved through moisture build up in the soil. On hot summer days, this makes a green roof cooler than the surrounding air temperature. Local landscape architect Andre Kelshall believes green roofs reap a multitude of benefits if properly designed and installed; stating that this roofing type could be particularly efficient for developers by ensuring a cut in energy consumption by tenants, thus ultimately lowering utility bills. He also concurs that the build-up of layers involved in the system could put homeowners in the Caribbean at an advantage when it comes to flooding and water mitigation. Installation costs can run between $90.00 – $150.00 BBDS per square foot. If wanting to opt for a less pricey, lower maintenance system, he recommends the use of turf instead of grass, as this can be engineered to grow at a slower rate.
Performance advantages of green roofs in the Caribbean include:
- cooler building interiors
- stormwater mitigation
- lengthening the life of the roof waterproofing membrane by two to three times
- increase indoor comfort by diminishing stress associated with heat waves
- noise reduction
- create an aesthetically pleasing or recreational roof landscape
- increased property value
- can prevent the overheating of solar panels if installed
- long-term cost efficiency
ENVIRONMENTAL BENEFITS OF GREEN ROOFS
Green roofs are capable of reducing surrounding temperatures by a process which releases moisture into the air known as evapotranspiration. Vegetation naturally removes air pollutants and greenhouse gas emissions through carbon sequestration and storage (the absorption and storage of carbon with immediate potential to become a CO2 gas) as well as through the reduction of energy demand and production.
Such factors aid the environment by:
- minimising heat island effect
- diminishing air pollutants and greenhouse gas emissions
- supporting habitat provisioning and biodiversity
- reclaiming land excavated from buildings footprint
Andre Kelshall, Design, [www.dla.design.com]
United States Environmental Protection Agency, ‘Using Green Roofs to Reduce Heat Islands’, epa.gov, [https://www.epa.gov/heat-islands/using-green-roofs-reduce-heat-islands]
United States Environmental Protection Agency, ‘Reducing Urban Heat Islands: Compendium of Strategies ’, epa.gov, [https://www.epa.gov/sites/production/files/2017-05/documents/reducing_urban_heat_islands_ch_3.pdf]
Cool Roof Rating Council, ‘Why Cool Roofs are Way Cool’, coolroofs.org, [http://coolroofs.org/documents/IndirectBenefitsofCoolRoofs-WhyCRareWayCool_000.pdf]
Energy Saver, ‘Cool Roofs’, energy.gov, [https://energy.gov/energysaver/energy-efficient-home-design/cool-roofs]