The floor to fall for this summer

Jagvir Goyal

It is scorching hot outside and stepping out on to the courtyards and terraces can be dreading during peak summer hours. While things get better once the sun goes down the horizon, areas in the west and south remain hot till late evening. However, there are floorings that remain comparatively cooler in summers.

Before we talk of various materials and their summer cool suitability for use in courtyard and terrace flooring, one important factor that needs to be understood is Solar Reflectance Index or SRI. It is sometimes referred to as Solar Reflective Index too. SRI is the ability of a material to reflect the solar radiation instead of absorbing it.

How SRI helps: SRI of a material helps in determining its suitability for remaining cool during summers. Higher the SRI of a material, cooler will it be during summers. For SRI to be higher, solar reflectance of the material must be higher. In other words, the material should be able to reflect solar radiation to the maximum possible extent instead of absorbing it. Similarly, for the SRI to be higher, thermal emissivity of that material should also be higher. The material should be able to release the heat it has absorbed to the maximum extent instead of retaining it. Both solar reflectance and thermal emissivity are measured on a scale of 0 to 1.

SRI values: SRI values vary for materials from 0 to more than 100. Higher the SRI value, cooler the material. A standard black material has SRI of 0.00 as it absorbs all heat. A standard white material has SRI of 100 as it reflects all heat. When a material is able to reflect the ultraviolet, infrared and visible rays of the sun, it has high SRI. Such a material helps in reducing heat transfer to the building and thus cuts the cost of air conditioning as lower roof temperature helps in reducing use of electricity for air conditioning.

Colour effect: The colour of a material is closely related to its SRI. Lighter colours reflect more sunrays while darker materials absorb them. Thus, white materials always have better reflection and better SRI. Therefore, while taking your pick, concentrate on two properties - SRI and colour. Always choose a material that has high SRI and comes in white colour or its shades.

Kota stone: This is the most prevalent material for courtyard flooring. It is bluish, grey, brown, green and red in colour. It is also amongst the cheapest floorings. However, it needs to be chosen carefully to avoid any colour variation. Mostly, it is supplied in tiles of size 575 X 575 mm. SRI of Kota stone is in the range of 40 to 60, light colours having more SRI value.

Marble: Using marble in courtyard or terrace is an expensive option. However, marble that is not as expensive as the one used inside the house, is often chosen for courtyard flooring. High-quality Makrana white marble has high SRI due to its colour. Marble for courtyard flooring should not have thickness less than 20 mm. Also, make sure you go for marble having low porosity, high density and low water absorption. SRI of marble is in the range of 60 to 80.

Vitrified tiles: A commonly used material in the indoor flooring of the house, these are not used in courtyards or on the terrace. Use of double-charged vitrified tiles in the house has become very popular, yet their use in courtyards or terraces is hardly accepted. These tiles are available in many sizes and it is entirely the buyers' choice to finalise a size as per his budget and taste. Size wise, 600mmX600mm tiles are most commonly used. Polishing of marble is a time consuming and messy affair while no polishing is required in case of vitrified tiles. Cost wise also, these tiles compete with marble and are much cheaper than Italian marble and granites. These also have high dimensional accuracy and zero water absorption property. Despite all these properties, their use in sun exposed areas has not become common.

Porcelain tiles: Though porcelain tiles fall in the category of ceramic tiles, these possess some properties that are better than those of vitrified tiles. While vitrified tiles are harder, porcelain tiles possess the property of non-staining and remaining scratch free. However, these tiles too have a medium SRI range and are not preferred for use in courtyards and terraces.

Burnt clay brick red tiles: Use of burnt clay brick red tiles on terrace is common as these are conventionally used and are cheaper than other materials. However, SRI of these tiles lies in the range of 30-36 only. Therefore, when viewed from summer cool effect angle, these are not a suitable material for terrace or courtyards.

Granite and natural stones: These materials are often used in courtyard flooring. High polished granite is quite costly and is used inside the house in selective portions like countertops, etc. and low cost, semi-polished or unpolished granite is used for paving the courtyard. Overall, SRI of natural stones and granites is between 50 and 80. 

Ceramic tiles: Some tile manufacturers have been producing special ceramic tiles to be used as summer cool tiles. These tiles are produced in 30cmX30cm size and are white in colour. These tiles are given a special coating to ensure better solar reflectance and thermal emissivity and have infrared resistive composition. Mostly produced in 10 mm thickness, these tiles reduce the surface temperature of the courtyard paving or terrace by 10 to 20 degree centigrade. Some manufacturers claim their tiles to be reducing surface temperature by 22 degree centigrade. These tiles have very low water absorption. If used on the terrace, care must be taken that the joints between the tiles, especially along the parapet, are grouted and sealed well to avoid any ingress of rainwater below the tiles. Solar reflectance of summer cool tiles is plus 0.8 and thermal emissivity too is plus 0.8. These tiles, therefore, have SRI of 100 or even more. However, before you pick these for your home, make sure they are in matt finish and come with anti-skid property.

— The writer is HoD and Engineer-in-Chief, Civil Engineering Department, in a Punjab PSU. (This column is published fortnightly)