DIY: Beat the summer heat with a white roof

Soaked by the relentless Coimbatore heat, we were looking for natural cooling solutions that were affordable. And chance upon white roofing.


I am a retired scientist with specialization in crop and natural resource management, specifically in rice-based farming systems. So, I am naturally interested in conservation and efficient use of all natural resources – land, water, air, biodiversity, and forests. My friend Dr. S.P. Periaswamy is a nature lover interested in finding simple solutions for our common problems.

We live in Coimbatore – poor man’s Ooty. Even here, we experience high temperatures this summer due to lack of rains and high solar radiation. We use solar water heater and solar power from solar panels in home. But we suffer from the summer heat with our tiled brown roof and we cannot sleep well inside the house. We found a simple solution to beat the summer heat that I want to share with others facing a similar problem:

Summer heat is increasing every day and many cities in India record temperatures above 100-110 oF (37.8-43.3 oC) or even higher. Many people, especially babies and the elderly, suffer from heat-related illnesses like perspiration, exhaustion, fever, difficulty in urination, collapse, and sometimes death due to high heat. Air-conditioners (ACs) may be able to ward off the heat, but the energy use and electricity bills will be going through your roof. With frequent cuts in grid power supply, you cannot even expect the ACs to save you from the summer heat.

We had to find a low cost solution to keep cool. The answer came in white.

My friend Dr. S.P. Periaswamy and I explored several options to reduce the heat in our house. Many options like the sun-reflective white paints were very expensive. After a long search on the Internet and several enquiries with paint companies, we found a cost-effective option for painting our roof white – the finely ground (microfine) lime powder. It is sold by commercial names like Janata Cool or Summer Cool. I bought the Janata Cool sold in 5-kg bags with a small packet of translucent crystal inside. The instruction says it has to be dissolved in 9 liters of water, further adding the lime powder and mixing it well, and leaving to dissolve for 10 minutes.

We used the following procedure:

We took 8 liters of water, dissolved the packet of crystals in it, added 500 ml of Fevicol (adhesive) and then mixed in it the 5 kg of lime powder well. We let it for 10 minutes, then mixed the solution well and painted the roof with a wide brush. It covered about 600 square feet (60 square meters) of roof surface. We have to paint the roof either early in the morning (06:00 to 10:00 am) or in the evening (04:00 to 08:00 pm) to avoid inhaling the pungent fumes that emanate from the solution when exposed to direct sunlight and high temperature. You can water the painted surface 12 h later for curing.  A second coating is applied 24 hours after the first application. We can water the painted roof for 3-4 times in two days for proper curing. After drying, we can see the bright white roof. We use the solar panels to get solar power for our home use.

The temperature inside the house before was 35 degree C and after was 30 degree C, a reduction of 5 degrees with just white paint.

We measured the temperature inside the house before and after painting the roof white with the lime powder: 35 oC  before and 30 oC after painting the roof white, a reduction of 5 oC in room temperature, under Coimbatore conditions (16-17 April 2013). We can now comfortably sleep in the bedroom with a fan only in the night. We have avoided the use of AC even during the peak of this summer, with a simple solution like painting the roof white with lime. The cost in Indian Rupees (Rs) of lime painting for 600 square feet (60 square meters) of roof surface is as follows:

Ingredients         Price (in INR)
Janata Cool lime powder (two bags 5 kg each) 360 (180X2)
Fevicol Adhesive(one litre)   80
Labour Charges 500
TOTAL 940 per 60 Square Meter

You can also use this simple solution to beat the heat this summer at an affordable cost.

FAQs (From comments)

1. Whether this will solve my problem?

Yes, it will reduce the temperature inside rooms by 3-4 C

2. Whether I will have to apply this coat every year? (Life of the lime coating)

The coating of lime solution mixed with pevicol adhesive will last 3+ years on sloping roof and 2-3 years on flat roof, if there is not too much trampling. If you walk over lime-coated terrace every day for drying clothes, etc., you may have to lime-coat the terrace once in two years. Alternatively, you can place a wooden plank on the terrace to walk over and dry the clothes or do other activities. Minimum trampling will keep the lime coating for longer.

Unlike some of the enamel paints that will come off like flakes, lime coating will not peel off (especially if the surface is a bit rough before lime coating). It is better to keep the lime-coated surface clean by periodic sweeping with a smooth broom (It is easy to clean with a smooth broom). The maximum you may need is an annual lime coating to get maximum reflection of the sunlight and thus an effective cooling of the rooms inside the building.

3. Whether it can be used by me (by brush) or will have to hire a machine or a labour or technician for the same?

You can do it yourself or with the help of a painter. Do the lime application early in the morning or in the evening to reduce pungent odors.

4. Whether all these products are readily available in the market?

This is available in a store in Coimbatore. The address is:

Janata Cool Micro-fine lime powder
Priya Corporation Limited
Gounder Mills area
Near Priya Hostel on KNG
Pudur road from Mettypalayam Road.
Mobile: 9994317663;
Landline: 0422-6579670
Cost Rs. 190/- per 5 kg bag.

5. Any particular name of product company would you suggest?

Same as in (4) above.

6. How much lime will be needed to cover 1000 sq. ft (100 sq. meters)?

Approximately 18 kg lime per 1000 sq. ft. area for two coatings (9 kg per 1000 sq. ft area for a single coating).

7. Any substitute, if one of suggested product is not available?

You can simply use any lime powder available in 10 kg bags at Rs. 120 per bag (Rs. 12 per kg). Use the proper ratio of lime, water and pevicol. For every 5 kg of lime powder, add 8 liters of water and mix well, then add 0.5 liter of pevicol (adhesive) and mix well everything and let it stand for 5-10 minutes before applying the lime + pevicol solution on the terrace. Clean the terrace, dry it, and then apply the
lime + pevicol solution with a brush. Leave it overnight, cure it by watering morning and evening the next day. Apply a 2nd coating of 5 kg lime in 8 l of water mixed with 0.5 l of pevicol on 3rd day and repeat curing with water for the next two days. That is it.

8. Is the ordinary lime powder equally effective as the micro-fine lime powder (Janata Cool)?

The finer the lime powder the better it is. Microfine lime powder by some brand name will be available in some hardware shops in big cities. If it is not available, ordinary lime powder is OK as it will also be more or less equally effective.

9. Can we increase the life of lime coating by doubling the amount of pevivol used and can we also mix Nano Silicone to make it more water soluble and thus withstand better the erosive power of rains?

There is no need to double the amount of pevicol. You can increase the amount of pevicol by 25% to 50% to make the lime stick better to the surface.

I have not tried the Nano Silicone to make the lime more water soluble and withstand the erosive power of rains. Please try one part with lime + pevicol and another part with lime + Nano Silicone + pevicol and let me know the results.

10. Can we substitute lime powder with Asian Paints white emulsion?

If you can afford, you can use the white exterior emulsion paint – ordinary (Rs. 2800 to 3000 per 20 l) or damp-proof (Rs. 4800-5000 per 20 l). However, some people experienced that the paint peels off as flakes after some time. This peeling off will not be a problem with lime coating, as far as I know.

I learnt that there is a company by the name Excel Coatings that is based in Chennai and have offices allover India is charging Rs 9500 for 30 L with a durability of six years plus waterproofing. I don’t know much about it.

11. What is the translucent crystal and is it absolutely necessary?

I don’t know the chemical name of the translucent crystal, but in my experience, it is not critical.

12. Can I apply the lime on roofs laced with brown tiles?

Yes, you can apply lime on brown tiled roofs. If the tiles are too smooth the lime coating may not stick well. You can use sand papers to make the surface slightly rough before applying the lime coating.

13.a Are there any effect of lime coating of terrace on human health, especially when you walk over it daily?

With simple lime coating, I don’t see or hear of any human health problem when you walk over the lime-coated terrace.

13.b When you walk over the lime-coated terrace, does it stick on the soles of the feet?

If properly cured after lime coating, very little lime will stick on the feet. However, avoid frequent trampling of the lime-coated surface
as much as possible.

14. Can I harvest the rainwater for domestic use from the lime-coated surface? Is it safe for drinking after proper treatment?

Unlike paints which contain many chemicals including water-soluble and volatile organic compounds that may be toxic to humans, lime is
pure Calcium carbonate (CaCO3) which doesn’t contaminate the rainwater, so rainwater harvested from lime-coated terrace is safe for domestic use, as far as I know. Moreover, calcium from lime is a nutrient that can improve bone health.

15. Do one has to paint the exterior walls also?

If walls are exposed to direct sunlight (east and west facing walls), it will help painting them white with lime or a paint.

16. Do one has to cover the entire roof or just the area above your bedroom/living room?

It is better to cover the entire roof for the whole house to be cooled. In case of frugality, you can just lime coat the roof area above
bed/living rooms. It will be equally effective.

17. Would constant rainfall reduce the effectiveness of the coating?

Continuous heavy rainfall may erode the lime coating, you may have to redo the lime coating once every two years or every year at the most.

You can reach Balasubramanian at vbalasubramanian@irrialumni.org


  ABOUT THE AUTHOR
V. Balasubramanian is an agricultural consultant and trainer based out of Coimbatore. more

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  • wmh

    In Australia, on galvanised iron roofs, use Dulux-Weathershield Vivid White which is self-priming (no undercoat needed) just scrub the roof first with detergent in water to degrease and clean off the bird shit. Protects the roof too. If you want to test it first, paint 500mm x 500mm on an old piece of iron and sit it in the sun for 20 minutes.

  • shaaz

    The combination of lime powder and fevicol, works for asbestos cement sheet as well ??

  • Virendra

    I could not find the translucent crystal.
    By what name it is sold?

    • v

      It is not critical. You can use Lime + Fevicol solution for lime coating. Thanks. Bala.

  • sD

    First of, thanks to the article author; and all others who shared their inputs. I painted my terrace white…difference is very noticeable. The terrace already had brick-bat coba and terracotta tiles.

    Steps:

    Day 1
    Cleaned the terrace (Scrubbed & removed moss, dirt etc.,)
    Painted regular wall primer (Asian)

    Day 2
    Painted 1st coat of Ace emulsion white

    Day 3
    Second coat of white emulsion

    While diluting emulsion, added nano silicone liquid (product from zydex industries) to the water then used it. Shop owner told me nano silicone is a water repellent which will ease water run off and cleaning after painting.

    • Jayaesh Singh

      Hi there sD, when you say very noticeable how much temperature difference inside the room you experienced and is it still giving you the same now ?? how much of Nano Silicone has to be mixed with Emulsion ?? did you use Fevicol as well ?? please do let me know… thanks

  • Sai Chakravarthy T

    Fevicol Adhesive…there are many available right? Can you let me know which one exactly to use?

    • Vethaiya Balasubramanian

      Any Fevicol from a paint shop will do. Thanks. Bala.

  • Pavithran G

    Hello Mr V. Balasubramanian. My mother is interested having a talk with you regarding the information in this article. Is there a contact info – email/phone – that you can share with me. thanks

    • v

      Mr. Pavithran,

      Greetings. I have given all the details of the lime coating as a Q&A response to Mr. Dayal. It will help solve many of the queries your mother might have. If needed, my contact No. is+91-9486394901 and my email id is: vbalasubramanian@irrialumni.org

  • The Alternative team

    Hi Pavithran, you can reach him at vbalasubramanian@irrialumni.org. Hope this helps. We have updated the article too.

  • Dayal

    Many thanks for this article.

    Last year, I spent a fortune to apply Dr.Fixit Thermal Shield to my roof. I followed the instructions meticulously and the cooling effect was very noticeable. However, my joy was short lived due to the following reasons. 1) during the rains, the water from the terrace was whitish and foamy. This continued even after quite a few days of rain and I had to permanently disconnect my rain water harvesting. 2) The terrace picked up dust which drastically reduced the reflectivity of the paint. I tried cleaning every 2 or 3 months, but the dirt is hard to remove and original effect cannot be regained. Now I am back to square one – with a dull white expensive roof paint without any cooling effect.

    This alternative idea is very useful; I am keen to try this. But I would want to know if the water coming off the roof is safe for harvesting? How easy it is to clean given that our cities are quite dusty.

    • shyam datla

      Hello Mr Dayal Even i am anticipating the same situation, i used Excel cool coat(pathetic qulity, and loot 6700/- for 20L) and Asian paint Smart Damp proof(4000/-for 20L) whose qulity is remarkable, thought post reading your article i am also worried about the same situation. May be a steel roof shed would be better thermal insulation in future.

  • Vethaiya Balasubramanian

    Dear Mr. Dayal,

    Greetings and thank you for your mail. Here is the Q&A on
    lime coating on terrace to reduce the temperature inside rooms:

    1] Whether this will solve my problem?

    Yes, it will reduce the temperature inside rooms by 3-4 C

    2] Whether I will have to apply this coat every year? (Life of the lime coating)

    The coating of lime solution mixed with pevicol adhesive will last 3+ years on sloping roof and 2-3 years on flat roof, if there is not too much trampling. If you walk over lime-coated terrace every day for drying clothes, etc., you may have to lime-coat the terrace once in two years. Alternatively, you can place a wooden plank on the terrace to walk over and dry the clothes or do other activities. Minimum trampling will keep the lime coating for longer.

    Unlike some of the enamel paints that will come off like flakes, lime coating will not peel off (especially if the surface is a bit rough before lime coating). It is better to keep the lime-coated surface clean by periodic sweeping with a smooth broom (It is easy to clean with a smooth broom). The maximum you may need is an annual lime coating to get maximum reflection of the sunlight and thus an effective cooling of the rooms inside the building.

    3] Whether it can be used by me (by brush) or will have to hire a machine or a labour or technician for the same?

    You can do it yourself or with the help of a painter. Do the lime application early in the morning or in the evening to reduce pungent odors.

    4] Whether all these products are readily available in the market?

    This is available in a store in Coimbatore. The address is:

    Janata Cool Micro-fine lime powder
    Priya Corporation Limited
    Gounder Mills area
    Near Priya Hostel on KNG
    Pudur road from Mettypalayam Road.
    Mobile: 9994317663;
    Landline: 0422-6579670
    Cost Rs. 190/- per 5 kg bag.

    5] Any particular name of product company would you suggest?

    Same as in (4) above.

    6] How much lime will be needed to cover 1000 sq. ft (100 sq. meters)?

    Approximately 18 kg lime per 1000 sq. ft. area for two coatings (9 kg per 1000 sq. ft area for a single coating).

    7] Any substitute, if one of suggested product is not available?

    You can simply use any lime powder available in 10 kg bags at Rs. 120 per bag (Rs. 12 per kg). Use the proper ratio of lime, water and pevicol. For every 5 kg of lime powder, add 8 liters of water and mix well, then add 0.5 liter of pevicol (adhesive) and mix well everything and let it stand for 5-10 minutes before applying the lime + pevicol solution on the terrace. Clean the terrace, dry it, and then apply the
    lime + pevicol solution with a brush. Leave it overnight, cure it by watering morning and evening the next day. Apply a 2nd coating of 5 kg lime in 8 l of water mixed with 0.5 l of pevicol on 3rd day and repeat curing with water for the next two days. That is it.

    8] Is the ordinary lime powder equally effective as the micro-fine lime powder (Janata Cool)?

    The finer the lime powder the better it is. Microfine lime powder by some brand name will be available in some hardware shops in big cities. If it is not available, ordinary lime powder is OK as it will also be more or less equally effective.

    9] Can we increase the life of lime coating by doubling the amount of pevivol used and can we also mix Nano Silicone to make it more water soluble and thus withstand better the erosive power of rains?

    There is no need to double the amount of pevicol. You can increase the amount of pevicol by 25% to 50% to make the lime stick better to the surface.

    I have not tried the Nano Silicone to make the lime more water soluble and withstand the erosive power of rains. Please try one part with lime + pevicol and another part with lime + Nano Silicone + pevicol and let me know the results.

    10] Can we substitute lime powder with Asian Paints white emulsion?

    If you can afford, you can use the white exterior emulsion paint – ordinary (Rs. 2800 to 3000 per 20 l) or damp-proof (Rs. 4800-5000 per 20 l). However, some people experienced that the paint peels off as flakes after some time. This peeling off will not be a problem with lime coating, as far as I know.

    I learnt that there is a company by the name Excel Coatings that is based in Chennai and have offices allover India is charging Rs 9500 for 30 L with a durability of six years plus waterproofing. I don’t know much about it.

    11] What is the translucent crystal and is it absolutely necessary?

    I don’t know the chemical name of the translucent crystal, but in my experience, it is not critical.

    12] Can I apply the lime on roofs laced with brown tiles?

    Yes, you can apply lime on brown tiled roofs. If the tiles are too smooth the lime coating may not stick well. You can use sand papers to make the surface slightly rough before applying the lime coating.

    13a] Are there any effect of lime coating of terrace on human health, especially when you walk over it daily?

    With simple lime coating, I don’t see or hear of any human health problem when you walk over the lime-coated terrace.

    13b] When you walk over the lime-coated terrace, does it stick on the soles of the feet?

    If properly cured after lime coating, very little lime will stick on the feet. However, avoid frequent trampling of the lime-coated surface
    as much as possible.

    14] Can I harvest the rainwater for domestic use from the lime-coated surface? Is it safe for drinking after proper treatment?

    Unlike paints which contain many chemicals including water-soluble and volatile organic compounds that may be toxic to humans, lime is
    pure Calcium carbonate (CaCO3) which doesn’t contaminate the rainwater, so rainwater harvested from lime-coated terrace is safe for domestic use, as far as I know. Moreover, calcium from lime is a nutrient that can improve bone health.

    15) Do one has to paint the exterior walls also?

    If walls are exposed to direct sunlight (east and west facing walls), it will help painting them white with lime or a paint.

    16) Do one has to cover the entire roof or just the area above your bedroom/living room?

    It is better to cover the entire roof for the whole house to be cooled. In case of frugality, you can just lime coat the roof area above
    bed/living rooms. It will be equally effective.

    17) Would constant rainfall reduce the effectiveness of the coating?

    Continuous heavy rainfall may erode the lime coating, you may have to redo the lime coating once every two years or every year at the most.

    Hope you will be able to apply this lime coating properly on your terrace and enjoy the cooler rooms inside the house or the office.

    Cheers, Bala

  • ecoratorio

    Dear Dr. Balasubramanian,

    Thank you for this article which is very interesting.

    I have seen metal roofs (Everlast) over concrete roof tops in Kerala,although aesthetically not pleasing,people say that it works well in reducing heat. Would you know how the white roofs compare to the metal roofs?

    Also green roofs where roof tops are covered with a liner on which vegetation is grown (succulents are very popular) is gaining popularity in the UK. Would such roofs be suitable in South India?

    All the best,
    Ruth

  • hassan

    Hi, This is very informative. I am not sure if we get pevicol here in Pakistan. It might have a different brand name. Can we use white glue instead. As we do walking regularly on the roof, would it be better to use emulsion paint or enamel paint(perhaps even better than emulsion) instead of lime. Do you think it they will be equally effective? are there any reflective dyes which can be added to enhance the effect (like titanium di oxide).

  • shyam datla

    I used Excel cool coat(pathetic qulity, and loot 6700/- for 20L) and Asian paint Smart Damp proof(4000/-for 20L) whose qulity is remarkable, way superior compared to Excel cool coat in reflection, adhesiveness…

    • natarajan vaniambadi

      dear shyam. is the excel coating very bad? i am planning to use that. can you please reply as soon as possible?

      • shyam datla

        Actually I happened to order it on eBay which got delivered very late, meanwhile I was searching for some water proofing paint when I came across Asian paints smartcare damp proof and used it before the delivery of excel paint, so I used both paints my self, due to which I feel Asian paints damp proof(it includes heat proof) is way superior product.

        • natarajan vaniambadi

          thanks shyam

        • T

          people here are talking about temperature change not damp proof while excel is heat reflective Asian paints damp proof(
          does not have heat proof

          • shyam datla

            Asian product mentions it includes heat proof also in it, since i happened to use both i felt excel has much large size of grinded lime in it, and on their excel website they have a different product for water resistent etc, since i heard from one of my friend that use of lime based apllication led to dampness i prefer asian one which has both properties in it…

    • amol kulkarni

      Hi Shyam,
      Can you please share cost incurred per 100 sq ft. I am also planning to use Asian paint Damp proof as finding Janata cool lime powder is hard here in pune. Can i use normal lime powder instead on Janata cool?

      • shyam datla

        Please visit asian paints websites, there they mention this many coats requires this much etc.. Regarding lime and even janata other panel people have discussed the topic, something like adding, grinding etc, as for myself my friend said that their rc roof started having issue of dampness, so i avoided it though it is dead cheap compared to paints….

        • amol kulkarni

          Thanks Shyam.

  • ramakumar

    Hi Bala, Very good article. I also follow the same principle at Sulurpeta, where I stay. The weather is as hot as Chennai. Apart from this in the eco-friendly house of ours to reduce energy consumption, we had built our outer walls with Laurie baker’s concept of RAT TRAP, blocked west and south suns with local vines / creepers, remove hot air 24 X 7 through a cut out in roof, covered by walls with small ventillators along with a pyramid, and cross ventilation through strategic windows. You can see all the details by going to http://www.cowgrazing.com and become a member and see the video self sustaining house under videos section. Mail me for more details to ramakumar_m@hotmail.com

  • rohit

    Nice article and very informative. Kindly tell if we replace lime with marble dust / powder and fevicol with white cement, what will be its effect as marble can reflect better than limestone and cement will be more durable ?

    Kindly also note that now-a-days limestone is not eazily found in states, in Delhi I am unable to find a shop selling limestone or limestone powder…..

  • Chemovate

    Are you ready for summer yet?? Beat the summer heat with our HEAT REFLECTIVE HIGH ALBEDO ROOF COATINGS. http://www.epoxyfloorsindia.com

  • Srikrishna Kireeti

    Is janata cool,lime powder are same product for roof coating.l don’t know difference pls help me guys….

  • Arun k

    Hi Sir,
    Thank you for this article which is very interesting and very useful.

    Am Arun then i have one doubt actually my home in THANJAVUR District . This idea suitable for my place . Please give me a solution . it u don’t mind can u give me u contact Number .

    Contact Details:
    Email : pkarunbe@gmail.com
    Cell No; 8012458716

    Thank You

  • Madhubala Mohan

    Hi sir,

    We are planning for terrace gardening after painting this coolant. Will it work or watering the plants will disturb the effect of this cool painting? Please guide.

    Thanks,
    Madhu

  • I am white washing my roof for this summer and that’s a spreadsheet i use for calculate everything. Hope it helps others too.
    https://docs.google.com/spreadsheets/d/1a7NxS4k9_eAnPAqBXirag8g_JyA37SFB-aIeqP-ZAcc/edit?usp=sharing

  • Mr Olive

    Can I add eggs and jaggery to this lime solution instead of Fecicol to get smooth finishing and i have heard that it gives 100 plus years life altogether. Because it was used in ancient days to coat walls of Mahals and Forts