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.

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.

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 Charges500
TOTAL940 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.

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