Nutrient film technique (NFT) is a hydroponic technique, whereby a very shallow stream of water containing all the dissolved nutrients required for plant growth is re-circulated past the bare roots of plants in a watertight gully, also known as channels. Problems commonly associated with NFT hydroponic system such as water temperature, can easily increase under direct sunlight in the tropics region, especially in the roof top garden, that can affect the quality of fertiliser used to cultivate the crop. Therefore, a study to develop a cooling system for NFT hydroponic technique is significant to control the water-dissolved nutrient temperatures suitable for crop growth. This paper highlights the studies conducted on fertiliser concentration distribution in the NFT hydroponics root zone cooling (HRZC) system for Lactuca sativa cultivation on roof top garden under the influence of water temperature, air temperature, relative humidity and ambient carbon dioxide. The fertiliser concentration distribution is determined by taking the electric conductivity (EC) reading of the fertiliser flowing along the NFT channels within three targeted points (left, middle, right) atfour different height levels of the cultivation beneath the roof top garden. The EC readings of the fertiliser remained steady, except for the tank along the levels from left, middle and right locations ranging from 1.64–1.66 μS. The water temperature, air temperature, relative humidity and ambient carbon dioxide fluctuated along these three points ranging from 20.50–22.80°C, 31.39–32.23°C, 67.06–68.65%, and 459.39–472.13 ppm, respectively. It was found that under the influence of those environment parameters and NFT root zone cooling system with different level and height, the fertiliser concentration distribution from point to point of data taken is not significantly different along the NFT channels. This finding is significant that integration of NFT root zone cooling system is an alternative to Lactuca sativa cultivation on roof top garden, despite the affecting surrounding temperature that may affect the quality and quantity of fertiliser and crops cultivation. This technique can be extended for the cultivation of other hydroponic vegetables, rice and flowers and promote the culture of roof top farming in the society to avoid the highly polluted soil on the ground environment that may bioaccumulate into the plant system that may ended up as a health threat to fellow consumers.