How Cool is a House With a Roof Top Garden?

Summary: My Science Fair question is: How Cool Is a House With a Roof Top Garden? I chose to test a house with a roof top garden, because I wanted to learn if a garden on the top of the roof of a house will keep the house cooler than a regular roof will. I live in Florida where it is very hot and sunny most of the year. Most homes in Florida have roofs covered with shingles. I decided to compare shingles with a roof top garden.

My hypothesis was: I think the roof top garden will keep the house cooler, because the plants on the roof will insulate the house and keep the cool air in and the hot air out. I think the soil and plants will help keep the hot air out of the house.

To test my hypothesis, I made two small 'houses' out of cardboard boxes. I used a pre-made shingle roof for one house, and I made a roof top garden roof for the other house using flowers held in by a frame, put on top of a piece of wood paneling covered with tar. I placed both houses outside at 10 am in a sunny spot with thermometers inside them every day for ten days. I checked the temperature inside each house every day at 11 am, 12 noon, 1 pm, and 2 pm. I recorded the temperatures in degrees Fahrenheit in the Observation section of my Daily Log.

After completing this experiment I found that roof top gardens do keep houses cooler than shingle roofs. In every test, every day the roof top garden house had a cooler temperature than the shingle roof house. After ten days of testing I figured out the average daily temperature for each of my houses for each day. On Day 7 the average temperature for my shingle roof house was 7.75o F warmer than my roof top garden house. That was the highest average daily temperature difference out of the ten days. On Day 2 the average temperature for my shingle roof house was 2o F warmer than the roof top garden house. That was the lowest average daily temperature difference out of the ten days.

I proved my hypothesis to be correct. In all ten days of testing the roof top garden house had a cooler temperature than the shingle roof house in every test, at 11 am, 12 noon, 1 pm, and at 2 pm. I learned that a roof top garden is a good way to help keep your house cooler. If I were to repeat this project I might try using grass or a different type of plant for the roof top garden. I might also test a different roofing material for the control house such as a PVC roof or a Spanish Tile roof. Also, I would like to try this experiment in the summertime when the temperatures during the day are warmer.