With a rooftop sprinkler system you can start pretty much anywhere as far as equipment and budget is concerned. Most people start with a hose and a simple yard sprinkler. I have seen many people choose the sprinklers that are set on a colored aluminum tripod that are available at Lowe’s and Home Depot. The tripod sprinkler does a great job covering a large section of a roof at a time and sprays very quickly.
Now the yard sprinkler on your homes roof is a very rudimentary solution but with just a few additional automation techniques you can have yourself a very good efficient method of creating an evaporation cooler for your entire home rooftop. The solution offers you the ability to cool your roof through evaporation which lets less heat into your attic which would normally go through your insulation and allow heat into your house. The reason your A/C works overtime in the summer and runs up your electricity bill is because excess heat goes through your roof, insulation, and into your living area causing the A/C to have to cool an already super hot room.
You can use a timer to allow your sprinkler to run for approximately 3 min out of 15 minute intervals and adjust if necessary to achieve maximum benefit. The point is it is easy to adjust the timer for different intervals so that you use as little water as necessary for maximum cooling benefit. It is actually easy to set it up so that you have zero water run-off to maximize the water to heat removal ratio of the evaporating cooling process — based on the climate in your area you simply adjust the timer as necessary to meet this goal. An inexpensive one hour repeatable timer is all you need as far as complex mechanisms are concerned. You run your water supply using 1/2 inch PVC pipe to the peak of the roof and clamp it down using plastic conduit clamps.
You can perforate the PVC every 3 feet with a nail or very small drill bit. You could take a size 8 nail and use a grinder to flatten out the flat sides of the nail to make it sharp on the edges. This creates a pattern for the hole like a diamond and allows the water to fan out instead of just streaming out. Experiment with letting the water sprinkler system run for 3 minutes every 10 minutes or every 15 minutes until you get optimal results. You should see your attic temperature decrease anywhere from 20 to 30 degrees in the hot of the summer.
Some people have simply used a defrost timer from an old refrigerator as their timer for the sprinkler to activate the solenoid. The point being is that you can purchase any cheap old timer to do the trick and get amazing results. Even if you let a sprinkler run all day without a timer you will see what a system like this can do for your hot house and electric bill and may want to proceed further with a more elaborate roof sprinkler system.
You can read more about rooftop cooling systems at this website: http://www.builditsolar.com/Experimental/RoofCooling.htm#NCSystem
The cooling cost savings by using a rooftop sprinkler system is about 30 – 40% lower than if you used none at all. The risks are potential mineral deposits onroof, wood rot, reduced life of roof. You ideally want to have access to a free water source like a well, pond, stream, lake, etc.
If you want a profesional kit that does not require that you puncture the roof membrane of your house I have found this company to be a good professional outfit for residential rooftop sprinkler kits: http://www.sprinkool-systems.com/HydroKool.htm