It's a good idea to grow grass on a house roof if you want to improve the heating and cooling in your home. The grass acts like an insulator, saving you money on your home heating costs. It is also aesthetically appealing. Any roof with a pitch between five and 20 degrees is a candidate for grass. You must, however, get the proper authority to make a vegetated roof in some communities. Check with the local planning department to see if you need a building permit.
Measure your roof and calculate the square footage to determine how much grass you need and how large the underlayment system must be. This system will make it possible to grow grass on top of roof shingles.
Set up a green underlayment system on your roof, following the manufacturer's instructions.
Spread soil or another planting medium such as a compost/soil mix on the system. Two to four inches should be sufficient for the grass seed to germinate.
Spray the soil lightly with a hose until it is moist.
Spread grass seed over the house roof. Use a hand spreader for small areas and a mechanical spreader if you are planting seed on your entire roof. Make sure there is even coverage for a thick lawn with no gaps. Too few seeds will result in a sparse grass roof and too many will be forced to compete for nutrients.
Rake the grass seed lightly to combine it with the very top of the soil. You want 1/4 to 1/8 inch of soil to cover it. This will hold it in place on the roof, despite wind, and encourage it to germinate.
Water the seeds daily. Do this until they sprout.
Water your grass roof once a week. Because it's not planted in the ground, the grass will dry out faster. There isn't as much water for the roots to suck up.