PURPOSE: To protect plants in cold season and to melt snow at low cost with air in room or underground air by taking advantage of a foamed plate of synthetic resin.

CONSTITUTION: In a structure having a piping of a drain pipe connected to a drainage hole on a roof, a foamed plate of synthetic resin having a great number of communicating holes opening to the top and sides is laid on the roof, a soil dressing layer for planting and culturing is placed on the foamed plate of synthetic resin, air in rooms can be taken in the drain pipe and the drainage hole is connected to openings of the sides of the communicating holes. Air in an underground cave instead of the air in rooms is taken in the drain pipe. An asphalt bituminous plate is laid instead of the soil dressing layer.