10 x roof vents (automatic opening)

The roof vents on this greenhouse open automatically. They don't require batteries, working from heat expansion alone. 

A cylinder filled with a special wax expends with heat, driving a piston and opening the vent for you. 

They can be adjusted to open  more or less according to what environment you need to create in the greenhouse.

Propably the best ever invention for greenhouses, they help prevent overheating, scorching and wilting - a must for any greenhouse!