Advice
RHS Help & Advice
Greenhouse ventilation and shading
Ventilation
The most effective ventilation is provided by ventilators positioned along both sides and the ridge, warm air rising through the top ventilators as air is drawn through the side ventilators. Hinged ventilators can be fitted to both roof and sides. Louvre ventilators are usually fitted below staging level. They must fit tightly to exclude draughts.
Extractor fans
Thermostatically-controlled fans draw and expel warm air from one end of a greenhouse, cooler air entering through a louvre set lower at the other end.
Autovents
These function automatically, opening hinged ventilators as greenhouse temperatures rise.
Shading
Shading helps to control temperatures when ventilation is inadequate, and to protect some plants (e.g. ferns, orchids) from strong sunlight. Materials used externally reduce both heat and light transmission through the glass. Those used internally are unlikely to appreciably influence temperatures. Systems in position throughout summer are less adaptable to changing weather conditions.
Roller blinds
When fitted externally roller blinds maintain cooler conditions but can cause too much light reduction in sunless conditions unless they are automatically controlled or have daytime attention.
Shading washes
These reduce heat problems, whilst light penetration is usually still adequate. Some become more transparent in dull, wet conditions.
Mesh and fabric
Woven and knitted fabric and flexible net materials provide varying shading qualities and values.
Further information
A conservation and environment leaflet, Energy Conservation in Greenhouses is available.