Short answer: Greenhouse roof and side vents should be sized from greenhouse geometry, crop and season, indoor heat and humidity load, outside wind and temperature, insect-net resistance, vent position, opening mechanism and control strategy. Vent percentage alone cannot guarantee airflow because location and pressure difference also matter.
State whether natural ventilation must remove daytime heat, manage humidity, support pollination, exchange air after heating or protect a seasonal crop. Confirm target months and crop height. A low tunnel, tall multi-span greenhouse and insect-screened nursery require different approaches even at the same floor area.
Provide span, bay, gutter height, ridge height, length, number of spans, roof shape, surrounding obstructions and orientation. Multi-span width and internal crop canopy can reduce air movement. Roof and side openings should be shown on drawings with net clear opening, not only frame dimensions.
| Opening | Design role and question |
|---|---|
| Roof vents | Use buoyancy and wind pressure; check ridge position, opening direction, rain entry and drive loads. |
| Side vents | Provide lower-level inlet or crossflow; check crop, dust, pests, wind and security. |
| Gable vents | May supplement flow in selected structures; check length and internal obstructions. |
| Doors | Should not be treated as primary controlled vents unless designed and operated for that purpose. |
Net aperture, porosity, dust, installation tension and contamination create pressure loss. Finer net can require larger openings or mechanical assistance. Ask for the net specification and resistance data where available, then include cleaning access. A vent-area comparison without net information is incomplete.
Natural ventilation depends on wind direction and speed as well as indoor-outdoor temperature difference. Nearby buildings, trees, terrain and other greenhouses can change pressure around openings. Use local climate information and recognized design methods; avoid assuming that one air-change number occurs in all weather.
Confirm rack-and-pinion, roll-up, cable or other mechanism, motor torque, travel, limit switches, transmission, supports and manual operation. The structure must carry drive and wind reactions. Provide safe access for adjustment and keep crop wires or screens clear of moving parts.
Define closing logic for rain, high wind, low temperature and power failure. Check which vents close first and whether a safe opening remains for crop protection. Rain sensors, wind sensors and controllers need calibration and manual override. Local emergency and storm procedures should be documented.
Measure net clear opening and full travel
Check direction, alignment, end limits and synchronized drives
Test rain, wind, temperature and manual commands
Verify screens and crop systems do not obstruct vents
Inspect net sealing, tension and cleaning access
Record current draw, gear noise and abnormal movement
Train operators on emergency close and manual operation
There is no universal percentage; geometry, climate, wind, crop, net and side openings must be calculated together.
Possibly for some designs, but inlet path, width, crop, wind and humidity must be evaluated.
It depends on aperture, porosity, pressure, dust and installation; use product data and project calculations.
The project needs a defined safe response, manual method or backup strategy based on crop and climate risk.
Use the ventilation system category, insect-net guide and equipment data-sheet checklist.
Send the site climate, dimensions, crop, openings and net specification through the contact page for a ventilation-input checklist.