Glazing and Covering Systems
This domain tests how the cover is fixed, sealed, ventilated and protected with screens. It is about the system around the glazing, not just the plastic or sheet itself.
Covering and venting rules
- Fix film with a trench, profile or locking channel and keep it taut; loose film flaps, abrades and tears.
- Provide ridge vents for hot air escape and side vents for cooler incoming air; combined they give cross-ventilation.
- Insect screens of 40–50 mesh exclude whitefly and thrips but reduce airflow; compensate with larger vent area.
- Seal gaps at gables, doors and vent edges; a 2 mm gap is an entry point for pests.
- Use thermal or shade screens independently of the main cover where needed.
Worked example
A cucumber house has side vents with 60-mesh screen. The crop shows heat stress and whitefly is still present at door edges. Reasoning: 60 mesh restricts airflow too much for cucumber, and the door seal is incomplete. Better plan: 40–50 mesh on vents, increase vent area, repair door brushes and add a double-door entry. The screen choice balances pest exclusion against ventilation.
Traps that cost marks
- Choosing the finest mesh without calculating airflow loss.
- Screening vents but leaving gaps under the sidewall.
- Fixing film loosely so wind rubs it against the frame.
- Ignoring condensation drip lines that wet foliage.