PAES 415:2001 Agricultural Structures - Greenhouses

Greenhouse orientation

Ridge should run north–south to reduce self-shading and provide more even light distribution

Bench width — access from both sides

Maximum 1.8 m

Bench width — access from one side

Maximum 0.90 m

Air circulation gap between sidewall and bench

Approximately 160 mm

Usable floor area — fixed benches

66–75%

Usable floor area — rolling benches

90%

Bench height against a wall

Maximum 0.90 m

Temporary benches for growing/bedding plants

Width 1.50–1.80 m; height 0.45–0.60 m

Bench height for shade plants underneath

Up to 1.20 m

Bench construction

Open bench floors allow air circulation; benches must be rigid enough to prevent sagging and pots from toppling

Commercial bench arrangement

Usually runs lengthwise along the greenhouse

Peninsular bench arrangement

Maximizes bench area per unit of aisle space and provides convenient access

Aisle for determinate crops

0.30 m

Aisle for indeterminate crops

0.80 m

Secondary aisle in large greenhouses

0.60–0.90 m

Primary aisle in large greenhouses

1.20–1.80 m

Wheelchair-accessible aisle

1.20 m, with ramps

Concrete, gravel, or stone walkway

0.60–0.90 m wide

Roof shape

Lean-to

Roof shape

Gable

Roof shape

Flat

Roof shape

Monitor

Roof shape

Quonset

Roof shape

Saw tooth

Roof shape

Arch

Roof shape

Uneven Arch

Roof shape

Arch Saw

Roof shape

Gable

Population density per square meter of bench based on pot sizes

Population density at recommended plant spacing for vegetables

Population density at recommended plant spacing for ornamentals

Maximum greenhouse length

50 m

Maximum total width of gutter-connected greenhouses

50 m

Extra plastic allowance for fastening

0.60 m

Minimum eave height — gable roof

1.70 m

Minimum gable height

2.40 m

Center height calculation

Eave height + ¼ of greenhouse width

Recommended gutter height — multi-span greenhouse

2.8–3.0 m

Minimum height over walk areas

2.0 m

Minimum eave height for tall crops

2.0 m

Desirable eave height for tall crops

2.10 m

Minimum foundation depth — permanent greenhouse

0.45 m

Foundation design

Resist uplift, overturning, and downward loads

Foundation for glass/heavy plastic

Permanent foundation required

Polyethylene greenhouse supports

Support posts set in concrete footings

Side-post and column height

0.30–3.0 m

Reinforced concrete wall for wooden structures

0.40 m high at the bottom

Trellising load capacity of frame

Up to 25 kg/m²

Maximum wind gust for structural framing

250 km/h

Wood rafter spacing

0.60–1.20 m, center to center

Greenhouse width requiring reinforced truss construction

Over 15.25 m

Wood purlin spacing

1–2.5 m

Steel framing

Paint or galvanize to resist moisture and corrosion

Aluminum framing

Lightweight, long-lasting, corrosion-resistant, and low-maintenance

Covering light transmission

Clear enough for optimum light transmission

Infrared radiation

Covering should reflect or absorb infrared to reduce overheating

Ultraviolet radiation

Covering should absorb some UV and may convert some into useful visible light

Polyethylene sheet minimum thickness

130 µm

Glass

Best light transmission among the listed covering materials

Fiberglass

Durable, rigid, available in different light-transmission levels

Corrugated plastic sheets

Good rain protection and light transmission; higher installation and maintenance costs

Screen

Used for shade and protection from falling branches; does not protect against rain

Glass greenhouse roof pitch

51%

Plastic-covered greenhouse roof pitch

58–70%

Gutter slope in connected greenhouses

2%

Covering selection criteria

Combustibility, durability, insulation, lifespan, maintenance, guarantee, and frame compatibility

Standard door for walking tractors

1.2 m wide

Minimum side-door width

0.8 m

Footbath

Provide for sanitation

Anteroom

Provide for insect protection

Fan at entrance

Helps prevent insect entry when the door opens

Walkway material

Concrete, gravel, or stone

Permanent flooring

Generally not recommended in growing areas because it can remain wet and slippery

Greenhouse floor

Must resist heavy equipment loads

Bench floor

Should be open to allow air circulation

Artificial lighting for workers

200 lux

Common greenhouse lighting

High-pressure sodium lamps

Growth chambers

Fluorescent lamps, rich in blue light

Incandescent lamps

Avoid for plant production because their red light encourages stretching

Most efficient irrigation method among those listed

Drip/trickle irrigation

Water applied per irrigation

10–15% more than container capacity to facilitate leaching

Recommended drainage rate

30–50% of the water dose applied

Slope of soil beds and benches

0.8–1.0%

Water quality testing

Conduct regularly

Irrigation system components

Central pump, pipes, and drip extensions as appropriate

High soluble-salt areas

Avoid subirrigation or capillary mats when leaching is needed

Water supply from household plumbing

Install a backflow prevention valve

Growing medium

Must drain well to prevent root diseases

Overhead sprinkler/hand watering

Avoid excessive foliage wetting

Drained water

Should be contained in a storage tank

Vent locations

Both sidewalls and roof ridge

Total vent area

15–25% of floor area

Single-unit greenhouse

Combined sidewall vent area = combined roof vent area

Ridge vents

Top-hinged and continuous along the greenhouse length

Fully opened ridge vent angle

60° with the roof

Automatic vent controls

Rain and high-wind sensors

Recommended maximum ventilation rate

¾–1 air change per minute

Fan capacity test/design static pressure

0.03 kPa

Maximum spacing between fans

7.5 m

Fan placement

Preferably on the downwind side or end