Protective environment framework structural materials - weight, strength, reduction of light transmission, aesthetics, relative cost
- Steel
- Aluminium
- Wood
- Plastic
Steel as protective environment framework structural material
Benefits:
- Used for most commercial greenhouses - low ‘cost to strength’ ratio
- Strong, durable
- Easily fabricated by welding
Limitations
- Heavy to handle
- Prone to corrosion so must be galvanised for protection
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Aluminium as protective environment framework structural material
Benefits:
- Lightweight to handle and strong enough for glazing bars
- Narrow glazing bar profile allows maximum light entry
- Corrosion resistant - little or no maintenance.
- Extruded easily into glazing bar shapes.
Limitations:
- Limited aesthetic appeal
- Expensive
- Stronger than wood but not steel
- Not strong enough for structural supports (just glazing bars).
- Doesn’t weld easily so construction nuts and bolts
- Doesn’t retain heat well
- High energy input to manufacture,
Wood (soft wood e.g. Western Red Cedar) as protective environment framework structural material
Benefits:
- Easily shaped into optimum glazing bar
- Secondary glazing or insulation easily attached to it and blends into the natural environment
- Retains heat reducing heating requirement
- Aesthetically pleasing
Limitations:
- Weaker material than metal—requires thicker bars to be strong (which reduces natural light entry and increases the area that’s shaded).
- Requires maintenance by painting or other wood treatment to minimise risk of decay
- Wood can warp or eventually rot.
Plastics as protective environment framework structural material
Benefits:
- Lightweight
- Cheap
- Maintenance free
Limitations:
- Not aesthetically pleasing
- May become brittle with age
Definition of cladding in protected environments
The material that covers the framework of the protected structure, so it’s suitable for production of protected crops e.g. horticultural glass.
Protective environment cladding materials - lifespan, light transmission, surface abrasion, strength, weight, safety, relative costs
- Horticultural glass
- Polyethylene film
- Twin-walled polycarbonate
- Acrylic sheets
- Shade netting
- Horticultural fleece
Horticultural glass as protective environment cladding material
Benefits:
- Good light transmission over long period of time
- Reasonable heat retention
- Long lasting
- Low maintenance
- Easy to clean
Limitations:
- Heavy
- not flexible
- difficult to work with
- fragile
- Expensive
Polyethylene film (e.g. walk in tunnel) as protective environment cladding material
Benefits:
- Less expensive than glass
- Versatile material that can pulled taut over curved framework
- Lightweight
- Easy to install
Limitations:
- Relatively short lifespan of 3-5 years
- Doesn’t retain long wave radiation (cools down quickly when sun goes down, doesn’t retain heat)
- Condensation occurs which reduces light transmission
Acrylic sheets (e.g. cloche) as protective environment cladding material
Benefits:
- More lightweight than glass
- Stronger than glass
- Good light transmission
- Can be moulded into shapes e.g. curves
- Doesn’t shatter
Limitations:
- Reduction in light transmission over time
- Scratches easily
Twin-walled polycarbonate (e.g. cold frame) as protective environment cladding material
Benefits:
- reasonable light transmission
- excellent heat retention
- easily cut to size
- lightweight and extremely strong
Limitations:
- More expensive than glass
- Light transmission deteriorates over time
- scratches
Shade netting as protective environment cladding material
Benefits:
- lightweight
- easy to handle / remove
Limitations:
- short shelf life
- can tear / get damaged by weather
Horticultural fleece as protective environment cladding material
Benefits:
- lightweight
- cheap
- easy to handle / remove
- Protects crops from frost and pests
Limitations:
- short shelf life
- can tear / get damaged by weather
- Can prevent pollution
