Lesson 3 - Know the structural and cladding materials used for a range of protected structures Flashcards
List a range of materials used for framework construction
Steel, aluminium, wood, plastics
Describe the characteristics of steel
Weight - heavy.
Strength - low cost to strength ratio.
Reduction of light transmission - loses heat quicker than other materials.
Aesthetics - cannot be extruded into complicated shapes. Prone to corrosion.
Relative cost - low cost to strength ratio
Describe the characteristics of wood
Weight -
Strength - The type of wood affects the strength, Teak and Oak are very strong whilst Western Red Cedar is not as strong.
Reduction of light transmission -
Aesthetics - Can be painted.
Relative cost - Requires more maintenance.
Describe the characteristics of aluminium
Weight - lightweight to handle and strip.
Strength - can’t be welded, has to be bolted.
Reduction of light transmission - loses heat quicker than other materials.
Aesthetics - Not prone to corrosion. Readily extruded into complicated shapes. Utilitarian and may change colour with time.
Relative cost -
Describe the characteristics of plastics
Weight -
Strength -
Reduction of light transmission -
Aesthetics -
Relative cost -
State the benefits and limitations of steel
Benefits - good strength to cost ratio, can be welded,
Limitations - Cannot to made into complicated shapes, corrodes
State the benefits and limitations of aluminium
Benefits - not prone to corrosion, can be made into complicated shapes, lightweight to handle and ship
Limitations - Not decorative, looks utilitarian
State the benefits and limitations of wood
Benefits - Aesthetically pleasing, can be strong if correct wood is chosen, can be painted easily.
Limitations - Can be weak if the wrong wood is chosen, requires regular maintenance to prevent decay and the timber changing shape
State the benefits and limitations of plastics
List different cladding materials
Glass, polyethylene film, polycarbonate, acrylic sheets, shade netting, horticultural fleece
State the benefits nd limitations of polycarbonate
Life span - between 5 and 20 years.
Light transmission - transmits approx 80% of light (glass is 90%)
Surface abrasion
Strength - strong
weight - lightweight
safety - less likely to break than glass
relative costs compared to other cladding materials - save on heating costs as they can retain heat overnight
State the benefits and limitations of glass
Life span - prone to damage.
Light transmission - Permits the entry of short wave radiation, which is taken up by the physical objects inside and released as long wave radiation, which isn’t allowed back through the glass. This increases the temperature of the greenhouse. Allows good light transmission that does not change significantly overtime. Must be kept clean.
Strength - Glass does not expand much when it’s warm.
safety - brittle. prone to damage.
relative costs compared to other cladding materials - expensive
State the benefits and limitations of polyethylene film
Life span - 3 years tops, with ultraviolet proofing. without the proofing it is 1 year. Long life is 5-10 years but discolours.
Light transmission - 85-95% transmission when new. Lose heat more rapidly than other cladding. Condensation forms which lowers light transmission even more. Can grow algae, on condensation, reducing light transmission.
Surface abrasion
Strength - fewer drafts than glass.
weight - lightweight
safety - doesn’t break as easily as glass
relative costs compared to other cladding materials - cheap. easy to install.
state the benefits and limitations of acrylic sheets
Life span - 15 years or longer
Light transmission - good
Strength - good. Can be bent into curves. Expand and contract with heat.
safety - doesn’t break as easily as glass
State the benefits and limitations of shade netting
Life span
Light transmission
Surface abrasion
Strength
weight
safety
relative costs compared to other cladding materials
