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Maharashtra SSC Green House Grade study materials
Maharashtra SSC Green House Grade study resources

Maharashtra SSC Green House Grade practice questions

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Question 1Greenhouse Site Selection, Orientation and Structural Design

A greenhouse is planned on land that slopes gently from north to south in Maharashtra. Which orientation of the ridge (gutters running north-south) is generally preferred for a naturally ventilated greenhouse in this situation?

  1. Ridge running north-south so that both long sides receive direct sun during part of the day Correct answer.
  2. Ridge running east-west so that the north wall faces the sun
  3. Ridge running east-west so that the whole south-facing wall is shaded
  4. Ridge running diagonally at 45 degrees regardless of site slope

Explanation

A north-south ridge line gives more even light distribution across both sides of the roof over the day, which suits crops grown in beds across the full width. East-west ridges concentrate light on the south side and create uneven crop growth. The slope direction affects drainage and levelling but does not reverse the basic light-distribution rule.

Question 2Greenhouse Site Selection, Orientation and Structural Design

Why should a greenhouse site be free from tall trees and buildings on the south side in India?

  1. To avoid winter shading that reduces light and raises humidity Correct answer.
  2. To increase the slope of the land for drainage
  3. To reduce the cost of fencing the plot
  4. To prevent roots from entering the beds

Explanation

In India the sun path lies to the south in winter, so tall obstacles on the south cast long shadows on the greenhouse. Shading lowers light transmission, raises relative humidity and encourages disease. Trees and buildings also block natural ventilation, so a clear south side is a basic siting rule.

Question 3Greenhouse Site Selection, Orientation and Structural Design

Which soil condition is most suitable for constructing a greenhouse foundation?

  1. Firm, well-drained soil with adequate bearing capacity Correct answer.
  2. Loose sandy soil with a high water table
  3. Rocky soil with many boulders at shallow depth
  4. Clay soil that stays waterlogged after rain

Explanation

Foundations must carry the weight of the structure, cladding and crop loads without settling unevenly. Firm, well-drained soil gives reliable bearing capacity and allows simple pad or strip footings. Loose, waterlogged or boulder-strewn ground needs costly treatment before construction.

Question 4Greenhouse Site Selection, Orientation and Structural Design

What is the main purpose of providing a side ventilation opening along the leeward side of a naturally ventilated greenhouse?

  1. To allow warm, humid air to leave as cooler air enters elsewhere Correct answer.
  2. To block sunlight from reaching the plants
  3. To increase the structural load on the frame
  4. To store irrigation pipes

Explanation

Natural ventilation works by the stack effect and wind effect: cooler air enters at low openings and warm humid air escapes at high or leeward openings. The leeward side is a low-pressure zone, which helps extract air. This reduces temperature and humidity inside without fans.

Question 5Greenhouse Site Selection, Orientation and Structural Design

Which of the following best describes the role of the gutter in a multi-span greenhouse?

  1. It seals the greenhouse against all air exchange
  2. It collects rainwater from the roof and carries it away Correct answer.
  3. It acts as the main heating element
  4. It supports the plants directly above the beds

Explanation

Gutters run along the valleys between roof spans and collect rainwater for discharge through downpipes. They also carry the roof load and provide fixing points for cladding. They are not heating elements and do not seal the house completely.

Question 6Greenhouse Site Selection, Orientation and Structural Design

A grower wants to build a greenhouse in a coastal area of Maharashtra where cyclonic winds are common. Which design measure is most appropriate?

  1. Remove side bracing to allow free airflow
  2. Increase the span width to save on columns
  3. Use a low roof pitch and stronger bracing with wind-resistant cladding fixings Correct answer.
  4. Use taller side walls to catch more wind

Explanation

Cyclonic zones require the structure to resist uplift and lateral loads. A low roof pitch reduces wind pressure, and diagonal bracing plus stronger cladding fixings keep the frame and covering intact. Removing bracing or increasing wall height makes the structure more vulnerable.

Question 7Greenhouse Site Selection, Orientation and Structural Design

What is the recommended minimum distance between a greenhouse and a source of dust, such as an unpaved road?

  1. Distance makes no difference to a greenhouse
  2. About 5 metres
  3. Enough distance or a windbreak to keep dust off the cladding Correct answer.
  4. About 1 metre

Explanation

Dust settling on the cladding reduces light transmission and can clog vents and insect screens. Siting away from dust sources, or planting a windbreak between the road and the house, protects the glazing. A metre or two is not enough to prevent deposition.

Question 8Greenhouse Site Selection, Orientation and Structural Design

Which cladding material is commonly used for greenhouse roofs because it is lightweight and transmits diffused light?

  1. Polyethylene film or polycarbonate sheet Correct answer.
  2. Galvanised iron sheets
  3. Reinforced concrete slabs
  4. Asbestos cement sheets

Explanation

Polyethylene film and polycarbonate sheets are lightweight, transmit photosynthetically active radiation and can diffuse light to reduce leaf scorch. They are fixed to the frame with profiles or clips. Concrete, asbestos and GI sheets block light and are unsuitable as cladding.

Question 9Greenhouse Site Selection, Orientation and Structural Design

A grower is choosing between a naturally ventilated greenhouse and a fan-and-pad cooled greenhouse in a hot, dry part of Maharashtra. Which statement best guides the choice?

  1. Fan-and-pad cooling can lower temperature where the air is dry, while natural ventilation alone may not cool enough in peak summer Correct answer.
  2. Natural ventilation always gives better cooling than fan-and-pad in every season
  3. Both systems work only when the greenhouse is fully sealed
  4. Fan-and-pad cooling is unsuitable in hot dry climates because evaporation cannot occur

Explanation

Fan-and-pad cooling relies on evaporating water into dry air, which works well in hot dry conditions and can lower the internal temperature below ambient. Natural ventilation alone depends on outside air and may not give enough cooling at peak summer temperatures. The choice depends on climate, crop and budget.

Question 10Greenhouse Site Selection, Orientation and Structural Design

What is the main function of the truss in a greenhouse structure?

  1. To hold the insect screen in place
  2. To provide a walkway for workers
  3. To carry the roof load and transfer it to the columns Correct answer.
  4. To collect rainwater from the roof

Explanation

A truss is a triangulated framework that spans the width of the greenhouse and carries roof loads, including cladding, wind and crop loads, to the columns. It gives stiffness without excessive member depth. Gutters collect water, and screens and walkways are separate elements.

Question 11Greenhouse Site Selection, Orientation and Structural Design

Why is a greenhouse usually oriented with its long axis parallel to the prevailing wind direction in a naturally ventilated design?

  1. To make the roof collect more rainwater
  2. To increase the wind load on the side walls
  3. To reduce the amount of light entering the house
  4. To improve cross-ventilation and reduce dead air pockets Correct answer.

Explanation

Aligning the long axis with the prevailing wind allows air to flow along the house and encourages cross-ventilation through side and roof openings. This reduces hot, still pockets and improves humidity control. It does not increase wind load or change rainwater collection.

Question 12Greenhouse Site Selection, Orientation and Structural Design

A site has a high water table at 60 cm depth. What is the most appropriate design response for a greenhouse on this land?

  1. Dig a deep pit inside the greenhouse to collect water
  2. Build the greenhouse at ground level and ignore the water table
  3. Reduce the roof pitch to shed water faster
  4. Raise the beds and floor level and provide subsurface drainage before construction Correct answer.

Explanation

A high water table causes waterlogging, root disease and foundation instability. Raising the floor and beds above the water table, with subsurface drains to lower it, protects the crop and structure. Roof pitch affects rain shedding but does not solve groundwater problems.

Question 13Greenhouse Site Selection, Orientation and Structural Design

Which factor most directly determines the required height of the side wall in a greenhouse?

  1. The crop height and the need for air movement above the canopy Correct answer.
  2. The number of workers employed
  3. The colour of the cladding
  4. The distance to the nearest market

Explanation

Side wall height must allow the crop to grow without touching the cladding and must leave space above the canopy for air to move and heat to rise. Tall crops such as tomato and cucumber need higher walls than low crops. Cladding colour, labour and market distance do not determine wall height.

Question 14Greenhouse Site Selection, Orientation and Structural Design

What is the purpose of a windbreak planted to the west of a greenhouse in a windy area?

  1. To increase wind speed at the greenhouse
  2. To collect rainwater for irrigation
  3. To shade the greenhouse completely
  4. To reduce wind speed and protect the cladding and vents Correct answer.

Explanation

A windbreak slows the wind before it reaches the greenhouse, reducing pressure on cladding and preventing vents from being forced open or damaged. It also reduces dust. It should be placed at a distance so that it does not shade the house or create turbulence.

Question 15Greenhouse Site Selection, Orientation and Structural Design

Which roof shape is most common for a single-span naturally ventilated greenhouse in India?

  1. Sawtooth roof facing north only
  2. Flat roof
  3. Gable or pitched roof with ridge ventilation Correct answer.
  4. Dome with no openings

Explanation

A gable roof with a ridge vent allows hot air to escape at the highest point and is simple to build with local materials. Flat roofs shed rain poorly, and a dome without openings cannot ventilate. Sawtooth designs are used in specific climates but are less common for simple Indian designs.

Question 16Greenhouse Site Selection, Orientation and Structural Design

A greenhouse frame is built with GI pipes. What is the main reason for using galvanised rather than plain steel pipes?

  1. Galvanising improves the taste of the crop
  2. Galvanising protects against rust in the humid greenhouse environment Correct answer.
  3. Galvanising increases light transmission
  4. Galvanising reduces the weight of the pipe

Explanation

Greenhouse interiors are humid and often have condensation on the frame, which corrodes plain steel quickly. The zinc coating on galvanised pipe provides a barrier against rust and extends the life of the structure. It does not change light transmission or pipe weight significantly.

Question 17Greenhouse Site Selection, Orientation and Structural Design

Why should the greenhouse floor be slightly higher than the surrounding ground level?

  1. To increase the water table inside
  2. To reduce the amount of light entering
  3. To make the structure taller
  4. To prevent surface runoff from entering the house Correct answer.

Explanation

A raised floor with a gentle outward slope keeps rainwater and surface runoff from flowing into the greenhouse. It also protects the foundation from standing water. Raising the floor is not about increasing height or reducing light.

Question 18Greenhouse Site Selection, Orientation and Structural Design

What is the main advantage of a multi-span greenhouse over a single-span greenhouse of the same total area?

  1. It eliminates the need for ventilation
  2. It requires no foundation
  3. It uses more land for the same cropped area
  4. It reduces the number of side walls and improves land and heat efficiency Correct answer.

Explanation

In a multi-span house, internal partitions are replaced by gutters, so less land is lost to side walls and the structure is more compact. This improves land use and heat retention compared with several separate single-span houses. Multi-span houses still need ventilation and foundations.

Question 19Greenhouse Site Selection, Orientation and Structural Design

A grower plans a greenhouse on a plot where the slope is steep. What is the most practical design response?

  1. Build the greenhouse across the slope without levelling
  2. Ignore the slope and build at the natural gradient
  3. Build on a levelled terrace or bench cut into the slope Correct answer.
  4. Reduce the number of columns to follow the slope

Explanation

Greenhouse frames and cladding panels need a level base so that gutters, vents and cladding lines work properly. On a steep slope, a levelled terrace or bench cut with retaining walls provides a stable, level platform. Building without levelling distorts the frame and causes drainage problems.

Question 20Greenhouse Site Selection, Orientation and Structural Design

Which type of foundation is generally used for the columns of a small greenhouse built on firm soil?

  1. No foundation, with columns simply placed on the soil
  2. Deep pile foundations
  3. Isolated pad or concrete footing under each column Correct answer.
  4. Raft foundation covering the whole floor

Explanation

For a light structure on firm soil, isolated pad footings under each column are sufficient to spread the load and prevent settlement. Piles and rafts are used for heavy loads or weak soils and are uneconomical here. Columns placed directly on soil would sink or shift.

Question 21Greenhouse Site Selection, Orientation and Structural Design

Why is insect-proof netting of 40-50 mesh used on greenhouse ventilation openings?

  1. To exclude small insect pests while allowing air to pass Correct answer.
  2. To collect dust from outside
  3. To increase the structural load on the vents
  4. To reduce light transmission to the crop

Explanation

Fine mesh screens block thrips, whitefly and other small pests from entering through vents while still allowing air movement. The mesh size is a balance between exclusion and airflow, because finer mesh reduces ventilation. Screens do not serve to shade crops or collect dust.

Question 22Greenhouse Site Selection, Orientation and Structural Design

In a greenhouse design, what does the term 'span' refer to?

  1. The length of the greenhouse along its ridge
  2. The horizontal distance between two adjacent columns or gutters Correct answer.
  3. The slope of the roof
  4. The height of the side wall

Explanation

Span is the clear horizontal distance between two supports, such as columns or gutters, across the width of a bay. It determines the size of the truss needed. Wall height, house length and roof slope are separate dimensions.

Question 23Greenhouse Site Selection, Orientation and Structural Design

A grower in a hot region wants to reduce heat gain through the greenhouse roof without reducing light too much. Which measure is most suitable?

  1. Seal all vents permanently
  2. Apply a shading net or whitewash on the roof during peak summer Correct answer.
  3. Increase the roof pitch to vertical
  4. Replace the roof with opaque GI sheets

Explanation

External shading nets or whitewash reduce incoming solar radiation and lower the internal temperature while still allowing some light through. Opaque sheets block light completely, sealing vents stops ventilation, and a vertical roof is structurally impractical.

Question 24Greenhouse Site Selection, Orientation and Structural Design

Two greenhouse sites are available: Site A has deep, well-drained loam and a clear southern exposure; Site B has shallow soil over rock, is shaded by a hill to the south, and is close to a market. Which site is technically better for greenhouse construction?

  1. Site B, because market proximity outweighs all other factors
  2. Both are equally suitable because market distance is the only criterion
  3. Site A, because soil, drainage and solar access are fundamental to greenhouse performance Correct answer.
  4. Site B, because rocky soil gives a stronger foundation

Explanation

Soil bearing capacity, drainage and unshaded solar access are fundamental requirements for a productive greenhouse; without them the structure and crop suffer throughout its life. Market proximity is an economic advantage but cannot compensate for shading and poor foundations. Site A is therefore technically superior.

Question 25Greenhouse Site Selection, Orientation and Structural Design

A naturally ventilated greenhouse has roof vents along the ridge and side vents at low level. Under still, hot conditions, which combination gives the best ventilation?

  1. Open both side and roof vents together Correct answer.
  2. Open only the roof vents
  3. Keep all vents closed and rely on fans
  4. Open only the side vents

Explanation

Ventilation by the stack effect depends on a height difference between inlet and outlet openings. Cooler air enters at the low side vents and warm air leaves at the high ridge vents. Opening only one set reduces the driving pressure difference and gives poor exchange.

Question 26Greenhouse Site Selection, Orientation and Structural Design

Which soil condition is most suitable for constructing a greenhouse without major foundation modification?

  1. Heavy clay that stays waterlogged for most of the monsoon
  2. Shallow soil over a hard rock layer at 30 cm depth
  3. Deep, well-drained loam with a stable subsoil Correct answer.
  4. Filled-up ground that has not been compacted or settled

Explanation

A greenhouse foundation must transfer column loads to a stable, well-drained subsoil so that settlement stays uniform. Deep loam with firm subsoil drains freely and compacts predictably under pad and column footings. Waterlogged clay, shallow rock and loose fill all cause differential settlement, tilted frames or poor drainage around the structure.

Question 27Greenhouse Site Selection, Orientation and Structural Design

A greenhouse is to be built on a plot with a gentle slope of about 2 per cent. What is the most practical design response?

  1. Build the frame following the natural slope without any levelling
  2. Increase the side wall height on the downhill side only
  3. Abandon the plot because any slope above 1 per cent is unsuitable
  4. Level the floor and cut-and-fill the plot so the frame sits on one plane Correct answer.

Explanation

Greenhouse frames, gutters and cladding are manufactured to lie in a single plane, so the floor must be levelled by cut-and-fill before erection. A gentle slope is easily corrected and also helps drainage if the levelled floor is kept slightly above the surrounding grade. Following the slope would distort the structure, and small slopes do not justify rejecting a site.

Question 28Greenhouse Site Selection, Orientation and Structural Design

In a region where the prevailing wind blows from the west, a grower must place a tall windbreak and a row of tall trees near a naturally ventilated greenhouse. Which placement best protects the structure without blocking ventilation?

  1. Windbreak and trees both immediately against the west side wall
  2. Windbreak on the west at a distance of roughly 5 to 10 times the windbreak height Correct answer.
  3. Windbreak on the east, close to the greenhouse, with trees on the west
  4. Windbreak on the west at a distance of about 30 times the windbreak height

Explanation

A windbreak reduces wind speed in a sheltered zone that extends downwind for several times its height, so it is placed on the windward side. Placing it at roughly 5 to 10 times its height gives effective protection while allowing air to flow back over the roof and through the vents. Too close a spacing creates turbulence and shade, while too great a distance leaves the greenhouse outside the sheltered zone.

Question 29Greenhouse Site Selection, Orientation and Structural Design

A grower wants a wide single-span greenhouse in a cyclone-prone coastal district. Which structural measure most directly improves resistance to uplift and racking?

  1. Reducing the number of purlins to lower the frame weight
  2. Increasing the span while keeping the same member sizes
  3. Using thinner cladding to reduce the load on the roof
  4. Bracing the frame with diagonal members and anchoring columns to concrete footings Correct answer.

Explanation

Cyclonic winds impose both lateral racking forces and uplift on a greenhouse, so the structure needs a continuous load path to the ground. Diagonal bracing stiffens the frame against racking, and properly anchored concrete footings resist uplift and overturning. Reducing purlins, thinning cladding or widening the span all weaken the structure rather than strengthen it.

Question 30Greenhouse Site Selection, Orientation and Structural Design

A designer must fix the ridge height of a naturally ventilated greenhouse in a hot, still region. Which reasoning best justifies a taller ridge?

  1. A taller ridge removes the need for side vents because air enters only through the roof
  2. A taller ridge lowers the internal temperature by increasing the thermal mass of the frame
  3. A taller ridge reduces the floor area available for beds and therefore lowers the crop load
  4. A taller ridge increases the stack effect, so warm air rises and exits through the roof vents Correct answer.

Explanation

Natural ventilation depends on buoyancy: warm air inside is lighter and rises, and the height difference between low inlets and high outlets drives the airflow. A taller ridge increases this vertical distance and strengthens the stack effect, so hot air escapes faster through the roof vents. Side vents remain essential as inlets, and frame height has no meaningful thermal-mass or floor-area effect of this kind.

Question 31Greenhouse Cladding Materials, Glazing and Covering Systems

In a naturally ventilated greenhouse in the Konkan region, which covering material is most commonly selected for its low cost and adequate light transmission?

  1. Acrylic cast sheets
  2. UV-stabilised polyethylene film Correct answer.
  3. Tempered glass panes
  4. Polycarbonate twin-wall sheets

Explanation

UV-stabilised polyethylene film is the cheapest common covering and gives good light transmission, so it dominates low-cost naturally ventilated greenhouses. Glass and polycarbonate cost far more and are used where durability or insulation justifies the expense.

Question 32Greenhouse Cladding Materials, Glazing and Covering Systems

Which property of polyethylene film degrades first when the film is exposed to sustained ultraviolet radiation?

  1. Resistance to condensation drip
  2. Thermal expansion coefficient
  3. Light transmission in the red waveband
  4. Tensile strength of the polymer chain network Correct answer.

Explanation

UV radiation breaks polymer chains, so the film first loses tensile strength and becomes brittle before other properties change noticeably. UV stabilisers are added specifically to slow this chain scission. Light transmission and condensation behaviour are affected only after physical breakdown begins.

Question 33Greenhouse Cladding Materials, Glazing and Covering Systems

A grower wants a covering that reduces heat loss at night while still admitting adequate photosynthetically active radiation. Which option best matches this requirement?

  1. Woven polypropylene ground cover
  2. Twin-wall polycarbonate sheet with a clear grade Correct answer.
  3. Black shade net of 75 percent density
  4. Single-layer clear polyethylene film

Explanation

Twin-wall polycarbonate traps air between two walls, giving a much higher insulation value than single film while clear grades still transmit useful PAR. Shade net and ground cover are not glazing materials and block rather than transmit light.

Question 34Greenhouse Cladding Materials, Glazing and Covering Systems

Why is glass generally fixed into a greenhouse frame with glazing clips or gaskets rather than rigid bolting through the pane?

  1. To increase the total weight of the roof structure
  2. To improve the electrical conductivity of the frame
  3. To allow controlled movement and avoid stress cracking from thermal expansion Correct answer.
  4. To reduce the light transmission of the glazing

Explanation

Glass expands and contracts with temperature and the frame also moves, so clips and gaskets hold the pane while permitting slight movement. Rigid bolting through glass concentrates stress and leads to cracking. The other options describe effects that are not design aims.

Question 35Greenhouse Cladding Materials, Glazing and Covering Systems

A greenhouse film labelled as having an anti-drip additive works because the additive does which of the following?

  1. Blocks infrared radiation from escaping
  2. Increases the film's tensile strength
  3. Kills algae growing on the film surface
  4. Lowers the surface tension so water spreads as a thin film Correct answer.

Explanation

Anti-drip additives migrate to the inner surface and lower surface tension, so condensing water spreads into a thin sheet and runs down the walls instead of forming droplets. Droplets otherwise fall on the crop and promote disease. The additive does not strengthen the film, block infrared, or act as an algicide.

Question 36Greenhouse Cladding Materials, Glazing and Covering Systems

Which factor most strongly determines the spacing of glazing bars in a greenhouse roof covered with rigid plastic sheets?

  1. The span load capacity of the sheet and expected wind and snow loads Correct answer.
  2. The number of vents in the side wall
  3. The pH of the irrigation water
  4. The colour of the frame paint

Explanation

Glazing bar spacing must keep the sheet's deflection and stress within limits under wind and snow loads, so sheet span capacity and local load conditions set the spacing. Frame colour, vent count, and irrigation water chemistry do not govern structural spacing.

Question 37Greenhouse Cladding Materials, Glazing and Covering Systems

What is the main reason polyethylene film greenhouse covers are usually replaced every two to four seasons in Indian conditions?

  1. The film loses strength and light transmission through UV and weathering damage Correct answer.
  2. The film becomes too transparent for plant growth
  3. The film absorbs too much carbon dioxide
  4. The film changes colour to green

Explanation

Continuous exposure to UV, heat, dust, and wind gradually embrittles the film and reduces its light transmission, so it is replaced periodically. Colour change, excessive transparency, or carbon dioxide absorption are not the reasons for replacement.

Question 38Greenhouse Cladding Materials, Glazing and Covering Systems

Compared with single glass, a twin-wall polycarbonate roof of the same projected area will typically show which combination?

  1. Higher light transmission and higher insulation
  2. Lower light transmission and higher insulation Correct answer.
  3. Lower light transmission and lower insulation
  4. Higher light transmission and lower insulation

Explanation

The second wall and internal ribs reflect and absorb some light, so transmission is lower than single glass. The trapped air layer, however, greatly increases thermal resistance, giving higher insulation. Hence the combination is lower transmission with higher insulation.

Question 39Greenhouse Cladding Materials, Glazing and Covering Systems

Which covering is most appropriate for the curved roof of a small Quonset-type greenhouse where the frame is made of bent galvanised pipe?

  1. Cement asbestos sheets
  2. Flexible UV-stabilised polyethylene film Correct answer.
  3. Rigid float glass sheets
  4. Cast acrylic flat panels

Explanation

Flexible film can be stretched over a curved pipe frame without cutting or special curved panels, making it the standard choice for Quonset houses. Rigid glass, acrylic, and asbestos sheets cannot follow the curve and are unsuitable.

Question 40Greenhouse Cladding Materials, Glazing and Covering Systems

A grower notices that condensation forms as large droplets on the inner surface of a new film, while an older film of the same brand showed a continuous sheet of water. What is the most likely explanation?

  1. The older film was installed upside down
  2. The new film's anti-drip additive has not yet migrated to the surface Correct answer.
  3. The new film has lost its anti-drip additive through leaching
  4. The older film had a higher UV stabiliser content

Explanation

Anti-drip additives must migrate to the film surface before they can lower surface tension, so a freshly installed film may show droplets until the additive blooms. Once migration occurs, water spreads into a continuous sheet. Leaching would reduce performance over time, not improve it in the older film.

Question 41Greenhouse Cladding Materials, Glazing and Covering Systems

Which measurement best describes the ability of a greenhouse covering to resist heat loss, expressed as the reciprocal of thermal transmittance?

  1. The light transmission coefficient
  2. The shading factor
  3. The ventilation rate
  4. The U-value Correct answer.

Explanation

Thermal transmittance is the U-value, measured in watts per square metre per kelvin, and its reciprocal gives resistance to heat loss. Shading factor, light transmission, and ventilation rate describe other aspects of greenhouse performance.

Question 42Greenhouse Cladding Materials, Glazing and Covering Systems

A greenhouse is to be built in an area with frequent hailstorms. Which covering choice best balances hail resistance with light transmission?

  1. Thin single-layer polyethylene film
  2. Twin-wall polycarbonate sheet Correct answer.
  3. Woven shade cloth
  4. Tempered glass

Explanation

Polycarbonate is highly impact resistant and shrugs off hail while still transmitting usable light. Tempered glass resists impact better than ordinary glass but can still shatter, and thin film is easily punctured. Shade cloth is not a glazing material.

Question 43Greenhouse Cladding Materials, Glazing and Covering Systems

Why are greenhouse films sometimes co-extruded with different additives on the inner and outer layers?

  1. To reduce the manufacturing cost of the film
  2. To allow the film to conduct electricity
  3. To make the film opaque on one side
  4. To place UV stabilisers on the weather-facing side and anti-drip or anti-fog additives on the crop-facing side Correct answer.

Explanation

Co-extrusion lets each surface carry the additive it needs: UV stabilisers where sunlight strikes and anti-drip or anti-fog agents where condensation forms. This uses expensive additives efficiently and improves performance. Cost reduction, opacity, and conductivity are not the purpose.

Question 44Greenhouse Cladding Materials, Glazing and Covering Systems

Which of the following best explains why glass greenhouses are described as having a long service life compared with film-covered houses?

  1. Glass is lighter in weight than polyethylene film
  2. Glass is chemically inert and does not degrade under sunlight in the way polymers do Correct answer.
  3. Glass requires no frame support
  4. Glass transmits more ultraviolet radiation to the frame

Explanation

Inorganic glass does not undergo the photochemical chain scission that embrittles polymer films, so it retains its properties for decades. It is heavier than film and needs a strong frame, and it does not transmit more UV in a way that benefits the structure.

Question 45Greenhouse Cladding Materials, Glazing and Covering Systems

A grower wants to reduce summer heat load in a polycarbonate-covered greenhouse without losing too much winter light. Which covering strategy is most suitable?

  1. Seal all vents permanently
  2. Apply a permanent whitewash that cannot be removed
  3. Replace the roof with black polythene
  4. Use an external shade screen that can be retracted in winter Correct answer.

Explanation

A retractable external shade screen cuts summer radiation while allowing full light in winter when it is removed. Permanent whitewash or opaque polythene would also block winter light, and sealing vents would worsen overheating.

Question 46Greenhouse Cladding Materials, Glazing and Covering Systems

Which statement about the light transmission of dusty greenhouse film compared with clean film of the same type is correct?

  1. Dust increases transmission by scattering light evenly
  2. Dust reduces transmission because particles absorb and reflect incoming radiation Correct answer.
  3. Dust increases transmission only in the ultraviolet band
  4. Dust has no measurable effect on transmission

Explanation

Dust particles on the film surface absorb and reflect light, so the fraction reaching the crop falls. Cleaning the film or using rain-washed surfaces restores transmission. The effect is measurable and reduces, rather than increases, the light available for photosynthesis.

Question 47Greenhouse Cladding Materials, Glazing and Covering Systems

In a greenhouse covered with a single layer of film, why does installing an inner thermal screen reduce heating demand at night?

  1. The screen reflects light back to the crop during the day
  2. The screen increases the U-value of the roof
  3. The screen creates an insulating air layer that reduces heat loss from the house Correct answer.
  4. The screen raises the thermal conductivity of the covering

Explanation

A thermal screen traps a layer of still air beneath the roof, adding resistance to heat loss and lowering nighttime heating demand. It does not increase the U-value, which would mean more heat loss, and its main night function is insulation rather than light reflection.

Question 48Greenhouse Cladding Materials, Glazing and Covering Systems

Which covering material would be least suitable for a greenhouse roof that must support occasional foot traffic for maintenance?

  1. Thin single-layer polyethylene film Correct answer.
  2. Tempered glass
  3. Twin-wall polycarbonate
  4. Reinforced acrylic sheet

Explanation

Thin film has almost no load-bearing capacity and would tear under foot traffic, so walkways or stronger panels are needed. Tempered glass, twin-wall polycarbonate, and reinforced acrylic can carry limited loads when properly supported.

Question 49Greenhouse Cladding Materials, Glazing and Covering Systems

A grower compares two films: one clear and one diffusing. Under high summer radiation, the diffusing film often improves crop uniformity. What is the main reason?

  1. It lowers the humidity inside the house
  2. It scatters light so that lower leaves and shaded areas receive more radiation Correct answer.
  3. It raises the total amount of light entering the house
  4. It blocks all infrared radiation

Explanation

Diffusing film scatters direct beam light, so radiation penetrates deeper into the canopy and reaches leaves that would otherwise be shaded. Total transmission is not necessarily higher, and humidity control is a separate ventilation matter.

Question 50Greenhouse Cladding Materials, Glazing and Covering Systems

Which practice best extends the useful life of a polyethylene greenhouse cover?

  1. Removing the UV stabiliser during manufacture
  2. Fixing the film tightly and avoiding sharp contact with the frame Correct answer.
  3. Coating the film with oil each season
  4. Stretching the film loosely so it flaps in the wind

Explanation

Tight fixing reduces flapping and abrasion, and padding sharp frame points prevents punctures, both of which extend film life. Loose film wears against the frame, and oil or removal of UV stabilisers accelerates degradation.