IV. Based on the
a. Single span structure: When only one
span is used as described in shape, and then they are called as single span
single span structures can be erected. It permits convenient expansion /
contraction of business.
permits the production of a different plant material by maintaining different
micro-climate in different units.
can be seen with this type and gutter is not required.
b. Multi spans
It is an economy in construction, for
cooling and heating operations and cultural operations. There is no flexibility
and different crops cannot be grown in one structure. The gutter is required.
material for the greenhouses
maintains the favorable climate suitable for growing crops.
objective needs to be achieved at an affordable cost.
greenhouse structure should be light yet it should be strong enough to withstand
greenhouse is considered to be semi-permanent structure and should be designed
for service life of twenty-twenty five years.
greenhouse must resist a load of its own weight, Wind load, Snow load and Crop
of GH designs loads
Load Minimum value (kg/m2)
Dead: a. Pipe frame 10
b. Bass frame, lapped glass, 25
c. Hanging baskets 20
Live: a. Snow
b. Wind To
be estimated based on area
recommended a live load of 68 kg/m2 of covered ground area.
greenhouse should be designed to resist a wind velocity of 100 km/hr.
load is affected by the direction of the wind, shape of greenhouse, wind breaks
and the opening of the greenhouse.
load depends upon the roof slope, snow fall, single span or multi-span and
whether heated or unheated.
should be strong enough to support the super structure against various forces.
or pile foundation is common because columns are widely spaced and the depth
should be at least 60 cm reaching too hard strata with a width of 60 cm.
foundation may be Reinforced Cement Concrete (RCC), CC or telescopic, whereas
the telescopic foundations are easier and cheaper than RCC or CC.
Greenhouse crop may be grown in soil or
soilless. The floor of the greenhouse should have drainage. For soilless
cultivation, sometimes porous concrete floors having the depth of 10 cm are
common materials of frame construction are steel, wood, bamboo, aluminum and
frame includes columns, bottom cord, truss members, purlins, knee bracing, wind
bracing, fitting members, etc.
should be treated for protection from high moisture and termites and painted
for better light conditions in the greenhouse.
tar is a good preservative for underground portion of wood.
components to be used in greenhouse frames should be hot dipped galvanized to
to reduce the cost, mild steel is used for the frame. Mild steel should be
painted with two coats of red oxide and two coats of oil paint to avoid
should be carried out at least once in two years.
or aluminum frames transmit more light as compared to wooden ones.
frame members should be smooth to avoid damage to the covering material.
Glazing material fixing
used glazing materials are glass, poly film, poly carbonate sheets, acrylic
sheets and FRP sheets.
for poly film, all other materials are rigid and comparatively heavy in weight.
the material used for fixing/fitting the glazing material remains more or less
are fitted with any of the following materials.
Generally 2.5-3.5 cm battens of suitable length are used. However, if the
length is less, then work of fitting increases. For poly-film, length of batten
may be 3 m or more to have convenient working. Battens may be salwood, teak,
mango, season or silver oak. Covering materials are fitted in the battens with
nut and bolts.
The gripper made in ‘U’ shape from plastic is used. They are available in coils
of 100, 200, 300 m. This type
of gripper has a protruding surface for
ensuring grip. Nevertheless, for additional firmness, spring clamps are
also used. Over the period, due to properties of plastic gripper may be
Aluminum profiles: Aluminum
profiles are shaped in ‘C’. The film is fixed in ‘C’ profile with hammering the
PVC pipe. Sometimes the film is also fixed with ‘Z’ shaped continuous GI wire.
Materials for greenhouses
The covering of a greenhouse or any
structure with the transparent material is known as glazing or cladding. The
glazing material includes glass, poly film, poly carbonate, FRP, PVA, acrylic,
polyester, PVF. Except for poly film and PVC, all other materials are rigid
properties of glazing material
When a beam of radiation is
incident on a material, a part of it may be reflected back, apart may be
absorbed by the material and remaining portion will be transmitted.
upon the material composition and surface properties, the radiation absorbing
ability, reflectivity and transmissivity values are determined.
a given material, the values of three coefficients must add to 1.0 with
reference to a particular radiation beam.
transparent material transmits a large portion of light through it, whereas, an
opaque material either reflects or absorbs the incident radiation.
translucent material may transmit a large portion of radiation but the
transmitted light is diffused in nature.
case of greenhouses, the transmissivity of radiation property is important. The
values of transmissivity for various glazing material are given below (Table