AVAG

Glasshouse Construction Services

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A glasshouse offers protection from outside influences and makes climate control possible. Dutch firms specializing in glasshouse construction possess an enormous amount of international know-how and experience in building glasshouses for horticultural products. For instance, in designing glasshouses they not only take into account climate and light but if necessary also the risk of earthquakes. Two types of glasshouses are mostly commonly built: the Venlo and the wide-span glasshouse. The type chosen usually depends on the height of the crop; the smaller the crop the bigger the area under cultivation. Hence, growers specializing in basic stock material and pot plants tend to choose wide-span glasshouses while flower and vegetable growers the Venlo.

The Venlo

  • The most commonly built type thanks to its ideal price/performance ratio.
  • Ideally suited for vegetables, flowers and plants.
  • International standard widths between the columns 6.40 m (2 x 3.20 span width) and 9.60 m (3 x 3.20 span width). In the Netherlands widths of 8.00 m (2 x 4 m), 9.60 m (2 x 4.80) and 12.80 m (3 x 4.267 m) are usual to give more light. Greater widths than these demand a more specific and more expensive structure.
  • Standard heights 4.5 m and 5 m or higher.

Wide-span

  • Thanks to the great volume of air and ventilation capacity, ideally suited for small crops such as cuttings, young plants and pot plants.
  • Standard widths between the columns 8.00 m and 12.80 m
  • Standard height 5 m, up to 6 m.

Working accomodation & other possibilities

  • A glasshouse made of glass is not necessarily only suitable for cultivation: a glass structure is also ideal as working accommodation, for example, as a display or sales area at a garden centre. A number of AVAG members specialize in such purpose-built structures.
  • There is no standard for working accommodation. In general, such accommodation is designed and built in consultation with the architect.

The components of a glasshouse 

The foundation:

  • The foundation is made of concrete. Each column in the glasshouse rests on a concrete pillar; under the frontage a concrete foot, either poured on site or of modular construction.
  • Before the foundation is laid, a soil analysis is carried out. This will determine the required dimensions of the foundation and whether pile driving is necessary.

The construction:

  • A steel structure is used. The stability of the structure is also calculated with reference to climatological conditions (snow, storms) and the equipment to be installed (the type of installations the structure has to support, now or in the future).
  • The gutters are coated steel or aluminium.
  • Good quality functional aluminium profiles are used to attach the glass structure to the glasshouse frame.

Automatic ventilation:

  • The Venlo has an alternating ventilation system with vents every two or three sections.
  • The wide-span glasshouse has a continuous roof ridge ventilation system to a maximum 1.70 deep.
  • The ventilation vents are centrally operated.
  • In the so-called cabrio glasshouse, the whole roof can be opened.

Roof cladding

  • In most glasshouses 4 mm-thick white glass is used. Float glass is used for the larger glass sheets. The glass gives an average light permeability of about 90%.
  • Instead of glass, energy-saving polyacrylate sheets or polycarbonate sheets (16 mm thick) can be used.

Needless to mention AVAG members comply with various standards NEN 3859, NEN-EN 1990, 'Bouwbesluit 2012'. Glasshouse constructions have a minimum technical life span of about 15 years. However, the life span of a glasshouse is also determined by economic developments.

The water supply

The first step is to determined the quantity of water required the whole year round for the crop in question. However, specialist firms designing and installing water and plant food systems for glasshouses work on the assumption that the water supply is the responsibility of the grower. The source of the supply may be a spring or lake, mains water or rainwater.

Storage

Various plant food systems are available ranging from simple, risk-free but labour-intensive methods (mixing trough for liquid fertilizers) to complex, high-risk, computer-controlled systems (water analysis in combination with a direct liquid fertilizer drip system). The choice of system often depends on the expertise of the user, the labour and cost involved and the desired quality of the feedwater. If the culture medium is rockwool or concrete the quality of the feedwater must be higher than that used for soil.

Plant food

Various plant food systems are available ranging from simple, risk-free but labour-intensive methods (mixing trough for liquid fertilizers) to complex, high-risk, computer-controlled systems (water analysis in combination with a direct liquid fertilizer drip system). The choice of system often depends on the expertise of the user, the labour and cost involved and the desired quality of the feedwater. If the culture medium is rockwool or concrete the quality of the feedwater must be higher than that used for soil.

Water control

The correct method of regulating the feedwater is dictated by a combination of such factors as the type of glasshouse, the plant food system, the crop and the individual situation. If water is scarce a drip system could be the solution. If plant density is very high, such as in glasshouses where only pot plants and basic stock material are cultivated, an ebb and flow system is a realistic option. If sufficient water is available crops growing in soil can be successfully irrigated from above and/or underneath. The correct choice based on the proper know-how ensures efficient water management.

The reuse of feedwater

Water is often scarce, fertilizers cost money and environmental requirements are becoming increasingly stringent. For these reasons Dutch firms have built up a great deal of expertise on the collection and reuse of superfluous feedwater. This can be achieved with a cultivation system using gutters or troughs in which the feedwater is collected. Gutters or pipes then transport the water to an underground tank where it can be stored, analyzed, disinfected or not, and reused.

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