Definition

Under Section 1-1(q) of Connecticut General Statutes, greenhouses and other structures, used primarily for the production of horticultural commodities, are considered agriculture and farming.

The International Building Code defines:

Production Greenhouse – a greenhouse used for growing large numbers of flowers and plants on a production basis or for research. Generally there is no public access to a production greenhouse.

Commercial Greenhouse – Any other greenhouse structure used for the display and sale of horticultural products and supplies. These come under a more restrictive mercantile section of the code.

Tax Exemption

Section 12-81 of Connecticut General Statutes exempts temporary devices or structures used in the seasonal production, storage or protection of plant material, from taxation. This covers hoophouses, poly houses, high tunnels, overwintering structures, and shadehouses that are used primarily to protect plants from weather elements.

Greenhouses are Exempt From an Engineer’s Seal

Section 20-298 of Connecticut State Statutes exempts any farm building or structure used for agriculture. A subsequent ruling in 1998 on a appeal by Len vanWingerden, of Somers, to the State Building Inspector, Architectural Review Board of the Consumer Protection Department and the Connecticut Attorney General reaffirmed this exemption.

Greenhouses are Classified Under Miscellaneous Use Group

The International Building Code places agricultural buildings and greenhouses under a miscellaneous use group ‘U’.  It states that “...these buildings shall be constructed, equipped and maintained to conform to the requirements of this code commensurate with the fire and safety life hazard incidental to their occupancy”.  As there are only one or two employees tending plants at any one time, the fire and safety hazard level is very low.

Section 1608.0 Snow Loads

Snow load calculations for greenhouses with a minimum 50F temperature and a temperature alarm system are lowered as compared to other buildings. Production greenhouses are placed in Category I that considers them to represent a low hazard to human life, in the event of failure. A typical design snow load for a conventional greenhouse in northern Connecticut would be 18.6 pounds per square foot (psf). The designs also comply with the National Greenhouse Manufacturers Association (NGMA) standards.

Wind Load

Greenhouses have generally been designed using a basic wind speed of 90 to 120 mph, to meet Appendix M of the State Building Code. For example: the velocity pressure for a production greenhouse with a 12 foot effective building height located in a suburban setting, in a non-hurricane area with potential 90 mph wind, would be about 14.4 pounds/sq ft.

Section 3103.3.2 Membrane Material

Most greenhouses in Connecticut are covered with 6 mil polyethylene or copolymer film plastic. For  greenhouses, where occupancy by the general public is not permitted this material is not required to be flame resistant. Independent tests indicate that this material melts but does not support combustion and has a low flame-spread rate. Another typical material is 8mm polycarbonate structured sheets. This are listed as self-extinguishing, do not give off toxic gases, and can be used in institutional greenhouses.

Americans With Disabilities Act (ADA)

The general interpretation for production greenhouses has been that access is necessary to the location where activity (seeding, transplanting, etc.) will take place. That does not mean that every bench or growing area has to meet the code, as this would significantly reduce the production area.

Heating Systems

Both hot air and hot water systems are used in greenhouses. Hot air systems are typically unit heaters located overhead or floor mounted furnaces. Hot water systems consist of boilers with distribution through iron pipe, fin radiation, radiant floor or radiant bench piping. Design criteria is based on a U-factor of 1.25 for single layer glazing and 0.8 for double layer. This is based on NGMA and American Society of Agricultural Engineers (ASAE) standards. Control sensors are placed in the plant growing zone, and may be thermostats, solid state controllers or environment computers.

Cooling Systems

Natural ventilation through louvers and fan ventilation with an intake vent system are common ways of cooling a greenhouse. Evaporative cooling, either fan and pad or fog, may be used to maintain temperature during the summer.  Fan ventilation systems are usually based on one volume change per minute for summer ventilation.

Shade/Energy Blankets

To reduce summer heat gain or winter heat loss, shade and/or energy systems are common. Energy/shade blankets installed in production greenhouses should be of firestop material to meet insurance codes. In greenhouses used for retail the material should be a fire-resistant material (such as Revolux manufactured by L.S.Svensson).

Electrical Systems

Electrical systems should be installed to meet the National Electrical Code. Fire and smoke detectors should be installed to indicate excess temperature, smoke conditions or power failure.

Resources

International Building Code

Greenhouse Engineering by R.A.Aldrich & J.W. Bartok.  Natural Resource, Agriculture and Engineering Service, Cornell Univeristy, Ithaca NY 14853.

Greenhouse Design Standards – National Greenhouse Manufacturers Association, 4305 North Sixth Street, Suite A, Harrisburg PA 17110 – Phone: 800/792-NGMA

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