Greenhouses are designed to take advantage of solar radiation to create a proper environment and temperature for plant cultivation. Solar radiation heats all greenhouse contents, and the glazing traps the heat generated within the structure. Even heating of the greenhouse contents mitigates the loss of heat by convection (warm air tends to rise and escape a structure), which is another important functional aspect of a greenhouse. Greenhouse building components consist of a foundation, framing, glazing, ventilation, utilities and thermal storage systems. Temporary and portable greenhouses may not require all these components.
There are two basic types of greenhouses, traditional framed with glass and plastic houses. The plastic category encompasses a handful of different synthetic glazings, including polyethylene films and sheets, polycarbonate, acrylic, and fiberglass. Each of these types of synthetic glazing offers various pros and cons. In general, the synthetic glazing options are lighter but more combustible than glass. The first decision will be what type of house best suits the intended needs of size, lifespan envisioned for the structure, local climate issues, and initial project and maintenance budget. The plastic houses are cheaper to install and heat. The traditional glass house has greater service life and excellent light transmission. For northern climates where sun exposure is not as prevalent, traditional glass houses may end up as a preference, particularly for a plant nursery business where the capital investment is logical. In climates with severe thunderstorms and hail activity, plastic houses may be preferred for a hobby greenhouse, when all other factors are considered.
Placement of the greenhouse is a very important consideration. The long axis of the floor plan should be oriented east-west so maximum exposure to the winter sun (facing south in the Northern Hemisphere) is ensured. This will allow for the greatest potential for solar heat gain. The location should be close to utility services, since water for the plantings and electricity for ventilation and night lighting will be required. A greenhouse site with firm soils for the foundation and wind protection to prevent damage to the glazing are important considerations. Greenhouse foundation and flooring systems may be as simple as natural turf, fabric covered earth with gravel ballast, or a concrete slab with wall footings for a very large structure.
Plants being cultivated are similar to people in their temperature range preference. A basic target is 70-75 degrees Fahrenheit during the day and ten degrees less at night. During the day, roof vents can be opened to control heat build-up. A stable temperature can be provided even in harsh exterior climates and at night if the greenhouse is carefully designed to include a thermal storage system. The thermal storage system may be as simple as water storage barrels that dissipate accumulated heat when the sun sets. The soil and paving inside of a greenhouse naturally serve this role as well. Fans in the greenhouse roof structure can be used to redirect warmer air toward the floor, stabilizing the temperature throughout the structure.
In addition to temperature control and ventilation, water delivery systems will need to be planned. In smaller greenhouses, this may be a manual task with water being carried from hose bibs to each planter. Larger commercial greenhouses may have irrigation piping installed over the planters with drip or spray nozzles, all of which can be operated with a remote controller.