The type of greenhouse you select depends upon the amount of money you want to spend, the location and space available, whether you are likely to be permanently content with a small house or will want to expand later; whether you plan to use your greenhouse exclusively for growing plants or expect to furnish part of it as a living or family room; the plants you want to grow now and in the future, reconciliation with the surroundings (trees and the architecture of your home), sunlight, and details of construction and installation.
There are two basic greenhouse categories: free standing and attached. A free-standing greenhouse is always even-span, while an attached greenhouse may be even-span or lean-to.
An independent, detached, self-supported glass structure that has two sides and two ends; it must have a door in one end and may have a door in each end. The heat, water, and light that must be provided may involve expensive installation costs if these facilities must be extended some distance from your residence.
Attached greenhouse: A glass structure that is connected to your residence, garage, or other solid building on your property; it may be an even-span greenhouse with one end connected to a building, or it may be a lean-to greenhouse. A greenhouse attached to your home is easier to tend and less costly to heat; the care and pleasure of plants are more readily shared, and you can enjoy your tasks even in inclement weather without having to go out into the cold. An attached greenhouse is made easily accessible through removal of a portion of a house wall or the installation of a door. Warmth from the living area can supplement that provided for the greenhouse, thus reducing heating costs.In an attached greenhouse, electric and water lines are easily connected to the house supply.
A balanced structure, alike on both sides from eave to sill, the glass covering an area large enough for at least two growing benches with a center walk between. An even-span greenhouse has the advantage of providing about twice as much growing area as a lean-to at only a moderate additional cost. When it is attached to your home, the greater part of the structure extends out from the house and adequate summer ventilation is more easily provided than in an attached lean-to. Or, the even-span greenhouse may be a free-standing structure.
Half of an even-span greenhouse—and, as the name implies, this type is attached (along the ridge line) to another structure, usually your residence, for support. The lean-to may be built along the side of a main building or fitted into the angle of an ell, or it can be butted against porch or patio. Essential for flowering plants is a location that provides a minimum of three hours of winter sunshine. Lean-to greenhouses cost less than the even-span type because there are fewer structural members and the supporting wall is already provided. They are ideal when space is limited.
Perhaps no one greenhouse can be the best. There are advantages to both types of construction. The even-span has double the growing area of a lean-to, but the lean-to is less expensive.