Greenhouse Insulation
Efficient greenhouse insulation is essential to keep heating costs down and to prolong the season of an unheated structure. The most efficient means of insulating your greenhouse is to install double-glazing or triple-glazed polycarbonate during construction. Both these systems retain the heat well and offer excellent light transmission.
However, if your greenhouse or conservatory has not been installed with double or triple-glazing, there are a number of other more temporary insulation systems that may be installed.
Thermal Screens
Thermal screens may be used to conserve heat. These sheets of clear plastic or laminated fabric may be drawn vertically across the eaves at night to prevent heat from escaping through the roof, thereby trapping the warmth for the plants below. Alternatively, they may be used horizontally to partition off unused areas of the greenhouse. This allows the gardener to heat a small portion of the greenhouse to overwinter tender plants or raise seedlings without wasting money or energy heating the unused areas.
When choosing an insulation system for your greenhouse or conservatory, bear in mind that some materials may limit the amount of light reaching your plants.
Plastic Insulation
A temporary form of winter insulation may be created using a layer of plastic sheeting to act as double-glazing. This may be attached to the inside of the windows using clips or suction-pad fasteners. Bubble wrap may also be used on the inside of glass; its double or triple layers of plastic with air cells in between acts as an excellent form of insulation, and could reduce your heating costs by one third.
Some gardeners have also reported success using a clear solar pool cover, which looks somewhat like a large sheet of robust bubble wrap. As this should be secured over the outside of the greenhouse, it is not suitable for gardens that may be exposed to moderate or high winds. The sheet should be placed so that the bubbles face down towards the glass and the smooth surface is uppermost - this will allow any snow to slide off easily. Make sure that you fasten the cover securely, so that there is no chance of it becoming detached and blowing away.
Base Cladding
Greenhouses with a solid base wall are much more efficient in conserving heat than glass-to-ground styles. However, adding a layer of polystyrene panels along the bottom panes of glass in an all-glass greenhouse may significantly reduce the amount of heat lost.