Greenhouse Gardening – glazing

Glass is the traditional material used in greenhouse construction. It’s an excellent material if you can afford the initial outlay as it has a life of at least twenty-five years (and has low maintenance requirements unlike plastics which may have a lower capital cost but increased annual costs in replacement and repair. Glass also transmits light better than any alternative.

The support for glazing may be made from a range of materials. Aluminium frames are long lasting, corrosion resistant and lightweight, and can be prefabricated but they are not cheap, and often their specialised construction may lead to your greenhouse having to be assembled by a professional. Galvanized steel frames offer high strength and long life at less expense than aluminium frames, although maintenance costs are usually higher.

Bear in mind that metals are excellent heat conductors, which means heat loss through such a frame can be a significant factor in winter heating. This is the opposite to wood, which may have a low initial cost, but higher maintenance costs and doesn’t significantly affect the winter heating scenario. However, wooden frames are flammable, and need to be treated to avoid rot, infection or drying out – all of which are increased by the alternating heat and humidity of the greenhouse.

Glazing also requires shading to control the intensity of light and lower interior temperatures. The cheapest and easiest way to provide this is to buy liquid shading (various forms of whitewash and other paint are available) which you paint on to block the sun's rays. The problem is that applied, it’s difficult to change the density of the shading and it has to be washed off in autumn. Fabric shading such as blinds is more expensive but can be coupled with devices to provide movable curtains offering control of the greenhouse temperature.

Greenhouse gardening glass photograph by net_efekt, used under a creative commons attribution licence