Grow Your Own Magazine

What are the disadvantages with the UPVC semi rigid safety glazed greenhouses (such as those from Norfolk Greenhouses) compared to glass greenhouses? Do plants receive enough light? Are they more difficult to erect/less wind resistant?

One advangage of not having glass is that in v high winds , when some panes will break, you will not have to look for broken shards of glass in amongst the crop inside the greenhouse. Also if you have children running around the area they are less likely to injure themselves and you can concentrate on your gardening. We have a glass one with plastic curved ares .I don't know much about the light side of things although our curved pieces do craze a little and start splitting after a few years.

There is variety and a true choice in the size of the glass panels. The larger the size of the panes the better the light transmission which is a benefit. The disadvantage of larger panes is the heat loss is increased and therefore heating costs are higher. One further disadvantage of large panes of glass is that the cost of replacing a broken pane will be higher. None of these factors are critical, so we wouldn't really recommend making the pane size a key factor in your choice of garden greenhouse.
Other considerations with glass are that it is a good transmitter of light (typically 94% of light goes through glass) which is the good news. The bad news is that it is a bad transmitter of heat which means the inside of a glass greenhouse can get very hot very quickly with disastrous results for some plants. Glass is also very heavy compared to the materials below which means the frame has to be stronger (and therefore more expensive) and packing costs are higher.

There is now a very wide choice of alternatives to glass as glazing material for a garden greenhouse. Many of these are beyond the scope of this article, but two of the more popular alternatives are noted below:
Polycarbonate Sheet The most common of these are acrylic and polycarbonate double (sometimes triple) glazed sheets with excellent heat retaining properties. These sheets perform at least as well as glass for light transmission, although they do deteriorate with age. This material is far less liable to breakage and very easy to form into curved sections. These really are an excellent alternative to glass, especially if children are liable to be in the same area as your greenhouse. Twin wall or double glazed polycarbonate has a light transmission of around 85%, single wall polycarbonate has a light transmission even better than glass, around 96%.

I hope this helps (and is not to technical!)

__________________
Geordie

Te audire non possum. Musa sapientum fixa est in aure

Hi Kathy,

I would have look in your local paper as you could pick up a 2nd hand greenhouse for less than the cost of one of the ones from Norfolk, My neighbour sold her 8' x 6' for £50! I've already got two so I couldn't squeeze it in. What ever you buy won't be big enough by next year so get the biggest one you can afford!

Hope this doesn't confuse things

Thanks, Nick. will look out.