Stefan Buczacki solves your plot problems
Stefan says: You say this is the fifth winter you have had the bubble wrap in place, and it’s never blown away in the strong winds of Blackpool. I’ve never seen it done before, because you’re correct in that the normal advice is to fix it on the inside. It does make your greenhouse look rather like something from outer space, but no matter, if it works for you, I can’t see a scientific reason not to do it. The only problem would be the weather, although that doesn’t seem to be so in your case.
Insulation is vital in keeping the greenhouse warm in winter and reducing the heating costs. From the many materials available, I favour the double-skin bubble polythene film you’ve used, but it’s important to choose the one sold for greenhouse use because superficially similar packaging film will probably not be UV stable; it will be degraded by sunlight.
Double-skin bubble film cuts down heat loss by about 40 per cent. Not surprisingly, the film cuts down visible light transmission inwards, as well as limiting the loss of infra-red radiation outwards but when the greenhouse is being used for maintaining plants rather than actually expecting them to put on growth through the darkest winter period, no harm will ensue.
I don’t do anything as unusual as putting the film on the outside, but I do leave it in place all year
round because it keeps the greenhouse cool in summer in the same way as shade paints.
Double-skin bubble film cuts down visible light transmission by about a further 10 per cent over the 10 per cent cut out by the glass itself. This compares fairly favourably with the 20 to 30 per cent reduction in both visible light and infra-red transmission claimed for the best shading paints and I find that it works very well for me. I renew the film every three years and then clean the glass.