Hanne Bech-Jensen wrote:

"Hanne Bech-Jensen" wrote in message
...

On the homepage

http://www.onlinegreenhouses.co.uk/navigation.htm

I am so sorry... you can tell that I am obviously quite new to this. BTW
how do you delete a message like this that went astray... from the entire
newsgroup, I mean?

Anyway... I was going to ask if it was true as they state on their website
above that you get algea growth in the gab inside polycarbonate glassing for
greenhouses. Anyone have any experience on that.

It is true after a fashion, but only if the inside of the twin wall
polycarbonate ever gets wet. You normally buy tape to put over the open
ends that lets it breathe and keeps dead flies, dirt and dust from
getting in. And the structure should be designed to support it.

They are also right that twin wall is polycarbonate is flexible so you
have to be careful about fixing it to a conventional greenhouse. Glass
clips will not work it will spring out.

On the plus side for polycarbonate - it diffuses the light in the
greenhouse so plants scorch is less likely to occur. It is practically
indestrutible and so even in a glass greenhouse useful for opening
lights that may get snatched by the wind. And if you intend to heat the
greenhouse the thermal insulation of the twinwall gap makes a big
difference to your heating bill. I intend to build my new greenhouse
from 1cm thick twinwall polycarbonate.

I have a couple of pieces of twinwall that have been seriously abused
for about a decade. There are dead spiders and allsorts of junk in the
gaps but hardly any algal growth. The risk is largely theoretical unless
you build a really badly designed greenhouse. It is the same technology
as is used for home conservatory roofs.

Regards,
Martin Brown