Hi Helga, you must live in a fairly dust free part of the world. I have to clean the grime off glasshouse roofs at least once a year to maintain optimum light levels.

So how long does vynil last? I know that the old fashioned fibreglass stuff clouded over and became useless after a couple of years.

The roof on one of my glasshouses has been replaced by stuff called lazerlite. .Might be called something else in the USA.

Thank you arthurum. Yes, we live in the country -nothing but trees and meadows around. The summers are sunny and quite warm, during which the GH is protected by 50% shade cloth.
Our winter weather is mostly cloudy, gray, rainy. I have an HD light over the middle table(cattlayas) on from 4:00 a.m to 7:00 a.m., but suspect it is not enough light all around, especially, since the HD bulb is also 3 yrs. old.
I hate to do away with an undamaged vinyl, but may not have a choice.

I have been growing orchids for 8 yrs. now, still consider myself a novice.

Appreciate your thoughts, Arthur.

Helga.