I want to put some shade cloth on a plastic covered hoop house, to moderate the temperature and soften the light levels. Would it be better to put the shade cloth over the plastic, or under it? If I put it over, it will stop snow from sliding off properly. (In my climate, there are hot weeks where shade is needed, while there is still a threat of late blizzards.) It would also flap in the winds. If I put it under, I would have more trouble getting it off if I wanted to remove or change it, dirt might build up between the layers, and I'm not sure if it would cool the house.
As I see it, the light striking the shade fabric would heat it up, in turn heating the surrounding air; if this happened outside the plastic, the greenhouse would be cooler. But it this happened inside the plastic, wouldn't the net heating be nearly the same?
Hi Gilbert, I have some experience with greenhouses, and my understanding is that you are correct - the shade cloth will be much more effective outside the plastic. Any energy that passes through the plastic or glass of a greenhouse has a much harder time escaping - hence the greenhouse effect. There may be some heat mitigation with the shade cloth inside the plastic, but not nearly as much. Good luck!
Something to consider is the abrasive action shade cloth will have on the poly due to wind if it is put outside. If you can sufficiently vent the heat from the greenhouse, maybe shade cloth inside would be a better way to go...
Hey Gilbert, in my experience the shade cloth works best inside the plastic. In really commercial agriculture that I have seen the plastic is replaced with shade cloth as the needs change based on the season (plastic to gain a bit of heat to start seedlings earlier and then shade cloth with no plastic to reduce light and heat levels when the summer sun is making it hot). However I have used it as you are describing and we put it between the plastic and the hoops, it was pretty easy to put up and take down and it definitely reduced light and heat levels.