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Re: CULT: converting to greenhouse

From: John I Jones <jijones@ix.netcom.com>

James Brooks wrote:
> The side poles, and their resulting roof rafter pipes are 5-6 feet apart,
> meaning there is an area on each side of the ridge pole that will involve
> 30-45 sq. feet of unsupported plastic, which I am reasonably sure will sag,
> stretch and fill with water in a good rain.

I have a couple of suggestions for you. First, be sure to get UV resistant
plastic or it will break down and you will have little pieces of very brittle
plastic all over the place. (experience speaking here). The second is, provide
a flow path for the water. That is the surest way to prevent it from building
up someplace and doing damage. I have had to use plastic to manage a leaky
roof, and it is lots of fun....

> Those of you who have had greenhouses, what do you feel is the minimum
> support spacing to prevent this from happening? Should it run bottom to top
> or parallel to the eave line? Any ideas for fastening this flush to the
> pole framework to prevent yet another pond from forming?
> I intend to put the roll plastic over the top and roll each end in a 2x4,
> stapling it in place, so the sides can be rolled up for ventilation, and so
> its weight will keep tension on the plastic.

Depends on a lot of factors. something between 6 ' and 1.5' is a reasonable
guess. I am trying to remember what I have seen around here on the large
commercial greenhouses.

What is the pitch of the roof? How long is the run down the rafter pieces from
the ridge line to the bottom edge. What thickness of plastic? Is there a
smooth edge for the plastic to ride on so the weight of the 2 X 4 doesn't
cause holes to poke in the plastic. Are you using 8' 2 X 4s. Are they dry or
green (they will loose a significant amount of weight as they dry).

It would seem that the water would flow down the plastic and collect at the
bottom edge. Maybe a piece of plywood along the bottom edge would support the
water drainage.

John                     | "There be dragons here"
                         |  Annotation used by ancient cartographers
                         |  to indicate the edge of the known world.

USDA zone 8/9 (coastal, bay) 
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