permaculture

["Sean Albiston" <lab@physics.umn.edu>]

Below is a response I wrote to another listserv regarding corrugated
polyethylene.

sean albiston
zone 4b

Lawrence F. London, Jr. wrote:

        A new thread perhaps: attached greenhouses or sunspaces.
        Anyone explored options for design and materials?
        Hint: clear flat polycarbonate sheets 1/8-3/16".


Can you elaborate?  There's a large porch on the south side of the
small farmhouse I recently bought.  Currently it's poorly designed
and sealed, but still heats up very nicely when the sun is out.
It'll be next summer before I can think about rebuilding it, but I'm
collecting information and ideas on it now.  I'd like to open it up
more and screen the whole thing, and have glass or plexi or whatever
panels to close it in during the winter.




---------------------------- Original Message ----------------------------
Subject: Re: [SANET-MG] greenhouse glazings
From:    "Sean Albiston" <lab@physics.umn.edu>
Date:    Mon, November 20, 2006 11:38 am
To:      "Sustainable Agriculture Network Discussion Group"
<SANET-MG@LISTS.IFAS.UFL.EDU>
Cc:      jewet006@UMN.EDU
--------------------------------------------------------------------------

>          I had a question from a CSA farmer who is looking for
information
> about the use of corrugated polyethylene as a hoophouse cover.  Does
anyone
> on SANET know if there is any independent research out there on this
product as to durability, strength, and general suitability for
> hoophouses?


Jane, in my opinion corrugated sheeting will not work well to cover an
entire hoophouse.  Far too many seams for the structure to be cheap and
still work effectively in the extremes.  Twinwall poly greenhouses
generally rely on aluminum flashing and silicone to stay sealed.
Corrugated polyethylene could work great for end wall and sidewall
applications.  It is intended for applications were rigid polycarbonate is
overkill, or too expensive to ship.

Corrugated polyethylene is cheaper than polycarbonate, however much more
expensive in comparison to films.  Corrugated polyethylene will last
approximately 8 years, versus 15 for polycarbonate and 4 for polyethylene
films.

Polycarbonate is UV inhibited on the outer surface only, in polyethylene
the UV inhibitors are embedded within the polymer, making both sides UV
stabilized equally.

Of interest might be woven polyethylene films.  Some are touted as being
able to last 6 years or more, withstand tearing and stretching and have a
greater r value over a standard film.  They also diffuse the light most
similarly to the corrugated polyethylene.

sean albiston