January 2025 - 44

SGAFT
and reaching halfway up the sidewall.
One can self twist into a pretzel
rationalizing that snow piled that
high offers insulative value against
cold outside temperatures. Still,
placing my hand within an inch of the
inside of the fabric and feeling cold
was concerning. Let's just say it was
going to cause a sleep deficit.
Compared to the double
poly-covered roof and twin wall
polycarbonate on the end walls, my
conclusion was that the sidewalls
were a weak link regarding the
structure's heat retention and energy
use efficiency. To be clear, and as
stated in previous articles, this is
not a complaint. I couldn't afford
a higher efficiency sidewall vent
and am grateful a more economical
version was available. I also knew
the performance of the walls needed
to be improved before the second
heating season.
POLY'S ALWAYS HANDY
Most of my commercial greenhouse
career has been tethered to
polyethylene. Poly to cover the roof,
sidewalls and endwalls. Sheets
of poly for partitions and covers
for almost anything. You name
it and poly has been economical
for as long as I have been around
greenhouses. It's versatile,
easy to work with, forgiving and
functional in countless settings.
My comfort level working with poly
instinctively motivated me to hang
a 4 mil sheet inside the sidewall to
create an insulative dead air space
heading into the second heating
season. It was attached to an
aftermarket rail mounted inside the
greenhouse at the top of the sidewall
as a psuedo-electrical raceway. For
reference, this raceway rail was
mounted an inch above the sidewall's
externally mounted knee rail but,
again, on the inside.
The poly draped loosely to the
ground and, following the heating
season, was bunched up and tied at
the top to allow sidewall ventilation
to occur. Visit sgaft.com for additional
pictures, details and discussion
of the entire sidewall evolution.
One additional note: the ends of
roll up sidewall vents are sealed
with common wiggle wire to prevent
air leakage and infiltration through
the heating season. Sealing the
vents this way requires that they
be deactivated for the winter.
Without side ventilation, winter
cooling in a northern greenhouse
is accomplished solely by the ridge
vent. With this in mind, hanging a
poly sheet inside the sidewall didn't
restrict ventilation performance
during the heating season.
SIDEWALL-CEILING
INTEGRATION
The single layer of poly worked well
during the second heating season by
creating a dead air space between the
exterior roll up sidewall fabric and the
heated interior similar to that created
between the inflated double poly on
the roof. The master plan for this
new greenhouse included an energy/
shade curtain system as soon as one
could be budgeted. That customized
package of design features referenced
earlier? Saving money on the side
vents factored into pulling the trigger
on the energy curtain prior to the
third heating season.
Once the curtain install started,
it was much easier to understand
installation diagrams by visualizing
how the puzzle pieces needed to fit
together. It became clear that my
seasonal approach to managing the
sidewalls needed to be integrated
with the curtain system to maximize
energy efficiency. The poly sheet
had worked for winter insulation, as
did bunching it up at the top rail for
spring through fall ventilation. How
the curtain would be integrated into
the sidewall insulation, however,
presented challenges.
First, the curtain system includes
So, being a poly guy
for most of my career finally
took a back seat to a better
alternative for insulating
the sidewalls.
44 JANUARY 2025 GPNMAG.COM
an apron, separate from the actual
curtain, to be installed along the
knee wall to provide a transition seal
between the ceiling curtain fabric and
the sides of the house. This was a
woven, white synthetic fabric whose
top edge provided support for the
edge of the curtain to slide over and
sit atop while closed.
Unfortunately, due to my
customized side/knee wall, this apron
was a little too narrow to offer enough
of a base upon which the curtain
http://www.sgaft.com http://www.GPNMAG.COM
January 2025

Table of Contents for the Digital Edition of January 2025
