http://www.teksupply.com/webapp/wcs/...tNumber=105206

Alternatively, a 30' long x 12' deep sunspace might have

1 105197 $189 30'x7' vinyl panel,
2 105192 $159 12' clear gable ends,
8 4'x12' $50 pieces of Dynaglas clear corrugated polycarbonate, and
1 308' $154 2x4 frame

That's $1061, ie $2.95/ft^2.

Two caveats:

1. If the glazing is flexible and the airpath to the house has 2 one-way
lightweight passive plastic film dampers, one near the top to let warm
sunspace air flow into the house and one near the bottom to let cool house
air flow into the sunspace during the day, this can act as an air pump on
a windy night: a wind gust pushes the glazing in, which makes cold air flow
into the house, and then it stops and the glazing expands and sucks warm
air out of the house. So maybe it's better to use motorized dampers with
2 thermostats in series, one that turns on when the sunspace is warm and
one that turns on when the house needs heat.

2. The sunspace needs a vapor barrier on the ground, eg plastic film under
a rug or some mulch (which is dustier), but even then, a single layer of
glazing can end up with a reflective layer of frost inside for most of
a cold sunny day. David Delaney's solution seems promising: put 1/4" black
dots on a 6" grid inside the glazing. I can imagine doing that with a 1'x2'
stencil and a paintbrush on a roll of flat polycarbonate. Or maybe wrap
a 2" x 1' paint roller with a plastic sleeve with 3 1/4" holes in it.

Nick