GardenBanter.co.uk

On 19 Nov 2003 08:57:31 -0800, (IC_Gardener)
wrote:

We did some remodeling projects around the house this summer, and I am
left with two sliding doors that I don't want to pay to take to the
dump. I thought that they would make a nice top to a coldframe. Is
there any place that has plans for one, or do people just improvise a
box for whatever size window they have?

I make them from scratch. Here are a few pictures of some I built
over the summer with scrap wood, spare white paint, Thompsons wood
sealer, and a few hinges. The glass (of varying sizes and shapes)
was purchased at garage sales. Some of these are for sale if anyone
is around nw NJ to pick them up :)

http://home.ptd.net/~vstevans/web/hobbies/cframes-2.jpg

The measurements are not very hard, if you have a scientific
calculator handy (one with sine & cosine buttons)...or simply use the
computer calculator :) A cold frame top (the glass part) slants
toward the sun. The concept of a cold frame, from a SIDE
persepective, is a 90-degree right-triangle on top of a box. The box
HEIGHT part is easy to measure; I usually make my frames a foot tall
(12 inches). The length is however long the glass frame is.

When starting, the only accurate measurements you have are the length
& width of the glass top, the angle of the glass slanted toward the
sun (usually 20 or 25 degrees), plus how high the cold frame "box"
part will reach (higher boxes will trap heat too high up for plants,
but a low box will be very cramped after pots & soil are added).

Now you need the width and height measurements for the cold frame. I
will make this "example" cold frame with a 20-degree slope. I make
cold frames in 5-degree slope increments because my circular saw only
has 5-degree sloped increments...if you have a circular saw that can
perform more accurate slopes, a 23.5 degree slope is the best angle
for most cold frames. I'll make the glass plate 24 inches in width
for the following example.

To make a long story short, you obtain the cold-frame WIDTH with the
following equation (the length is however long the window is).

CosA° = adjacent / hypotenuse
or
Cos20°= width / 24 inches
(the glass plate width = the hypotenuse of the triangle)
A = slope, which in this case is 20°

width of cold frame = 22.55 inches

The cold frame REAR HEIGHT is made with the following equation. The
FRONT HEIGHT is however high the box part is. In this case, I'll make
it 12 inches high.

SinA° = opposite / hypotenuse
or
Sin20° = rear-height / 24 inches

rear-height = 8.2 inches, pluse the FRONT HEIGHT (12") = 20.2 inches

Now you've got all the cold frame dimensions you need. Cutting at
angles with the circular saw is tricky, but Im sure you'll get the
hang of it. Remeber to factor the slope of the cuts into your
measurements, plus _thickness of the wood_ (a 24-inch long cold frame
using inch-thick wood only has to be cut 22 inches in length). A cold
frame with these dimensions and 3/4 to 1-inch thick wood will be
extremely snug and retain heat extremely well. Adding a layer of
insulation, inside or out, surrounding the frame never hurt, either.

Also, if I build one in early
January, when could I put plants (lettuce, spinach, etc) inside?

Depends on where you live, and what your winter temperatures are.
You can always risk it in colder weather, the soil might be able to
retain enough warmth during the day to keep the plants alive at night.
Gallon-jugs of water placed inside the frame will also retain heat
during the day and release it at night (water has a very good capacity
to store heat).

Dan