About eight years ago I designed and built a shed with an attached greenhouse from surplus and salvaged materials.  The shed itself was 12 feet by 16 feet and built over a cement block basement into a gentle west facing slope.  The gravel floored greenhouse attached to the south side. The foundation was half cement block and half treated wood sunk deep enough to be below the frost line.  I used salvaged windows for the glass on the east and west sides.  The south side was glazed with 2 foot by 4 foot single pane glass I obtained for free when the hospital where I work installed insulated windows several years ago.  I built a triple hung window/door, inspired by one I saw at Thomas Jefferson's Monticello, for access between the shed and greenhouse and used a door left over from building our house for the east outside exit.  Heat was supplied by an old vented, gas space heater and cooling by an exhaust fan on the west wall.  For two years it worked quite well, but it had some design flaws. It tended to overheat on sunny days, especially in spring and fall.  The heater wasted heat through the vent and occupied too much floor space to suit me; space I knew could be better used for plants.  The heat distribution was also too uneven and it was drafty.  During cold weather the condensation on the windows froze in thick, uneven sheets, denoting excessive heat loss. But in general I was happy to have the greenhouse and it served its purpose well.


One nice sunny day in March 1996 I got a call at work that the greenhouse was on fire.  I rushed home to find five fire departments there and the structure totally aflame.  When the fire was out, I'd lost everything from the floor up in the shed and the complete greenhouse. Much of the glazing had been melted from the extreme heat. A fire marshall came to investigate the cause and determined it was probably the exhaust fan which had overheated and caused the conflagration.  I don't know if that was correct, but it appears to be as good an explanation as any.  Other possible causes were a defective GFI electrical outlet, a radio, and a seed soil heater. It might also have been caused by what I understand is the most frequent cause of old house and barn fires, mice chewing on electrical wires. It's a mystery that will never be solved with no doubts.

Some things I learned that are good rules of thumb to prevent such fires include:
Mount any electrical devices like exhaust fans, radios or heaters in or on a nonflammable box or surface. Keep space heaters away from the wall by the manufacturer's recommended clearance. Try to line the nearest wall with a nonflammable material of low heat conductivity.
Use only the highest quality electrical fixtures. Avoid the cheapest bargain grade receptacles and switches
Follow the National Electrical Code and your local or any other applicable building code to the letter. Shortcuts taken here could invalidate your insurance or reduce the insurance company's liability.
Keep the vermin under control. Especially control rodents like rats, mice and squirrels. Reduce their access to the building by sealing any openings. Mice can squeeze through a crack as small as 1/4 inch and rats don't need much more. Squirrels will chew a small opening until it's large enough. As an insurance step, place poison bait boxes in strategic locations. Be sure to keep it away from pets and children though.
Make regular safety inspections of heating equipment. Especially look for gas leaks if you use gas. Use a soapy water solution to find the leak, not a match! Also check thermostats and any safety thermostats that may be present. Install smoke detectors with alarms that you can hear when you're not in the greenhouse.
Though this won't prevent fires, try to obtain full replacement value insurance if you can afford it and be sure you're not underinsured. If your insurance is for less than the actual value, the insurance company may only pay a fraction of the loss. You won't automatically get the full amount you thought you'd insured. Talk to a trusted insurance agent to be sure you're covered adequately.

Though I was sorry to lose the greenhouse, my greatest sorrow was the loss of some very special plants.  Not because they were so rare, but because I'd invested so much time in them.  I lost a 15 year old bonsai sycamore tree I had started from a seed that had just begun to develop a fine shape and the trunk coloration of a mature tree.   I also lost a long sought miracle fruit plant and several special orchids among others.  A Golden Muscat grape was blooming for the first time on the day of the fire. Even today I still regret their loss. It surprises me that although they were just plants, my feelings of loss were almost as great as if I had lost family members.


After some initial delays (another story) by the insurance company's adjuster, I was able to begin rebuilding in June.  The one bright side to the whole situation was that the insurance was for total replacement value. That meant I could rebuild it with all new materials and with some addition of my own funds, I could make it better than ever.

In the interim I had done a bit of research on better glazing materials and an improved heating system.  I decided to use 8 MM double skin polycarbonate plastic glazing instead of glass for the roof and south side. There were several reasons for this. Economically, although glass was cheaper, several factors worked against it. It is much heavier and the wooden structure needs to be stronger to support it. Glass is also much less heat efficient, and needs to be double or triple pane filled with inert gas to approach the heat loss efficiency of the polycarbonate. Finally the polycarbonate has a ten year guarantee against breakage. I expect it will last longer here in the cloudy eastern Great Lakes region because it will receive low levels of ultraviolet radiation. On the internet I found a fine supplier of greenhouse supplies in Berkeley, California. Bob Daley of Sundance Supply (now located in Olga, Washington) was able to provide me with the materials I needed and answered any questions I had. If you call him and order from him, be sure to tell him I sent you.

I hired my friend the contractor, took a few days off work and helped him get the shed built in just a few days. One more day spent on framing the greenhouse and I was on my own. The polycarbonate was delivered, two days later than the trucking company promised, but the order was complete and undamaged. My father and I installed that in one morning. I now had the greenhouse fully enclosed.

Because in the old greenhouse I had always begrudged the loss of 16 square feet of floor space to the gas space heater, I considered alternative methods of heating. Besides the loss of space, the old system had also been drafty and produced uneven heat; sometimes one side of the greenhouse was as much as 10 or 15 degrees F colder than the side close to the heater. I chose to use hot water baseboard heat to help this problem. For the hot water source I installed a domestic gas fired hot water tank in the basement beneath the shed. I calculated the BTUs necessary to keep the greenhouse warm and chose a tank rated about 50% above the value I expected to need. I installed the baseboard units around the outside walls and next to the tank placed a circulating pump with a manual bypass valve for emergency use. The pump provides forced circulation of the hot water, but if the ppower fails, the bypass can be opened and the water will still flow convectively through the piping, though at a slower rate. A simple thermostat controlled the pump when heat was required.

The finish work involved painting inside and installing benches. Everything was finished in time to move tender plants inside before the cold weather arrived.

Since then I have made some improvements. The biggest one is a computer operated climate control system I designed and built myself. I used the Experimenter kit from Fascinating Electronics as the data collector and controller. In addition to controlling the heat it also monitors the outside weather and will eventually be used to control humidity and water many of the plants.

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Greenhouse Control