and a view during construction of the inside.
Later changes added a sunken cold frame across the front, an 8' x 12' back section and finally an 8' x 28' greenhouse made almost entirely of used window glass which dovetails into the back of the original structure.
Almost all the glazing of the walls can open for ventilation and the entire back side of the roof has casement windows which fold open to allow heat when unwanted to escape.
This photo shows the paired greenhouses puffing away in the cold depth of winter.
Since then I actually raised the glass house another foot higher. The heating costs for the 600 sq.ft. reached a maximum in the year pictured of about $600 for the heating season. In this last year's milder winter heating costs were only $200. Bear in mind that the greenhouse is only heated to keep the inside temperature above freezing and most winter nights reach below 40 degrees by morning. This is quite a bit lower than anyone recommends, but the plants inside thrive and vegetable production is substantial.
On the coldest nights I have had to burn propane from a small tank. The greenhouse is NOT especially airtight though I seal it as best I can with foam, mud, or caulk. On sunny winter days I always end up opening a vent in the roof. After a 45 year career with greenhouses in horticulture I can categorically state that the ability to ventilate a greenhouse is more important than an airtight construction to keep heat. (P.S. heat escapes anyway because greenhouses by definition are not insulated structures.)
The greenhouses use NO electricity for ventilation, so there is zero expense for cooling. Other greenhouses I have know of this size require a 1/4 hp electric motor operating a 24" fan all day long on warm days or else heavy shading. Many greenhouses in this part of the country are not used at all in the summer because of the expense of ventilating. My structure is only a degree or two hotter than ambient on the hottest summer day and the western shading means I can use the structure all year with no shade cloth and no fan. Its just a really good design. Even in winter ventilation is required to grow good plants. The casement windows on the west side of the glass house roof are hinged. Here's a view through an open roof window down into the greenhouse:
When heat builds in May I remove the front panels and open the glass windows.
Spring production from greenhouse and cold frames amounted to roughly 80 flats of bedding, about 4500 plants and roughly 200 one gallon overwintered perennials and bulbs. In addition a large permanent collection of succulants, four large citrus trees and a substantial crop of winter vegetables and herbs were produced. Here are a few pictures of those crops:
compost
Plants Alive
