GREENHOUSE CONSTRUCTION

In the planning stages of building our house here we had always thought we would eventually build a greenhouse. At our former location in Wellington we had a small, non-heated greenhouse, which provided us with cold-tolerant things like spinach, kale, chard, lettuce and beet greens throughout most of the winter. It also provided a place to finish and harden the seedlings I had started under lights indoors. It was attached to the south side of our house, under our deck, so the north side of the greenhouse was protected by the house. (See photos of this one below.) It was a great addition to the garden there, so we planned to do it again.

We mulled over whether to attach it to the house or build a free-standing greenhouse. Here are some of the pros & cons:

Attached to the house:

Water and electricity readily available
North side protected by house
Easily accessible in winter

Free-Standing:

More available space for a larger greenhouse
More available light for the plants
Would be farther from the house; less accessible
Water and electricity would be more of a challenge
Would require insulation, particularly on the north wall

We chose to attach the greenhouse to the house, under our deck on the south faces. (I say “face-s” because with a 14-sided house, we used two of the sections.) We also decided we would like some sort of heat source, to allow for more growing throughout the winter. While thinking through the options, Tim decided we could have radiant heat in the floor, with a solar collector to provide that heat as well as enough capacity to provide hot water for the house.

The greenhouse is now complete! It is full of beautiful, growing vegetables. Tim is now working to complete the solar collector and the system for heating. The solar collector is standing to the left of the greenhouse in the photo above. Inside the crawlspace, at the back of the greenhouse, is the mechanical room, which houses the water collection tank and controls. Tim is in the process of writing a detailed document of how the greenhouse was built, which will be included when complete.

Pond holds 200 gals water for thermal storage

Since the greenhouse is attached to the house, water and electricity are readily available. The glazing is 5-wall polycarbonate, about 5/8″ thick. It includes approximately 100 square feet of raised bed space 28″ deep, radiant in-floor heating, concrete floor to maintain thermal mass, a pond filled with about 200 gallons of water for thermal mass. Eventually we may remove the lid and put fish and/or water plants in the pond, perhaps a waterfall, but that’s a “someday” project. There is also a lighted grow-bench area for starting seedlings.

Venting is provided by two large ceiling vents equipped with automatic openers, in addition to the door which may remain open as needed. We have installed an oscillating wall fan to help with airflow.

For our first winter, Tim devised a way to put down insulation over the glazing at night to keep the cold out and the warmth inside. After the time-consuming efforts of installing them nightly and removing them each morning, we decided it was not worth the effort. We still put up the insulation on the sides (see

photo) and leave them there day and night throughout the winter. It doesn’t restrict the light all that much during the day, and provides some extra warmth, particularly when it is windy.

Tim has created a detailed document describing all the “nuts and bolts” of how the greenhouse was made and why we did what we did. It does need to be updated with a few recent changes but can be viewed HERE.

UPDATE NOVEMBER 2019

Since our first successful winters with the greenhouse, we have since made some improvements to the heating system. The concrete floor, the soil and the pond (which holds about 200 gallons of water) all provide thermal mass storage. When the greenhouse was planned and built, we installed radiant in-floor heating, to be heated with water from our solar collector. Over time, we determined that this was not necessary. The concrete floor and the soil beds stay plenty warm without the in-floor heat, but what needs more warmth overnight and on the coldest days is the air. This past year Tim purchased and installed a used wall heater which uses the hot water from our solar collector as its heat source. This has worked quite well to keep the greenhouse warm overnight most nights, and we have an electric space heater to add additional warmth on the coldest of nights, when it has been too cloudy to heat enough water with the sun. Tim has these all set on with thermostat sensors and computer programs that turn everything on and off as needed. Good to have a geeky guy around! We also no longer put up the insulation over the glazing each night, which was labor-intensive and not all that helpful.