Solar Greenhouse – Detached or Attached?

by nan on 2010/03/23 · 11 comments

(This is the sixth in a 10-part series. The previous post is here, or you can start at the beginning.)

When I bought my house, it was an upside-down T, with the stem facing southwest. In last week’s post, I talked about installing sunny windows in the southeast and southwest walls for passive solar daytime heating. Now I was trying to decide how to further remodel for more solar gain.

I could have added a greenhouse on the southeast corner adjacent to the kitchen. This was very appealing as far as harvesting food and herbs. I’d also envisioned it as a sitting area, the breakfast nook, I suppose. But I enjoyed the new windows, and one was in my bedroom. I’d have missed that if it went into a greenhouse instead of to the moon, trees and coyotes.

The warmest winter sun hit the southwest corner, so I decided to add something there. I wasn’t sure what, but many pencils and eraser goobers later, I came up with this plan. A contractor friend of mine fleshed out the details for me.

This is the floor plan when I bought the house.

This is the design of the attached greenhouse on the southwest side and the rearrangement of the interior for better traffic flow and air circulation.

I was content enough with the heat produced through the new windows that I put these drawings away. I was also a working single mom of two young girls, and my time constraints prevented me from doing a lot of research into this project, never mind starting and completing it! I rolled up the drawings and propped them up on my desk.

Backtrack to 1997

I lived in an old block home on an irrigated acre of land in Ojo Caliente – almost the adobe dream home! I was more interested in the land than the house, and we cultivated half of it with beans, corn, tomatoes, squash, herbs and flowers that we sold to friends and co-workers.

Out near the garden, there was a small frame greenhouse with translucent polycarbonate walls. I checked the overnight temperature in early spring to see if I could start my seeds in it. It was too cold, since it was not heated or insulated. It was essentially a cold frame with an 8-foot ceiling and roof.

I started researching greenhouses and was disappointed to find all standard greenhouses need supplemental heat. This is usually generated with electric heaters for something as small as I was looking at. Aside from growing food to eat healthy, cost needs to be taken into consideration. Heating a non-insulated building of plastic walls with electricity was not cost-effective.

I came across the Growing Dome® Greenhouse in a gardening magazine. It is still available, and I see them popping up across the landscape as food and energy costs rise. This is a passive solar, geodesic design with glazing on the south side and insulated solid walls on the north side. Planting beds and the concrete slab floor are the thermal mass, along with a pond. Do you remember the 55-gallon drums in the solar pods? Poisson knew water is one of the best materials for thermal mass. It must be sized properly so it can radiate heat effectively. The pond can hold fish or water plants, or boards can be placed across it to make more room for container plants.

The combination of masses in this greenhouse meant no supplemental heat. It was an environment that took care of itself – an ecosystem of sorts. I was sold on it immediately!

For a variety of reasons, though, I didn’t purchase one at the time, but this is the only greenhouse I recommend to anyone. It needs no extra heat, and the larger ones double as a small living space as well.

Ten Years Later

It is spring 2007, and I want to start my vegetables from seed. I am toying with the idea of buying a 12′ diameter dome greenhouse and putting it about 100′ from the house down the hill on my property. This is a sweet, quiet, sunny spot with completely different views and feel than the house. A few cottonwoods along the irrigation ditch give the space a cozy feel and summer shade. A passive solar greenhouse here would be an excellent get-away.

As I walked the land, I began to picture it. I imagined bringing in electricity and water, and building a path of crusher fines between the greenhouse, the house and the garden. I considered views, sun, neighbors and the heat the greenhouse would produce. I wanted to somehow move the extra heat back up to the house in winter. I thought of underground ductwork, insulation, fans….. My little greenhouse project was getting complicated, the kind a contractor would balk at.

In a split second, like the cartoon cliche of a light bulb going off over your head, my face went from bewilderment to wonderment and glee! I decided to build an attached passive solar greenhouse for heat and food. Remember this book?