A passive solar home needs sun and an air-lock entrance.  A greenhouse design can combine both.

In 1986, when builder Rich Davis was designing a new home for himself and his wife Beth Zaring, he didn’t think of it as a passive solar design. He was planning to heat the new house with a wood furnace and just wanted less work at cutting and splitting logs. He researched energy efficient design and air tight home details. But, he also got some inspiration from Bruce Anderson’s Solar Home Book.

The 3,000 square home that he built is a marvel of efficiency and a model of what we can do to save energy in our own home designs. Rich and Beth burn just one or two cords of wood each year. That translates to about a quarter of the energy used by most homes of that same size and in a similar climate. Wouldn’t you like to save 75% on your heating bill? Sure, you’d be saving the planet too, but wouldn’t you like to save 75% on your heating bill? And, most of the details that keep the house warm in winter also cut cooling cost in summer.

Here’s how Rich did it. He created an efficient layout: a slightly off-square plan with the longer side facing south, and a stack of three floors. The lowest level is half into a hill, and the upper level is nestled under the roof. He insulated the concrete lower level walls with 4″ rigid foam on the outside surfaces. Exposed areas of foam were protected with a cement stucco finish. Another 1″ of foam insulation was placed below the floor slab. He built 12″ thick walls (two 2x4 walls with a 4″ air space between them) and used 2x12 roof rafters. He stuffed the walls and roof with insulation. Rich paid careful attention to caulking and making sure that the home’s envelope was air tight. He ducted fresh outside air to his wood furnace so that it wouldn’t draw cold air across living spaces from windows and doors.

The most interesting part of Beth and Rich’s home, and the only component that really supplies solar heat, is the room that they call the Greenhouse. It serves a variety of purposes. First, it’s an air-lock entrance. There are doors into it on the east and west ends that are the main entrances into the house. A big sliding glass door separates the greenhouse from a combination living/dining room. In cold weather, people enter through the greenhouse, but cold gusts of air don’t. Second, it’s a mud room. The masonry floor stands up to the mud from Beth’s garden and goat farm in the summer and snow on boots and skis in the winter. Third, it really is a greenhouse. Beth and Rich start their seedlings there each spring.

Last, and most importantly, it’s a solarium. It’s actually a comfortable sitting room, with no extra heat but the sun’s, on most winter days. The south facing windows warm the space up enough on most days to send heat into the main house.

As you can see in the photo above, Rich built a deep roof overhang to shelter the Greenhouse’s windows. That blocks the rays of the sun when it’s high in the summer sky. That detail, and Venetian blinds, keep the space shady and cooler in summer and early autumn.

So, a series of fairly simple and low-tech details and a functional, multi-purpose sunroom combined for great results. This isn’t a theoretical design. It works. Beth and Rich have been enjoying the benefits for over twenty years. A similar greenhouse/entry/mud room could be added to the south side of many homes, at a fairly reasonable cost. It’s something to think about.

Don Berg, Todays Plans