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Should I Attach a Greenhouse to my Home?

Author Marc Plinke

Author Lindsey Schiller

This excerpt is from the best-selling bookThe Year Round Solar Greenhouse: How to Design and Build a Net-Zero Energy Greenhouse by Lindsey Schiller with Marc Plinke.  

Lindsay and Marc founded Ceres Greenhouse Solutions to research, design and build energy-efficient year-round greenhouses.

 

Excerpt from the book The Year Round Solar Greenhouse

Attached greenhouses are dual-purpose structures. Not only are they a lush year-round garden, but the greenhouse also serves as a vital heat source for the home. Greenhouses are such large solar collectors, they have the ability to dramatically reduce a home’s winter heating bill — 30%–50% in many cases. Even if supplemental heating is not the primary purpose of the greenhouse, attached greenhouses have several benefits over freestanding ones. But, they create some unique challenges as well.

Amory Lovins’s “banana farm” is not your typical home. The structure is beyond-net-zero energy (i.e., produces more energy than it consumes), heated mostly by a greenhouse; and grows banana trees high in the Rocky Mountains. The chief scientist and co-founder of the Rocky Mountain Institute renovated the 3,000 sq. ft. home to accomplish this. The original walls were made out of 12"-thick stone. Along with many other materials, they contribute to the large thermal mass of the building. There is so much mass (and insulation) that Lovins predicts if there were a solar apocalypse, cutting off all heat and energy to the home, it would only cool down 1 degree per day. Credit: Tila Zimmerman

Integrating the Greenhouse and the Home
Pros and Cons

If done properly, the typical attached greenhouse presents many benefits for both the home and greenhouse:

Free heat

A greenhouse is a large solar collector, a source of free home heat during cold winter days. The home, in turn, absorbs excess heat during the day. Combined, the two environments work synergistically, requiring less heating and cooling as one.

Supplemental CO2

The home provides a source of CO2 and air circulation for the greenhouse. Plants naturally filter the air and add oxygen to the home.

Controlled humidity

In the winter, the greenhouse adds humidity to the home’s drier air. Air from the home lowers the relative humidity in the greenhouse.

Added home value

A site next to the home takes up minimal yard space. The greenhouse can blend aesthetically with the home, adding significantly to a property’s value.

On the other hand, attached greenhouses come with some particular challenges:

Permit costs

Most people will tell you an attached greenhouse is cheaper to build than a freestanding one. That is true only if a building permit isn’t required. In many places, local building codes consider an attached greenhouse an addition, like an extra bedroom, and mandate the same foundation type as the house (usually a concrete wall and footer) to prevent the greenhouse from shifting and damaging the home. Normally, the project requires stamped engineered construction documents, and a more robust foundation. These can easily add a few thousand dollars to the cost of the project. Even if a permit is not required, attached structures require more careful building, which often means more expense, not less.

Excess heat and humidity

A hot, humid environment adjacent to the home is beneficial for much of the year. At other times, heat and humidity are unwanted and create a climate burden for the home. Excess humidity is probably the number one problem with attached greenhouses: it can damage books, furniture and electronics, or allow mold to grow in the shared wall. For that reason, much of this chapter focuses on controlling air exchange between the two environments so the greenhouse does not over-humidify the home.

Underground Attached Greenhouse

Pest risk

If pests, like aphids, get established in the greenhouse, there is the risk that they will spread into the home. Most pests stay where their food source is (the greenhouse), but it is possible for them to expand into the home. Here too, controlled air exchange helps keep pests out of the home. Partitions also help.

Takeaways

Attached greenhouses present many benefits, such as home heat gain and climate control for the greenhouse.

Airflow between the home and greenhouse should be controlled to prevent the greenhouse from overheating or over-humidifying the home. Sidings and adjacent surfaces should be well-protected to avoid damage from moisture.

Controlling air flow depends on where the greenhouse is sited. Thermostatically operated fans offer the greatest level of climate control for the greenhouse and home.

Attached Greenhouse. CREDIT: Ceres Greenhouse Solutions

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