Bubble Greenhouse Q&A

Q: Why would I build a bubble greenhouse?

You don't have to pay the high heating costs associated with a 'regular' greenhouse during harsh winters. By using a natural and renewable energy source (the Sun) the greenhouse is very environmentally friendly. For more information, download the brochure here.

Q: How much do the plans cost?

A: The plans are $250.00 for the digital PDF version, $350.00 for 11x17 mailed plans + e-mailed PDFs, and $500.00 for 11x17 mailed plans + PDF with one hour of technical support. Additional tech support can be purchased for $300/hr.

Q: How do I get the plans?

A: Go to the buy plans now page, and click the Buy now button at the bottom of the page. This button will take you to an acceptance-required terms and conditions page, then to a PayPal page where you can enter your payment information (credit cards accepted as well as PayPal). After your payment transaction is complete, plans will be mailed to you within two weeks or emailed to you within four business days.

Q: Are these plans copyrighted?

A: The concept of the bubble greenhouse is not patentable by anyone - we've taken steps to ensure that the idea is legally in the public domain (published and presented at IFOAM in 2002, among other things).

The idea was originally patented in Sweden by an inventor by the name of Zelon in the 70s as a means to insulate large shop windows, and further developed by Richard Nelson in Montreal as a "solaroof" in the 80s; all patents have expired, and new patents have been successfully blocked by the intentional public domain status of our work.

Our greenhouse is the first fully-operational and successful application to a hoophouse design. The plans and the patented bubble solution are the result of hundreds of unpaid hours on our part, along with somewhere over $30,000 in personal expediture (no funding of any kind has ever been received for our work), thus the plans and formulation are not public domain and are copyright © Homesol Building Solutions.

Q: How does the "bubble" part of bubble greenhouse work?

A: A cavity is created by creating two concentric greenhouses, one on top of the other. This cavity is separated into two parts by a plastic barrier along the top of the greenhouse. Filling the south side of the greenhouse with bubbles in the summer will cool the greenhouse, and filing the north side in the winter will warm the greenhouse. The bubbles act as reflective devices to either focus solar energy into the greenhouse or away. See concept images below by Richard Nelson (which, by the way, are the ONLY plans we had when we built our greenhouse on September 11, 2001), or in the Bubble greenhouse image gallery.

Q: What is the total cost of building a bubble greenhouse?

A: Here's a rough cost breakdown:

Assuming 30' x 40' structure:

• 2 frames and 2 poly glazing $5,000 (we recommend anti-condensate coatings on both layers and IR (infrared) coating on the inner layer, for better light transmittance and heat retention)
  (Triple polycarbonate hard outer shell add $5,000)
• 2 commercial foam generators $6,000
• Pump, tanks, controls $2,000
• Wiring, plumbing, site prep $3,000
• End walls $2,000
  (End rooms with radiant slabs $10,000)
• Skilled construction supervision $5,000
• You may also have to pay for building permits, backup heating, or other costs
• Home-made generators are possible but not recommended

Expect to pay approximately $20,000 to $40,000 for a 30' by 40' greenhouse.

Q: How much do the bubbles insulate the greenhhouse?

A: The bubbles have approximately R30 insulation value for a 30" wide cavity (R1 per inch)

Q: Where can I get the bubble solution?

A: Our patent-pending bubble solution is available for purchase on the buy plans now page. Five gallons of the soap solution concentrate can be purchased for $250 plus shipping. When diluted, the five gallons of concentrate makes 600 gallons of solution. This will last "forever", except for any losses from small leaks or evaporation: even continuous poly has a small permeability that allows solution to slowly escape, so in our experience we find we need to top up the solution tanks once a month or so, and 5 gallons of concentrate will be more than sufficient for 2-3 years or so as long as you have no leaks.

Q: Will I need a backup heat source such as oil or electric heating?

A: Yes. Or maybe. Depending on what you're growing. Either use radiant floor heating or heat the half-circle greenhouse ends with an alternate a heat source (if the greenhouse is being used for starting seedlings in winter). It is necessary to have a heat backup, such as a wood stove, for the main greenhouse in the event of extreme temperatures or a power failure. Remember to ask us how to ensure your foam generators will never freeze even in the event of extreme cold and no backup heat.

Q: Will I need electricity to run my bubble greenhouse?

A: Yes. The thermostat and timer that control the greenhouse, as well as the bubble generator pump and ventilation need a source of electricity. You will also need electricity to pump water and other basic greenhouse needs. Consider putting solar panels on your greenhouse for additional electricity which may offset most of the electricity used, but being grid-tied is advantageous for starting up an electric pump motor, because it would take a lot of panels, battery storage and inverter capacity to hit it with enough juice to get the water pressure and flow needed at start-up. Despite the relatively high current draw of running a 3 HP / 240 volt pump motor, it only runs typically 30 minutes in total over a 24 hour period so is roughly equivalent to leaving an incandescent light bulb on all the time - equivalent to 25 cents of electricity per day to run the bubble generators. Compared to heating costs, the energy requirements of a bubble greenhouse are virtually nothing.

Q: How do the bubbles help store the sun's energy to moderate the greenhouse temperature overnight or in winter?

A: The bubbles act as insulation and shading, but also provide some measure of cooling and heating. The thermal envelope underneath the bubble greenhouse consists of soil and concrete, and a liquid mass from the rainwater collection tanks and the heat sink trench. This mass absorbs the sun's energy during the day in winter, warming the bubble solution. In the summer, the bubble solution is cooled by the ground temperature, so year-round the temperature of the bubbles being blown into the cavity surrounding the greenhouse is about 10C (50F). The bubbles absorb or release this heat energy to moderate the inner temperature.

Q: What size are the rainwater collection tanks?

A: Depends on what you need to hold a one inch rainfall event. We have 300 gallon rainwater tanks, which collect all the water that falls on the greenhouse via eavestroughs down both sides. However, unless the greenhouse is already over-watered, we usually let all the collected rainwater be delivered immediately via an overhead sprinkler system throughout the greenhouse - when it rains outside, it also rains inside!

Q: What kind of plastic covers the greenhouse?

A: The interior greenhouse frame uses regular 92% transmittance, UV stabilized greenhouse poly with an IR and anti-condensation coating on interior. The exterior frame is covered with triple glazed polycarbonate with a R2+ value and 73% light transmittance. Alternatively, you can use two layers of regular greenhouse poly instead of the triple glazed polycarbonate, which would be much cheaper and have increased light transmittance but is not recommended in high snow load areas, based on our own experiences with double greenhouse poly. It is much more challenging, however, to achieve the required air and watertightness with triple polycarbonate panels, "don't try this at home" without supervision!

Q: Are the half-circle ends mandatory?

A: The half-circle ends are used as mechanical-room/potting shed/processing area. They create a thermal buffer zone between the interior greenhouse temperature and the outside. While not necessary, they do help moderate the temperature of the greenhouse during cold periods. Ventilation fans at either end of the greenhouse moderate temperatures between these three zones as needed, which also have radiant floors heated with a high efficiency wood gasification boiler. This allows us precise temperature control as needed for seedlings, while letting the growing beds experience wider temperature swings.

Q: How is the greenhouse controlled?

A: The greenhouse temperature is monitered using a thermostat and a timer.

In the summer, if the daytime temperature rises above 20 degrees Celcius, the bubble pumps are activated and active shading is provided. The pumps operate for up to three minutes each cycle, to a maximum of three to four times per hour.

In the winter, if the temperature drops below 10 degrees Celcius, the bubble pumps, and then supplemental heating systems, are activated. The pumps operate for up to three minutes each cycle to a maximum of two to three times per hour. Supplemental heating is seldom needed to stay above freezing once the bubbles are in place, regardless of how cold it gets outside.

The bubbles break down faster in the heat of summer than in the cold of winter.

Q: Can I visit your greenhouse?

A: We hold a free annual public open house in mid-November, simply ask us to add your name to our mailing list, visits at all other times are strictly by appointment only (we've had more than our share of people showing up uninvited and monopolizing our entire day!), please purchase the plans and appropriate amount of consulting time before scheduling your visit. Go to the Contact Homesol page for further info.