Designing Mushroom Growing Rooms
Key Parameters

Mushroom growing houses range from simple greenhouses to specially constructed buildings. The book Growing Gourmet & Medicinal Mushrooms features several different types of growrooms. In most cases, functional growing rooms share some common features. They are:

• resistance to high humidity
• minimal use of wood
• sloping floors, for improved drainage

In terms of equipment, each growing room is equipped with:

• fans for input of fresh air and exhaust of CO₂-rich air
• coarse and/or electrostatic air filters
• humidification of air prior to introduction to growing room
• humidification of air post entry into growing room
• heating and/or cooling system
• insect monitoring and trapping systems

Depending upon the species being grown, the containers holding the mycelium include trays (preferably not wood, or with a non-biodegradable insert); racks for holding bottles or bags filled with substrate; and columns for vertical harvests.

The interior walls must be made of a non-biodegradable material such as metal, plastic (polyethylene), fiberglass (fiber reinforced plastic or FRP), or coated cement panels. External walls are customized to the climate and building codes for agricultural buildings. (Note: Growing rooms ultimately are spore rich environments and should be physically separated from the spawn laboratory. Do not locate your growing room in a common building complex!)

Growrooms are typically filled 1/4 to 1/8 of their volume with substrate, and depending upon incubation and fruiting temperatures, the free air exchange is minimally 4 times per hour to a maximum of 12 per hour. To calculate net exchange, simply calculate the volume of free air and divide a prospective fan's net cubic feet per minute (CFM) downstream air volume. For instance, a 20,000 cubic foot room (40' wide x 50' long x 10' high) would require a fan(s) emitting 2000 cubic feet per minute. This means that 20,000 cubic feet / 2000 cubic feet per minute = 10 minutes for a full air exchange, or 6 air exchanges per hour, not accounting for the fraction of space filled by the substrate. Such a room as described may better benefit from two 1000 CFM fans than one because the width is nearly the same as the length. Generally, grow rooms are rectangular with a 2:1 or more length to width ratio.

Many other parameters in designing a growroom are affected by the mushroom species being cultivated. As these parameters vary substantially please factor into your decision making process the particulars of the strains you wish to grow, the substrates utilized, the ambient weather conditions outdoors, and the particulars of your site location.