Perimeter and Floor Insulation

Figure 6: Perimeter insulation.  Photo courtesy A.J. Both, New Jersey Agricultural Experiment Station, Rutgers University

Figure 6: Perimeter insulation. Photo courtesy A.J. Both, New Jersey Agricultural Experiment Station, Rutgers University

It is recommended that two inches of closed-cell foam insulation be buried at least 24 inches into the ground around the entire perimeter of a greenhouse to reduce heat loss through the soil (Figure 6). This is especially important if you will be growing plants on the floor or using in-floor hydronic (hot water) heating. It is usually not cost-effective to add perimeter insulation to an existing greenhouse due to the cost of installation, i.e. the labor to dig the trench.

Insulation should be considered if installing a heated floor system or growing plants on the ground. In northern climates two inches of rigid closed-cell foam insulation should be used with heated floor systems, otherwise one inch foam board can be used. For a large greenhouse, laying insulation horizontally under the floor abutting the sill plate or footing around the perimeter for a distance of four to eight feet will reduce the heat loss through the floor. This is a less expensive way to reduce perimeter heat loss on an existing greenhouse than digging to install vertical sheet along the sill plate.