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SHOP TALK   Choose Your Glazing Carefully for Optimum Light and Energy Conservation - BY MIKE FOLEY Mike Foley VP Of Construction      Let’s look at some common glazing material for R-Value and Light Transmission. (See chart below.)    The higher the R-Valve (resistance to heat flow) the better the heat savings.    First determine the light level requirements for the crop to be grown. Let’s take a two bay gutter connected greenhouse and see the savings we would realize with different glazing materials on roofs, sidewalls, and gable ends. If we covered the entire greenhouse with a single layer (glass, Dynaglas, poly, etc) and then compared it to a double layer (inflated double poly, twin wall polycarbonate, 16mm acrylic) you could expect a minimum of 30% to a maximum of 50% lower heating cost.    If we glazed the greenhouse completely with triwall material we could reduce your heating cost by an additional 14% over the twin-wall material. Possibly a combination of glazing materials would best suite your crop requirements, for example Dynaglas on the roof gives high light transmission and tri wall poly polycarbonate on the sides and ends gives high R-value. Keep in mind the light requirements of your crop. Your #1 business is the greenhouse crop. While you should keep energy needs as a priority, they should not be the final determining factor in glazing materials.    A shade/heat retention blanket can also save you heating dollars. Depending on the material used, savings could range from 20% to 38% on heating costs.   R-VALUE LIGHT TRANSMISSION (% of available) Class Single layer (Double Strength) .88 88% Polyethylene Single Layer .83 85% Polyethylene Double Layer Inflated 1.43 73% Single Sheet Polycarbonate Dyna Glas Plus (Clear) .83 85% 8mm Twin Wall Polycarbonate (Clear) 1.72 80% 8mm Tri Wall Polycarbonate (Clear) 1.99 76% 16mm High Impact Twin Wall Acrylic (Clear) 1.82 86%