Insulation - Know How
With rising energy costs, a good return on investment may be obtained by adding insulation to heated buildings, such as the headhouse, office, work area or the boiler room. Insulation can provide benefits in both winter and summer; in winter by keeping the expensive heat in and in summer by keeping the heat out.
Insulation is basically trapped air and air is a good insulating material. Air entrapped in the small bubbles of foam or the small spaces in fiberglass retards heat flow. The small bubbles in a sheet of foam or in the small spaces in a batt of fiberglass entrap dead air. The thin film of air surrounding these spaces also retards the heat flow. Together a thermal resistance (R-value) is established. Technically it is measured in ºF – square foot – hour/Btu. The greater the R-value, the greater the insulation effect.
Insulation has different R-values depending on the material and thickness. When you purchase insulation at a home center or lumber yard it will have an R-value printed on the package. For example, the R-values of common types of insulation and other construction materials on a per inch basis are:
Fiberglass - 4.0
Expanded polystyrene with smooth surface – 5.0
Polystyrene beadboard – 3.6
Expanded polyurethane – 6.2
Poured concrete – 0.2
Plywood – 2.8
Sheet metal wall – 0.78
How much insulation do you need?
The amount of insulation that should be installed depends on several factors including:
- The climate where the structure is located. For example, the heat loss from a headhouse in St Paul MN will be nearly twice as much as in Cincinnati OH or Albuquerque NM .
- The design temperature used. A headhouse heated to 70ºF will require 40% more heat than if it is heated to only 50ºF.
- The amount of ventilation needed for moisture removal. This make-up outside air has to be heated during the winter. The heat from equipment and employees in the building can be conserved and used for heating the ventilation air if more insulation is installed.
- The cost of fuel to heat the building or the cost of electricity to run fans or air conditioning. With increasing fuel costs, this is the major reason to install more insulation.
- The local building code. The R-value for floors, walls and ceilings in some buildings is specified in the code to meet national energy conservation goals.
Choosing an insulation material
Most insulation materials reduce heat flow caused by conduction or convection. Those that have an aluminum surface may also resist radiant losses if the shiny surface faces inside and has an air space in front of it.
There are many choices in insulation and most insulation is available in several forms. When selecting insulation, consideration should be given to the following:
- R-value – Select a material with the highest R-value. When new construction is planned, build with 6" thick walls rather than 4" as more insulation can be used.
- Ease of installation – Blanket or batt type insulation is easy to install in walls during new construction but placing rigid board material on the surface or fill-type material blown in through holes may be the only type that can be conveniently installed to insulate an existing wall. Fiberglass or rock wool is commonly blown into attic space as it can be applied at 12" thickness or more.
- Fire resistance – Materials that create toxic gases or contribute to flame spread should not be used unless covered with a non-flammable material. There have been a number of fires in buildings that had unprotected, sprayed-on urethane foam insulation.
- Vapor barrier – moisture is a good conductor of heat. Moisture from inside the building that migrates into the insulation reduces the R-value and can contribute to deterioration of the wall. Either a vapor barrier as part of the insulation or a separate 6 mil polyethylene sheet should be installed on the heated side of the ceiling and walls. Fiberglass even with a vapor barrier is not a good choice for a connecting wall between an attached greenhouse and a headhouse as the moisture in the greenhouse is driven into the insulation by the high temperatures developed. Also polystyrene beadboard is permeable to moisture and should not be used where a vapor barrier is needed.
- Cost – a comparison based on total cost/unit R-value may be the best way to compare materials. Cost includes materials, labor and equipment if needed. For example, 12" of blown-in insulation with an R26 will have the approximate cost of 29¢ for the material, 23¢ for labor and 17¢ for the equipment to put it in place for a total of 69¢/sq ft. Nine inches of kraft faced fiberglass batt insulation with an R30 will cost about 55¢ for materials and 13¢ for labor for a total of 68¢/sq ft. Based on R-value the batt material is a better buy costing about 14% less. The above figures were adapted from Means – Light Construction Cost Data.
Although insulation can reduce heating cost considerably, windows with an R-value of 0.9 for single glazing and 1.4 for double glazing can have a significant impact. Infiltration of cold air around doors, windows and other openings also increases heat loss. Research on one group of homes found that infiltration caused 45% of the total heat loss in the average home.
Payback for investment to bring ceiling/wall insulation values up to a minimum of R40/R20 in northern states and R30/R20 in southern states is usually less than 3 years. As fuel prices increase, this payback will be shortened.John W. Bartok, Jr., Extension Professor Emeritus
University of Connecticut , Storrs CT 06269-4087
Natural Resources Mgt. & Engr. Dept.
University of Connecticut , Storrs CT