Metal Roof Insulation – Making Energy Efficient Homes
Metal roofs are prone to condensation and thermal loss and so metal roof insulation is a must to prevent too much energy loss from the roofs. Metals are great conductors of heat and when the temperature gradient between the outside environment and the home interiors is high the transfer of heat takes place. Similarly, if the temperature drops suddenly the metal cools down fast and the water vapor that comes in contact with the cool metal condenses. When insulation is added to the metal roof it controls or overcomes this problem and helps keep the home insulated.
Fiberglass batts were the most commonly used insulation till a few years ago. The metal roof and the interiors are separated by a layer of fiberglass insulation. These batts which come in rolls are placed side by side under the metal roof. This does not form a continuous layer and the gaps between the batts allow for the air to escape between them causing the heat transfer to take place. The batts themselves are not airtight and allow a small amount of air flow through which is again another source of thermal loss from the building. The batts need a vapor barrier in order to effective. Batts need to be placed around 150 mm below the metal sheets. This prevents the condensation formed under the metal roof from entering the fiberglass batts and ruining them. Water is good conductor of heat and if it gets into the batts then you can forget about any insulation function that the batts perform. The gap between the batts and the roof allows the airflow which prevents condensation. The batts are not the best solution for metal roof insulation as they are not able to address either the problem of condensation or thermal loss completely. Also, their very nature adds to the cost of roofing construction.
Polyurethane Spray Foam
A more effective solution to the problem of thermal loss and condensation in metal roofs are addressed by spraying a thick layer of polyurethane spray under the metal roofing. This solves both the problems of water condensation and thermal loss from the roof in one stroke and keeps the building warm in winters cool in summer. There are no gaps or crevices through which heat/cold escapes from the building. The foam can be sprayed into all the nooks and crevices and completely seal off all gaps. It is directly applied to the roofing metal. Even a minimum layer of about an inch will eliminate the problem of condensation from occurring. It is simple to apply the foam to either the underside or on the upper side the metal roof. A suitably thick layer does not get damaged even if there is foot traffic over it. Applying the spray foam can be done on new roofing or older roofs. The thickness of the foam applied will determine the U value of it. For the same amount of thickness polyurethane spray foam offers better insulation capacity than fiberglass batts.