Roof Insulation Selection

Choosing the type of insulation that is best for your roof can be challenging, but it is only one of the factors the maintenance managers need to consider. The type of roof insulation selected should be in harmony with the building’s thermal requirements.

Various types of rigid insulations are available for application – a few are listed below.

  • Wood Fiber:  The insulation board is organic, made of wood, cane or vegetable fibers compiled with binders and fillers. It can be embedded with asphalt or asphalt coating to increase moisture resistance.
  • Perlite: This type of insulation board is inorganic, composed of expanded silica volcanic glass and combined with organic fibers and binders with an exterior asphalt coating.
  • Polyisocyanurate: It is a closed-cell foam plastic insulating core placed between organic or inorganic felt facers, glass fiber mat facers, or aluminum facers with glass fiber reinforcement.
  • Polystyrene: This insulation is made in two ways, expanded and extruded. The expanded polystyrene is made of polystyrene polymer embedded with a foaming agent that expands with heat, and is molded into uniform closed-cell insulation. The expanded polystyrene is available in densities of 0.70 to 3 lbs per cubic ft (pcf).The minimum density requirement for roof covering is 1.25 pcf.
  • Cellular Glass: It is comprised of crushed glass mixed with a foaming agent. The mixed components are placed in a mold and heated, which melts the glass and decomposes the foaming agent. Thus, causing the mixture to expand uniformly and create closed-cell insulation.
  • Gypsum: This insulation board is a non-structural, water resistant, non-combustible treated panel with a gypsum core. The board is available with a non-asphalt coating on one side to increase adhesion of the roof membrane. It is typically used as a cover board over foam-plastic insulations as a heat barrier over a steel deck, or as a substrate for vapor retardation.

But the work doesn’t end at choosing the right insulation for your roof; the insulation should be properly secured to the roof deck to provide desired substrate for covering the roof.

These are some of the commonly practiced fastening methods of roof insulation:

  • Mechanical fastening: The insulation boards are fitted with self–tapping screws and plates into the roofing deck.
  • Pros: This is the commonly used and approved method for attaching the insulation on steel and wooden roofs. This method of fastening is also appropriate with concrete and gypsum deck types.
  • Cons: This procedure requires pre drilled pilot holes and usage of special fasteners. Added labor for pre drilling, potential damage to the deck and the loud noises during the drilling, make this method of fastening less popular when fastening decks other than wood or steel.
  • Hot Asphalt: This is an acceptable method for fastening insulation to concrete decks.
  • Pros: It can be used over base sheets made of gypsum, cement wood fiber, and lightweight concrete on decks that workers can nail into.
  • Cons: The odor of asphalt is objectionable as it may be repulsive to some people. Transport of hot asphalt to the roof decks is not practical in some cases.
  • Low-rise polyurethane adhesives: These are approved fastening agents that service managers can use for fastening insulation to the roof decks.
  • Pros: Without the bad odor, the low-rise polyurethane adhesive provides a substitute to hot asphalt. The deliverance of the adhesive can be easily done to roof decks without much hassle.
  • Cons: A research study done by FM Global—a provider of property insurance, has rejected low-rise polyurethane adhesives for attachment of insulation to steel roof decks.

 

Be certain about your choice of insulation and the fastening methods that are being implemented. Also keep in mind the R–value of the insulating material, membrane compatibility, and energy-code requirements. All these factors will help you get the best out of your well insulated roof.

 

 

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