Rigid Board Insulation

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Rigid board insulation


Rigid insulation is prepared from either fibrous materials or plastic foams. It is generally designed in the shape of boards and molded pipe casings. This type of insulation tends to provide full thermal protection resulting in minimal heat loss only. Hence, it offers higher R-value in places having insufficient space. A reflective foil facing can be applied on these boards which will minimize the transfer of heat flow as soon as they are installed subsequent to an air space. Rigid foam board insulations are available in diverse thicknesses ranging from1 inch to 2.5 inches. They provide excellent thermal resistance which approximately varies between R-4 to R-8 per inch. The thermal resistance of rigid board insulation will vary depending upon the thermal resistance of different insulation materials. This type of insulation is found to be little more expensive as compared to other insulation types.

Insulation Materials

Materials which are commonly employed for rigid foam board insulation are listed below:

  1. Polystyrene,
  2. Polyisocyanurate or Polyiso
  3. Polyurethane
  4. Fiberglass

Fiber duct board insulations are constructed by making use of resin-bonded, inorganic glass fibers. To safeguard these duct boards from various environmental hazards, reinforced aluminum air barrier and water vapor retarder are usually incorporated on the outer surface of boards.


Fiber board insulation is generally installed in air ducts via an HVAC contractor. HVAC contractors can carry out production of fiber board insulation either at their workplace or at the installation site. “On exterior duct surfaces, they can install the insulation by impaling it on weld pins and securing with speed clips or washers. They can also use special weld pins with integral-cupped head washers. Unfaced boards can then be finished with reinforced insulating cement, canvas, or weatherproof mastic. Faced boards can be installed in the same way.”[1] It is always recommended to hire a professionally skilled installer to execute the rigid foam board installation procedure. In cases where the installation is done by a non professional, the manufacturer's instructions must be followed carefully. One must also be aware of the local building fire codes. Following points must be strictly kept in mind while installing rigid board insulation:

  • The ultraviolet radiations emitted from sun can prove very dangerous to rigid board insulation installations. Hence, they must be properly guarded against direct sun rays. The coating of different materials like tar, rubberized paint, plastic or rubber membrane etc. can be applied on insulations.
  • Moisture is another major hazard which can affect the efficiency of these insulations. Therefore, it becomes necessary to employ vapor diffusion retarder for dealing with moisture related problems.
  • Attack of insects can also affect the performance of insulation installations, since their presence beneath the foam boards results in lower thermal resistance of the installation. Hence, an insect infestation test must be carried out prior to the insulation installation.
  • If accidentally, insulation catches fire then it becomes very difficult to control it. Also rapid fire spread causes emission of extremely noxious gases. To prevent this, a thick layer of fire protection material for example, a gypsum wallboard must be applied upon the insulation.


Following are the main benefits offered by rigid foam board insulation:

  • It provides best insulation solutions for areas facing space constraints.
  • As compared to other insulation types having same thickness, it offers high thermal resistance i.e. R-value. Hence, it is considered ideal for improving building insulation conditions.
  • The installation procedure of rigid board insulation is very simple, since no time is wasted in mounting the foam board via staples. The installer can just make use of glue or nails to finish the installation.
  • It can be applied in nearly every part of our homes ranging from roof top to the foundation of the building.
  • In addition to thermal insulation, it also makes the structural elements of the building stronger.


Major application areas of rigid board insulation include:

  • It can be employed in several places in a building like curtain walls, roofs or ceilings etc.
  • It can shield and insulate building foundations as well.
  • It provides thermal protection for entrance and overhead garage doors.
  • It can provide insulating layer for pipes and tanks.
  • It can be applied between studs on internal and concrete walls too.
  • It is also considered valuable for reproofing work on level roofs and basement walls in a building.
  • It can be implemented as external perimeter insulation at concrete slab edges and in cathedral ceilings.
  • Air ducts in homes can be also insulated by this method.
  • Besides, this type of insulation is frequently employed in areas requiring high temperature tolerance.

“For interior applications it must be covered with 1/2-inch gypsum board or other building-code approved material for fire safety. For exterior applications it must be covered with weather-proof facing. Check the applicable codes to determine local requirements for covering rigid board insulation to achieve fire resistance.”[2]

See Also

Reflective Insulation

Foam Insulation

Blanket Insulation

Loose Fill Insulation