Commercial Roof Insulation

By Rick Brown • October 5th, 2011

Exploring the elective components of a commercial roofing system in Florida, we now take a look at types of insulation.

Roof insulation performs two basic functions:

  • Acts as a thermal barrier for the top of the building.
  • Serves as the base for the roof sytem.

Secodary functions include:

  • Enhancing drainage through the use of tapered insulation systems and stiffened roof decks.

Poly-isocyanurate

Far and away the most common roof inulation installed, ISO is available in flat or tapered panels and is the base for many roof systems with an average LTTR value of 5.56 per 1″ of product. Polyisocyanurate features a closed cell iso core integrally laminated to fiber reinforced felt factors. Iso has a perforated facer on one side for use with hot asphalt applied systems while the non-perforated side is for use with single-ply systems.

Pros

High R value of 5.5 per inch and good compressive strength. Excellent dimensional stability and very lightwwight.

Cons

Contains CFCs or HCFCs which may be released into the environment, causing ozone depletion. It is also expensive in comparason to other insulations. Contains a petroleum by-product increasingly in demand worldwide, resulting in availability problems and lengthy lead times for orders.

Perlite

Perlite insulation is an inorganic, rigid board insulation available in 2″ x 4″ or 4″ x 4″ panels. The panels are composed of expanded volcanic glass and wood fibers bonded with asphaltic binders. Until recently, perlite was the most common insulation used in roofing. Although still popular, its low R-value of 2.78 per inch and tendency to absorb moisture have diminished its frequency of use.

Pros

Perlite has an excellent fire protection resistance rating. It also has good compressive strength which allows normal roof foot traffic. It also has great dimentional stability and the ability to absorb outgassing common in foam and iso insulations. It is often used as a cover board in hot asphalt sytems.

Cons

Very friable and relatively easy to break panels. Complete deterioration when in contact with moisture. Low R value and poor tensile strength.

Expanded/Extruded Polystyrene

As the lead times required for isocyanurate insulation increases, EPS has risen as a low-cost alternative for roofing insulation. Both types are manufactured from polystyrene, one as a fused board made of beads while the second is formed from a molten sheet pressed into shape.

Pros
  • Dimensionally stable with lower water absorbtion.
  • Extremely lightweight, minimizing roof dead loads.
  • Easy to handle, cut, and form.
  • The extruded form is used widely as a base for achitectural shapes at wallsand parapets.
  • Decent R values between 4-5 depending on type.
  • Relatively inexpensive
Cons
  • Poor fire resistance
  • Low compressvie strength equates with poor wind load resistance
  • Releases potentially toxic combustion product if ignited

Dens-Deck

Dens-Deck is an ever increasingly popular roof insulating product in roof assemblies. It is the roofing version of an exterior board used most commonly as an exterior stucco backer board. This board is a mold resistant roof panel that consists of a moisture-resistant, non-combustible core of specially treated gypsum with glass mat facings.

Pros
  • Approved by all manufacturers.
  • Highest performance rating for fire, wind uplift, and moisture resistance.
Cons
  • Very heavy board increases handling costs and deck requirements.
  • Difficult to cut and form
  • Primed version must be used in hot applications to avoid blistering membrane.
  • Low R value

Wood Fiber

The final insulation we will examine is wood fiber. It is the oldest type designed for roofing. It is normally found in a “high density” form and is inexpensive and durable. It is also often used as a cover board over iso in hot applications to reduce outgrassing.

Pros
  • Durable, easy to handle, and relatively easy to cut and form.
  • Decent compressive strength provides reasonable wind uplift ratings.
Cons
  • Dimensionally unstable in contact with moisture.
  • Rapid deterioration when wet, also providing possible medium for mold growth.
  • Poor fire rating with low R value of 1.9 per inch.

Other types of roofing material used in commercial roofs across Florida are foam-glass, gypsum wallboard, and mineral board. Please call us if you have any questions or would like a further analysis of the insulation in your roof system.

Each project and roof assembly has its” own subtle differences that may lend itself to a particular size, type, or thickness of insulation. Additionally, the expense at insulation should be cost-factored in comparison to heating or cooling billd over the expected life of the assembly to determine the most effective insulation for a particular project. Your contractor, consultant, or manufacturer can all play vital roless in helping with the final decision based on R value needs, anticipated length of ownership, and local codes..

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