Insulation Types, Application Methods and Physical Characteristics Must Be Reviewed, Understood and Selected to Ensure Roof System Performance

Designing and constructing roof systems (see my previous articles about roof decks, substrate boards and vapor barriers) continues with the thermal insulation layer. The governing building codes will dictate the minimum R-value required and, based on the R-value of the selected insulation, the thickness of required insulation can be determined. This plays into the design of the roof edge, which will be the subject of future articles. For now, let’s focus on insulation.

Photo 1: Polyisocyanurate (ISO) with organic facers

Photo 1: Polyisocyanurate
(ISO) with organic facers

Thermal insulation has multiple purposes, including to:

    ▪▪ Provide an appropriate surface on which the roof cover can be placed.
    ▪▪ Assist in providing interior user comfort.
    ▪▪ Assist in uplift performance of the roof system.
    ▪▪ Provide support for rooftop activities.
    ▪▪ Keep the cool air in during the summer and out during the winter, resulting in energy savings.

INSULATION OPTIONS

For the designer, there are numerous insulation material choices, each with its own positive and negative characteristics. Today’s insulation options are:

    ▪▪ Polyisocyanurate (ISO)

  • »» Varying densities
  • »» Organic facers (see photos 1 and 2)
  • »» Double-coated fiberglass facers (see photo 3)
  • ▪▪ Expanded polystyrene (XPS) (see photo 4)

  • »» Varying densities
  • ▪▪ Extruded polystyrene (EPS) (see photo 5)

  • »» Varying densities
  • ▪▪ Mineral wool (see photo 6)

  • »» Varying densities
  • ▪▪ Perlite
    ▪▪ High-density wood fiber

With today’s codes, the use of perlite and high-density wood fiber as primary roof insulation is very limited. The R-value per inch and overall cost is prohibitive.

Some attributes of the more commonly used insulation types are:
POLYISOCYANURATE

Photo 2: Polyisocyanurate (ISO) with organic facers

Photo 2: Polyisocyanurate
(ISO) with organic facers

    ▪▪ Predominate roof insulation in the market
    ▪▪ Organic and double-coated fiberglass facers (mold-resistant)
    ▪▪ Varying densities available: 18 to 25 psi, nominal and minimum, as well as 80 to 125 psi high-density cover boards
    ▪▪ Has an allowable dimensional change, per the ASTM standard, that needs to be understood and designed for
    ▪▪ Can be secured via mechanical fasteners or installed in hot asphalt and/or polyurethane foam adhesive: bead and full-coverage spray foam
    ▪▪ Has an R-value just under 6.0 per inch but has some downward drifting over time

EXPANDED POLYSTYRENE (EPS)

    ▪▪ Has good moisture resistance but can accumulate moisture
    ▪▪ Direct application to steel decks is often a concern with fire resistance
    ▪▪ Has varying densities: 1.0 to 3.0 pound per cubic foot
    ▪▪ Very difficult to install in hot asphalt; basically not appropriate
    ▪▪ Certain products can be secured with mechanical fasteners or lowrise foam adhesive
    ▪▪ Has stable R-values: 3.1 to 4.3 per inch based upon classification type

EXTRUDED POLYSTYRENE (XPS)

    ▪▪ Has good moisture resistance and is often used in protected roof membrane systems and plaza deck applications
    ▪▪ Direct application to steel decks is often a concern with fire resistance
    ▪▪ Has varying compressive strengths: 20 to 100 psi
    ▪▪ Not appropriate to be installed in hot asphalt
    ▪▪ Has stable R-values: 3.9 to 5 per inch based on classification type

MINERAL WOOL

    ▪▪ Outstanding fire resistance
    ▪▪ Stable thermal R-value: 4.0 per inch
    ▪▪ No dimensional change in thickness or width over time
    ▪▪ Available in differing densities
    ▪▪ May absorb and release moisture
    ▪▪ Can be installed in hot asphalt or mechanically attached

PHOTOS: HUTCHINSON DESIGN GROUP LTD.

Pages: 1 2 3

New Family of Roof Boards for Commercial Assemblies

National Gypsum's DEXcell product line features high-performance roof boards for commercial roofing systems.

National Gypsum’s DEXcell product line features high-performance roof boards for commercial roofing systems.

National Gypsum has launched DEXcell, a new family of high-performance roof boards for commercial roofing systems.

The DEXcell brand family includes three products:

    1. DEXcell brand Glass Mat Roof Board
    2. DEXcell brand FA Glass Mat Roof Board (for fully adhered membrane systems)
    3. DEXcell brand Cement Roof Board (a lightweight cement board for the roofing industry that will withstand prolonged exposure to moisture)

National Gypsum’s new DEXcell family has gone through rigorous third-party testing and carry a number of approvals and meet various industry standards to resist mold and provide a fire barrier for commercial structures, such as schools, hospitals and hotels.

DEXcell Glass Mat Roof Board and DEXcell FA Glass Mat Roof Board are mold resistant gypsum boards designed for use as a coverboard and/or thermal barrier in commercial roofing applications. Both are produced in 1/4-, 1/2- and 5/8-inch thicknesses and 4-foot wide in 4- and 8-foot lengths. These products score and cut easily and are specially coated on the front, back and sides for easy handling.

DEXcell Glass Mat Roof Board is ideally suited for mechanically fastened roof systems and has coated fiberglass facers with an enhanced gypsum core.

DEXcell FA Glass Mat Roof Board is designed for fully adhered roof systems, and is manufactured with heavy-duty coated fiberglass facers with an enhanced gypsum core.

DEXcell brand Cement Roof Board is a lightweight moisture- and mold-resistant cement board designed for use as a cover board and/or thermal barrier in all commercial roofing applications. It provides a fire barrier and a thermal barrier. These boards are manufactured of Portland cement, lightweight aggregate and glass mesh that provide an exceptionally hard, durable surface. It is produced in 7/16-inch thickness and 4-feet wide in 4- and 8-foot lengths.

Attention Roof System Designers: Numerous Roof Components Work Together to Affect a Building

There has been a great deal of opinion expressed in the past 15 years related to the roof cover(s), or the top surface of a roof system, such as “it can save you energy” and “it will reduce urban heat islands”. These opinions consequently have resulted in standards and code revisions that have had an extraordinary effect on the roofing industry.

The building type should influence the type of roof system designed. Some spaces, like this steel plant, are unconditioned, so insulation in the roof system is not desired.

The building type should influence the type of roof system designed. Some spaces, like this steel plant, are unconditioned, so insulation in the roof system is not desired.

Let’s say it loud and clear, “A single component, does not a roof make!”. Roofs are systems, composed of numerous components that work and interact together to affect the building in question. Regardless of your concern or goal—energy performance, urban heat-island minimization, long-term service life (in my opinion, the essence of sustainability) or protection from the elements—the performance is the result of an assembled set of roof system components.

Roof System Components

Energy conservation is an often-discussed potential of roofs, but many seem to think it is the result of only the roof-cover color. I think not. Energy performance is the result of many factors, including but not limited to:

Building use: Is the building an office, school, hospital, warehouse, fabrication facility, etc.? Each type of building use places different requirements on the roof system.

Spatial use and function be low the roof deck: It is not uncommon in urban areas to have mechanical rooms or interstitial spaces below the roof—spaces that require little to no heating or cooling. These spaces are typically unconditioned and unoccupied and receive no material benefit from the roof system in regard to energy savings.

Roof-deck type: The type of roof deck—whether steel; cast-in-place, precast and post-tensioned concrete; gypsum; cementitious wood fiber; or (don’t kill the messenger) plywood, which is a West Coast anomaly—affects air and moisture transport toward the exterior, as well as the type of roof system.

Roof-to-wall transition(s): The transition of the roofing to walls often results in unresolved design issues, as well as cavities that allow moisture and vapor transport.

Meanwhile others, like this indoor pool, require extreme care in design and should include a vapor retarder and insulation.

Meanwhile others, like this indoor pool, require extreme care in design and
should include a vapor retarder and insulation.

Roof air and/or vapor barrier: Its integration into the wall air barrier is very important. Failure to tie the two together creates a breach in the barrier.

Substrate board: Steel roof decks often require a substrate board to support the air and vapor barrier membranes. The substrate board also can be the first layer of the roof system to provide wind-uplift resistance.

Insulation type: Each insulation type—whether polyisocyanurate, expanded polystyrene, extruded polystyrene, wood fiber, foam glass or mineral wool—has differing R-values, some of which drop with time. Many insulation types have differing facer options and densities.

The number of insulation layers: This is very important! A single layer of insulation results in a high level of energy loss; 7 percent is the industry standard. When installing multiple layers of insulation, the joints should be offset from layer to layer to avoid vapor movement and thermal shorts.

Sealing: Voids between rooftop penetrations, adjacent board and the roof-edge perimeters can create large avenues for heat loss.

Pages: 1 2