Polyisocyanurate Foam Insulation

Polyiso Insulation – A Renovation Weapon to Combat Rising Energy Costs

polyiso1During most renovations, people tend to focus on the design of the home and its most noticeable features, such as light fixtures, countertops, and wall colors. Given the rapidly rising price of energy in the United States, those considering renovation work may want to turn their attention to a less glamorous, but more effective, target—insulation.

As many design professionals are well aware, choosing energy efficient insulation can be one of the most effective ways to save energy and money. Adding or exceeding the recommended levels of insulation during renovation can lower energy consumption and reduce utility costs, while enjoying the strong possibility of a payback upon project completion. Architects and builders should assume the role of not only specifying the best insulation package for each project, but also educating homeowners.

Specifying polyisocyanurate

Polyisocyanurate (polyiso) insulation is an excellent choice for a variety of renovation applications because of its excellent energy conserving qualities. It has a high R-value per inch, which helps reduce energy costs for the homeowner over the life of the building—an especially important factor considering the expected sustained rise in fuel costs.1

Polyiso insulation is a thermoset, closed-cell, rigid foam plastic insulation manufactured in board form. Via a continuous lamination process, liquid raw materials that expand and become light (yet strong) are applied between engineered facing materials. These facings provide strength, improve rigidity, and enhance thermal performance. Polyisocyanurate (polyiso) is most commonly supplied as 1.2-x-2.4-m or 1.2-x-2.7-m (4-x-8-ft or 4-x-9-ft) sheets in various thicknesses.

The boards are available in a range of compressive strengths, meeting various marketplace requirements. Compressive strength refers to the ability of a rigid foam plastic board to resist deformation and maintain its shape when subjected to a force or load. Common construction applications require compressive strengths adequate for polyisocyanurate (polyiso) to maintain its shape during installation, as well as during use.2 ASTM International C 1289, Specification of Polyiso Insulation, mandates all polyisocyanurate (polyiso) products have a minimum stated compressive strength of 110 kPa (16 psi). Practically speaking, wall applications require polyisocyanurate (polyiso) to support flexible siding materials; for roofing projects, it must withstand limited installation traffic, support fastener loads, and sustain the total roofing system.

Polyisocyanurate (polyiso) can contribute to a more fire-safe home or building after renovation work. It passes both American National Standards Institute/Underwriters Laboratories Inc. (ANSI/UL) 1256, Fire Test of Roof Deck Constructions, and Factory Mutual (FM) 4450, Class I Insulated Steel Deck Roofs, without a thermal barrier. Additionally, polyisocyanurate (polyiso) stays intact during fire exposure in ASTM E 84, Standard [Tunnel] Test Method for Surface Burning Characteristics of Building Materials, forming a protective char layer and remaining in place to meet building code requirements.

Polyisocyanurate (polyiso) for renovations
Adding polyisocyanurate (polyiso) sheathing in the renovation of houses and buildings can be inherently more energy-efficient due to the plastic material’s thermal properties. Typically, polyisocyanurate (polyiso) is used to insulate the entire wall (including the framing), thereby significantly reducing heat loss through both convection and conduction. Additionally, properly insulating a structure with polyisocyanurate (polyiso) can decrease condensation in the walls, potentially lowering moisture-related problems.

When properly specified and installed, polyisocyanurate (polyiso) insulating sheathing can be one of the best values available for those upgrading or renovating a home or facility.

When re-siding a building, vinyl siding can be placed over a layer of polyisocyanurate (polyiso) installed atop the existing exterior cladding. Polyisocyanurate (polyiso) can also be used with exterior products such as fiber cement siding, wood siding, stucco, and metal siding.

Interior walls
For interior wall refinishing projects, a layer of polyisocyanurate (polyiso) insulation can be installed prior to the addition of new gypsum wallboard.

Non-insulated basement walls can be a significant source of heat loss. When finishing a basement, a layer of polyisocyanurate (polyiso) sheathing can be placed over the interior wall and covered with 13-mm (0.5-in.) gypsum board to insulate and upgrade the basement to a more comfortable space.

When turning an attic into a living space, one can place polyiso on the interior over the studs before installing gypsum board. It can also be practical to fill the cavities with polyisocyanurate (polyiso) insulation.

Should the renovation include adding square footage to the home, such as a new family room or new master bedroom, the inclusion of polyisocyanurate (polyiso) insulation as the exterior sheathing can provide the homeowner with energy-efficient construction and potentially add to the long-term thermal performance of the entire home.

About the Author

Jared Blum is the president of the Polyisocyanurate Insulation Manufacturers Association (PIMA), the Washington, D.C.-based national trade organization.


1 As insulation formulation may vary from manufacturer to manufacturer, design professionals should consult the suppliers’ specification sheets to understand the exact properties, including the actual R-values. Factors affecting the R-value include thickness of application (i.e. the thicker the foam, the better the aged R-value), the substrate, and the covering systems used (i.e. the lower the perm-rated covering and substrate, the higher the aged R-value).

2 For more information, see Polyisocyanurate Insulation Manufacturers Association (PIMA) Technical Bulletin 102, Compressive Strength.Visit pima.org/technical_bulletins/tbull102.html.