About Polyiso

  • R-values of R-6 or more per inch.
  • Come in many thicknesses, compressive strengths, and densities.

Polyiso products shall be installed in accordance with:

  • Code compliance requirements per DrJ and ABTG Research Reports
  • Manufacturer’s installation instructions
  • The following general installation guidelines

Step 1

Verify Code Requirements

  • Benchmark for performance:
    • “One layer No. 15 Asphalt Felt, free from holes and breaks, complying with ASTM D226 for Type 1 felt or other approved WRB…” (R703.2)
  • All WRB products other than 15# felt, achieve building code acceptance through the alternative material section of the code
  • R104.11 Alternative materials, design and methods of construction and equipment.
    • Not intended to prevent the installation of any material or to prohibit any design or method of construction not specifically prescribed by this code.
    • Shall be approved where the Building Official finds that the proposed design is satisfactory and complies with the intent of the provisions of this code, and that the material, method or work offered is, for the purpose intended, at least the equivalent of that prescribed in this code.

Step 2

Confirm Equivalence

  • To determine equivalence, three separate water resistance tests are performed:
    1. Water resistance of Polyiso material alone
    2. Water resistance of taped joints
    3. Water resistance of full assembly
  • Tests 1 and 2 are done under conditions of accelerated aging
  • Durability of WRB systems is addressed through aging of materials prior to testing, field studies, and years of practice
  • Accelerated aging procedure (used prior to tests 1 and 2):
    • Ultraviolet light exposure: 10 hours per day for 21 days (210 hours at 135-140 degrees)
    • 25 cycles of drying/soaking
    • No visible delamination or blistering of the facing layer is required for acceptance

Test 1: Water Resistance (AATCC Method 127)

  • Test is done under conditions of accelerated aging
  • Test specimens must be held at a hydrostatic head pressure of 21.6" for a period of 5 hours
  • No water leakage on underside of specimen required for acceptance

Test 2: Taped Joints

  • Test is done under conditions of accelerated aging
  • Test conducted for substrate materials forming foam-to-foam or foam-to-flashing joints
  • Two 3"x6" pieces of foam sheathing, butt-jointed on 6" edge with joint-sealing treatment
  • Exposed edges of tapes must be exposed to a hydrostatic head of 21.6" for a period of 5 hours
  • No water leakage on underside of specimen required for acceptance

Test 3: Water Penetration - Full Assembly

  • Test assemblies must be at least 4’ wide x 8’ high
  • Must include at least one vertical and at least two horizontal unbacked joints
  • No exterior wall covering
  • Assemblies tested at a pressure differential of 6.24 psf for 2 hours
  • Water shall not penetrate to the unexposed face of the sheathing for acceptance
  • Openings in the assembly are not required
    • If tested without openings, Polyiso must be recognized in an evaluation report as part of a wall covering system
    • Manufacturers typically test with openings so that uses are not limited to specific systems

Correlation of Accelerated Aging Tests to Real Time Aging

  • Real-world exposure testing:
    • Building Science Corp “Skunkworks” Exposure Facility
    • To test tape resistance to UV, heat and rain they stick the tape outside for years and watch them
    • While this testing was not specific to polyiso foam sheathing, the durability of properly installed taped joints exposed for long durations is confirmed.
  • BSC’s rule of thumb is that if it works after 2 years of this kind of exposure, you are pretty much good to go

Photograph taken of tape 15 years after application. 

“WRB is a code requirement (IRC 703.1.1, IBC 1403.2) to keep bulk moisture away from things within a wall that need to stay dry, but not all approved WRB systems are created, nor tested equally.” Dr. Lstiburek, Building Science Corp.

Step 3

Install Insulation Boards

Ensure wall is square and true and align boards with bottom edge of wall.

Verify stud spacing, blocking, and bracing requirements with manufacturer. Provide framing or blocking for attachment of siding and trim at transitions. Seams should not be visible from interior unless allowed by manufacturer.

Space fasteners per manufacturer’s instructions around edges of panel, through panels and into interior members.

Drive nails flush and snug. Do not overdrive or underdrive nails.

Step 4

Trim Boards at Openings

Trim boards at all window and door openings and cover all framing with Polyiso. Fit joints tightly.

Step 5

Apply WRB Tape

  • Ensure clean and dry surface for proper adhesion
  • Apply tape in shingle fashion, working upward from the bottom of the assembly
  • Center tape over joint to cover fasteners
  • Seal all joints and openings and penetrations per manufacturer’s installation instructions

Step 6

Seal Penetrations

At pipe and other small penetrations, seal gaps with silicone or expanding spray foam sealant. Seal joints and openings with joint tape per manufacturer’s instructions.

Repair damaged areas per manufacturer’s instructions.

Step 7

Apply Cladding

Install cladding as soon as is practical or per manufacturer’s instructions. See Installation Instructions for Attachment of Exterior Wall Coverings Through FPIS and ABTG RR 1503-02 for additional guidance.
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