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Continuous Insulation – Cladding/Furring Attachment - Code Compliance Brief

Overview: 

The intent of this brief is to provide code-related information to help ensure that the measure will be accepted as being in compliance with the code.  Providing notes for code officials on how to plan review and conduct field inspections can help builders or remodelers with proposed designs and provide jurisdictional officials with information for acceptance.  Providing the same information to all interested parties (e.g., code officials, builders, designers, etc.) is expected to result in increased compliance and fewer innovations being questioned at the time of plan review and/or field inspection.

Guidance is needed for code-compliant installations of various cladding materials when installed over thicker foam sheathing also known as insulated sheathing or continuous insulation (c.i.). The code has generally provided generic prescriptive attachment requirements without consideration of c.i. thickness or deferred to the manufacturers to provide guidance on fastener selection. But, many manufacturers’ installation instructions have limited the thickness of c.i. applications to 0.5 inch to 1.5 inches of thickness, or not addressed it at all. Therefore, warranty, liability, and potential code conflicts exist when using thicker (>1.5") levels of c.i. due to the limitations cited in manufacturer installation instructions for exterior finishes and code provisions that prescriptively require c.i. > 1.5" in certain climate zones. In such cases, a designed alternative solution may be required to address these concerns. However, newer codes have now begun to provide engineered prescriptive solutions for use by builders, designers, code officials, and siding manufacturers.

As the energy codes continue to become more stringent, the thickness of c.i. has increased prescriptively. Only recently have codes begun to question whether all applicable loads were being addressed. Loads include seismic, wind, and dead load. Seismic and wind loads can be identified by referencing current codes and standards. The concern with adding thicker c.i. to a wall assembly is whether the cladding fastener can withstand the dead load from the weight of the siding or c.i. In practice, there has been little concern with typical light-weight sidings, such as vinyl and wood, or separately supported claddings such as anchored masonry veneer installed over c.i. up to 1.5 inches thick. The main issues have been identifying fasteners that are an appropriate length to maintain embedment in wood framing for wind and seismic resistance with a diameter and head type that is suitable for the siding material. However, for heavy claddings such as Portland cement stucco or adhered masonry veneer, concern with rigidly supporting the weight of the cladding installed over thick c.i. grows.

  • Increased thickness of c.i. introduces the following practical considerations:
  • Selecting the appropriate cladding fasteners that can withstand the dead load from the weight of the siding for a given thickness of c.i. while also still complying with the siding manufacturer’s fastener type and diameter specifications.
  • Identifying and specifying non-standard fasteners where required by the thickness of c.i. and cladding connection detail.
  • Siding manufacturer's installation instructions may be limited to c.i. thicknesses <1.5" (or not address such installation at all).
  • Siding manufacturer's warranties might be void when >1.5" of c.i. is used.
  • Where furring is used, the lack of any prescriptive connection solutions in the code for furring applications with or without an underlying layer of c.i.
  • For thick c.i. applications, additional framing or detailing may be required at some locations to provide a fastening base for corner trim.

Based on further research and technical validation, provisions were added to the 2015 International Residential Code® (IRC). States and local jurisdictions adopt different building and energy codes and code versions (e.g., 2009 IRC/IECC, 2012 IRC/IECC, or 2015 IRC/IECC). For states and locations that have not adopted the 2015 IRC, one approach to overcome this barrier would be to reference the most recent version of the IRC for guidance. The building code (IRC/IECC) allows for alternative materials, design, and methods of construction and equipment not specifically prescribed by code and this would include consideration of new guidance published in more recent versions of model codes. Consequently, the code official has the authority and responsibility to review and approve the proposed design as satisfactory and compliant with the intent of the provisions of the code (per Section R104.11/IRC, Section R102.1/IECC) as a means of achieving code compliance. The alternative materials, design, and methods provision has been a long-standing allowance and this important tradition has been continued in every version of the IRC/IECC.

This brief addresses code-compliant cladding attachment over foam sheathing to light-frame wood and cold-formed steel wall assemblies. For guidance regarding cladding attachment over foam sheathing to masonry or concrete wall construction refer to the 2015 IRC, Section R703.17.

Plan Review: 

Per the 2015 IECC/IRC, Section R103.3/R106.3 Examination of documents.  The code official/building official must examine, or cause to be examined, construction documents for code compliance.

This section lists the applicable code requirements and details helpful for plan review regarding the provisions to meet the requirements for “continuous insulation and cladding attachments.”

Construction Documentation.  Review the construction documents to identify the materials, installation specifications, and design.

  • 2015 IECC/IRC, Section R103.2/N1101.5 Information on construction documents.  Construction documents should include:

-      Insulation materials and R-values

-      Moisture management, vapor retarders, and flashing specifications

-      Cladding attachment materials and specifications

-      Air barrier materials and specifications

 

  • Insulation:  Verify insulation R-value(s) specified on construction documents meets or exceeds the insulation levels per the applicable code.  The amount of insulation is generally dictated by the energy codes, and generally determined by building type (e.g., R1, R2, R4), framing material (wood, steel, concrete), and climate zone.
    • (The prescriptive insulation R-values in the 2009, 2012, and 2015 IECC are referenced below.)
    2009 IECC Prescriptive Above-Grade Wall Insulation R-values

    Climate Zone

    1

    2

    3

    4

    5

    6

    7 - 8

    Wood Frame Wall

    R-13

    R-13

    R-13

    R-13

    R-20 or 13+5

    R-20 or 13+5

    R-21

    Steel Frame Wall 16" o.c.

    R-13+5 OR R-15+4 OR R-21+3 OR R-0+10

    R-13+5 OR R-15+4 OR R-21+3 OR R-0+10

    R-13+5 OR R-15+4 OR R-21+3 OR R-0+10

    R-13+5 OR R-15+4 OR R-21+3 OR R-0+10

    R-13+9 OR R-19+ OR R-15+7

    R-13+9 OR R-19+ OR R-15+7

    R-13+9 OR R-19+ OR R-15+7

    2012 and 2015 IECC Prescriptive Above-Grade Wall Insulation R-values
    (R-values are the same for both versions)

    Climate Zone

    1

    2

    3

    4

    5

    6

    7 - 8

    Wood Frame Wall

    13

    13

    R-20 OR R-13+5

    R-20 OR R-13+5

    R-20 OR R-13+5

    R-20+5 OR R-13+10

    R-20+5 OR R-13+10

    Steel Frame Wall 16" o.c.

    Wood frame R-value equivalent R-13

    Wood frame R-value equivalent R-13+3

    Wood frame R-value equivalent R-20

    Wood frame R-value equivalent R-20+5

    Wood frame R-value equivalent R-20+5

    Wood frame R-value equivalent R-20+5

    Wood frame R-value equivalent R-21

    R-13+4.2 OR R-19+2.1 OR R-21+2.8 OR R-0+9.3 OR R-15+3.8 OR R-21+3.1

    R-0+11.2 OR R-13+6.1 OR R-15+5.7 OR R-19+5.0 OR R-21+4.7

    R-0+14.0 OR R-13+8.9 OR R-15+8.5 OR R-19+7.8 OR R-19+6.2 OR R-21+7.5

    R-13+12.7 OR R-15+12.3 OR R-19+11.6 OR R-21+11.3 OR R-25+10.9

    R-13+12.7 OR R-15+12.3 OR R-19+11.6 OR R-21+11.3 OR R-25+10.9

    R-13+12.7 OR R-15+12.3 OR R-19+11.6 OR R-21+11.3 OR R-25+10.9

    R-0+14.6 OR R-13+9.5 OR R-15+9.1 OR R-19+8.4 OR R-21+8.1 OR R-25+7.7

    Steel Frame Wall 24" o.c.

    Wood frame R-value equivalent R-13

    Wood frame R-value equivalent R-13+3

    Wood frame R-value equivalent R-20

    Wood frame R-value equivalent R-20+5

    Wood frame R-value equivalent R-20+5

    Wood frame R-value equivalent R-20+5

    Wood frame R-value equivalent R-21

    R-0+9.3 OR R-13+3.0 OR R-15+2.4

    R-0+11.2 OR R-13+4.9 OR R-15+4.3 OR R-19+3.5 OR R-21+3.1

    R-0+14.0 OR R-13+7.7 OR R-15+7.1 OR R-19+6.3 OR R-21+5.9

    R-13+11.5 OR R-15+10.9 OR R-19+10.1 OR R-21+9.7 OR R-25+9.1

    R-13+11.5 OR R-15+10.9 OR R-19+10.1 OR R-21+9.7 OR R-25+9.1

    R-13+11.5 OR R-15+10.9 OR R-19+10.1 OR R-21+9.7 OR R-25+9.1

    R-0+14.6 OR R-13+8.3 OR R-15+7.7 OR R-19+6.9 OR R-21+6.5 OR R-25+5.9

  • Moisture:  Verify the design and specification of the weather-resistive covering, water-resistive barrier, flashing and drainage are specified on the construction documents and meet the applicable building code.
  • Vapor Retarders:  The IRC (Section 702.7) states Class I or II vapor retarders are required on the interior side of the frame walls in Climate Zones 5, 6, 7, 8, and Marine 4 with some exceptions for basement walls, below grade portion of any wall, or construction where moisture or freezing will not damage the material.  A Class III vapor retarder (latex or enamel paint) is permitted where c.i. exceeds the R-values specified in Table R702.7.1.  Confirm the c.i. thickness meets the values specified per climate zone or construction documents specify a Class I or II vapor retarder (refer to Section R702.7 Vapor Retarders for further details).  Where a Class III vapor retarder is used in colder climate zones on 2x6 walls, the amount of c.i. required may exceed the minimum energy code insulation requirements reported in the tables above. This can be used as a means to improve wall assembly and overall building performance or provide flexibility in other envelope and energy efficiency provisions (e.g., use of trade-offs).
    Table R702.7.1

    Climate Zone

    Class III Vapor Retarders Permitted for:

    Marine 4

    c.i. R-value ≥ 2.5 over 2 x 4 wall

    c.i. R-value ≥ 3.75 over 2 x 6 wall

    5

    c.i. R-value ≥ 5 over 2 x 4 wall

    c.i. R-value ≥ 7.5 over 2 x 6 wall

    6

    c.i. R-value ≥ 7.55 over 2 x 4 wall

    c.i. R-value ≥ 11.25 over 2 x 6 wall

    7 and 8

    c.i. R-value ≥ 10 over 2 x 4 wall

    c.i. R-value ≥ 15 over 2 x 6 wall

  • Air barrier:  Verify the construction documents identify a continuous air barrier and installation practice that complies with the applicable code (e.g., IECC).  In the United States, air barrier requirements are addressed only in the energy code even though they also serve an important role in actually meeting the moisture vapor control intention of the building code.
  • Cladding/Furring Attachments:

    • Determine and verify wind load requirements for the project in accordance with applicable code.
    • Review cladding manufacturer's approved instructions and any limitations including thickness for cladding or furring attachments through foam plastic sheathing to framing, or an approved design.
    • Verify cladding or furring attachments through foam sheathing to framing are specified on the construction documents and meet or exceed minimum fastening requirements per the applicable code based on:
      • Framing types (wood, cold-formed steel, masonry, or concrete)
      • Furring (16" o.c. or 24" o.c.)
      • Fastener type and size
      • Fastener spacing

    Direct Cladding Attachment:

    For direct cladding attachment over foam sheathing where cladding is installed directly over foam sheathing without the use of furring, specify cladding minimum fastening requirements to support the cladding weight in accordance with Table R703.15.1 (wood frame) or Table R703.16.1 (steel frame) of the 2015 IRC, or an approved design.

    If an exception has been identified on the construction documents confirm it meets one of the exceptions per the IRC:

    1. Where the cladding manufacturer has provided approved installation instructions for application over foam sheathing, those requirements shall apply.
    2. For exterior insulation and finish systems, refer to Section R703.9.
    3. For anchored masonry or stone veneer installed over foam sheathing, refer to Section R703.7.
    Table R703.15.1
    Cladding Minimum Fastening Requirements for Direct Application over Foam Plastic Sheathing to Support Cladding Weight1

    Cladding Fastener Through Foam Sheathing

    Cladding Fastener Type and Minimum Size2

    Cladding Fastener Vertical Spacing (inches)

    Maximum Thickness of Foam Sheathing (inches)3

    16" o.c. Fastener Horizontal Spacing

    24" o.c. Fastener Horizontal Space

    Cladding Weight

    Cladding Weight

    3 psf

    11 psf

    25 psf

    3 psf

    11 psf

    25 psf

    Wood Framing (minimum 1/1/4 inch penetration

    0.113" diameter nail

    6

    8

    12

    2

    1

    DR

    2

    .75

    DR

    1

    DR

    0.5

    DR

    0.5

    DR

    DR

    DR

    0.120" diameter nail

    6

    8

    12

    3

    1.5

    0.5

    3

    0.75

    DR

    1

    DR

    0.5

    DR

    0.5

    DR

    DR

    DR

    0.131" diameter nail

    6

    8

    12

    4

    2

    0.75

    4

    1

    DR

    1.5

    0.5

    0.75

    DR

    0.75

    DR

    0.5

    DR

    0.162" diameter nail

    6

    8

    12

    4

    4

    1.5

    4

    2

    1

    3

    1

    1.5

    0.75

    2

    0.75

    1

    DR

    DR = Design required, see Technical Validation, manufacturer literature references

    1. Wood framing should be Spruce-pine-fir or any wood species with a specific gravity of ≥ 0.42 in accordance with AWC NDS.
    2. Nail fasteners to comply with ASTM F 1667, except nail length is permitted to exceed ASTM F 1667 standard lengths.
    3. Foam sheathing must have a compressive strength of 15 psi in accordance with ASTM C 578 or ASTM C 1289.
    Table R703.16.1
    Cladding Minimum Fastening Requirements for Direct Application over Foam Plastic Sheathing to Support Cladding Weight1

    Cladding Fastener Through Foam Sheathing Into:

    Cladding Fastener Type and Minimum Size2

    Cladding Fastener Vertical Spacing (inches)

    Maximum Thickness of Foam Sheathing (inches)3

    16"o.c. Fastener Horizontal Spacing

    24"o.c. Fastener Horizontal Space

    Cladding Weight

    Cladding Weight

    3 psf

    11 psf

    25 psf

    3 psf

    11 psf

    25 psf

    Steel Framing (minimum penetration of steel thickness + 3 threads)

    No. 8 screw into 33 mil steel or thicker

    6

    8

    12

    3

    3

    1.5

    3

    2

    DR

    2

    0.5

    1.5

    DR

    1.5

    DR

    0.75

    DR

    No. 10 screw into 33 mil steel

    6

    8

    12

    4

    3

    2

    4

    3

    0.5

    3

    1

    2

    DR

    2

    DR

    1

    DR

    No 10 screw into 43 mil steel or thicker

    6

    8

    12

    4

    4

    3

    4

    4

    2

    4

    2

    3

    1.5

    3

    1.5

    3

    DR

    DR = Design required, see Technical Validation, manufacturer literature references

    1. Steel framing a minimum 33 ksi steel for 33 mil and 43 mil steel, and 50 ksi steel for 54 mil steel or thicker.
    2. Screws must comply with the requirements of ASTM C 1513.
    3. Foam sheathing a minimum compressive strength of 15 psi in accordance with ASTM C 578 or ASTM C 1289.

    Furred Cladding Attachment:

    Where wood or steel furring is used to attach cladding over foam sheathing, specify furring minimum fastening requirements to support the cladding weight in accordance with Table R703.15.2 (wood frame) or Table R703.16.2 (cold-formed steel frame) of the 2015 IRC, or an approved design.

    Where placed horizontally, wood furring shall be preservative-treated wood in accordance with Section R317.1 or naturally durable wood and fasteners shall be corrosion resistant in accordance with Section R317.3 of the IRC. 

    Steel furring to have a minimum G60 galvanized coating.

    Table R703.15.2
    Furring Minimum Fastening Requirements for Application over Foam Plastic Sheathing to Support Cladding Weight

    Furring Material

    Framing Member

    Fastener Type and Minimum Size

    Minimum Penetration into Wall Framing (inches)

    Fastener spacing in Furring (inches)

    Maximum Thickness of Foam Sheathing (inches)

    16"o.c. Furring

    24"o.c. Furring

    Siding Weight

    Siding Weight

    3 psf

    11 psf

    25 psf

    3 psf

    11 psf

    25 psf

    Minimum 1X Wood Furring

    Minimum 2 X Wood Stud

    6

    8

    12

    1 1/4

    8

    12

    16

    4

    2

    1

    4

    1.5

    DR

    1.5

    DR

    3

    1

    DR

    1

    DR

    3

    0.5

    DR

    6

    8

    12

    1 1/4

    8

    12

    16

    4

    4

    1.5

    4

    2

    0.75

    2

    0.75

    4

    1.5

    DR

    1.5

    DR

    4

    1

    DR

    6

    8

    12

    1

    12

    16

    24

    4

    2

    0.75

    4

    1.5

    DR

    1.5

    DR

    4

    1

    DR

    1.

    DR

    3

    DR

    DR

    6

    8

    12

    1 1/2

    12

    16

    24

    4

    3

    1

    4

    2

    0.5

    1.5

    DR

    4

    1.5

    DR

    1.5

    DR

    4

    0.75

    DR

    DR = Design required, see Technical Validation, manufacturer literature references

    1. Wood framing and furring should be spruce-pine-fir or any wood species with a specific gravity of ≥ 0.42 in accordance with AWC NDS.
    2. Nail fasteners to comply with ASTM F 1667, except nail length is permitted to exceed ASTM F 1667 standard lengths.
    3. Where the required cladding fastener penetration into wood material is > ¾" and is ≤ 1½", a minimum 2 x wood furring or an approved design must be used.
    4. Foam sheathing a minimum compressive strength of 15 psi in accordance with ASTM C 578 or ASTM C 1289.
    5. Furring must be spaced ≤ 24" o.c., in a vertical or horizontal orientation.  In a vertical orientation, furring must be located over all studs and attached with the required fastener spacing.  In a horizontal orientation, the indicated 8-inch and 12-inch fastener spacing in furring must be achieved by use of two fasteners into studs at 16" o.c. and 24" o.c., respectively.
    Table R703.16.2
    Furring Minimum Fastening Requirements for Application over Foam Plastic Sheathing to Support Cladding Weight1

    Furring Material

    Framing Member

    Fastener Type and Minimum Size2

    Minimum Penetration into Wall Framing (inches)

    Fastener spacing in Furring (inches)

    Maximum Thickness of Foam Sheathing (inches)4

    16" o.c. Furring5

    24" o.c. Furring5

    Siding Weight

    Siding Weight

    3 psf

    11 psf

    25 psf

    3 psf

    11 psf

    25 psf

    Minimum 33 mil Steel Furring or Minimum 1 x Wood Furring3

    33 mil Steel Stud

    No. 8 screw

    Steel thickness + 3 threads

    12

    3

    1.5

    DR

    3

    0.5

    DR

    16

    3

    1

    DR

    2

    DR

    DR

    24

    2

    DR

    DR

    2

    DR

    DR

    No. 10 screw

    Steel thickness + 3 threads

    12

    4

    2

    DR

    4

    1

    DR

    16

    4

    1.5

    DR

    3

    DR

    DR

    24

    3

    DR

    DR

    2

    DR

    DR

    43 mil or thicker Steel Stud

    No. 8 screw

    Steel thickness + 3 threads

    12

    3

    1.5

    DR

    3

    0.5

    DR

    16

    3

    1

    DR

    2

    DR

    DR

    24

    2

    DR

    DR

    2

    DR

    DR

    No. 10 screw

    Steel thickness + 3 threads

    12

    4

    3

    1.5

    4

    3

    DR

    16

    4

    3

    0.5

    4

    2

    DR

    24

    4

    2

    DR

    4

    0.5

    DR

    DR = Design required, see Technical Validation, manufacturer literature references

    1. Wood furring must be spruce-pine-fir or any softwood species with a specific gravity of ≥ 0.42.  Steel furring minimum 33 ksi steel.  Steel studs a minimum 33 ksi steel for 33 mil and 43 mil thickness, and 50 ksi steel for 54 mil steel or thicker.
    2. Screws must comply with the requirements of ASTM C 1513.
    3. Where the required cladding fastener penetration into wood material is > ¾" and ≤ 1½", a minimum 2-inch nominal wood furring or an approved design shall be used.
    4. Foam sheathing must have a minimum compressive strength of 15 psi in accordance with ASTM C 578 or ASTM C 1289.
    5. Furring must be placed ≤ 24" o.c., in a vertical or horizontal orientation.  In a vertical orientation, furring must be located over all studs and attached with the required fastener spacing.  In a horizontal orientation, the indicated 8-inch and 12-inch fastener spacing in furring must be achieved by use of two fasteners into studs at 16" o.c. and 24" o.c., respectively.
Field Inspection: 

 

Per the 2015 IECC, Section R104 Inspections.  Construction or work for which a permit is required is subject to inspection.  Construction or work is to remain accessible and exposed for inspection purposes until approved.  Required inspections include footing and foundation, framing and rough-in work, plumbing rough-in, mechanical rough-in, and final inspection.

Per the 2015 IRC, Section R109 Inspections.  The wording is somewhat different in that for onsite construction, from time to time the building official, upon notification from the permit holder or his agent, can make or cause to be made any necessary inspections.  Further details are provided for inspections regarding foundation, plumbing, mechanical, gas and electrical, floodplain, frame and masonry, and final inspection.  Any additional inspections are at the discretion of the building official.

This section provides details for inspecting to the specific provisions for continuous insulation and cladding attachments where one or more specific type of inspection per the IECC or IRC may be necessary to confirm compliance.  Verifying code compliance would typically be at the framing and rough-in work inspection.

Inspections should provide verification in the following areas:

  • Cavity insulation completely fills the cavity with no compression or gaps, the manufacturer’s R-value mark is readily available, and meets the approved R-value per plans.
  • Continuous insulation is installed in accordance with manufacturer’s installation instructions, the manufacturer’s R-value mark is readily available, and meets the approved R-value per plans.
  • Cladding or furring attachments are installed in accordance with manufacturer’s installation instructions and fastening requirements included in the locally applicable code, designed, or otherwise approved by the code official and specified on construction documents.
  • Joints, seams, and penetrations in the c.i. are caulked, gasketed, weatherstripped, or otherwise sealed. 
  • Vapor retarder (if applicable) is properly installed on the interior (warm-in–winter) side of the exterior wall and in compliance with the locally applicable building code (e.g., only required in mixed or colder climate zones).
  • Air barrier is properly installed on the interior or exterior (or both sides) of the exterior wall, or in the cavity if using an air-impermeable insulation product.  All seams, gaps, and holes are sealed properly.  Confirm corners and headers are insulated and the junction of the foundation and sill plate is sealed.  The junction of the top plate and top of exterior walls are sealed.  Confirm the exterior thermal envelope insulation for framed walls is installed in substantial contact and continuous alignment with the air barrier.