A common question arises when re-roofing older commercial buildings: If my existing roof sheathing is made of wood boards or planks instead of continuous OSB or plywood, will I have to re-sheath the entire roof?
The 2018 International Building Code (IBC) does not specifically prohibit using wood boards or planks for roof sheathing under composite asphalt shingles in commercial buildings. However, you need to consider several requirements to comply with the code.
Key Points to Consider
- Structural Adequacy:
- The sheathing must support roofing materials and live loads, such as snow or maintenance personnel. This includes lateral and uplift loads for wind design. The 2018 IBC mandates that all building materials and construction methods ensure safety and stability.
- Section 2304 – General Construction Requirements:
- This section outlines the general requirements for wood construction. It specifies that all wood structural panels used as roof sheathing must meet performance standards and grading rules. While it mainly discusses plywood and OSB, planks can be used if they meet the performance criteria.
- Section 1507.2 – Asphalt Shingles:
- This section requires applying asphalt shingles over an approved roof deck. The deck should be smooth, solid, and securely nailed to the structural supports. You must install wood boards to prevent gaps and ensure a smooth surface for the shingles. Jurisdictional authorities and building inspectors may take exception to wood plank sheathing if gaps result in poor nailing support for the shingles. Your roofer can help get approval based on their shingle installation methods to ensure nails won’t end up in the gaps.
- Installation Guidelines:
- Securely fasten wood planks and minimize gaps. The surface should be as smooth and continuous as possible to provide a suitable substrate for the asphalt shingles.
- The roof product warranty may also determine allowances in board or plank sheathing. Replace boards with more than an 1/8” gap due to the manufacturer’s installation instructions before nailing on roofing materials.
- Referenced Standards:
- Ensure that the boards meet applicable standards for wood used in construction. This includes proper grading, moisture content, and treatment if necessary.
Practical Considerations
- Spacing and Gaps:
- When using boards, ensure no significant gaps could affect shingle performance or allow moisture infiltration.
- Compatibility:
- Verify with the asphalt shingle manufacturer that their product is compatible with installation over wood board sheathing. Some manufacturers may have specific requirements or recommendations.
Summary
While the 2018 IBC does not explicitly prohibit wood boards or planks for roof sheathing under composite asphalt shingles, the installation must meet the code’s performance and safety requirements. Ensure structural adequacy, proper installation, and adherence to manufacturer guidelines for compliance and long-term roof performance.
If you have specific questions or need more details on a particular aspect of the code, contact our team of experts at EVstudio. We can assist with a roof inspection and evaluation of your existing roof and provide recommendations for a proposed roof system, complete with a full engineering report.
