Dear Green Building Community,

I’m currently planning a roof assembly for a project located in Climate Zone 5B (Eastern Washington), where we experience significant snow loads in the winter and high temperatures in the summer. I’m looking for advice on the best roof assembly approach to maximize drying potential, prevent ice dams, and ensure long-term durability.

The design features vented attics and vaulted ceilings with multiple 2/12 mono-pitch roofs. I understand that this low slope is not ideal for effective venting, and I’m aware of condensation issues in similar nearby projects. I suspect those problems may be related to the use of spray foam insulation or non-permeable underlayments such as Grace Ice & Water Shield directly over the sheathing.

My current plan is as follows:

• Roof sheathing: CDX plywood

• Vapor-permeable roll on WRB (e.g., Prosoco Cat 5) applied over the sheathing

• Vented over-roof assembly using CDX Plywood with 1×4 or 2×4 strapping running vertical to create an air gap (this would be separately vented from the Attic)

• Grace Ice & Water Shield installed over the vented cavity

• 2” standing seam metal roofing as the final layer

Is this assembly appropriate for my goals, or does it represent unnecessary complexity? I’m open to any recommendations or alternatives you might suggest to improve performance and durability in this climate and design.

Thank you for your time and expertise. I look forward to your insights.

Best regards,

Nick Felt