Appeal 34832

ASHRAE Standard 90.1-2022

ASHRAE Standard 90.1-2022, Table 5.5-4 – Building Envelope Requirements for Climate Zone 4 (A, B, C)
Nonresidential Roof Assemblies with insulation entirely above deck must have a minimum continuous insulation (c.i.) R-Value of R-30.

We request approval for a design alternative that utilizes 1½” of XPS insulation (R-6.75 to R-7.5) above the structural deck in a roof/plaza assembly, in lieu of the prescribed R-30 c.i.

The plaza roof assembly of the 16-story Standard Plaza office building (constructed in 1963) currently includes a non-structural deck over a concrete structural slab. The proposed retrofit will:
• Remove the existing deteriorated 1½” insulation, protection board & waterproofing, and surface tile & grout (approximately 6” overall thickness)
• Apply 215 mils of hot rubber waterproofing, followed by:
• A drainage mat
• 1½” of XPS insulation (to match the original profile)
• A new concrete topping slab
This replacement maintains existing elevations, including door thresholds, and avoids raising the deck above interior finish floor elevation.

Historic Assembly Constraints:
• The structural slab sits only 6” below the existing finish floor.
• Installing the R-30 c.i. (which requires ~6” to 6¾” of insulation) would raise the plaza surface above interior Level-1 building entry doors, storefront glass and exterior materials and stair landing, violating accessibility requirements and creating drainage and waterproofing issues at the building envelope.

Preservation of Existing Conditions:
• The original 1963 plaza design used 1½” insulation.
• The proposed replacement keeps the thermal profile consistent with the original design, avoiding adverse impacts on door thresholds, transitions, and facade detailing.

Improved Waterproofing & Thermal Continuity:
• The new system will significantly improve the waterproofing integrity with a modern hot rubberized membrane.
• While thermal resistance is below current code, the assembly will not degrade current performance and includes all feasible improvements without reconfiguring the building envelope.

Minimized Energy Impact:
• The plaza is above partially conditioned spaces (parking/storage/mailroom), which limits the thermal penalty.
• The new assembly is an improvement over the existing deteriorated insulation and membrane, resulting in a net gain in performance.

Hardship / Feasibility:
• Compliance with the R-30 requirement would necessitate major structural and architectural reconfiguration of the slab and door thresholds—an infeasible and disproportionate burden for a repair scope.
• Raising the deck height introduces substantial challenges with ADA compliance, water drainage, and waterproofing transitions.

Conclusion:
We respectfully request approval for this alternate design per Section C103.1 and C401.2 of the IECC / applicable modification authority to allow for preservation of building integrity while improving performance under current physical constraints. This proposal is consistent with the intent of the code to improve energy efficiency to the maximum extent practical within existing conditions.
We appreciate your consideration and are happy to provide further documentation or meet for discussion as needed.