RoofingCode: Chapter 15

Roofs and Roof Structures 1507.2.3, Underlayment:

Unless otherwise noted, required underlayment shall conform to ASTM D 226, Type I, ASTM D 4869, Type I, or ASTM D 6757.

1507.2.4, Self-Adhering Polymer Modified Bitumen Sheet. Self-adhering polymer modified bitumen sheet shall comply with ASTM D 1970.

Code Interpretation:

These sections imply that underlayment used for asphalt shingle applications shall be manufactured of fiberglass felt, organic felt, modified bitumen or selfadhering modified bitumen. The underlayment shall be applied in one layer for slopes of 4:12 or more and in accordance with Section 1507.2.8, “Underlayment Application,” which states:

Underlayment shall be applied in shingle fashion, parallel and starting from the eave and lapped 2 inches (51 mm), fastened sufficiently to hold in place. Distortions in the underlayment shall not interfere with the ability of the shingles to seal.

Underlayment securement to the deck shall be completed in accordance with ASCE 7. Application of underlayment in high-velocity wind regions shall comply with Section Section 1507.2.8.1, “High Wind Attachment.”

WaterproofingCode: Section 1807

Dampproofing and Waterproofing 1807.1.3, Ground-Water Control:

Where the ground-water table is lowered and maintained at an elevation not less than 6 inches (152 mm) below the bottom of the lowest floor, the floor and walls shall be dampproofed in accordance with Section 1807.2. The design of the system to lower the ground-water table shall be based on accepted principles of engineering that shall consider, but not necessarily be limited to, permeability of the soil, rate at which water enters the drainage system, rated capacity of pumps, head against which pumps are to operate and the rated capacity of the disposal area of the system.

Code Interpretation
This section implies that dampproofing is required if the water table is maintained a minimum of 6 inches below the bottom of the structure. If the water table is maintained within 6 inches of the bottom of the structure or if hydrostatic pressure exists, then waterproofing is required.

It is the designer’s responsibility to review siteengineering analysis for water table conditions and soil analysis to determine if and what type of dampproofing or waterproofing is required.

The section also implies that the ground-water table must be lowered by implementing a drainage system that is designed to meet the following engineering principles:

• Permeability of the soil.
• Rate at which water enters the drainage system.
• Rated capacity of the pumps.
• Head against which pumps are to operate.
• Rate capacity of the designed area of the system.