Roofing Codes, Standards and Plan Reading
Code hierarchy
For one- and two-family dwellings, Chapter 9 (R905 and R806) of the International Residential Code governs roofing; commercial work falls under Chapter 15 of the IBC. Louisiana adopts the I-codes statewide with local amendments, so the first question in a code dispute is which edition and which amendment applies. Above the code sit manufacturer's printed installation instructions, which are enforceable and usually stricter. Standards you should recognize: ASTM material specs, UL 790 fire classification, UL 2218 impact (Class 4 hail), ASTM D7158 wind, and ASCE 7 for design wind pressures.
Wind. Uplift is highest at corners and edges and lowest in the field, which is why edge metal, perimeter fastening and corner nailing patterns are more demanding than field nailing. Hurricane-prone coastal parishes add opening protection and product approval requirements.
Reading the documents
A roof plan shows ridge, hip, valley and eave lines, slope arrows or slope triangles (e.g., 4:12), drain and scupper locations, expansion joints, and roof-mounted equipment. Keynotes, general notes and detail callouts carry requirements that the plan view cannot show. Sections and details give flashing heights, curb dimensions and termination details. Always check the scale block before measuring.
Traps. Confusing slope triangle notation; treating a "typical" note as covering an atypical penetration; missing a general note that supersedes the plan; and assuming the code minimum satisfies a contract that specifies more.
Worked example. A roof plan drawn at 1/4 inch = 1 foot shows a valley 3½ inches long on the drawing. Actual length = 3.5 × 4 = 14 feet. Always scale drawings, then verify against a dimension string when one is given.