The underlayment codes have been criticized as being confusing.
A change to Florida’s Building Code mandates roofing underlayment and updates its installation guidelines. The underlayment codes have been criticized as being confusing.
Many interpret the code to say that old D4869 regular felt can only be used in very limited situations of lower slope applications, according to a column in the Daily Commercial. For other applications, builders and roofers must use D226 Type II roofing felt or a synthetic felt that has met Florida Building Code approval. Florida’s code, with its emphasis on minimizing hurricane damage, influences the development of codes in other states.