Select code-compliant underlayment type (organic felt, synthetic, or self-adhering membrane) for a steep-slope re-roof

Steps

1. Identify which ASTM underlayment standard the product is manufactured to: ASTM D226 covers asphalt-saturated organic felt (Type I ~#15, Type II ~#30) for general roofing/waterproofing use, while ASTM D4869 is the steep-slope-specific organic felt underlayment standard with its own type/weight classes and a water-shedding ('shower') performance test.
2. For self-adhering ice-dam/underlayment membranes, confirm compliance with ASTM D1970, the standard covering self-adhering polymer-modified bituminous sheet materials used as steep-slope underlayment.
3. For synthetic underlayments (non-bitumen), verify the product carries a current code-recognition path (ICC-ES evaluation report or equivalent) since synthetics are not covered by D226/D4869/D1970 and are accepted via alternative-materials/code-report provisions rather than a single ASTM felt standard.
4. Match the underlayment's fastening pattern, lap requirements, and exposure-to-weather limits to the manufacturer's instructions, since code compliance for underlayment is tied to both the material standard and the installation method.
5. Confirm the roof covering manufacturer's warranty terms don't require a specific underlayment brand/type beyond code minimums — many shingle warranties condition coverage on using an underlayment from an approved list.