Manufacturers have their own requirements for issuing longer term warranties. We focus here on single-ply systems as that is the majority of the New England market and what we are most familiar with. This gives you some idea of the differences. EPDM systems: There are different methods to attach insulation and the EPDM membrane. Adhesive or screws/plates can be used to secure insulation boards. Adhesive (called fully adhered) or screws/bars/plates (called mechanically fastened) can be used to secure the EPDM membrane. It is possible to install both insulation and membrane unsecured then cover with round ballast rocks to secure both (called ballasted). For longer term warranties manufacturers will take a more active interest in making sure all the wet materials are removed. If the roof is to be entirely removed this is not an issue. A moisture scan may be required.
20 year systems generally have to use heavy duty fasteners on the insulation (and membrane if mechanically fastened system), enhanced perimeter (either with extra membrane or special metal details), enhanced seam details (extra EPDM over the seams and around penetrations), thicker or reinforced membrane and thicker insulation or cover boards. Fiberboard insulation is not acceptable.
25-30 year warrantees are not obtainable for ballasted systems – mostly due to the dirt that will accumulate between the rocks and dry rot the rubber (like car tires on an old car). Expect to have to completely strip the existing roof to the deck, utilize .060 or thicker reinforced EPDM or .90 mil thick non-reinforced EPDM. All materials used will have to be by the same manufacturer. No tie-in’s to adjacent roofing areas would be allowed. Enhanced perimeter, seam and penetration details are usually required. Pull-out tests to determine whether the deck will provide sufficient integrity to install the roofing system on are often required.
TPO systems: Most of the same rules that apply to EPDM apply equally to TPO with the main exception being less extra work at the seams. Since TPO (and PVC) seams are heat welded they are already about 3x stronger than any joining EPDM together. As the membrane already is reinforced, you can usually obtain up to a 25 year warranty with .060 TPO membrane. To get a 30 year warranty will require a thicker membrane (likely .080″ thick).
PVC systems: Interestingly you don’t find too many PVC manufacturers offering warranties greater than 20 years, even though their products have been around that long (and TPO hasn’t). The two PVC manufacturers Sika-Sarnafil and Duro-last both stack up equal or better than TPO in our opinion.