Informal interpretations, numbers 9462 and 9475, appear to be based only on the prescriptive provisions of FBC R905.11 and do not consider or address the alternate material provisions in the code. FBC 104.11 allows for alternate materials and methods to be approved by the building official where certain criteria are met. State Statute, Title XXXIII, Chapter 533 describes the process for product evaluation and approval and specifically lists evaluation entities that are recognized. One of those entities—the International Association of Plumbing and Mechanical Code Officials Evaluation Service (IAPMO UES)—publishes an evaluation report that addresses the use of ZIP System® roof sheathing in the application described in your informal interpretations. Please refer to IAPMO UES ER-424 Section 3.1.2 and Florida DBPR Product Approval No. FL17147-R7.
Is the use of State product approval issued using a product evaluation based on 3rd party testing and rational analysis by an approved product evaluation entity listed in Chapter 533 in lieu of the prescriptive method?
Interpretation #9486
Published February 03, 2026
Original Request
- Code Version
- 2023
- Code
- RESIDENT
- Code Description
- Chapter
- 9
- Section
- 905.1.1.1
- Topic
- Roof underlayment
Question
Answer Published 01/22/2026 at 12:15 PM
The information provided indicates the change made in the product approval which authorizes this product as indicated.
Commentary
If installed as per manufactures recommendations, Zip systems sheathing will meet the code requirements of 905.1.1 if used for asphalt shingle applications only. If other roofing materials will be used, (clay tile) then additional secondary water barrier would be required. So, the answer depends on the type of roofing being applied. If installing clay or concrete tile roofing, a second underlayment is needed regardless of slope. See section 2.3 of the revised evaluation report in FL17146-R12.