Interpretation #9487

Published February 06, 2026

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Original Request

Code Version
2023
Code
BUILDING
Code Description
Chapter
Section
Test Protocols for High Velocity Hurricane Zone, Eighth Edition, Roofing Application Standard (RAS) No.118-20 and No.120-20
Topic
Drawing 3 of RAS 118-20 and RAS 120-2-: non-wowen underlayment at valleys

Question

The Technical Director of Building Codes & Standards Office, advised me that, the Florida Building Code does not permit woven underlayment installation at valleys in the High Velocity Hurricane Zones (HVHZ), and that he was unaware of any other authority that allows weaving underlayment at valleys in HVHZ.
From the Drawing 3 in RAS118-20 and RAS120-20, Owens Corning's Technical Bulletin (see attached), and #11 of page 4 of Miami-Dade Notice of Acceptance (NOA, see attached), I drew an illustration of the way to install the Owens Corning’s underlayment (see attached). Please note that the Westlake Tileseal HT Underlayment is manufactured by Owens Corning and distributed by Westlake Royal Roofing LLC.
On Page 4, Number 11, the NOA says: “11. When applying the membrane in the valley, start at the low point and work to the high point, rolling the membrane from the center outward in both directions. For ridge applications, center the membrane and roll from the center outward in both directions.”
Referring to Owens Corning's Technical Bulletin’s V-shape picture:
(1) "the low point" in Number 11 equates to the low point of "V."
(2) "Start at the low point and work to the high point" means that, to start, on either arm of the V, place the 1st strip of underlayment at "V"'s bottom point, "rolling the membrane from the center outward," either left outward or right outward.
(3) Repeat steps (1) and (2) with the 2nd strip of underlayment, at a high point.
Are my understanding and illustration correct, please?

Answer Published 01/22/2026 at 12:21 PM

Items are required to be installed in accordance with manufacturers instructions, their listing (if applicable), and the requirements of the code. When there is a test protocol that has been approved, there is an indication of compliance as the product was installed per the instructions and was tested successfully.

Commentary

None.