Effective 1/1/2021:
Update to underlayment requirements in the
7
th
Edition (2020) FBC-Building and FBC-
Residential:
A sealed roof deck (SRD) is required.
• where felt underlayment is used, it must be
30# or equivalent (ASTM D 226 Type II,
ASTM D4869 Types III or IV)
• installation techniques such as number of
plies, lapping, and fastener spacing has been
strengthened
• For concrete and clay roof tile,
underlayment is required to be in
accordance with the FRSA/TRI Florida High
Wind Concrete and Clay Roof Tile
Installation Manual, 6
th
edition.
For asphalt, metal, mineral surfaced, slate and
slate- type roof coverings, there are essentially
three options for creating a sealed roof deck that
vary a bit depending on the type of roof covering.
A summary of the three options available is as
follows:
Option #1 – a self-adhering polymer-modified
bitumen underlayment complying with ASTM
D1970 applied over the entire roof.
Option #2 – a minimum 4-inch wide strip of self-
adhering polymer-modified bitumen complying with
ASTM D1970 or a minimum 3 ¾ - inch wide strip of
self- adhering flexible flashing tape complying with
AAMA 711, applied over all joints in the roof decking. A
felt underlayment complying with ASTM D226 Type II,
ASTM D4869 Type III or IV,
or ASTM D6757, or a synthetic underlayment meeting
the performance requirements specified, is required to
be applied over the strips/tape over the entire roof.
(See Table 1507.1.1.1 of the FBCB or Table R905.1.1.1
of the FBCR for fastener type and spacing).
Option #3 – two layers of felt underlayment comply
ASTM D226 Type II or ASTM D4869
Type III or IV, or two layers of a synthetic
underlayment meeting the performance
requirements specified, lapped and fastened as
specified.
Last Rev 11/9/2020 DOCUMENTS SUBJECT TO CHANGE WITHOUT NOTICE