Please add as a comment on the gravel issue for the meeting on the 19th.

 

Thanks

--------------------------

Sent from my BlackBerry Wireless Handheld

 

 

 

----- Original Message -----

From: David Roodvoets [dlrconsul@charter.net]

Sent: 03/07/2008 02:57 PM

To: <Mo.madani@dca.state.fl.us>

Subject: Ballasted Roofs

 

Mo

 

The following summarizes the basic industry position on ballasted roofs:

 

Wind design for aggregate and ballasted roofs.

 

For the last few cycles of the IBC code change process the roofing industry

has been trying to educate the structural committee on the differences

between aggregate as used in asphalt built up roofs (BUR) and stone and

other materials used to ballast single-plys.  Since the late 1970šs the

roofing industry has separated the aggregate used in BUR from the stone or

other ballast used in single-plys.

 

The aggregate used for BURšs has been well defined in ASTM D1863 and

incorporated into the code. This is relatively small in size usually less

than 1Ž2˛ in diameter.  It can perform well in high winds if it is adequately

embedded into the asphalt matrix, or is on a roof with a high parapet.  BUR

roofs are designed to be fully adhered to the underlying roof matrix, either

the roof deck or insulation that is above the roof deck.

 

The stone used for ballast has been sized using ASTM D448.  The wind

performance of this material was extensively studied in wind tunnels and by

field inspections during the 1970šs and 1980šs resulting in the development

of ANSI/SPRI/RP-4.  The key reason for developing RP-4 was to eliminate

improper use of stone ballast.  The standard considers two common sized

stones, those of about 1 1Ž2˛diameter or #4 stone, and those of about 2 1Ž2˛

diameter or #2 stone.  The tables in RP-4 have a large safety factor, and

there have been additional safeguards added to prevent systems being

installed using small aggregate in hurricane prone areas. See Paragraph 2.6

of RP-4.

 

RP-4 requirements were again validated during the RICOWI inspections

following the 2004 Florida hurricanes, and hurricane Katrina.

 

Table 1504.8 in the IBC was developed by a structural engineer based on load

factors.  It does not correspond to wind tunnel or field reported data for

products commonly used in the roofing industry.

 

 

Further Questions please cal me at 231 893 1291

 

Dave

David L. Roodvoets

DLR Consultants

6710 Lakefront Dr

Montague MI 49437

Phone 231 893 1291