AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products

November 23, 1999

To: Director, Engineering
Florida Building Commission

RE: Protection of glazed openings in buildings design in accordance with ASCE 7-98

We have been asked to comment on the requirements for protection of glazed openings in buildings designed in accordance with ASCE 7-98. In short, it is our opinion that the requirement for protection of glazed openings in certain hurricane exposure areas is appropriate for the construction of hurricane-resistant buildings. Depending on the situation, design of the structural members of a building for accidental overloading due to penetration of flying debris may have some value, but must be evaluated on a case-by-case basis.

The consensus of the ANSI group overseeing development of our new Wood Frame Construction Manual for One and Two-Family Dwellings (WFCM) is that designing the structural members of a building for partially-enclosed pressures does not provide the same benefit as protecting the building envelope from flying debris. Designing a building for partially-enclosed pressures only protects structural members against accidental overloads. It does not protect the more valuable interior finishes, contents, and occupants. Further, safety factors on structural elements are generally adequate to cover Aaccidental" loading conditions that might occur due to wind-borne debris penetration. Therefore, we believe that buildings need only be designed for partially-enclosed pressures when the building will be intentionally Aopen@ during the wind event. Finally, the tradeoff of adding 20-30% to the cost of the structural members in a partially-enclosed building vis-a-vis the marginal increase in cost of adding window and/or door protection should be carefully considered. Both are achievable; however, it is our belief that window/door protection provides significantly more value and return on the investment, for the reasons stated above.

Attached are span tables for wood stud walls from the most recent draft of our new national version of the Wood Frame Construction Manual for One and Two-Family Dwellings (WFCM). These tables have been developed using the ASCE 7-98 wind provisions for Exposure B, enclosed building pressures. Spans for other exposures and partially-enclosed conditions, can be approximated with the following factors

If I can assist further please contact me at (202) 463-2770 or, alternately, please feel free to contact our Southeast Regional Manager, Dr. Jeffrey Stone, at (727) 864-9966.

Sincerely,

Bradford K. Douglas, PE

Director, Engineering