Volume 9, Issue 8 - September 2008

AAMA Analysis 

Sill Height Code Proposal Poses Hurdles

Today’s windows must address many issues while meeting a multitude of requirements, some of which conflict and require reasoned trade-offs. A case in point is accommodating the dual missions of preventing children from falling and providing an emergency exit. What’s Safest: 36 or 24?

Attempts to regulate the minimum sill height began with a 2001 recommendation for 36 inches. The latest requirement, codified in the 2006 International Building Code and International Residential Code, calls for a minimum sill height of 24 inches for operable residential windows located more than six feet above grade (unless the window is fixed, equipped with a window guard or cannot be opened more than four inches). Given the opinion that such a requirement would compromise egress for fire safety, many state jurisdictions that otherwise adopted the 2006 I-codes elected not to include the sill height minimum.

Consequently, the ICC Code Technology Committee (CTC), established by the International Code Council’s (ICC) Board to study various code issues, introduced a change proposal (RB173) into the 2007/2008 code revision cycle that would preserve the 24-inch minimum sill height requirement but would introduce four exceptions. These include the provision of fall prevention devices or guards that comply with ASTM F 2006, Standard Safety Specification for Window Fall Prevention Devices for Non- Emergency Escape (Egress) and Rescue (Ingress) Windows, or ASTM F 2090, Specification for Window Fall Prevention Devices With Emergency Escape (Egress) Release Mechanisms, and those equipped with load-resistive screens that meet the requirements of ANSI/SMA 6001, Specifications for Metal Protection Screens. The Screen Manufacturers Association (SMA) has decried such referencing of this standard, as it addresses security screens intended to prevent forced entry and was not designed to address fall protection.

Also exempted from the minimum sill height requirement would be windows with a self-acting window opening limiting device (WOLD) capable of prohibiting the free passage of anything larger than 4 inches through the maximum permitted opening. The WOLD must have a clearly identified and easily operated release mechanism to allow for emergency escape.

This proposal, which the industry judged as posing significant compliance problems, was disapproved by the ICC at its February hearings.

Public Comments Could
Reverse Decision
But the issue is still up for consideration at the September 17-23 Final Action Hearings. The original RB173 proposal, although disapproved in February, could be resurrected and “approved as modified” per public comments (PCs) received in the interim.

Foremost of these PCs would reintroduce the formerly attempted 36- inch minimum sill height. Raising the minimum sill height to 36 inches greatly limits the opportunity to provide an adequate opening size to meet egress requirements and could make it difficult for some types of window products to serve as a means of egress/ingress during the event of a fire or other emergency. It is mathematically impossible for double-hung and single-hung products to meet the minimum egress opening requirements in an eight foot wall if the sill has to be 36 inches above the floor.

Another PC would replace the requirements for WOLD that were in the original RB173 with a reference to ASTM F 2090. However, as ASTM F 2090 is undergoing the revision balloting process and not yet published, there is currently no standard defining WOLDs.

A third PC would remove reference to the SMA 6001 standard and clarify the requirements for operable sections of windows that are within 24 inches of the floor.

Given the possible consequences, the AAMA Codes Working Group and the WOLD Sub-Task Group have highlighted the need to inform stakeholders of the problems if such requirements are codified.  Chuck Anderson serves as certification manager for the American Architectural Manufacturers Association in Schaumburg, Ill. He may be reached at canderson@aamanet.org. His opinions are solely his own and do not necessarily reflect those of this magazine.


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