Understanding & Specifying Openings

Rough opening, clear or unobstructed opening are terms that can cause costly disruption in the construction process. Understanding each of these openings will help in reducing costly errors and time delays with sensitive deadlines.

  • openingRough Opening refers to a framed opening. With items such as windows, access doors and floor doors, the product is generally installed inside the opening. For items such as roof hatches, scuttles, smoke and fire vents, the curbs line up with the rough opening.
  • Clear Opening, often referred to as net-clear or unobstructed opening, is the cross-sectional area available for a person or object to pass through. This space must be unobstructed from all elements, including handles, springs, frames, cables – nothing but air.

When specifying smoke vents, an important metric is the effective venting area. This is calculated using the square area of the curb opening minus any frame/mullions and operating parts that obstruct smoke and other noxious fumes from escaping. For roof hatches, such as the Personnel series, elements such as spring packs, hold open arms, catches, handles and ladders are obstruction objects that must be accounted for. This is especially important when configuring for firefighter egress as required per IBC 1009.166.1.

For best practices, when communicating with manufacturers, specify both rough and clear opening sizes as clear openings will vary. Nystrom understands these codes and requirements. For more information or to see how Nystrom can assist with your next project, please visit www.nystrom.com.