Coverage of Window Sprinkler for a Tall Facade?

4/24/2025

I am trying to understand the criteria for designing window sprinklers for a tall glass space.

The application is a very large façade greater than 300 feet (91 m) long and 45 feet (14 m) high. The vertical mullions are 14'-9" center to center (4.5 m).

What is the definition of a story, and how does it apply as stated in NFPA 13 8.7.8.1 "A single line of sprinklers is permitted to protect a maximum of two stories of wall area or two levels of vertically aligned windows where architectural features are sufficiently flush to allow rundown?"

This height seems like it would be well above a two-story height, but what would that be reasonably defined as?

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4 Comments

Pete H

4/24/2025 09:44:26 am

In NY Fire Code "Story" is defined as:

That portion of a building included between the upper surface of a floor and the upper surface of the floor or roof next above (see "basement", "building height", "grade plane", and "mezzanine"). A story is measured as the vertical distance from top to top of two successive tiers of beams or finished floor surfaces and, for the topmost story, from the top of the floor finish to the top of the ceiling joists or, where there is not a ceiling, to the top of the roof rafters.

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In my opinion, "story" doesn't really apply to your situation due to the lack of floors.

However, "two levels of vertically aligned windows" may very well apply, as I doubt the facade is one singular 45 foot tall by 300 foot wide piece of glass. So how tall are the windows?

If this does not work, another tactic might be to take the story distance where the building actually does have two floors and apply the worst case scenario.

Either way, I'd say please make sure there's some form of baffle keeping your lower "level" of sprinklers from being cold soldered by the ceiling level.

Dan Wilder

4/24/2025 09:50:07 am

So there is a slight description issue I wanted to ask about....

You are asking about providing sprinklers for exposure protection as allowed within 8.7 (2019 Edition of NFPA 13, possibly later editions but this is the one open in front of me currently).

The definition of 'Story" in the IBC is "...portion of the building included between the upper surface of a floor and the upper surface of the floor or roof next above..." (in a nutshell)

Window sprinklers (Like the Tyco-WS & the Reliable WP) has specific installation criteria for widow width, height, and other factors so watch for those. I don't think the height will be the limiting factor so much as trying to get the correct GPM for the window that large without multiple levels.

I have seen a story be al little as 9' and as large as 50' so not sure there is a height limiting factor for that definition.

Todd Delisle

8/22/2025 11:09:14 am

Most window sprinklers that I have found to date limit the MAXIMUM EXPOSED HEIGHT OF GLAZING to 13'-0", I'm looking for a head right now that allows more.

Jack G

4/24/2025 12:23:00 pm

While the applicable use of fire sprinklers for the protection of windows appears to be a simple process it is, in accuality a rather complex consideration.
The first is to understand what a window sprinkler is and is not, and how to appropriately integrate them into the sprinkler design of the building; this is a much more complicated process than one might assume. Nfpa 13 treats window sprinklers as " special application sprinklers", and does not include design parameters in its text. Section 8.15.26 was added in the 2016 edition and gives limitatiins on when they max be installed,/ used.
For this reason, window sprinklers should be incorporated into the design by the A&E design
Proffessional and it is they that should present the design to the AHJ.
Section 104.1 of the IBC refers to aternate material, methods of construction and equipment. and gives latitude to utilize the use of window sprinklers in lieu of fire rated glass.
Time of separstion ( up to 2 hrs)
Look to see if the walls are fire walls( non load bearing fire walls as in IBC 707.
WS are not allowed in areas where frequent .
Detonation occur.
The building must be protected with 100% sprinkler protection.
Size of glass. must be vertical not sloped or curved
Glass must be at least 1/4 inch thick and tempered.
and must be fixed glass.
The IBC 404.6 allows for closely spaced sprinklers to be utilized with rated glass and frames as an alternate to the 1 hour separation for atriums. This allowance gives a sprinkler designer the luxury of using sprinklers that are specifically listed for glass per nfpa 13 11.3.3 for water curtains.
For 2 hour separations window sprinklers are used on the interior and exterior glass and must be installed per the listed manufacturers design/ data sheet.
For closed space sprinklers are used 15 gpm per liners foot dhould be used or 20gpm for sprinklers 6-8 ft on center. The length of the hydraulic length of the remote area determines the quantity.
The ooenings in the wall and the depth of the horizontal mullies will determine how many levels to be used.
Consult your manufacturerds databsheet for the approved installation.

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Coverage of Window Sprinkler for a Tall Facade?

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