Have you had a project with an overhang that needed sprinkler protection and extended just beyond the throw of a dry sidewall sprinkler?
It’s a smooth, flat or nearly-flat overhang that’s, say, 21’-6” wide, and in an environment that will dip below 40 degrees F at some point.
What are your options then?
All of the extended coverage dry sprinklers we know on the market cap out at 20’-0” horizontal throw. That would have been our best option.
We could look at using a dry system. There’s the additional cost of the valve, slope requirements, a hit on the remote area size, more corrosion potential – and on and on. It’s costly.
We could look at an anti-freeze system. Those come with more restrictions than they used to, but at a minimum would involve an RPZ and now pre-mixed antifreeze solution. Additional cost.
Heat trace the pipe? That’s problematic, at best. It needs to function 100% of the time that it’s needed, or pipe will freeze. It needs to be supervised. It needs to be maintained. And when in conjunction with pipe insulation it looks terrible.
In short, an overhang that’s just beyond the reach of a dry sidewall sprinkler can take us to a whole new cost tier in the design of a sprinkler system.
We had just this situation on a project a few weeks ago, and tried to think creatively to get a code-compliant solution that’s best for the owner, yet doesn’t spike the cost for a dry sprinkler system that only serves four sprinklers.
Now normally, sprinkler design tends to be a one way street. An architect designs a building. It gets bid and handed down to the sprinkler contractor. The sprinkler contractor “makes it work” with what they’ve been given.
If a consultant is on-board, this would be a great opportunity to pick off challenges like this and advice the architect and owner on ways to mitigate this cost spike for a small project. Perhaps the overhang is designed at 19’-6” instead of 21’-6”. Perhaps they build it with all non-combustible materials if it otherwise didn’t have storage below.
Those could be helpful changes that reduce the overall cost in a major way, but may not be a major detriment to the owner’s goals for the building.
#1 SHORTEN THE OVERHANG
Regardless, we suggested that the width of the overhang be actually shortened to allow a sidewall’s throw to cover the distance and prevent the need for a whole dry system.
That didn’t go anywhere.
#2 EXTEND THE REACH OF A DRY SIDEWALL
We then asked if a soffit could be built to allow a sidewall it’s spacing of no more than 20’-0”.
The soffit wouldn’t have to be heated. It could simply be framed (hopefully of non-combustible studs) with sheetrock or a “Hardie Board” or some other skin. It could be almost completely empty on the inside.
The goal would be to give a dry sidewall sprinkler a back to collect heat and be installed properly.
There’s a few notable rules that come into play here, though.
So working backwards, a soffit that is say, 2’-0” wide and 2’-0” tall would allow a dry sidewall sprinkler to:
But then, we need coverage below the soffit too, right?
This could be accomplished with a flexible dry pendent, such as the V3517 dry flexible pendent sprinkler. Just like the dry sidewall, the flexible dry pendent could contain water back on the warm interior space.
We also would want to offset these locations on plan, so a pendent isn’t immediately under a dry sidewall. Offsetting the locations in plan could help potential cold-soldering concerns.
We’d also want to be sure that both the dry sidewall and the dry flex pendent would be able to be replaced at some point in the near future. NFPA 25 used to require sample testing or replacement every 10 years starting at 10 years after installation, but the 2020 edition bumped that starting point up to 15 years and the 2023 Edition bumped it again to 20 years after installation (NFPA 25 2017-20 Section 188.8.131.52.1.6, 2023 Section 184.108.40.206.1.5).
To accommodate replacement and testing, we might need a way to get access to the inside and the soffit in the future (access panels or future cutout).
COST & CONSEQUENCE
After all this effort – will the soffit cost more? Sure.
Would it cost as much as a dry or anti-freeze system? No, it shouldn’t.
Does it help with corrosion and IT&M in the future, considering we wouldn’t have a dry valve and an additional nitrogen system or air compressor? Yes, that’d help too.
Just an idea that might help address those “in-between” situations that could spike cost for a smaller-sized project that otherwise wouldn’t need it.
What are your thoughts? Have you tried this before? What tips would you suggest?
Hope you’ve found this interesting and perhaps moderately helpful, and I hope you have a great rest of your week!
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Joe Meyer, PE, is a Fire Protection Engineer out of St. Louis, Missouri who writes & develops resources for Fire Protection Professionals. See bio here: About