Wood Joists + Sound Channel Sprinkler Strategy?

5/18/2020

We're designing a wood, NFPA 13 apartment with a flat TJI roof (engineered floor and roof joists) with batt insulation at the top of the TJI bays and drywall screwed to the bottoms of the TJI's.

The top floor units are protected using a wet system with the required 8 sprinkler calc. The architect wants to switch to sound channel (thin metal channel strips that run perpendicular to joists) which creates gaps between the TJI's and drywall ceiling.

We informed him that with channel, the batt insulation would need to be at the bottoms of the TJI space - which would separate our pipe from the heated space and present freeze issues. Of course, he and the GC never have had this 'problem' with any of their other similar roof structures and they're looking at me, the bad guy, for a solution.

Short of a complete roof re-design to trusses, what have others seen done with TJI roofs with sound channel in areas subject to freezing?

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9 Comments

Casey Milhorn

5/18/2020 10:15:42 am

Couple questions. Are you positive you need an 8 head design. I haven't double checked, but I thought this would meet one of the allowable omissions of a non-sprinklered concealed space and would still only require 4 residential sprinklers to be calculated.

On your main question. Why does the insulation have to move down? Just to avoid sprinklers in the newly created concealed space? Can the entire space be filled with insulation with your pipe running between the "sound" channel bays?

Darren

5/18/2020 10:26:37 am

Typically the channel is left off of the top floor (roof structure), since there is no reason to isolate from sound above.

Anon

5/18/2020 10:34:07 am

I'm heading into a meeting not so I will have to check back in a bit, but NFPA 13 addresses issues such as this, including use of hat channels. But one annoyance that usually comes up, is what about roof vent space above the insulation?

5/18/2020 10:42:20 am

Again, I am replying on the run, so I apologize if I am misunderstanding the question, but NFPA #13 (2016) 8.15.1.2.6. 8.15.1.2.7, and 7.1. As they say, mind the (air) gap, they usually want more than 2".

Jonathan Joseph

5/18/2020 12:16:33 pm

There is a lot of things to consider with TJI construction 11.2.3.1.5.2 2016 and check the Annex material to really get a sense.

As far as the top floor and worried that temperature will reach below 40 Degrees. Just fully insulate and they wouldn't have to worry about the combustible concealed space and your pipe.

If they fully insulate all combustible concealed spaces and joist channels typically we can use a 4 head calc in 1500sqft. instead of adding the 4 because of TJI contruction.

Mike

5/19/2020 10:11:13 am

Why would the insulation need to be moved to the bottom?

I don't know a lot about architectural design in freezing conditions.

Seems like the whole space would need freeze protection since I assume plumbing will be installed there, too. Or, do they come from the floor below?

How many floors is the apartment? Is a separate system required for each floor?

Dave

5/19/2020 08:38:00 pm

Both 11.2.3.1.5.2.10 (2016) and the chapter 8 section defining spaces not requiring sprinks state that the 3.5" of batt insulation must be at the bottom. I'm assuming it's to block the passage of air/fire through the channel space between the composite joists and gyp board.

I believe the OP is concerned that locating the insulation at the bottom will isolate the pipe in the space from the heated space, which has the potential to freeze the pipe.

I'd suggest what Darren said - fully insulate the spaces. However, to keep from freezing, the pipe will still need to be tented so that there isn't insulation between the pipe and the drywall ceiling. We've done similar and the AHJ bought off on it being 'fully insulated'.

5/19/2020 11:20:54 am

By the way, when faced with not having a heated attic space to run upper floor piping, companies I worked for would often pipe sprinklers for the top floor vertically, from the floor below, going up walls with stand-off hangers, maybe even supply rooms on opposite sides of the wall with the same vertical.

Dale Morris

5/19/2020 12:18:26 pm

I've had owners decide they want a dry system for the top floor in lieu of providing a heated space. I am located in Massachusetts, so this issue of how to protect the wet pipe system comes up quite often.

Wood Joists + Sound Channel Sprinkler Strategy?

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