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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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.
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.
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) 18.104.22.168.6. 22.214.171.124.7, and 7.1. As they say, mind the (air) gap, they usually want more than 2".
5/18/2020 12:16:33 pm
There is a lot of things to consider with TJI construction 126.96.36.199.5.2 2016 and check the Annex material to really get a sense.
5/19/2020 10:11:13 am
Why would the insulation need to be moved to the bottom?
5/19/2020 08:38:00 pm
Both 188.8.131.52.5.2.10 (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.
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.
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.
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