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Looking for an inventive way to fireblock in an unfinished part of a basement right under an upstairs tub (regular cast iron).

I won't bother with a picture because too much going on. But the "hole" is a ~18"x18" square that includes the tub drain, part of the tub, and the interior wall it is attached to (guessing this is what got it dinged).

Underneath it... wow... main stack, every water run in the house, electrical, the main I beam... and under that is a walkin closet. So there is (bottom to top) a walkin closet then a mess of stuff above it in a cavity then the hole to the tub.

Cannot really put anything on the adjoining walls due to the mess of pipes, almost zero wood to secure it (pipes are that close) and electrical... This is the first time in 20+ years I have been flagged for a firestop in the middle of a house!

Suggestions, questions, creativity needed or I am going to have to build a big box and section of a ceiling to cover this area...

Let's complicate matter even more... the square I need to fireblock... it is basically out of reach. No tool will get in between the pipes and there is a solid 2 feet of cavity - emptiness from bottom of pipes to the square.

Note: Was explicitly asked not to use spray foam by inspector.

DMoore
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2 Answers2

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I was surprised that any fire blocking is required in single family residences. I had to look it up.

Section R602.8 requires it for “all concealed draft openings (both vertically and horizontally), to form effective barrier between stories, and between top story and roof space.” Also required at “openings around vents, pipes, and ducts at ceiling and floor level.

Approved materials are in Section 602.8.1 and includes: 1) 2” nominal lumber, 2) 2 layers of 1” nominal lumber with lap joints staggered, 3) 23/32” structural panels (plywood), 4) or 3/4” particle board, 5) 1/2” gypsum board, 6) 1/4” cement board, 7) batts or blankets of mineral or fiberglass is approved for compliance with the 10’ horizontal fire-blocking in walls constructed using rows of studs, but must be held in place. “

Also, Section R602.8.1.1 says “unfaced fiberglass batt insulation shall fill the entire cross section of the wall cavity to a minimum height of 16” measured vertically. When piping is encountered the insulation shall be tightly packed around the obstruction.”

Lee Sam
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Interesting call with inspector and thankfully got a guy who knows his stuff and not looking to be a jerk.

Me: Bob (fake name). Got this big hole in my unfinished ceiling with a mess of stuff around it. You can barely even see the cut out (you have to be at the exact right spot and angle to see it), how did you see the wall exposed?

Bob: I see everything haha.

Me: You going to make me enclose that whole area. You know that will screw over the new homeowners bigtime. (main stack, half the plumbing in the house, few electrical runs... all inaccessible)

Bob: I am not supposed to give advice but enclosing it does seem to hurt next home owner.

Me: So I can just stuff the thing with rock wool?

Bob: That seems like an option.

Me: OK good, that is like a whole batt but I will put it up there.

Bob: Well that would have about triple the fire rating as you throwing up some flashing or sheetrocking around it.

Me: OK thank you. Was going to ask you if the city had a 2' drill extension it would let me borrow.

So answer: stuffing cavity with insulation (fire rated).

Just to be clear was a pain in the ass this location is I don't think I can get the roxul in unless I cut it in pretty small squares. This will take 20-30 mins.

DMoore
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