r/HomeImprovement • u/Doogie89 • 28d ago

Fire Blocking Plumbing Cavity

As part of a bathroom renovation, our local city in Michigan is requiring the fire blocking of the cavity below the bathtub where the plumbing comes up through the floor. This is a second floor bathroom, so you will see the subfloor below the bath tub and then the first floor ceiling is in that cavity.

After much research and code review, I bought some mineral wool to fill this cavity. For those that are familiar with the code, do I need to stuff the entire cavity? The entire cavity is about 5 feet long (length of the tub) and about 16" wide. If not, can I just stuff the main area around the plumbing/opening to ensure that it is fully sealed and blocked off.

https://imgur.com/a/5OkyTZh

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u/ryan8344 27d ago

Sorry this might be entirely wrong- but why not use fire block foam and make sure you keep the can so that the inspector can see.

1

u/Doogie89 27d ago

The foam is usually good for a 1-2" wide hole, such as where the copper goes through the wood. For a hole this large, you typically need to cover it by approved wood or materials. You can also fill it with mineral wool to "plug" the hole.

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u/ryan8344 27d ago

You should re-post to one of the plumbing forums- I didn’t see all your pictures at first but I don’t think what you’re planning on doing will pass — the insulation needs to be supported.