I'm going to install a 2" conduit from my unfinished basement into the attic, through the first and second floor. It will be used primarily for getting Cat6 cables into upstairs bedrooms. 2" diameter is just for future-proofing it.

I know I need to use a fireblocking caulk around the conduit in each penetration through the bottom or top wall plate, but what about the conduit itself? I'm essentially creating a 2" chimney from basement into attic, and the conduit will be only 25% filled initially. How can I create removable "plugs" for that conduit so I can add more cables later?

  • 1
    Suggest you read up on local electrical (and fire) codes to see what's required. Meanwhile, why not just stuff a blob of insulation into each end? That'll block all airflow and is easy to remove when you want to fish more wires. Commented Aug 9, 2016 at 14:23
  • I've read the NEC, but it was pretty vague... Moreover, the code is MINIMAL requirements, not necessary the best practice. Thanks for the suggestion about insulation, though, I'd do just that unless there is a better way.
    – haimg
    Commented Aug 9, 2016 at 14:42

4 Answers 4


My favorite is to use a thin plastic bag and inject some fireblocking foam into the bag while it's stuffed in the open end of the conduit. That way it expands and plugs the conduit but the plastic bag keeps it from making a mess on the inside of the conduit and your cat6 wires. If you need to add more wires you can just pull the plastic bag + foam out.

  • This may defeat the fireblocking properties of the foam, though.... Commented Aug 10, 2016 at 0:35

Duct seal is another option. Duct seal is a dough-like product that often carries some form of fire rating (depending on manufacturer specification) and it remains flexible.

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    As long as you get stuff that has a fire rating standalone, this I think is the best bet... Commented Aug 10, 2016 at 0:36

A bit of fiberglass (or any fluffy material you have on hand) stuffed in a plastic bag would provide both an air barrier and some insulation value. For an opening that small, that's all that's warranted. The payoff period in heating cost for anything more expensive would be in the decades.


I have seen on some sites expanding foam used, it does have the benefit that it is fairly easily to smash back out at a later date if needed to clear the conduit and is available in fire rated variants.

Comes in a can.

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