What's the minimum clearance required when installing rigid duct work on vertical walls with drywall and 2x2 framing.

If I don't install drywall behind the rigid duct work for which there's only 1/2" of clearance, can I install mineral wool in the wall cavity?

I will build a soffit using 2 x 2's spacing them 1" away from the ductwork on two sides to the left of the duct and the front of the ductwork

bathroom wall to install Duct work


  • 1
    Is this ductwork for environmental air? Or is it for combustion exhaust?
    – DrSparks
    Commented Sep 29, 2021 at 0:30
  • Its from the Furnace in the basement
    – Jeff84634
    Commented Sep 29, 2021 at 0:38
  • They had a 7" Round Duck, but it takes up to much space, next to the toilet, with that said it will have a 3.43" clearance from the Right side of Toliet Tank with New drywall and 2x2's to cover the 7" Ductwork it's OD Dimensions are 11.56" Wide with the 7" Round Duct inside it.
    – Jeff84634
    Commented Sep 29, 2021 at 0:46
  • 1
    So, at the bottom the long face of the duct is parallel to the brick pillar, however at the top the duct is shown with the duct long face perpendicular to the pillar. How are you going to achieve this? Or is this an Escher diagram?
    – Solar Mike
    Commented Sep 29, 2021 at 5:16
  • 1
    @Jeff84634 SolarMike is saying the orientation of the duct at the floor is 90 degrees from where the duct is at the ceiling. It looks physically impossible like this mcescher.com/gallery/most-popular/#iLightbox[gallery_image_1]/…
    – Brad
    Commented Sep 29, 2021 at 17:20

2 Answers 2


As DrSparks answered, no clearance is needed for this. HVAC people will even sometimes even use part of a joist (or other) cavity itself as part of the air path when doing retrofit work, and there isn't another way to get the ducting into the space.

  • You have enough rep now, please delete your "not an answer" and make it a comment in the appropriate location.
    – FreeMan
    Commented Sep 29, 2021 at 12:18
  • 2
    @FreeMan If he deletes his answer, he will lose the rep and thus the ability to comment on others' posts. The information about going through framing members is also worth the answer standing on its own, I think.
    – TylerH
    Commented Sep 29, 2021 at 13:54
  • What's a rep mean? Is Rep an Acronym? I'm brand new to this site.
    – Jeff84634
    Commented Sep 29, 2021 at 15:19
  • 1
    @Jeff84634 "Rep" is an abbreviation for "reputation", which is the Stack Exchange Network's name for the points which accumulate from votes on your questions and answers and various actions (editing, accepting answers, having an answer accepted, and bounties). The amount of reputation is used for various privileges on the site, including the comment everywhere privilege at 50 reputation. Prior to having >= 50 reputation, a user can only comment on their own posts and any answers posted on their own question.
    – Makyen
    Commented Sep 29, 2021 at 15:47

You don't need any clearance for drywall and environmental air ducts. It could be touching it if you wanted. Heck, you could glue the drywall to the ducts if you wanted to 🤣

  • 1
    but can the ducts hold up the roof? That is the real question... Finally I get to realize my dream of building a house out of only ducts! Commented Sep 29, 2021 at 16:33
  • 1
    @user253751 As long is it is a duct roof you'll be fine.
    – psaxton
    Commented Sep 29, 2021 at 18:37

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