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Community and Q&A

Subfloor air sealing

Vivian Girard | Posted in Energy Efficiency and Durability on

I am currently building a small affordable multifamily building in Boston.  It’s a slab on grade 4-floor building with standard wood frame.   We are getting close to installing the subfloor sheathing for the second floor.  We picked GP DryPly -a tongue and groove plywood with a coating that makes it (supposedly) more water resistant during construction. Probably not as good as Advantech sheathing, but big price difference. Currently Advantech is $70/sheet in my area.  With some discount I was able to purchase DryPly for $40/sheet.  I decided to take a chance.   

We need to do air sealing between the floors. Doing a quick online search on the web and on this site I couldn’t find much info on this topic.  I am considering taping the joints with 3M 8067 tape (Found some online for $25 for a 75′ roll). I’ve used some of that tape on various material in the past. When properly applied (dry and clean substrate + lots of pressure on the roller) it’s tenacious.  

If anyone has some experience to share with air sealing a tongue and groove subfloor, I would welcome the advice. Thanks

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  1. Expert Member
    Malcolm Taylor | | #1


    There was a very good blog about two years ago on GBA on building a high performance multi-storey residential building (which I'm afraid I can't find. Perhaps other readers remember more about it).

    The main takeaway was that air-sealing the top storey was where to put the emphasis, to reduce the stack-effect. As I recall, they sheathed the underside of the trusses with OSB and limited penetrations.

    A T&G subfloor with the sheathing bedded in adhesive should be pretty air-tight. I doubt tape would survive the construction process. I would concentrate on detailing any penetrations, most of which would occur in wall cavities and chases. The ceiling is another place which might be fruitful to detail similarly to those under attics, with air-tight electrical boxes, etc.

    Edit: found it.

  2. Expert Member
    Zephyr7 | | #2

    Malcolm sort of beat me to it, I was going to suggest putting in the T and G sheathing the same way you do T and G flooring -- a bead of adhesive in the joint as you lay each sheet down. That would at least get all the seams in one direction, leaving only the perpindicular joints to deal with.

    I'm curious why you want to air seal all the floors though. As Malcolm also mentioned, you only really need to seal the top floor to deal with stack effect. Do be sure to get all the penetrations though. A canned foam gun and some caulk are your friends here. You might even have to use intumescent fire stop caulk in a 4 story building. I can't say for sure on that though, I've never worked in a wood framed building of that size. Intumescent fire stop caulk will make a good air seal too if you have to use it, as will fire stop putty (which is usually sold in small sheets) for larger things. Fire stopping works for air sealing too.


  3. Vivian Girard | | #3

    Thanks Malcolm and Zephyr for your input. I went back to reread the article about Jesse Thompson's projects -I now remember reading it a while back. There are some useful points from multifamily energy efficiency expert Jesse. On a side note, I actually made the trip to Portland-ME a couple of years ago to take the NESEA-organized tour of the Paris Terrace project he was working on. I even got to talk to him and was a little starstruck!

    Not many details in the article on floor-to-floor air sealing but I am leaning toward taping the floor as late as possible in the construction phase to limit damage. Caulking the tongue and groove doesn't feel as dependable to me.

    I can see why sealing the top floor and roof matters most, but compartmentalization of every unit is a big deal for energy efficient apartment buildings. This took me back to reread another article written 5 years ago by air tightness and ventilation guru Sean Maxwell. For people interested in this topic, it's well worth revisiting this piece and the associated links.

    1. Expert Member
      Malcolm Taylor | | #4


      Thanks for the link. That's very interesting.

  4. Expert Member
    Akos | | #5

    Air sealing assemblies is a lot of manual labor and even then small shortcuts can negate a lot of the benefits especially when it comes to sound. Sealing all those flanking paths is a lot of work and easy to miss section.

    For the my rental places I don't allow indoor smoking, so most of the air sealing was done for sound. For that, I found that T&G + subfloor adhesive was good enough.

    Generally the bigger issue is dealing with all the hidden air paths and flanking, I think in some ways it would be simpler to flash the underside of the subfloor with an inch or so of spray foam. This way there is less chance of the air barrier getting damaged during the build and easier to cover those hard to seal places. Spray foam does a great job of air sealing, but doesn't do all that much for absorbing sound, so the floors would still need to be insulated with batts.

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