March 25, 2014

5 Reasons Why Airtight Drywall Is Obsolete

air barrier crack

Cracked Gypsum Board Joint

After perhaps keeping the rain out, airtightness is the most important thing we can do to make our buildings energy efficient and comfortable.  That’s a building science fact.  A fully functional air barrier is fundamentally important to the proper functioning of the building.  Consequently we should take necessary steps to ensure that the airbarrier works, not just on the last day of construction but until the last day of occupancy: 50 years, even 100 years in the future.  And we should help optimize its ability to succeed through the materials and means and methods we use to construct the air barrier.

In our quest for greater airtightness, the Airtight Drywall Approach (ADA), which was developed in the 1980s, does not sufficiently optimize chances for success, nor does it last. Consequently ADA has lost its usefulness.

Let’s look at the reasons why:

1.  ADA connections are often inflexible.   Air barrier connections should be flexible.  Buildings move. Components expand and contract.  Taped gypsum board joints are not flexible.  Often, after the first winter, there are cracks in taped joints (see above photo).  Often, the spray foam and caulking used to connect gypsum board to wood framing elements harden, embrittle, shrink, crack, and fail after just a few years.  Even if hiding behind base and crown moldings, the holes are lurking.

airtight drywall floor connection

Building Science Corporation

2.  ADA is not continuous.  Continuity is an essential characteristic of an air barrier.  Gypsum drywall, the primary air sealing material, is not continuous.  It stops and starts at floor and ceiling construction and often at perpendicular interior walls.

3.  ADA is a sacrificial layer.   Air barriers should not be sacrificial layers, they should be protected from damage. Occupants cut, hit, bang and otherwise assault the drywall – don’t leave your air barrier’s fate in the hands of unruly occupants.

4.  ADA doesn’t minimize the number of penetrations.   Every penetration is a potential failure point.  We should minimize the quantity of penetrations and ADA air barrier cut holedoes the opposite – every electrical outlet box and every wire going into the box multiplies the chances for failure.  The best practice instead, is a service cavity.

5.  ADA is not vapor intelligent.   Gypsum wall board is vapor open and vapor retarding paints are not intelligent.   With an inboard air barrier, in a cold climate, there is a unique opportunity to combine air control and vapor control in a robust system by utilizing vapor intelligent membranes like Pro Clima INTELLO and DB+, thereby minimizing wetting potential, maximizing drying potential and increasing the drying reserves and the safety of the assembly.

For these five reasons ADA doesn’t ensure success; it ensures failure. So like single pane windows, exhaust only ventilation, and code minimum insulation levels before – as we push for higher performance – it’s time to remove ADA from your tool box.

Instead, for a complete approach to robust, resilient and long lasting airtightness see:

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5 Responses to 5 Reasons Why Airtight Drywall Is Obsolete

  1. Cody Farmer March 26, 2015 at 5:33 am #

    Removing drywall as an air barrier is a wise choice. Particularly when the code is looking at individual unit air tightness. Passing a blower door with Drywall is temporary. As people move in and out of buildings drywall can become holier than a vegetable strainer.

  2. Scott June 18, 2015 at 4:01 pm #

    Remember, we aren’t looking for LITERAL AIR-TIGHT. We are not trying to accomplish a hermetic seal. We are only trying to eliminate the largest air exchange areas in order to bring the exchange rate down to acceptable levels, NOT eliminate it all together. Your house does need to breath and even if you could make it air tight you would not want to. Furnaces nowadays have a required inlet for fresh air introduction, so the tighter you make your house, the more air your furnace will pull in from outside through this inlet. Hence, there is a point of diminishing returns. You also don’t want stinky air coming in through your chimney when you turn on the exhaust fan on the range or in the bathroom which will happen if your house is too tight. If you caulk the sole plate to the subfloor and use at LEAST 1 inch of spray foam in your walls and around the rims to get a seal, you are pretty much all set. Going further than this is generally a waste of your time or money.

    Note you can SKIP trying to seal the drywall to the cap and sole if you simply go up in the attic and spray the wall caps with spray foam (after drywall, before attic insulation). If you want, you can caulk the ceiling joist / wall intersections with small beads of caulk prior to drywall too to further seal the attic from the wall cavities.

    • Ken July 15, 2015 at 7:07 pm #

      Hi Scott,
      Actually we are trying to make the enclosure literally air tight. The furnace should be direct vented to the outside. Exhaust air flows should be balanced with supply air – with heat recovery provided.

  3. Reg November 19, 2015 at 12:56 pm #

    I agree with your comments. I lived in Sweden back in the 70’s when they were already building units air tight. Here we are 35-40 years later and we are now finally understanding the need for air tight buildings. Recently I was involved in building and inspecting a passive house for the west coast of BC Canada, Bella Bella which was a great experience.
    I have a question for you, do you know if installing 6 mil poly (rated as a type 2 vapor barrier) behind vinyl cover drywall (that also is a type 2 vapor barrier and a air barrier) will be a problem with black mold forming between the two layers? Is there a way of doing this application without having this potential problem?

    • John November 20, 2015 at 5:30 pm #

      Our recommendation is to always increase the drying capacity of your assembly. The greater the capability of your wall to dry out, the less risk. I would typically assume 6 mil poly and vinyl drywall to be Class 1 vapor barriers, essentially vapor closed. Even if they are Class 2, greater ability to dry will always be a less risky assembly. I don’t believe there is a way to assemble the materials you reference in a manner that decreases their risk. We detail our optimum assemblies in our ebook, which you’ll find in the knowledge resources section of the site(https://foursevenfive.com/product-category/quality-control/books/). We recommend INTELLO Plus as the interior vapor retarder / air barrier along with a service cavity (insulated or uninsulated), followed by drywall. Hope that helps.

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