In our quest for greater airtightness, the Airtight Drywall Approach (ADA), developed in the 1980s, does not optimize for success, nor does it last. Consequently ADA has lost its usefulness. Like the old oil-fired boiler, once “state of the art” - lose it.
Let's look at the reasons why:
1. Drywall connections are inflexible
And 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. 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.
We’ve all see cracking drywall. Is patching that in your building operations maintenance manual? We didn’t think so.
2. The drywall 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.
Credit: Building Science Corporation
It’s like looking at the blueprint of a transistor radio. Sub-optimal.
3. Drywall 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.
|Drywall will be abused and compromised. Don’t kid yourself.|
4. Drywall doesn't minimize the number of penetrations
Every penetration is a potential failure point. We should minimize the quantity of penetrations and ADA does 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.
A service cavity with wood strapping limits penetrations to just windows and all the electrical outlets and switches are no longer an airtightness concern.
5. Drywall is not vapour intelligent
Gypsum wall board is vapour open and vapour retarding paints are not intelligent. With an inboard air barrier, in a cold climate, there is a unique opportunity to combine air control and vapour control in a robust system by utilizing vapour intelligent membranes like Pro Clima INTELLO, thereby minimizing wetting potential, maximizing drying potential and increasing the drying reserves and the safety of the assembly.
For these five reasons the Airtight Drywall Approach does not help to ensure airtightness; it ensures failure, if not in the short term, most certainly long term. 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.