Air Control Layer

The second most important building envelope control layer is the Air control layer. Here’s the list of control layers again as a reminder:

  1. Water
  2. Air
  3. Vapour
  4. Thermal

A strategy that can be implemented is to use the wall wrap as an air barrier. In order for this to be an effective strategy the wall wrap must be flashed, taped and secured well to connections at the top and bottom of the wall, and around any penetrations such as doors, windows and services. If water can get through, air can get through.

If Air gets into the structure it carries dust, toxins, pollen, and MOISTURE which in turn causes health issues and structural damage. Air moving through insulation also dramatically decreases the performance of the insulation. Air leakage from the building can also equate to up to 60% of your heating/cooling bill.

As you can see in the supplied images, air tightness is not being achieved with this wall wrap.

Understanding the purpose and location of the control layers is essential in achieving a good result for the building envelope. A wall wrap that is not applied properly is a poor water control layer and a hopeless air control layer.

Therefore, due to the typically poor installation of the wall wrap, it is often better to address the Air control layer at the internal plasterboard line. Plasterboard is a good air barrier and is vapour permeable. Attention to air sealing the penetrations through this layer of the building envelope may be the best option.

It is best practice to deal with air sealing at both the plasterboard line and the wall wrap line. Neither will be perfect but in addressing both there will be a higher chance of achieving adequate air tightness.