Thermal Control Layer

The last on the list of building envelope control layers is the Thermal control layer. Here’s the list of control layers again as a reminder:

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

The thermal control layer is important. So why is it at number four on the list?

It’s at number four because it won’t work effectively if the other three items haven’t been addressed first.

When we talk about increasing the thermal performance of a building it is important to get our priorities right. Increasing from 6 stars to 7 or 8 stars won’t work unless we address items 1-3. Increasing insulation values can actually make our moisture problems worse if we treat ‘Thermal’ in isolation and don’t address moisture & air management.

Having adequately addressed the Water, Air and Vapour layers, we can now get serious about achieving a good thermal result. This is where extra insulation, continuous insulation, good quality thermally advanced windows, and thermal breaks can be successfully implemented into the building envelope.

In order to address the thermal layer correctly it is important to think of it in relation to the ‘building envelope‘. The ‘Thermal Layer’ is not just insulation batts. It is every surface that separates inside from outside, conditioned space from unconditioned space. This includes windows and doors. It also includes the structure itself. Understanding each of these items in relation to heat transfer is vital in applying a successful strategy for thermal performance.

Once we have adressed our control layers adequately, we then have more assurance that our heat load calculations are valid. Conversely, a leaky, poorly insulated house will not live up to its calculated heat load.

Click here to vistit my heat load article. Below is an overview.

Heat Transfer = Conductance x Area x Temperature difference; OR,

The basic calculation for a heat load is:
Q = U A ΔT
Q = heat transfer (Watts)
U = overall heat transfer coefficient (U-value is the Conductance, which is the inverse of an R-value), 1/U-value=R-value
A = Area (m2)
ΔT = (Delta T is the temperature difference between inside and outside)