Floor slab perimeter insulation

For quite a few years it has been a requirement in the NCC that a ‘heated’ concrete slab on ground needs to have perimeter insulation installed to the edge beam to a minimum depth of 300mm below ground level.

Perimeter insulation is a good idea even if the slab is not heated. The slab edge is a direct thermal bridge to outside, so it makes sense to detail it with the intent to insulate.

Recently the Firstrate 5 thermal performance assessment software was upgraded with the capacity to nominate slab edge insulation……..yes, this means that up until now this energy sucking part of our building envelope was not considered in the computer simulation.

Now that we’re thinking about this particular part of the building envelope it’s worth looking at the detail as provided in NCC with a view to improving on it for your own projects.

Here are a few things to consider to get you going:

  1. Insulating to 300mm below ground level is the requirement, but what about the gap between the ground and the bottom of the wall?
  2. Where does the wall insulation terminate?
  3. Is the floor insulated?
  4. How and where is the floor insulated?
  5. Where are the control layers?

It might pay to get back to basics and follow these links to remember the Water, Air, Vapour & Thermal control layers, and do a red pen test on your drawings.

Lastly, remember that the key to the control layers is CONTINUITY.