Written by Jon Davies
Technical Sales Support and Education Manager, Pro Clima New Zealand

In the previous two articles in this series, we presented the challenge of finding materials that work extremely well in both summer and winter conditions. This is challenging. If we prevent moisture movement into the frame, we will likely prevent any moving out again. Ideally we need two directions for drying using materials that prevent moisture-loading into the structure in winter, and allow moisture out in the summer.

One solution to this challenge is to use a humidity-variable vapour control layer such as INTELLO that operates predictably in both summer and winter to prevent moisture accumulation within the insulated structure.

Why would you do this?

1. Knowledge of materials and how they relate/react to each other is expanding.
2. Understanding moisture and how it relates and interacts with materials is increasing.
3. Combining understanding with practical application in buildings creates four things:

• • Health (occupants in a mould-free structure)
  • Investment protection (durability)
  • Comfort (whole-house warmth) — see image below
  • Energy efficiency (building envelope)

These are in no particular order — the point being, attempt to achieve one and the others should follow. It could be argued you can just buy comfort, and while this may be true, homes should not be inefficient by default — only just meeting H1 requirements — when we know there is going to be 'line loss' away from energy efficiency during construction.

Airtightness and Intelligent moisture management

Achieving energy efficiency starts by insulating continuously and preventing drafts (leaks). Dealing with internal moisture should be achieved by ventilation and with intelligent moisture management that is capable of reacting to the current ambient conditions, i.e. by reducing diffusion in the winter and being permeable to permit diffusion in the summer.

These characteristics are provided by the intelligent airtightness and vapour control membrane INTELLO which has variable diffusion resistance. Installed on the inside of the insulation layer/framing, it is:

• Diffusion-reducing in the winter, when the vapour diffusion flow current is from the inside toward the outside
• Diffusion-open in the summer, when the vapour diffusion flow current is from the outside toward the inside.

The airtightness of the building envelope ensures optimum effectiveness of the thermal insulation and a healthy living environment.