Building Performance – Lesson 7

Building Performance – Lesson 7

7. Everything gets wet, let it dry.

There is no stopping water, so the key is to build homes that allow the building materials to dry out once they get wet.

As mentioned in an earlier lesson, all cladding lets some amount of water through. We need to manage this water in the way of drainage and drying. A ventilated air gap behind cladding systems facilitates this process.

We also need to keep wall cladding off the ground. It has long been standard practice to include a damp proof course in our masonry walls to prevent rising damp. We need to remember this principle when we install light-weight cladding as well.

When cladding stays in contact with the soil, it will wick water causing paint film failure and degradation. Capillary action is the wicking of water against gravity. When timber or cement sheet materials get wet, the water can move upward, against gravity, within the timber or cement sheet. Also, if the water wicks far enough up the wall it can begin to cause trouble with our thermal envelope.

To control this process, the material needs a method that either allows it to dry out, or a system that keeps it from getting wet. If we can’t prevent the material from getting wet, then we need to control the extent at which it wicks. So by keeping building materials up off the ground or by sealing them, we can prevent capillary action.

Remember, if it doesn’t dry it’s gonna die.

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