Building Performance – Lesson 6

Building Performance – Lesson 6

6. Rain follows gravity.

The goal is to have the rain spend as little time as possible in contact with the building materials. To do this, we need to drain the rain. If we don’t drain the rain and flash our openings properly, water can enter the structure and cause decay, material failure and mould growth.

This means we should:
– install gutters that drain to the downpipes,
– Properly discharge downpipes to the storm water,
– Slope site drainage away from the building,
– manage landscaping,
– use appropriate footing waterproofing and drainage systems.

It’s tempting to believe that everything is OK if we have installed gutters and downpipes. However, rain usually comes with wind. The wind driven rain passes through all exterior cladding. It doesn’t matter if it’s timber weatherboard, vinyl, steel, aluminum, brick, stone or fibre cement cladding; in climates with heavy rain and high wind, some rain will get through. It is highly recommended that external cladding should be installed over a vented *drainage plane or *rain screen to allow gravity to do its thing and get rid of the water.

* ‘Drainage Plain’ and ‘Rain Screen’ are terms commonly used in North America. More about the technicalities of these in a later post.

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