Rain Screen Principle of Primary and Secondary Defence

A rain screen, in the context of siding is a double moisture barrier. The outer siding could leak between the joints in an extreme storm. A falling branch on the crest of gust of heavy wind could crack or chip it. Either of these could allow moisture through. This could in turn cause damp on the inside of the wall. Applying the rain screen principle can help prevent this happening. Let’s find out more.

The Theory Behind The Rain Screen Principle

Overlapping siding should prevent rainwater or sleet penetrating, unless this strikes the surface almost horizontally with force. In that case, some moisture may penetrate past the joints, and find its way inside the wall through capillary action.

The rain screen principle tackles this problem head on by adding airspace between the siding and the moisture barrier on the inner wall. Any moisture that does admit can then escape via a drain at the bottom of the gap.

Several Names for the Same Thing

The first ‘rain barrier’ we know of appeared in Norway in the 1980’s. In 1963, the Canadian National Research Council published a pamphlet titled “Rain Penetration and its Control” using the term ‘open rain screen’.

Other terms for rain screen systems we have come across include basic, open, conventional, pressure-equalized, pressure-moderated rain screen systems or assemblies. These may cause confusion by distracting attention from the rain screen principles of primary and secondary defences,

We create rain screen walls by separating the inner and outer defences with a system of battens to which the siding attaches. Nobody need know SilverLine Exterior Solutions did this for you because the air gap is usually less than a half inch wide.

More About the Rain Screen Drainage Plane

A drainage plane is the air space between the primary and secondary defenses against water intrusion. Any moisture that enters it, finds its way to a drainage point at the lowest point in the wall where it exits.

Regular seepage is a sign that outer siding has failed somewhere. Investigate this as soon as convenient before water damage affects the battens. We provide this information in the interests of warmer, drier Calgary homes without a spot of inside mold in sight

Don’t hesitate to give us a call at 604-942-0488 if you need more information or advice. Perhaps you have more questions regarding the rain screen principle, or other aspects of the exterior of your home.

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