Exterior Water Management

Matt Risigner When HardiePlank covers the walls, ripped strips of the material can be used to form the rainscreen. Rainscreens can also be made with 1x3 solid wood strapping.

Water will always get behind siding. Wind blows in through gaps, and when the sun beats down on wet siding, it drives moisture inward. If the siding is pressed tight against plastic housewrap or applied over foam sheathing, the front of the siding tends to dry while the back stays wet. This stresses all types of siding: It cups boards, curls shingles, accelerates stucco cracks, and weakens mortar bonds in brick veneer.

Don't rely on caulks and sealants to stop water, as they will deteriorate over time. Instead, apply the siding over a good weather-resistive barrier (WRB), or sheathing wrap, and properly installed flashing. This system should be used under any type of siding.

A WRB does not act as a drainage plane by itself; you need to create a space between the WRB and the siding. The most effective way to do this is with a rainscreen: battens or a drainage mat that creates a space behind the siding. The space should have vents at the top of the wall to promote convective air flow, and weep holes at the base of the wall to let water drain out. Nailing the siding to battens has the added advantage of reducing the nail penetrations through the house wrap.

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