A.Joe Lstiburek responds: The main benefit of a rain screen is to increase moisture removal by creating a ventilated cladding. The ventilated cladding allows drying of both the siding (from the back surface) and the wall assembly (through the sheathing and building paper) into the air space behind the siding. Some sidings, including vinyl, aluminum, and brick veneer, are inherently self-ventilating. Other claddings, like wood siding, need help. In a rain-screen installation, the wood siding is installed over vertical battens. Alternatively, some installers vent clapboard siding by using wedges, clips, or oval-headed ("bumpy") nails to separate the siding laps.

What is the real benefit? Well, is it a benefit for the siding not to rot, and the paint not to peel? Before the days of plywood, OSB, foam sheathings, cavity insulation, and interior poly vapor barriers, wet siding could dry towards the interior. Today’s walls have low drying potential, due to the use of impermeable or semi-permeable sheathing,...

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