Water always finds a way behind siding. Once it has done so, its potential for causing problems increases, and its potential for escaping or drying is greatly reduced. To prevent this trapped water from causing damage behind the siding, we need to give it an easy way out. It needs a place to go and a way to dry—and a vented rain screen offers both. Although the details of building a vented rain screen can be tricky, senior editor Justin Fink explains the steps involved and answers some common questions about matters such as how big the gap should be behind the siding, how to keep insects out, whether to vent at both the top and bottom, whether it's OK to tie the exhaust into the attic vents, and whether to vent corner boards. He also includes information on materials—battens, wraps, mats, and membranes.