The moisture content of air in crawl spaces beneath suspended timber floors

Moisture build-up in the crawl space beneath suspended timber ground floors causes wet or dry rot and leads to structural damage to the floor. Ventilation is intended to prevent this, but is often inadequate, and calculations are presented indicating the amount of ventilation needed under a range of conditions. Measurements of crawl space ventilation rates and humidity made in an occupied house are given, and other methods of reducing moisture build-up are considered.