BU594 Excessive moisture in enclosed subfloor spaces (2016)

Insufficient ventilation under the house can lead to high subfloor moisture levels. This, in turn, can lead to problems such as rot, corrosion, borer infestation, loss of insulation performance and reduced durability in building materials. This bulletin outlines ways to avoid the build-up of moisture levels in subfloor spaces and how to manage the moisture that does occur.

This bulletin updates and replaces Bulletin 457 Ventilation of enclosed subfloor spaces.

The bulletin covers:

• Building Code and standards requirements
• sizing and positioning of vents
• sources of subfloor moisture
• effects of subfloor moisture
• signs of excessive subfloor moisture
• steps to remedy excessive subfloor moisture
• moisture entry through a retaining foundation wall.