Module 2 · Buildings & Moisture Basics
2.2 How Buildings Manage Moisture
7 min read
The instinct of most beginners is to look for the hole. But a great many damp problems involve no hole at all: the water arrived entirely normally and the building simply failed to get rid of it. This lesson covers the four mechanisms a building uses to manage moisture, and what happens when each one stops working.
Learning objectives
By the end of this lesson you will be able to:
- Describe the four ways a building manages moisture.
- Explain the difference between a resistant construction and a breathable one.
- Identify which management mechanism has failed in a given case.
- Recognise why sealing a building tighter often makes damp worse.
Key terms
- Breathability
- A construction's ability to let water vapour pass through it and evaporate rather than accumulate.
- Vapour permeability
- How readily a material lets vapour diffuse through it. Lime is high, cement and vinyl are low.
- Buffering
- Materials absorbing moisture when humidity is high and releasing it when humidity drops, damping the peaks.
- Air change rate
- How often the air in a room is replaced. The main route by which internally generated moisture leaves.
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Read the rest of Buildings & Moisture Basics
Module 1 is open to everyone. The remaining six modules — building science, each damp mechanism in depth, meters and thermal imaging, the full inspection method, and report writing — are free too. We just ask for an email so you can pick up where you left off, and so we can send your certificate when you finish.