Module 2 · Buildings and How They Handle Moisture
2.7 Roofs, Floors and Basements
9 min read
Walls get most of the attention in damp surveying, and a large proportion of the water that ends up in them arrived through something horizontal. Roofs concentrate the catchment of an entire building into a few metres of junction detail. Floors sit on ground that is permanently moist. Basements are below the water table for part of the year and are subject to a pressure that no wall detail above ground ever faces. Each changes what the evidence means.
Learning objectives
By the end of this lesson you will be able to:
- Trace water from a roof-level entry point to the internal evidence, allowing for travel.
- Distinguish suspended and solid ground floor problems by their evidence.
- Explain hydrostatic pressure and why it makes below-ground work a different discipline.
- Identify where thermal bridging at junctions produces condensation misread as ingress.
Key terms
- Hydrostatic pressure
- Positive water pressure from a head of ground water. Below ground it drives water through any breach, which is why below-ground work manages water rather than resisting it.
- Type A / B / C protection
- The BS 8102 categories for below-ground protection: barrier (tanking), structurally integral, and drained cavity. Type C manages water rather than excluding it.
- Cold roof / warm roof
- Whether the insulation is at ceiling level with a ventilated void above, or at rafter level with the void inside the insulated envelope. Determines where condensation forms.
- Sub-floor ventilation
- Cross-flow air movement beneath a suspended floor, which keeps timbers below the moisture content decay needs. Blocked air bricks are among the commonest causes of floor decay.
Read the rest of Buildings and How They Handle Moisture
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.