CONDENSATION! Clive Gibbs

WHAT IS CONDENSATION? Condensation occurs where moist air comes into contact with air, or a surface, which is at a lower temperature. Air contains water vapour in varying quantities, its capacity to do so is related to its temperature - warm air holds more moisture than cold air. When moist air comes into contact with either colder air or a colder surface, the air is unable to retain the same amount of moisture and the water is released to form condensation in the air or on the surface. Condensation is generally noticeable where it forms on non-absorbent surfaces (i.e. windows or tiles) but it can form on any surface and it may not be noticed until mould growth or rotting of material occurs

WHAT IS CONDENSATION? RELATIVE HUMIDITY AIR TEMPERATURE MOISTURE As the temperature increases the ability of the air to hold more moisture in the form of water vapour increases – therefore the RH decreases

CONDENSATION: Normally occurs in the colder months Starts on the coldest internal surfaces Most often occurs in rooms of high moisture production Also in unheated rooms, or rooms with paraffin or butane heaters or unvented tumble dryers Concentrates in areas where air movement is restricted Two types: Surface Interstitial

SURFACE CONDENSATION: Air contains water Higher temperature more moisture Saturation point

SURFACE CONDENSATION: Can occur

SURFACE CONDENSATION: Cold bridging

SURFACE CONDENSATION: Be careful

SURFACE CONDENSATION:

MOISTURE The moisture in the air comes from a number of sources within the house.

INTERSITIAL CONDENSATION: Surface condensation and mould growth produce immediately visible problems on the inside surface of buildings. Interstitial condensation is more insidious; before it becomes visible, it can already have caused severe structural damage. During normal winter occupancy there are greater differences in temperature and vapour pressure from inside to outside IC occurs in the fabric of the building and is often not identified until some surface damage has occurred

INTERSITIAL CONDENSATION: How?

INTERSITIAL CONDENSATION:

INTERSITIAL CONDENSATION:

PARTIAL FILL:

FULL FILL:

INTERNAL INSULATION:

TIMBER FRAME:

EXTERNAL INSULATION:

FLAT ROOF:

CONCRETE ROOF:

DESIGNING: Balance of factors

VAPOUR CONTROL LAYERS: Used within the construction to control the vapour passing through the fabric of the building Placed on warm side of insulation EG Foil backed plasterboard or cavity insulation

VAPOUR CONTROL LAYERS: Partial Fill

VAPOUR CONTROL LAYERS: Partial Fill Insulation DEW POINT

REFERENCES: BRE Hollis – Surveying Buildings Digest 54 Digest 163 Digest 329 Digest 380 Understanding Dampness Tackling Condensation Hollis – Surveying Buildings Hoxley – Construction Companion to Building Surveys Marshall – Understanding Housing Defects Parnham – Residential Property Appraisal http://www.diydata.com/problem/condensation/condensation.htm