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Water caused defects_buildings
- 1. Defects in existing buildings Most buildings are old Most buildings have defects Royal Agricultural College
- 2. Topics covered Defects due to water damage Defects due to biological agents Defects due to mechanical damage Royal Agricultural College
- 3. Why is water a problem? Water is everywhere, you cannot keep it out Universal solvent Water is required for biological activity Water expands when it freezes Royal Agricultural College
- 4. Rust, corrosion Black Spot Mould damage Dissolving of materials Dry rot fungal damage Royal Agricultural Damage to finishes College Frost damage
- 5. Rising damp (ground water) Penetrating damp (rain) Wet services (leaks) Condensation (humidity/dew point) Royal Agricultural College
- 6. Rising damp: remedial work Solutions to rising damp problems: Internal tanking, placing an impervious layer between the wet wall and the interior. Inject a chemical DPC but these can be ineffective in some situations Insert porous tubes, open to the outside to ventilate the interior of the wall Cut out a course of bricks and insert a full DPC. Royal Expensive and disruptive. Agricultural But it works College
- 7. Cavity wall: rain exclusion Preventing penetrating damp Cavity construction: the cavity is there to drain away penetrating water. Impermeable rain shield wall covering, such as metal or plastic sheeting rain shield Complete DPC systems often glass or sheet metal around all sides of all openings Good detailing Royal Agricultural Good maintenance College
- 8. Remedial work Overcoat Fix any damage to soaks up rain roofs and openings. Apply a breathable render, the over coat principle DONT apply waterproof paints or coatings. This is will not work Moisture dries Royal out in dry Agricultural College periods
- 9. Water damage from services Many problems caused by water are due to leaks from water and central heating pipes Check that what appears to be a leak in a cold pipe or tank is not in fact condensation on the outside of a perfectly sound fitting. Cold water Cold tank Royal Condensation drips Agricultural College
- 10. Condensation The air holds water vapour as a dry gas. The quantity it can hold depends on the air temperature. When the maximum amount is held for the prevailing temperature, the air is saturated (100% relative humidity). The temperature at which air becomes saturated by the amount of water it holds is called the dew point If further water vapour is added to saturated air, or if the temperature falls, the excess water vapour condenses out as liquid water. Royal Agricultural College
- 11. Surface condensation Surface condensation occurs when the temperature of an internal surface falls below the local dew point temperature. Liquid water condenses out on the surface. Risk of surface condensation is high when internal temperatures drop water vapour increases (in a shower room or kitchen during cooking) Royal Agricultural College
- 12. Boundary layer of still air The few mm of air adjacent to the surface is held still by friction and acts as an insulating layer. This is more pronounced on the internal surface than on the external, where wind blows the boundary layer away Outside Inside Royal Agricultural College
- 13. Temperature gradient through a wall 20属 C in body of room 10属 C on surface 5属 C outside Air temp drops sharply in boundary layer on a cold wall Outside Royal Inside Agricultural College
- 14. Low dew point scenario Air is holding only a small amount of water (low relative humidity) and so the dew point is low, say 4属 C 20属 C inside air 10属 C on surface 5属 C outside Royal Outside Inside Agricultural College
- 15. Low dew point scenario Air is holding only a small amount of water (low relative humidity) and so the dew point is low, say 4属 C 20属 C inside air 10属 C on surface Dew point 4属C 5属 C outside Low risk of surface condensation Royal Outside Inside Agricultural College
- 16. High dew point scenario Air is holding a large amount of water (high relative humidity) and so the dew point is high, say 12属 C 20属 C inside air 10属 C on surface 5属 C outside Royal Agricultural Outside Inside College
- 17. High dew point scenario Air is holding a large amount of water (high relative humidity) and so the dew point is high, say 12属 C 20属 C inside air Dew point 12属C 10属 C on surface 5属 C outside High risk of surface condensation Royal Agricultural Outside Inside College
- 18. Remedies for surface condensation Reducing water vapour content in the internal air Ventilation Cut down on water generating activities Air conditioning Keeping surfaces warm (i.e above the dew point temperature), but theres a problem Royal Agricultural College
- 19. Internal insulation can cause interstitial condensation Internal insulation 20属 C inside air Thermal gradient temp through wall 5属 C outside Inside air temp dew point 12属C Outside dew point 4属C Royal Agricultural College
- 20. Internal insulation can cause interstitial condensation Internal insulation 20属 C inside air Thermal gradient temp through wall Dew point gradient 5属 C outside Inside air temp dew point 12属C Outside dew point 4属C Royal Agricultural College
- 21. Internal insulation can cause interstitial condensation Internal insulation 20属 C inside air Thermal gradient temp through wall Dew point gradient 5属 C outside Inside air temp dew point 12属C Interstitial Outside condensation dew point 4属C could occur in Royal this zone Agricultural College
- 22. Solution: Vapour barrier on warm side of insulation 20属 C inside air temp Dew point 12属C 5属 C outside air temp Layer impermeable Dew point 4属C to water vapour added on warm side: plastic or aluminium foil Royal Agricultural College
- 23. Internal insulation can cause other unexpected problems 20属 C inside During freezing weather air temp Temperature gradient without insulation Wall surface temp 2属C 0属 External air Temp -4属C Royal Agricultural College
- 24. Internal insulation can cause other unexpected problems 20属 C inside During freezing weather air temp Temperature gradient without insulation Temperature gradient with insulation Wall surface temp 2属C 0属 External air Temp -4属C Royal Agricultural College
- 25. Internal insulation can cause other unexpected problems 20属 C inside During freezing weather air temp Temperature gradient without insulation Temperature gradient with insulation Wall surface temp 2属C 0属 External air Temp -4属C Royal The wall is below freezing. Agricultural College If it is wet, it could break
- 26. Summary Liquid water is the damaging agent Determining the source of liquid water is vital to avoid ineffective remedial action The most difficult problems usually result from uncontrolled condensation Royal Agricultural College