Causes of Damp
Condensation Damp:
Mechanism: Excess humidity or water vapor in the room condenses on cold surfaces, especially in poorly ventilated areas.
Scientific Explanation:
Air's capacity to hold water vapor decreases with temperature.
Example: Room air at 20°C and 60% humidity cools near a 12°C wall, exceeding its vapor storage capacity, causing water to condense.
Common Locations: Corners and areas with thermal bridging (e.g., metal fixtures reducing wall insulation).
Lateral Damp:
Mechanism: Water penetrates the building envelope, entering from the outside.
Causes:
Leaky gutters or downpipes.
Rotten windowsills.
Rising Damp:
Mechanism: Moisture is drawn up from the ground via capillary action due to a missing or compromised damp-proof course.
Causes:
High water table or leaking drains.
Lack of an effective damp-proof course in older houses (e.g., pre-mid-19th century).
Early damp-proof courses included slate layers, engineering bricks, or bitumen.
Solutions for Damp
Condensation Damp Solutions:
Improve ventilation, especially in poorly ventilated areas (e.g., corners).
Ensure walls and surfaces are adequately insulated to reduce thermal bridging.
Lateral Damp Solutions:
Repair gutters, downpipes, and windowsills.
Address external sources of water ingress.
Rising Damp Solutions:
Soil Drainage:
Install French drains:
Perforated pipes in trenches filled with pea shingle to divert groundwater.
Pipes wrapped in geotextile material to prevent silt blockage.
Maintain a minimum distance of 500mm from walls and ensure trench depth avoids foundation pressure (45° angle clearance).
Include a rodding eye for maintenance and cleaning.
Lower ground levels around external walls to enhance evaporation.
Evaporation Zones:
Create gravel zones alongside walls to allow moisture to escape.
Trial Excavations:
Before digging near old walls, check foundation depth and soil conditions to avoid destabilization.
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Disclaimer:
The information provided in these posts is for informational purposes only and should not be considered design advice, specifications, or a calculation template. We assume no responsibility or liability for the use of the information presented. For professional advice or design services, please contact us via our contact form.
Reference:
Roger, H., Marianne, S. (2017). Old House Handbook: A Practical Guide to Care and Repair. Quarto Publishing PLC.
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