This article explains the multiple causes of the severe damp affecting many ground floor flats on the Hanger Hill Garden Estate and describes the solutions.
There are 84 ground floor flats on the Hanger Hill Garden Estate, many of them suffering from quite extreme damp and condensation problems in comparison with first and second floor flats.
All the ground floor flats are adjacent to at least between 3-5 drain pipes serving the flat including one to three rainwater downpipes (from the roof) , a soil stack and an open gully collecting grey water such as bath and shower water.
If any of these drains are cracked at the base they will be leaking water into the soil immediately adjacent to the nearest ground floor flats.
Recent experience shows that the large majority of these drains are cracked at the base and leaking water. Only a small proportion of the drains have been repaired since the flats were constructed around 1935. The majority of the underground drains are of original construction i.e. cast iron and clay pipes. The local soil is London clay which is very prone to shrinkage in dry weather which results in cracks in the drains.
At the time the flats were built (c. 1935) there was no requirement under building regulations for a damp proof membrane to cover the loose soil under the flats. Instead a thin layer of water porous “oversite” concrete was used to cover the soil.
The serious condensation in many of the ground floor flats is the result of a combination of factors;
- Tenant lifestyle: Cooking, breathing and washing.
- Reduced ventilation (blocked chimneys and air bricks ) since the original 1935 construction.
- Broken drains leaking water into the soil under the flat.
- Blocked underfloor ventilation.
- Overflowing gutters which pour water on to the outside surface of the windows rotting the frames and leaking inside the flat.
How broken drains contribute to internal damp and condensation;
- Broken underground drains next to the base of the building result in wet soil under any adjacent flats.
- Warm air in the flat rises pulling up the damp air through the gaps in the wooden floorboards.
- This damp from below air adds to the humidity in the flat map and will condense on the coldest part of the flat usually the windows and the walls of the small bedroom at the rear.
Why is the small rear bedroom particularly prone to condensation damage ?
- The smallest room gets the least air circulation.
- End terrace rear single rooms have two outside solid walls, therefore they are much colder than the cavity walls at the front of each block.
- The majority of the drains are at the back and immediately adjacent tot he small rear bedroom. Therefore if the drains are broken under the ground the first room to be affected by damp air rising through the floor will be the rear bedroom.
What can be done to prevent ground floor flats from suffering from damp ?
- Educate the flat owner to unblock the original air vents and install additional active and passive ventilation such as humidistat extractor fans particularly in the kitchen and bathroom.
- Educate the flat occupant to adopt a damp free lifestyle by opening kitchen and bathroom windows after use and ventilating the whole flat by opening windows in all rooms for at least 30 minutes a day each room.
- Insist that the HHGE Block management treat all water leaks as an emergency to be fixed within 48 hours. Water leaks include all leaking gutters, blocked downpipes and cracked gullys and drains.
- Insist that the HHGE Block management systematically dig out all the old and leaking drains throughout the HHGE and replace the cast iron and clay with plastic drains to current building regulations standard.
- Insist that the HHGE Management reduce the soil level in all the flowerbeds surrounding the base of the flats to two bricks depth below the damp proof course.
- Insist that the HHGE Management remove all pebble dash render from the external brick layers below the damp proof course and the bottom layer of render be finished with a bell mouth drip groove.