For attention of Rendel House residents in particular.
Tony Fenton, retired surveyor, gives his kind opinion on the issues with condensation in general, and more specifically to the conditions in many Rendel House flats.
- please ventilate flats efficiently
- use a dehumidifier 24/7 (costs a few pence per minute); and always if drying washing inside
- heat flat adequately
- clean around bottoms of windows behind curtains regularly where Air can get stale
Those are the basics but here is the background.
“You may already know this, but I’ll start with the obvious.
Condensation occurs when air containing water vapour reaches a cold surface at ‘dew point’, the temperature at which the air can no longer hold the vapour.
Water vapour naturally gets into the air when we breathe, but more so when we use hot water in cooking, bathing, showering and clothes washing.
We can lose most of the air containing water vapour by venting at the source. Bathrooms have extractor fans, so they should be on, preferably with the bathroom door closed while running hot water. They should have an overrun to continue extracting for a short period after being used. The fans in cooker hoods should be on while cooking on the hob. The trickle vents in the window frames should be open most of the time for background ventilation. Drying clothes should be done outside or near to open windows.
The warmer the temperature in a property, the greater amount of water vapour can be held in the air, so condensation is more likely if internal temperatures fall below 18C. I have noticed that some apartments are not using the space heating appliances available, so temperatures are less than desirable.
In most buildings condensation will form first on the coldest internal surface, which is often glazing. Unusually for a relatively modern flat conversion, the coldest internal surfaces in Rendel House are the columns next to the large windows and the beams supporting balconies above. Being solid concrete and with no insulated internal lining, the concrete forms a cold bridge to the external surface, so the temperature of internal surfaces will not differ significantly from outside. In extremely cold spells of weather the internal surfaces will be at their coldest and prone to condensation. I have also noticed that mould is more prevalent behind furniture or curtains, as there is little warm air movement and the surfaces stay colder.
This is not to say that there can’t be any leaks due to weatherproofing defects, especially with so many stepped balconies above apartments. The difference is that leaks will tend to be isolated, and condensation will form in a number of areas.
Unfortunately, a number of design errors were made when Rendel was converted to apartments. Originally, the hospital wards windows would not have been well sealed, so very leaky and well ventilated. However, there would have been huge radiators keeping the temperature up. Now, with well sealed windows and expensive to run heating systems, a lack of natural ventilation and low temperatures can lead to condensation forming. The balconies should have had thick insulation on the top surface of the concrete slabs, underneath the waterproof layer, but doesn’t look like they do. If they did, the ceilings and beams would be at a higher temperature than they are. The columns between the windows should have been lined with insulation, but may not have been. This may have been because they were prevented from doing this because of the building’s historic status. Something to think about if a balcony needs re-roofing in the future. Or else the NHBC checks missed it. NHBC warranty ran until 2015.”
NHBC: under the NHBC warranty, and individual leaseholder had the right to make a claim. It had to be done individually. But in 2015 the then directors, spearheaded by Diane Drain, managed to put together a group claim and get a membrane added to the roof of the balcony, and later install lead flashing.
Later still, in 2023, further works were done around mortar and filling gaps at bottoms of railings as part of regular maintenance.
This has all helped enormously. Most flats now do not suffer from black mould if the above recommendations are followed.
However condensation will still happen especially around the Crittall windows old metal windows which gather a huge amount of water on windowsills et cetera. We recommend using the little plastic pots of dehumidifier balls you can buy easily online, but this continues to be a problem in many flats. Please ventilate well et cetera.
Please note the latest conversations around debating critical windows et cetera happens on the residence WhatsApp group. Please join.
Any queries please email directors and [email protected]
Tony Fenton, retired surveyor, gives his kind opinion on the issues with condensation in general, and more specifically to the conditions in many Rendel House flats.
- please ventilate flats efficiently
- use a dehumidifier 24/7 (costs a few pence per minute); and always if drying washing inside
- heat flat adequately
- clean around bottoms of windows behind curtains regularly where Air can get stale
Those are the basics but here is the background.
“You may already know this, but I’ll start with the obvious.
Condensation occurs when air containing water vapour reaches a cold surface at ‘dew point’, the temperature at which the air can no longer hold the vapour.
Water vapour naturally gets into the air when we breathe, but more so when we use hot water in cooking, bathing, showering and clothes washing.
We can lose most of the air containing water vapour by venting at the source. Bathrooms have extractor fans, so they should be on, preferably with the bathroom door closed while running hot water. They should have an overrun to continue extracting for a short period after being used. The fans in cooker hoods should be on while cooking on the hob. The trickle vents in the window frames should be open most of the time for background ventilation. Drying clothes should be done outside or near to open windows.
The warmer the temperature in a property, the greater amount of water vapour can be held in the air, so condensation is more likely if internal temperatures fall below 18C. I have noticed that some apartments are not using the space heating appliances available, so temperatures are less than desirable.
In most buildings condensation will form first on the coldest internal surface, which is often glazing. Unusually for a relatively modern flat conversion, the coldest internal surfaces in Rendel House are the columns next to the large windows and the beams supporting balconies above. Being solid concrete and with no insulated internal lining, the concrete forms a cold bridge to the external surface, so the temperature of internal surfaces will not differ significantly from outside. In extremely cold spells of weather the internal surfaces will be at their coldest and prone to condensation. I have also noticed that mould is more prevalent behind furniture or curtains, as there is little warm air movement and the surfaces stay colder.
This is not to say that there can’t be any leaks due to weatherproofing defects, especially with so many stepped balconies above apartments. The difference is that leaks will tend to be isolated, and condensation will form in a number of areas.
Unfortunately, a number of design errors were made when Rendel was converted to apartments. Originally, the hospital wards windows would not have been well sealed, so very leaky and well ventilated. However, there would have been huge radiators keeping the temperature up. Now, with well sealed windows and expensive to run heating systems, a lack of natural ventilation and low temperatures can lead to condensation forming. The balconies should have had thick insulation on the top surface of the concrete slabs, underneath the waterproof layer, but doesn’t look like they do. If they did, the ceilings and beams would be at a higher temperature than they are. The columns between the windows should have been lined with insulation, but may not have been. This may have been because they were prevented from doing this because of the building’s historic status. Something to think about if a balcony needs re-roofing in the future. Or else the NHBC checks missed it. NHBC warranty ran until 2015.”
NHBC: under the NHBC warranty, and individual leaseholder had the right to make a claim. It had to be done individually. But in 2015 the then directors, spearheaded by Diane Drain, managed to put together a group claim and get a membrane added to the roof of the balcony, and later install lead flashing.
Later still, in 2023, further works were done around mortar and filling gaps at bottoms of railings as part of regular maintenance.
This has all helped enormously. Most flats now do not suffer from black mould if the above recommendations are followed.
However condensation will still happen especially around the Crittall windows old metal windows which gather a huge amount of water on windowsills et cetera. We recommend using the little plastic pots of dehumidifier balls you can buy easily online, but this continues to be a problem in many flats. Please ventilate well et cetera.
Please note the latest conversations around debating critical windows et cetera happens on the residence WhatsApp group. Please join.
Any queries please email directors and [email protected]