for People with a Passion for Period Property

Sweating stones and mouldy tenants

By Greg Pullen

Post Modern Mould

Damp is the perennial bugbear of many a period home, but it's usually the owner's fault, says Greg Pullen

We manage almost one hundred buy-to-lets, and I need to check each of these every three months. Unfortunately, some tenants see this as an opportunity to bend my ear about the perceived shortcomings in the building, and to lobby for landlord-funded improvements. So when one of our most attractive tenants invited me into her bedroom, my heart sank rather than fluttered. Sure enough, as she perched on the edge of the bed it was to point out the patch of black mould breaking out from behind a bedside cupboard.

Black mould is always, always caused by condensation. It's a feeble fungus, unable to cope with the salts and impurities of damp that have pushed through a wall or floor, and it loves the purity of condensation. Most commonly seen around the glazing bars of single-glazed windows, it will also thrive on cold spots of northern walls, or areas of low air circulation, such as behind bedside cupboards. This winter I seem to have seen far more black mould than usual, and I suspect the problem is not unconnected with the eye-watering rises in fuel prices which are tempting people to nudge the heating down a notch and keep windows firmly shut.

It helps to understand exactly what condensation is. At any temperature, air will hold a certain amount of water vapour. The warmer the air, the more moisture it will hold until it reaches saturation. The Building Research Establishment reckons a typical family will introduce five litres of water vapour into a house every day, which is more than three bucketfuls a week. We even make it easy for the air in our homes to become saturated by introducing this water via showers, kettles and boiling pans. But it all has to go somewhere.

The most visible destination is usually single-glazed windows. These are much colder than the rest of the house, so as the air comes into contact it cools rapidly and dumps the water vapour onto the glass. Double glazing does not cure the problem - it merely hides how much damp is in the air. Because damp air rises, black mould often appears in bedrooms where low air circulation and cooler temperatures mean the air settles and unloads water vapour onto a wall.

The answer to these problems is familiar. Use extractor fans and dehumidifiers, or you could even take a leaf out of Queen Victoria's book and restrict yourself to one bath a year. The funny thing is, we think of this as a modern problem, brought on by lifestyles undreamt of when our period homes were built. But I recently read an extract from an 18th Century journal which made me realise nothing could be further from the truth.

The piece related the case of the traditional Wiltshire cottage, which was made of chalk with a thatched roof. Chalk is famously good at absorbing moisture - this can be a disadvantage, because if you don't keep it dry you risk frost damage or dry rot. But in this case it turned out to be a good thing.

By the 18th Century, England was becoming wealthy and there was a rapid expansion in building. Folk in Avebury, Wiltshire, started to eye up the large stones scattered about in the town, thinking that they would make much more solid walls for their houses than chalk ever could. This, however, turned out to be a very bad idea.

Almost as soon as these stone houses were built, the occupiers found themselves sweating. The problem was clearly condensation. Live in a virtually unheated house built of cold, hard stone, then start boiling water on the hearth, and you're going to get problems. The neighbours in their old-fashioned chalk cottages were sweat-free, because the chalk simply absorbed the damp through the winter months and dried out again in summer.

In these security-conscious times, our houses are sealed up all day and become a little like those stone houses. Fifty years ago, the traditional spring clean involving throwing the windows open all day, every day for a week was the answer - and this is still a good idea. If you have problems with damp in the winter months, wipe away the worst of any black mould with soapy water. Then, when spring arrives, get the house back to its natural equilibrium with a good old fashioned spring clean, windows thrown open, ready to make the most of summer - mould free...

How do modern houses cope?

The building regulations recognise that our current obsession for energy efficiency and insulation means that damp can build up. There are therefore minimum requirements for window sizes and the ability to create a through draught by opening windows. If these requirements can't be met, rooms need to be fitted with permanent extractor fans. Yes, all of your expensively heated air is being sucked out and thrown at the ozone layer. And if the cost doesn't keep you awake at night, maybe the perpetual hum of the electric extractor motor will.

Greg Pullen is a consultant to Strakers, Devizes. Tel. 01380 723451 or visit


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