A Science Lesson from a Mould Inspector

An unwanted visitor settled into our flat a couple of weeks ago and he goes by the name of Mould, ugly, black, fury mould. With disgust, I made a complaint to the landlord and he put us in contact with a mould inspector (his name was Sukh and I’m pretty sure he doesn’t specialise in mould… but today he is the mould-master!).

After a quick inspection of our flat he was assured that we had a serious ventilation problem this followed a fascinating lecture about the creation of water vapour in our home.

We create up to 11 litres of water a day inside our homes, it’s true, I checked.

Water vapour source in an ‘average’ house per day Approximate water generated (in litres)

4/5 people asleep


2 people active




Washing up


Washing clothes


Drying clothes




Approximate total 15.7 litres

This water is created through breathing, laundry, cooking and showering. The water vapour follows the rules of convection and makes its way to the colder area of the room i.e. our window pane, where it loses energy and transforms into water droplets, harbouring an environment loved by many kinds of mould.

In old buildings where single paned windows are used, this excess water is usually released into the atmosphere. If I ever had a complaint for double glazing, being good at what they do would be one.

Sukh explained to us that our flat was producing its own weather system, we were essentially creating rain. There was little to stop me raising my arms and shouting ‘Let there be Thunder!!!’ but I don’t think we’ve gotten that advanced yet.

I wonder did Kate and Leo consider proper ventilation?

The warmer the air in our flat the more water it can hold. If our kitchen was 10ᵒC, believe me, sometimes it’s colder, it can hold 7.6g water per kg of dry air but if we heated the air to 20ᵒC it can hold 15.3g water per kg of dry air. At this point the air is said to be saturated i.e. it’s holding the maximum amount of water.

Relative Humidity (RH) is calculated by what portion of actual water vapour is in the air compared to the maximum amount that can be held at a given temperature. So air, at 10ᵒC could hold 8g of water at its maximum but if in reality only 4g was actually found, the RH would be 4/8 x 100 = 50% i.e. the air is 50% saturated. For mould to be a happy camper, a RH of 75% or higher is required and my home appears to be the best vacation spot.

When asking Sukh if we should be cautious of the dangers of mould in the home, he replied ‘’I’m not qualified to give health advice but I would not stay here’’ as he walked towards the front door.

Thankfully, we haven't gotten that bad yet!

Turns out that the black, slimy mould on our window sill is not great as it can produce toxins known as mycotoxins, it’s called Stachybotrys Chartarum. However, this only affects people with lung damage or compromised immune systems. As we’re a healthy-ish bunch of students, the worst that could happen would be hay fever like systems or a slight cough. Still, it better be gotten rid of.

I leave my appointment with Sukh the mould master feeling slightly disappointed. My dreams of creating more interesting weather systems in the home such as hail or typhoons will never come true as he will be installing an extractor fan on the side of our flat that pumps in dry air.

So my future looks like it’ll be mostly dry with some sunny patches and warm spells… Probably for the best.

Dutch artist Berndnaut Smilde uses a smoke machine, combined with moisture and dramatic lighting to create an indoor cloud effect.

To end this blog, here’s a joke to make you cringe: What do you can a person who’s not into tractors anymore? An extractor fan! Get it?


4 responses to “A Science Lesson from a Mould Inspector

  1. Am I the only one I have a good laugh at the ‘2 people active’ statistic? Haha.
    Great blog, glad its being resolved!

    • Tara's eco science blog

      Never thought I could create my own weather 😀 Next time you visit my house should be lovely and dry! Thanks you reading it ❤

  2. I like material like this. This is a great article and I really enjoyed reading it. You have an original style that makes your ideas stand out from other writers.

    • Tara's eco science blog

      Thank you very much for your lovely comment :). I wrote that quiet a long time ago so I hope my writing skills have improved slightly. Great to know you enjoyed it.

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