Humidity problems explained

Humidity, coastal Galicia’s bête noire! If you own a Galician home then humidity is a topic you need to be familiar with, because if you aren’t the chances are that soon enough you will be unpleasantly au fait with its negative consequences.

Air is capable of holding water vapour within it, and “relative humidity” is basically how much water air holds as a percentage of its capacity, and this capacity changes primarily depending on the temperature of the air.

It may seem like this article has already decended into physics; it can’t really be helped! But in fact we are all familiar with relative humidity in practice – when your bottle of cold, crisp albariño beads up with condensation on a warm day, the wet surface of tiles in a bathroom or kitchen after showering/cooking, the dew falling and, of course, rain. All of these things are examples of air cooling down, its relative humidity exceeding 100% of its capacity to hold water, and that water coming out of it.
The opposite effect of air absorbing water is also all around us: clothes drying on the line or on radiators, skin drying and cracking in winter, and that bottle of cold, crisp albariño going down inexplicably fast on a warm summer’s day …well, it probably accounts for a few drops anyway!

OK, so this goes on but how does it actually affect you and me? Within the air, furniture and construction materials of any house there is a lot of water, and we rely on the air in all those substances to keep it in its fairly harmless vapour form and to maintain furniture, fabrics and construction materials in a dry condition. When the air’s capacity to do this gets exhausted (because it changed temperature and/or because we added more water into the equation) the results are:

  • An uncomfortable environment (feels colder in winter, hotter and closer in summer)
  • Condensation on windows and cold walls
  • Mould growth (especially on badly ventilated external walls, eg. behind fitted furniture)
  • The proliferation of bacteria (airborn and surface dwelling)
  • The proliferation of house dust mites (which can cause severe allergic reactions)
  • The proliferation of woodworm
  • Furniture and building materials deform

…so when you visit a Galician property that the agent rushed to first to open the windows and air and it still feels clammy and smells bad you know why. And this is just the immediately obvious stuff – the woodworm, dust mites, mould and bacteria will all become apparent later on if you buy it!

I would love to say at this point that galiciaproperty’s search and survey services can help you find a coastal Galician house without a humidity problem …but to be honest they’re rare as hen’s teeth and so it’s best to assume that there is a humidity problem that requires active management unless someone proudly shows you a functioning system in place to prevent one.

Why is humidity such a problem in Galicia?

Galicia is 3/4 surrounded by sea and any air coming in over the sea (and in Galicia this is most of it) has had ample opportunity to get its relative humidity up very high. This also explains the rainfall levels, by the way. The main problem, however, is actually (coastal) Galicia’s mild climate.

Let’s relocate briefly to the Sweden. It is also largely surrounded by sea and yet any normally heated house, even the old ones, there doesn’t have an excess humidity problem. In fact they often have the opposite and are uncomfortably dry inside in winter.
The reason for this is daily temperature swings and an inside/outside temperature difference.
Earlier we said that air’s capacity to hold water changes depending on its temperature. Let’s expand on that with a graph now:

When we are sitting in the perpetual darkness of the Swedish winter with only the various happy glows of a mug of glögg and the adventsljusstake to hold introspection and depression at bay, the air that fills our house and that we heat to 19 C (for example) is drawn in from outside where the temperature is perhaps -5 C.
Let’s suppose that that air was at 95% relative humidity at -5 C, how does that change when we heat it? To see this we look along the horizontal axis, and we find that that same air, once heated to 19 C, has a relative humidity of only 20%. To put that in context, the average relative humidity in the Sahara is 25%. Of course this gets added to by people breathing, bathrooms and cooking, but it’s still far drier than the 70%+ relative humidity levels where the problems above start.
Is it always -5 C in the Swedish winter? No, but as that’s a typical nighttime temperature any warmer daytime air has recently been cooled to that sort of temperature and it won’t have picked up so much moisture since, so it’s rather like air that has recently been through a dehumidifier. This is the benefit of a large daytime/nighttime temperature swing.
So in Sweden unless a house is sealed against all ventilation or you don’t heat it it won’t have a humidity problem.

Now let’s travel south and west to the UK, making sure not to read or watch any news lest it start us ranting about Brexit and idiocy. Again we have a lot of water all around, but now the outside temperature in winter averages more like 5 C. Let’s assume it’s grey and drizzling intermittently with 95% humidity; what happens to that air if we let it into our cramped, cheaply built and yet insanely expensive little English house? Looking along from 5 C @ 95% RH we can see that at 19 C that air is now at around 40% relative humidity, and so, again, with reasonable ventilation and heating there won’t be a humidity problem.

And now we arrive in Galicia. In coastal Galicia the average winter temperature is around 12 C and the swing between day and night temperatures is typically not that large. Looking again at 95% relative humidity and assuming we heat that air up to 19 C we find that our heated, inside air is at 65% relative humidity. Even if we add to that the minimum of human breathing and perspiration, cooking and bathroom use it’s clear that the humidity is going to go well above the 70% level where problems start in earnest.

…and unfortunately the answer is not as simple as opening the windows to ventilate the house, because, unlike inland or in northern Europe, there just isn’t a natural source of relatively dry (when heated to 19 C) air to be had because of Galicia’s combination of high average humidity (c. 80%) from it’s proximity to the sea and mild average temperature that doesn’t produce much temperature swing dehumidification effect.

The result, if you don’t take action, looks like this and can seriously impact your and your property’s health and wellbeing.

As this isn’t what we like to see here at our next article, Managing Humidity, explains the various strategies for dealing with this problem.