Construction for health & comfort

It’s a common misconception that the feeling of comfort within a house comes just from temperature. That is a large component but whether a house feels comfortable is also very much a factor of the relative humidity of the air within it, and in few places in Europe is this more true than in Galicia.

Unfortunately what is also true in Galicia is that the commonly used building technology, big, strong houses as it may make, incorporates very little of the many excellent modern technologies available to heat, ventilate and control humidity and damp.
As a result, in even recently built buildings you will often find some evidence of damp penetration and also problems (unpleasant feeling air, mold, flaking paint, discolouration) resulting from humidity produced within the building (bathrooms, kitchens and people).

To construct a healthy and comfortable home (and invariably this also means an energy efficient one too) it is necessary to understand and apply right from the earliest design stages five core issues:

  • Humidity (control of)
  • Damp (prevention of)
  • Ventilation
  • Heating
  • Insulation

And in Galicia it’s sensible to add a sixth:

  • Radon (prevention of)

Get all of these six areas right and you will find that your home feels comfortable and healthy year round. I can’t state this as fact, but I also believe that living long term in a healthy and comfortable house leads to better general health and possibly even increased longevity for its occupants.
And if resale values are on your mind, don’t underestimate the value that getting all of the above right adds to a property, not least because there are so very few properties in Galicia of which this can be said.

(Relative) humidity

Humidity is the amount of water vapour in the air, and for a building that is healthy and feels nice for humans the ideal level of humidity is about 45-55%. These numbers, though, are actually relative humidity, which means the amount of water vapour held in the air relative to its capacity to hold water vapour.

The key point to get here is that air’s capacity to hold water vapour is not a constant thing; it varies, and the main thing it varies according to is the temperature of the air, with hotter air able to hold more water vapour than cooler air.
When your breath becomes visible on a cold day, rain falling from the sky, condensation on windows in the morning and on cold beer cans in the summer – all of these things are relative humidity in action, and the common denominator is that when the temperature of air falls its relative humidity gets higher, and when this reaches 100% the water vapour that the air can no longer hold falls out of it as condensation (a.k.a. rain or dew).

The reasons that an understanding of relative humidity is so important in construction are:

  • Most building materials are air and water permeable.
  • We maintain temperature differences between the inside of our buildings and the outside world.
  • Kitchens, bathrooms and humans breathing emit a lot of moisture into the air of our buildings.
  • When this warmer, moist air inside our buildings contacts colder surfaces (typically exterior walls and windows) it drops its moisture as condensation, often within building materials (interstitial condensation).
  • Moisture can eventually destroy most building materials and it also makes them breeding grounds for mold, insects (eg. woodworm) and so on that in turn make the surrounding air unpleasant and unhealthy for humans to breathe and bad for the fabric of the building.

And the reason that this is so much of a problem in Galicia is:

  • Condensation is generally only a problem in the colder months when we have less ventilation and keep our buildings warmer than outside
  • Further north or inland, outside winter temperatures are quite low, eg. on average 4C in London. When that 4C air gets into a house and is heated up to 20C its relative humidity is very low because even if that air entered the house with 100% relative humidity, at 4C the capacity of that air to hold water vapour was very low (100% at 4C becomes about 35% at 20C, which is actually a major reason so many people get dry skin in the winter in the UK). When heated up its capacity increases, the amount of vapour in the air is the same, and so relative humidity becomes lower.
    In (coastal) Galicia, however, the average outside winter temperature is 10C and it’s invariably at very high relative humidity because of the Atlantic. When this air enters the building and gets heated up to 20C it therefore has far more water in it than eg. London air at 4C, and therefore a higher risk of condensation (100% at 10C becomes about 55% at 20C).
    Add some moisture from kitchens, bathrooms and people to that and you have relative humidity which is too high.

Galicia has a profusion of molds and wood-boring insects that thrive in building materials with a high moisture content, and these molds and insects are very bad for the health of both the building and its occupants.

In Galicia it is, therefore, of vital importance to consider the effects and control of relative humidity at every design stage when building or restoring.
Invariably what needs to be considered is how to reduce humidity within the building and also how to prevent interstitial condensation where warm, moist air penetrates building materials and then dumps its water there.

To achieve this you need to use as appropriate:

  • Damp proof membranes to prevent all passage of moisture
  • Breathable membranes to allow moisture to pass in one direction only
  • Impermeable surface coatings to prevent absorption of water
  • (Moist) air extraction and therefore ventilation

You can find specifics about using these relative modern technology buildings materials in our eco building, stone walled problems and solutions, and concrete framed problems and solutions sections.


Damp simply refers to obvious moisture. In a building this can come from condensation, but more typically it is used to refer to either water ingress due to gravity or pressure (leaks) or rising damp.

  • Rising damp: walls are typically made of substances that absorb water (bricks, concrete render, plaster, plasterboard), and if these walls are standing in moist conditions the absorption capacity of the wall materials will effectively suck up water (and salts contained within it) from the ground.
    Not necessarily, but with typical wall construction rising damp normally goes to a maximum of around 1 metre above floor level. It also, because of the salts contained in the ground water, tends to produce a sort of white, furry tide mark at its highest point, and, of course, a breeding ground for moulds and fungi.
  • Leaks, on the other hand, are more likely to come downward from roofs (particularly valleys, joints and chimney surrounds), areas in contact with broken guttering or leaking pipes.
    This type of water ingress can also come from a bridged wall cavity or from blocked (or missing) weep holes inside a cavity wall or over window frame.
    However water gets into the fabric of a building it’s a problem for the reasons mentioned in the relative humidity explanation above (structural degradation, mould and the general feel of a building for living in).

In Galicia it rains a lot and most houses are cut into sloping hillsides, so damp penetration needs to be extensively guarded against when building and needs to be carefully considered at the earliest stages when restoring an old property.

You can find specific solutions to common Galician damp problems in our stone walled problems and solutions and concrete framed problems and solutions sections.


The term “fresh air” does not crop up so widely as a good thing for no reason.

When humans breathe they extract some of the oxygen from the air and emit some carbon dioxide, plus some of the odours from the digestion of their last couple of meals and a load of germs. A non-ventilated home is basically a diluted equivalent of being in sealed public transport at going home time in winter.

The obvious solution is to open some windows, and in summer, mosquitos and incredibly annoying Galician flies notwithstanding (I always advise windows with fitted flyscreens), this is great.
In winter, however, most Galician houses are fighting away and sucking up energy to maintain a feeling of only mild discomfort, and opening a window feels like you’re not aiding that fight.
Instead, many people sit out ghastly winters inside humid buildings filled with stale air.

You have to ventilate!

Fortunately modern technology provides answers, and a Galician house adequately heated by conduction rather than convection (ie. water based, or electric if there’s no option, underfloor heating) and with an active ventilation system with heat recovery will be healthy, feel comfortable and, in fact, use much less energy than even the standard construction in use today.

Alternatively, as some air source heat pumps also include dehumidification and heat recovery systems these are an excellent convection based heating solution.


Galicia has a very mild climate but for comfort and also for humidity control heating is necessary for at least 4 months of most years.

All but high end recently built or renovated properties in Galicia will tend to have one or more of the following forms of heating:

  • Wood fired oven/stove (“estufa de leña”) – previously the heart of every traditional Galician kitchen, you can also find these big iron installations in many modern builds as a nostalgia item. They are actually a nice thing to have in a kitchen and can heat a big room well if you have the right type of well dried firewood and keep it going dawn till dusk. They are, though, messy and take time and effort, and perhaps they work best as an occasional top-up heating system.
  • Oil (diesel) fired boiler heating radiators using water circulation – variations of this system have been the standard for the last 50 years or so, and it’s effective enough and with a modern boiler even reasonably efficient.
  • Electric radiators – whilst reasonable for background heating using storage heaters on a cheap night time tarriff, electric radiators are generally inefficient and expensive and also mean you either need to contract an expensive high capacity electricity supply or run round turning off radiators every time you want to boil the kettle. The reason this system is used so widely is that it’s the cheapest to buy the components for and install, and so the cheap-n-nasty developer’s choice to tick the “heating system” box.
  • Instant gas water heaters – normally these are installed as a standalone system for domestic hot water in a kitchen and a bathroom. Occasionally you will see one connected to a heating system, but not often for the simple reason that although gas is a fairly efficient fuel for heating there are only piped gas supplies in cities and some town centres.
    Weekly gas bottle lorries are common across the countryside, and using gas bottles works fine for a stove and domestic hot water heating, but for a heating system for an average sized house a gas bottle would last only some 3-4 days, which just isn’t practical.

Fortunately modern technology now provides much better ways of generating the heat needed to keep a house comfortable, and two of these are extremely well suited to Galicia’s climate:

  • Solar panels (the evacuated tube collector type that heats water, not photovoltaics which are much less efficient and, rather unbelievably, now taxed by the Spanish government).
    Solar panels need a small pump, a heat store (a big insulated water tank) and a heat delivery system, which means either radiators or water based underfloor heating, and are generally a great solution in Galicia.
  • Air source heat pumps. As Galicia has a mild winter climate (typically 12 C during the day) air source heat pumps work extremely well here. They can either be used to heat water or to heat air, and some can also be used as air conditioners in the summer. Some of the latest air to air pumps also provide dehumidification and heat recovery functionality, which makes them an ideal solution for Galicia.

The core theme above is maintaining a different climate inside the house from that outside it, and to do this in an efficient manner it is necessary to minimise the transfer of heat through the outer shell of the house by insulating it.

It’s actually hard to have too much insulation, but for most houses there is a reasonable compromise position between cost, difficulty of construction and also what degree of heat loss the house’s heating and ventilation system can run comfortably against.

In Galicia, however, the traditional level of insulation is none, and so unless you’re buying a good quality property built within the last 10-15 years this is always an area that needs to be improved.
Unfortunately the two standard Galician construction types, stone walled and concrete framed, are both difficult to retrofit insulation to, and really it’s a case of jamming in insulation (rigid, soft or cavity fill) wherever and whenever you reasonably can.

As a final note on insulation, it’s very important if you are fitting windows to consider the thermal conductivity of what you are buying. Double glazing is pretty much a given these days, but there are two additional elements to consider:

  • Thermal bridging – In Galicia they use a lot of aluminium windows. Nice and strong, cheap, don’t corrode, don’t need maintenance. So far, so good, but connecting the two different temperatures of the inside and outside of a house with a metal window frame is a great way to lose heat from the house and also generate condensation.
    Wooden window frames have naturally good insulation (but cost more and need maintenance and care), and better modern aluminium or PVC systems have built in barriers against thermal bridging.
  • Infra red reflectivity – heat can’t conduct through a vacuum, so how does the heat of the sun get to the earth? The answer is as electromagnetic radiation, largely light and infra red.
    In fact all warm things emit infra red radiation, and so ideally you want to stop this leaving your house in winter and entering your house in summer.
    Fortunately thin film coatings that reflect infra red (whilst not noticeably affecting the level of light that passes through the window) can now be ordered as standard, and it doesn’t even cost much more.
    Although there are some possible situations where it wouldn’t be desirable to have this coating, they are very few and far between.

Radon is a carcinogenic gas (linked mostly to lung cancer especially in conjunction with smoking) that you find seeping from the soil above fractured granite bedrock, and it’s very prevalent in especially the south of Galicia.
This map shows the radon levels across Galicia, and here is a detailed study of the problem.

If you are doing a new build planning laws require a radon barrier over the ground or a ventilated air cavity between the ground and the building’s ground floor, and if you can access below the ground floor in a restoration it’s also advisable to fit below ground floor ventilation or a radon barrier membrane to the extent that you can (not least because it and the damp proof membrane can be one and the same).

If, however, you recondition an existing house and don’t re-lay the ground floor there is the possibility that some radon could be filtering into your home. Whilst not really a solution, a good ventilation system will help lower any potential exposure.