09 Apr 2020

Wet walls and heat loss

Wet walls and heat loss

With high winds and heavy rain a seemingly ever-present feature of the British climate, we are increasingly asked to advise our customers on how to deal with the dampness threat caused by driving rain.  Whether you live in a brick built Victorian town house or a stone country cottage the problem of moisture ingress poses the same challenges.   Not surprisingly most property owners simply want to know the best way to stop dampness and protect perishable plaster or decorative finishes.

Of course we are more than happy to advise on correct repair methods, material specifics and our range of professional water seal products / masonry paints, all of which have been outlined in previous discussions.

Today however, we want to highlight a forgotten but very significant advantage of protecting your home from damp walls, namely energy efficiency.

A wet wall is a cold wall

We all know that as human beings, if we get wet we tend to cool down much faster than if we stay dry.  In fact it has been calculated that we cool 25 times faster immersed in water than in air of the same temperature.  This is why mountain survival advice focuses on the importance of the right weather proof clothing to keep us dry and warm for as long as possible.  Soaked to the skin without waterproofs we lose heat much faster as our body fights to maintain core temperature, wasting vital energy.

What is less well understood is that the same principle applies to our homes.  If we have damp walls which have absorbed large quantities of wind-borne rain during a storm for example, that water will begin to evaporate as soon as the rain stops.  That process of evporation takes heat with it, cooling the wall significantly.   This explains why heating systems have to work harder in wet conditions – evaporating moisture saps heat out of our homes and is bad news for energy efficiency.

In essence then, a wet wall is a cold wall.

Damp wall problems

Damp walls can lead to a range of problems including; salt damage to plaster, black mould growth, dry rot and ultimately structural timber decay.   Even if a wall is not actually leaking moisture back into the living space it can still hold excessive moisture, which cools the wall and often results in “cold spots”, especially in older properties with less insulation.  

“Cold spots” in turn attract condensation which is simply the process of warm air vapour converting back to liquid when it comes in contact with something cold.  We see this when we take a chilled bottle from the fridge and moisture quickly forms on the surface.  These cold spots usually occur on the inside of external walls and the condensation they produce is a magnet for fungal growth.

Unfortunately, turning up the heating to dry out the wall can actually exacerbate mould growth as it thrives in warm moist conditions.   So it is better to prevent the condensation from developing in the first place.

Breathable, Invisible Treatments

So a wet wall is a cold wall and damp walls can cause condensation even if they aren’t actually leaking!  ….What to do?  

The answer is relatively simple; if it is bare brick or stonework, treat it with a professional grade water seal such as “Kingfisher Extreme Climate” or “Kingfisher Stormseal” (if weather is persistently wet).  These colourless sealers are easy to apply by brush or low pressure spray and are 100% breathable.  Unlike resin sealers they are pore liners, not pore blockers which repel liquid water droplets whilst allowing the much smaller water vapour molecules to escape.   Thus you can treat a damp wall to stop further rain ingress, without worrying about trapping any existing moisture.  

If the wall is a painted finish, you must be diligent about maintaining this and if you know your home is prone to lateral penetrating damp, only use premium grade paints.  “Kingfisher Weatherflex” masonry paint gives protection for up to 15 years and has been widely used to control penetrating damp.

It is extremely difficult to be accurate on how much energy you will save by protecting your walls from moisture absorption, simply because without X-ray vision we cannot know the full extent of moisture migration into our walls.   Infra-red camera surveys and damp meter readings may reveal obvious weak points but cannot provide a full measure and of course the weather itself is infinitely variable.  What we can say with certainty is that both practical and academic studies have shown that a dry wall has over 25% higher insulation compared to a wet wall.    We also know from experience that well-protected, damp resilient homes feel more comfortable to live in and are less prone to condensation derived problems.