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    Categories: Blog

Leaky & cold homes, mould and climate change

When I look what’s happening and is most discussed in the building industry new at the moment, the headline above sums it all up.

Leaky buildings, either from exterior or interior, are all too common. They happen due to a combination of wrong materials at the wrong place wrongly designed and badly installed – usually it’s a combination unless it’s incredibly badly designed or incredibly badly installed. Similar things are applicable to cold houses with a lack of insulation that is incorrectly installed with thermal bridges that were not designed out.

On top a lack of airtightness that is contributing to both water ingress into the construction and voiding insulation – insulation where the cold exterior wind can blow through, has no insulation value. Have you ever tried to stand outside just with a woolen jumper in cold heavy wind? What happens when you put a jacket over it – one of those membrane layer jackets? Warm, suddenly. The same works for buildings, we need to put an airtighness layer on.

Airtightness should maybe called something like “windthightness”, which would probably lead to better acceptance and understanding by the public – and some building professionals. An airtighness layer simply prevents unwanted air infiltration into the building envelope that would also bring moisture with it, be it from inside or outside.

If it is raining outside and you have a heavy wind going with gaps and cracks in your building envelope, the wind may drive rain into those gaps and you have leaks. Likewise the same may happen from the inside to the outside, particularly in high-moisture areas like bathrooms, kitchens and even bedrooms. The air movement presses warm, moist air into envelope gaps and cracks where the air cools down – particularly at night – and condenses within the wall.

This has all to do with physics, warm air can hold more moisture than cold air, if you cool air down, condensation happens when the relative humidity reaches 100%. You see this on your cold windows, you cannot see it in the walls – yet it happens there, too.

There’s the old argument that this all did not happen in the olden days with the good old buildings. Correct to a certain extent as those buildings were generally more drafty and not insulated. Your ventilation was kindof a permanent, built-in “feature” which also made the buildings very hard to heat, pretty much all the time.

More insulated buildings can be heated better, as long as there is no wind. They can be heated very well if there is an airtightness layer because the cold wind does not blow through them any more but now you have condensation happening. To prevent this from happening, we add vapour-control layers on the inside face of walls. Now we have condensation only happening on windows as they are still the coldest spot within your building envelope – if you have successfully designed out any thermal bridges in the walls, otherwise it will happen there, too. This is then called mould – which is both a sign that you have cold-bridges plus a lack of ventilation – or too high moisture load. If you cannot reduce your moisture load, ie stop cooking, stop taking baths or showers and most importantly stop breathing – oops, then you need to ventilate.

The purpose of ventilating is get get rid of pollutants, CO2 and moisture and get oxygen in to breathe. When you are ventilating, you are losing a lot of air that transports all those pollutants out but also the warmth.

Clever people have invented a heat recovery ventilation system (short HRV) that has nothing to do with a certain company. The idea is to create a balanced ventilation system that crosses the incoming air with te outgoing in a heat exchanger, pretty similar to a condensing drier. By crossing the cold incoming and the warm outgoing air in separate channels, the heat of the outgoing air is partially transferred to the cold incoming air and “pre”-heating it, significantly reducing your heating demand. This concept has been around in Europe since the 1970s and we are slowly catching up with that idea in NZ.

Now that you already have an HRV system, you can throw in lots in insulation, good airtightness, vapour-control and well insulated double or possibly even triple glazed windows and reduce your heating demand to virtually zero. The building is heated by your toaster, your TV, your computer or your body heat. This is called “passive house”. You have heard about it.

It’s a really simple concept. Result: No heating bills, healthy indoor climate, happy people, no building-related sickness and way less climate change. Did I mention that less heating means less emissions?

Oh, and also with the better indoor climate, and less moisture and mould, the asthma rate would be much lower with much lower hospitalisation and cost to the health system.

So, why is the NZ government not targeting that, if that would really tackle pretty much all our building related issues plus climate change targets, all in one?

Ingo Ratsdorf:
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