Thanks to the previous articles, you now know that the choice of walls is important because:

  • They cannot be replaced.
  • But they can be improved (in renovation).
  • They should be good insulators.
  • And have significant thermal inertia.
  • With a phase shifting period of 12 hrs, this would be perfect

But it’s lacking an essential quality. They should be “VAPOUR PERMEABLE”. Simply put, they should allow the natural management of relative humidity (RH).

How relative humidity works in your house

A healthy RH is around 50%. If it isn’t, it could have a negative impact on your health. Why does the RH change? And even dramatically?

Different factors generate a house’s humidity:

  • The occupants: we breathe and we perspire.
  • The kitchen: we boil water for cooking.
  • The bathroom: we take hot showers or baths.
  • The air outside is warm and humid or cold and dry when we air the house.

And these sources create or remove water vapour throughout the day, every day.

The consequences of poor relative humidity on your comfort

Comfort described as “Hygrothermal” is influenced by the RH rate:

  • Below 30% RH and the air is too dry.

  • Above 70% RH and the air is too humid.

Moreover, we all know these frequent problems:

  • Condensation on cold walls and panelling (windows, tiles, mirrors, etc.).
  • Mould and mildew (or their odours).
  • Feeling of saturated air that makes for a stuffy atmosphere (a high RH + a high temperature).
  • Cold or “raw” feeling (a high RH + a low temperature).
  • More expensive heating bill to heat up humid air.
  • Or feeling that the air is too dry (irritated nose and throat).
  • Using humidifiers or dehumidifiers...

But aside from comfort, the most serious impact is on the health of the residents.

The consequences of poor relative humidity on your health

It has been proven that there is an ideal RH for your health... Excess RH over 70% in a heated house fosters:

  • Significant propagation of bacteria, viruses, mildews, moths and mites.
  • Acceleration in pre-asthmatic conditions.
  • Interactions with VOC (Volatile Organic Compounds) released by chemicals in your home (cleaning products, paints, furniture varnish, etc.) that get trapped in water vapour and breathed in.

In contrast, air that is too dry, that is, below 30% RH in the house, has very little suspended water vapour and so dust (from the floor, carpets, your couches, your clothes, etc.) is always in the air. This suspended dust in air that is too dry fosters:

  • Rhinitis (dry or irritated nose and throat).
  • Pre-asthmatic conditions.
  • Other respiratory infections.
  • And the proliferation of other bacteria or viruses that prefer these conditions.

To avoid these health issues, the RH should always be around 50%.

How to benefit from ideal relative humidity?

Aside from natural ventilation (open the windows when possible) or forced ventilation (Mechanical Ventilation Unit), the solution that is the most natural, the easiest and the most effective for 50% RH is to have walls that are “Vapour Permeable”. The excess RH in the air in your house will be absorbed into the walls and your walls will release the stored humidity if the air in your house is too dry.

Cement does not allow vapour absorption and so does not allow the natural regulation of RH. Insulation made from petrochemicals form air and watertight envelopes. Glass wool does not breathe very well. On the contrary, the smooth texture of the glass fibres allows water vapour to condense on them, which will degrade its insulating power and offer a favourable environment for mildew inside the insulation. This is why it is imperative to use a vapour barrier...

Poor or no breathability, these conventional solutions require a high-performance, always active Ventilation unit.

By contrast, “microporous lime-hemp and bio-sourced insulation absorb excess RH and naturally restore it when the RH drops too low. This is a natural and optimal regulation that lets you avoid the potential negative impact on your health and guarantees an ideal RH constantly around 50% RH for perfect comfort at all times."

High performance, significant thermal inertia, a 12-hour phase shifting rate, acoustic dampening, regulation of the relative humidity for an always healthy atmosphere... Now you are perfectly informed to make the right choices to define the priorities of your future home.


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