Thermal inertia has 6 crucial advantages for your home to be comfortable, affordable and sustainable...

Advantage 1: Managing heat input

Whether heat input is external (the sun’s rays behind a bay window) or internal (your heating system), the inertia will store this heat in the walls or in your floor until it is released for free during the night and so prevent your home cooling down at night.

Advantage 2: Avoid overheating in the summer and suffering from heatwaves

While the temperature of thick walls doesn’t go up much and leaves your house fairly cool, at night the walls will radiate their energy outside and will cool down this way.

Inside, night-time ventilation will dissipate the excess energy stored by the walls so that you start with a cool house again at the beginning of the day. This ventilation may be natural (open windows) or forced (mechanically controlled ventilation).

Advantage 3: Increase glass surfaces without the risk of overheating

Modern architecture favours large glass surfaces that allow light in and enlarge the inhabited space by creating a continuity with the outside (your terrace and garden and what’s more it’s beautiful!). However, in summer, the risk of overheating are much greater and besides other expensive solutions (roof overhangs or pergolas) only thermal inertia will guarantee continuous coolness. By contrast, in the winter, thanks to large glass walls, this thermal inertia will capture the sun’s rays and will automatically heat your house without it cooling too much at night.

Advantage 4: Phase shifting temperatures

Thermal inertia and phase shifting play the role of thermal regulation. If absorption lowers the temperature peak, phase shifting moves the appearance of this change in temperature over time. By absorbing the heat when it is high and restoring it when it isn’t present, it will “smooth” out these variations.

Remember: light insulation and light walls will heat up quickly. Wood-framed houses with light walls insulated with mineral wools will have a phase shift of 3 to 4 hours. When the sun starts to heat up, around 10 o’clock, the house will start to heat up around 2 in the afternoon when the sun is still strongest. And all the walls will continue inexorably to heat up, overheating the house in the afternoon and the evening.

With strong thermal inertia, phase shifting takes 12 hours. Excess energy is stored in the mass of the walls which only heat up slightly (absorption) between 10 AM and 10 PM (phase shifting) keeping the house cool. And around 10 PM, when there is zero input from the sun’s rays, the temperature of the walls drops by radiation and ventilation until 10AM the next morning, regaining their coolness for that day.

 A concrete example

If summer temperatures vary from 16°C in the morning to 30°C in the afternoon, the average daytime temperature will be (16 + 30) / 2 = 23°C.

A house with low thermal inertia will vary a great deal around this average value. For example, between 17°C in the morning (Brrr…) and 29°C in the afternoon (Ffff!)

A house with high thermal inertia will also vary around this average but this will be a variation of around 22°C in the morning and 24°C in the afternoon (Aahhh…).

These 2 houses have the same average temperature of 23°C but the comfort is not at all the same!

Let’s take this logic further and consider two concrete examples of the benefits of thermal inertia and of phase shifting EVEN WITHOUT INSULATION...

If the building is very solid, phase shifting will be very significant over time. The coolness of the winter will be released in the hotter months. Haven’t we all wanted to visit a cathedral in the middle of an overly hot Italian city in the summer to enjoy a little relief from the heat? Phase shifting may thus even be inter-seasonal if the mass is very great!

If the thickness is very very (very!) great, we might even have zero day/night and inter-seasonal phase shifting… And still without insulation!

That is what it is like in a cellar where the inertia of the walls is expanded by the inertia of the mass of the earth adjoining the walls.

In cellars, the temperature is constant in summer and in winter. Now you can see how, thanks to thermal inertia, you can age your best wines longer without risk!

Advantage 5: Open your windows: healthy air in a healthy home

In a house with low inertia, even if it is well insulated, opening the windows is not neutral:

  • In the winter, you chill the inside air and the walls of your house, and you will have to put the heat on to return to the comfort felt (it’s expensive!).

  • In the summer, the warm air will increase the speed with which your house heats up (not cool!)

In a house with high inertia, as the air is much lighter than the mass of the walls, opening the windows will allow:

  • In the winter, freshening the air without affecting the energy stored in the walls which in turn retain their temperature. This means the cool air you let in will heat up when in contact with warm walls and your comfort will be maintained without having to put the heat on (cool!)
  • In the summer, even if the air is hotter, because it is much lighter than your walls, it will not have any effect on the walls of your house and in fact, it will cool down when it touches them. Your comfort is guaranteed and that… is cool!

Advantage 6: Insulation against outside and inside noise

The characteristics of the block of hemp go beyond the only thermal advantages for comfort. Acoustic comfort belongs to their outstanding properties. Acoustic absorption is the term used for noise reduction in the same room. The walls, carpets and furniture, they all play a significant role in this.

Acoustic insulation is the term used for noise reduction between 2 separate rooms. Here the insulating quality of the dividing wall is essential. Children playing, practising their favourite musical instrument, entertaining their friends or listening to their favourite music are incompatible with teleworking or the simple fact of having a calm and peaceful spot to recharge after a very full day.

With smaller housing spaces – which is more popular for financial and energy-savings reasons, buildings with strong inertia can dampen indoor noise for increased comfort for the whole family. Even outdoor noise (traffic, planes, neighbours, etc.) will be dampened and will ensure pleasant and calm days and nights.

This also works from the inside out: if you want to rehearse with your band or bang on your drum set, let yourself go. You won’t risk annoying your neighbours!

How can thermal comfort and impact on the environment be reconciled ?

Here is a whistle stop tour of insulation versus thermal inertia. You’ll understand now that insulation is not the ultimate “Panacea”!

If the thermal inertia of concrete blocks and of bricks is good, at IsoHemp, it’s not our favourite solution… CO2 released from cement plants or brick factories is enormous and recycling them is nearly impossible (reusing bricks is possible, which is good, but it can be expensive).

And to reduce the impact on the environment, primary energy consumption (petrochemical products, using petrol in their production, transport and even recycling) must be reduced or even wiped out. IsoHemp wants to decarbonise the construction industry and have zero carbon footprint on the environment while guaranteeing a more comfortable, affordable and sustainable house. Our lime-hemp blocks:

  • Are excellent insulators
  • Offer significant thermal inertia for ideal comfort.
  • Are all in a single wall and without the complications of blocks, insulation and vapour barrier (just a mono-wall).
  • Are CO2 neutral because they are bio-sourced.
  • Are sustainable (they resist everything over time like limestone).
  • Are short-chain products.
  • And are 100% recyclable…

To compare the various insulating materials and if you have not yet done so: Download here your summary of the different properties and limitations of insulating materials

In our next article, we’ll deal with managing Relative Humidity.

It’s a very important aspect for your comfort and your health (and is also underestimated when planning a project).

©2024, IsoHemp - Natural Building