Updated: Feb 5, 2021
Humanity has been building Straw houses for a very long time. Some houses had straw roofs and some were plastered with mud. Behind thick walls these homes have sheltered people against the harsh winters and scorching summers around the world. Nowadays people are increasingly feeling the pressure of modern life and becoming more interested in the qualities of natural materials.
Why would you be interested in living in a straw house built of natural materials?
Is it because of its low carbon foot-print or is it because of the excellent energy efficiency and sound proofing?
A quality straw house can easily cover the above important points but they are not what makes it unique - The straw house can regulate the humidity in the air inside and make up for significant deviations from the recommended level of 40-60 percent Relative Humidity (RH).
Conventional houses achieve such RH levels with machines like the humidifier (in winters) and respectively - the dehumidifier.
Humidity is also an important factor- both for our health and the house’s. This is why a good and reliable roof is a must.
So how does the magic happen?
It is a partnership - a dance. A house is nothing without its inhabitants, but once a person or a family settles in - then it would begin.
As you know, clay plaster is notoriously prone to easy wetting, one of its few shortcomings in a sense, but this exact quality is what makes it able to easily regulate its moisture in accordance with air humidity. There is an exchange occurring. Clay is vapor permeable so it can simply “let” humidity out while capturing a tiny portion for itself. That permeability is essential to the “breathing” quality of the walls.
But there is another aspect of the effect clay has to complete the straw wall. The thicker the clay plaster is , the more capacity for moisture transfer and the greater thermal mass.
Remember that the clay is plastered right onto the cut, pressed straw and dried together solid - with straw fibers stuck into the hardened clay (as small tunnels).
It is the fibrous structure of the straw that starts from the base, or “scratch coat” of clay plaster that acts as the bridge for moisture transfer between the volumes occupied by clay and straw. These fibers are interconnected as they are mixed and tightly packed together in a sturdy panel to allow for even moisture distribution. The more homogeneous the spread of straw when it’s compacted, the better.
The pressed straw inside the straw walls has a large capacity of storing moisture without becoming wet and may literally act as a large battery to tap into to either store excess humidity or pull from it - in case the inside air starts drying the clay plaster (is the heater on?).
The natural materials have known water in all its forms - they have coexisted in nature and selected by men for their combined properties to build a wall that can breathe easily. The outside walls can be protected by an air-ventilated façade to even further this effect.
Sadly, the “breathable” or “vapor permeable” labels are misleadingly attached to various conventional building materials bragging about a fraction of what a straw wall can achieve.
Humidity of air inside the house is a critical parameter when we think of personal comfort and consider one’s health.
Allowing the clay plaster to tap into stored moisture, “breathe in” from the outside, takes care of the dry air in the building - it is preferred by all kinds of pathogenic organisms; Same structure but reverse process helps lower the humidity so no condensation on the walls or windows form at all.
What we have covered above should be enough to get you started on your own concept of the perfect straw house look for you. You see - the rest is up to nature and it has you covered!