Breathable Structures | Thermafleece

Breathable Structures

17th July 2017

The characteristic way moisture interacts with natural fibres makes natural fibre insulation the most appropriate choice for high performance timber buildings.  Read the views of Eden Renewable Innovations Ltd, MD Mark Lynn and the Natural Fibre Insulation Group on just how this process works and what are the properties of natural fibres.
 

Fabric that allows for the sorption and desorption of moisture helps create a durable structure that is less susceptible to decay.  Water makes up around 30% of a living fibre.  This water is bound within the molecules that form the natural fibre through a process known as hydrogen bonding and is commonly known as ‘bound water’.  When natural fibres are processed and dried, most of the bound water is removed. Even after drying, the moisture reactivity of the fibres continues, so they can use the same process to bind water within their structure only to release it as conditions change.  This gives all types of natural fibre their characteristic breathability.

Water makes up around 30% of a living fibre.  This water is bound within the molecules that form the natural fibre through a process known as hydrogen bonding and is commonly known as ‘bound water’.  When natural fibres are processed and dried, most of the bound water is removed. Even after drying, the moisture reactivity of the fibres continues, so they can use the same process to bind water within their structure only to release it as conditions change.  This gives all types of natural fibre their characteristic breathability.

Natural fibres breathe by responding to humidity.  As humidity increases, natural fibres want to increase their moisture content.  This is achieved by stripping water vapour from the air.  The reverse happens as humidity drops with the fibre releasing water vapour into the air.  What’s special is when water is absorbed it becomes chemically incorporated into the fibre and is released as water vapour which is a gas so no liquid water is involved so no wetting occurs.

As we know, condensation is wet.  It generally occurs when temperature drops and excess water vapour in the air condenses into liquid water.  Relative humidity (RH) is a measure of how much water vapour air can hold, 100% RH being the maximum.  The amount of water air holds varies greatly with temperature.  Warm air can hold more moisture than cold air so as air cools, its RH increases.

RH fluctuates greatly with air temperature whereas the moisture content of natural fibres varies greatly with RH not temperature.  This enables natural fibres to moderate RH and buffer moisture as temperature changes.  In practice, natural fibres reduce RH in response to falling temperature.  This has the effect of buffering moisture from the surrounding air as temperature drops.  The moisture is then released as temperature rises when the risk of condensation has passed.

The amount of moisture natural fibre insulation can absorb in this way varies with conditions but generally speaking, 1mm of natural fibre insulation can bind the moisture from about 1m3 of air.  Put another way, each m3 of natural fibre insulation can buffer the moisture in about 1000m3 of air.

Why is this important? Breathability is about allowing the passage of moisture in a ‘non-wet’ form.  In order to be ‘non-wet’, water can be present as bound water or water vapour.   A vapour open system such as mineral fibre insulations only allows the passage of water vapour.  A breathable system allows the movement of moisture in both forms and is a much more complete way to manage moisture within the fabric.  When it comes to insulation, this can only be achieved through the use of natural fibres.

See the Full article with Case Study in The Structural Timber Magazine Summer 2017 Issue Page 26

Mark Lynn is one of the UK’s leading experts on sustainable insulation with over 20 years’ experience in the field of natural building materials, he is also an active Board Member of the Alliance for Sustainable Building Products (ASBP) and a Member of the Natural Fibre Insulation Group, which aims through collaborative actions to better communicate the benefits of natural insulation products and system.

To find out more on the work of the NFIG and the ASBP why not attend the CPD accredited seminar in London on the 19th September where expert speakers including our own Managing Director Mark Lynn will discuss the many benefits of natural fibre insulation. Click here to book.
 

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