Resolving uncertainty in the thermal performance of natural fibre insulation materials.

Lead Research Organisation: University of Bath
Department Name: Architecture and Civil Engineering


Nearly half of the total energy generation in the developed world is inefficiently used to heat, cool, ventilate and control humidity in buildings. Unfortunately, the concepts developed through many research and demonstration projects have struggled to become assimilated into main-stream construction. In Europe, the most successful passive design standard, the German PassivHaus standard, has certified only 30,000 buildings in 15 years. Comparing this with the UK Government's 2016 target for the construction of 240,000 new homes per year and current quarterly output of around 29,380 homes it is evident that additional routes to achieving low and zero energy buildings must be investigated and developed if deep cuts in energy use and associated carbon emissions are to be attained by the building sector. Furthermore, there must be a focus on whole-life impact. To achieve the space heating energy targets of the PassivHaus standard, walls typically require insulation to a thickness of at least 300 mm and this level of conventional insulation material significantly increases the embodied energy content of the finished building. At present, inorganic insulation materials dominate the building industry, although interest in the use of natural fibre insulation products is steadily increasing. In Europe inorganic fibrous materials, e.g. stone wool and glass wool, account for 60% of the market. Organic foamy materials such as expanded and extruded polystyrene account for 27% of the market, whilst all other materials combined make up less than 13%. In the case of the mineral fibre materials adhesives are often added as are water-repellent oils as both increase mechanical strength. Expanded and extruded polystyrene are both oil-based polymerised polystyrol and the production process requires blowing agents which, since the phase-out of ozone depleting materials, are typically pentane and carbon dioxide, respectively. Pentane contributes to smog and ground level ozone and carbon dioxide, due to its low solubility and high diffusivity in polymers, make it difficult to produce low density foams which result in poorer thermal performance compared with those insulation materials made using HCFC blowing agents.

Natural fibre insulation (NFI) can be seen as an excellent form of carbon emission mitigation. NFI not only reduces the in-service carbon emissions of buildings through reduced energy demands, but through the use of plant based fibres carbon is stored within the material, as a result of plant photosynthesis, so significantly reducing the global warming impact of the insulation material. However, much is unknown about the performance of NFI materials. Where evidence-based data are available they are almost universally based on steady-state test performance data rather than the more complex dynamic variations experienced in real buildings. Frequently, where test data relating to thermal conductivity are presented, it is based on standard test conditions of a material in a dry state and at one mean temperature. Accordingly practitioners use such test results for prediction of in-service energy performance or evaluation of retrofit benefits, often without consideration for variability due to the changeability in the thermo-physical properties of the material or the validity of the test conditions. Whilst this situation affects all building materials attempts have been made to evaluate sensitivity and the impact on energy performance for more conventional products but there is little evidence of the same approach for NFI. Furthermore, the hygroscopic nature of NFI materials results in much greater variability in their thermal performance.
The primary aim of this project is the quantification of the dynamic thermal performance of NFI materials through experiment and simulation, which will help to support a growing 'green economy' and provide valuable data for building designers and developers of building simulation models.

Planned Impact

There is a growing world-wide market for sustainable green building materials and this proposal seeks to provide much needed independent experimental data on the steady-state and dynamic thermal performance of such materials. At the last Budget, the Government set out its ambition for increased investment in low-carbon technologies and a commitment to benchmark the UK against the top countries in the world. The global low-carbon market was worth more than £3.2 trillion in 2009/10. The UK share of that market was more than £116 billion in 2009/10 and provides employment for 910,000 people. The total UK market for insulation is £1 billion whilst the Natural Fibre Insulation market in the UK is estimated to be only £15 million and is clearly an area with great potential for future growth, which would be a key contribution to a successful UK green economy. This research will deliver improved outline design guidance based on robust laboratory and field experiment data. In collaboration with our industrial partners, the development of design guidance will promote the use of transient heat transfer parameters capable of capturing the dynamic behaviour of Natural Fibre Insulation materials and, we expect, will explain the whole-building energy performance benefits of materials such as hemp-lime that have been observed and reported in earlier studies such as those performed by the BRE at the Haverhill Hemp Houses.
There is a general lack of awareness of, and information on, sustainable building materials in the market place. Additionally, independent assessment of products, including proof of the product's suitability for the intended use as well as its 'sustainable' criteria is often not available. This lack of knowledge stifles development of the low and zero carbon buildings that are desperately needed in order to reduce the carbon impact of the built environment, and to work towards a green economy that is more resilient to climate change. Our experimental and simulation data will provide industrial partners with greater knowledge of the dynamic performance of hemp-lime, hemp fibre quilt, wheat straw, and sheep's wool insulation, which will enable them to compete with established producers of inorganic fibrous materials and the oil-based foamy materials such as expanded and extruded polystyrene that currently dominate the market place.

Through the generation of robust data quantifying the variability in the thermal performance of Natural Fibre Insulation (NFI), software developers, practitioners, and academics engaged in the development of building energy simulation models will be able to incorporate NFI materials in to their simulations. NFI materials are used across the world and evaluation of their dynamic thermal performance and insight gained form this project has the potential to be exploited through the licensed use of the data in commercial and non-commercial Dynamic Simulation Modelling (DSM) software suites. Previous research by the author generated empirical data that were successfully integrated with one of the UKs leading DSM software packages. In the UK the demonstration of compliance with building regulations in relation to energy performance (Part L) requires use of an accredited DSM software package. Accordingly, it is vital that NFI materials are incorporated in to such a model in order to demonstrate compliance and thus there is a commercial benefit to the software house through the sale of add-on applications and to the product manufacturer through association with a software package that is accredited for use in building regulation compliance. Our project partners are leaders in the design, development, and distribution of such software. Not incorporating data on NFI in to accredited DSMs will negatively impact the growth of a green economy based on UK-produced plant fibre insulation materials as designers will be unable to evaluate energy performance against the conventional, often oil-based, insulations.


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Description We have quantified a range of variation in the thermal performance of natural plant-based insulation materials based on their manufacture, material composition, density, and moisture content. These materials can, and are, used to produce low energy buildings (low in both in-use energy and material embodied energy). Quantification of the thermal performance of such materials is of benefit to building designers and end-users as it enables more reliable estimation of their likely performance when applied to real buildings. A previous lack of reliable data has, historically, led to a lack of confidence in the marketplace and perceived increased risk in the use of these natural building materials.
Exploitation Route The findings are of immediate use to our industrial partners who are seeking to develop complete building envelope systems that incorporate natural fibre insulation materials. The findings are being put to use by students, researchers, and construction practitioners who need the material characterization data to populate computer simulation models investigating building energy performance and indoor environmental conditions in buildings.
Sectors Construction,Education,Energy,Environment

Description The detailed hygro-thermal data output from this research grant have been used to populate simulation models to support promotion and development of natural fibre insulation building materials for use in low energy buildings.
First Year Of Impact 2014
Sector Construction,Energy,Environment,Manufacturing, including Industrial Biotechology
Impact Types Economic

Description Workshop for practitioners, uses and researchers of natural fibre building materials 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Around 25 attendees, mainly practitioners, attended a workshop in 2013 to share information on the use of natural fibre building materials and to agree an approach to more widely disseminate good practice. A follow-up meeting was held in 2014 and we have agreed to work towards developing a design guidance publication presenting research output and case study examples of real buildings.

We have agreed to work towards developing a design guidance publication presenting research output and case study examples of real buildings.
Year(s) Of Engagement Activity 2013,2014