Which Fibre in Your Insulation Diet?

cellulose fibre insulation
Until recently, insulation has always been something of an afterthought. We built first and then, well, just stuffed some insulation in afterwards!

Everyone in building knows about itchy mineral-fibres, glass-fibre and rockwool. But there is a third insulation fibre that not all builders have discovered yet – cellulose fibre. Cellulose is far more friendly to both the builder and the environment.

What is cellulose insulation?

Made from recycled newspaper, cellulose insulation contains natural salts which give amazing resistance to fire, mould and insects. On top of this the material is carbon negative – more carbon is locked away than is released in its manufacture. This puts cellulose insulation at the forefront of environmental materials.

With ever-increasing demands for better U-values, airtightness and green credentials, sophisticated building now starts with insulation and asks which type of construction gives the best environmental performance overall? In many cases the answer is timberframe. This can provide the easiest way to get the insulation thickness needed for the target performance. Furthermore, there is the attraction of engineering with the most sustainable materials, in factory conditions.

Builders have to choose which of the fibre insulations, or even petrochemical foams, to install. But the question is, how do you get the best results for both environmental performance and build cost? To answer to that, we also need to look at the methods of installation.

The installation method

Cellulose is installed with a blowing system, being pumped under pressure to tightly fill every space. This measurably improves airtightness, yielding better pressure test results and lower heat loss in the finished building. The majority of alternative insulations are installed by hand. Even with painstaking care, cutting rolls or slabs of material into shape cannot give such good results.

Another feature of the system loved by builders is the speed – large buildings can be insulated in days rather than weeks. Time is money for builders, but don’t forget  the environment. Less time means less energy to get the job done.

How do we know how good cellulose fibre is?

A study by Colorado University compared cellulose and glass-fibre in two otherwise identical buildings. Airtightness with cellulose was 36% better than with glass-fibre and 26% less energy was needed to heat the cellulose building. After turning off the heating overnight, the cellulose building held its temperature better and was 4°C warmer at the start of the next day.

A similar study by Wimpey Environmental Ltd concluded that cellulose insulation wasted 24% less heat than glass-fibre. Significantly, measured U-values were not as calculated – cellulose was 6% better, while glass-fibre was 15% worse than predicted. U-value calculations do not tell the whole story when using nominal values for thermal conductivity!

A brighter future?

Looking ahead, insulation will be even more central to building design. We all have to find better ways to reduce energy needs and carbon-emissions, but not by going backwards with the performance of our buildings in other ways. Now is the time to ask which fibre to use for the best results? We asked this question and chose to specialise in the installation of cellulose fibre. It is the greenest insulation, is highly cost-effective for the builder, and  has an astonishing range of further benefits.

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