WHY IS WOOD FIBRE INSULATION’S POPULARITY ON THE RISE? Natural insulation, especially wood fibre, is experiencing a huge uplift in sales Will Kirkman from sustainable builder’s merchant Ecomerchant explains why wood fibre insulation’s popularity is on the rise.

Littelpits SW: Certifed Passivhaus Plus. Built using Steico I Joists, wood fibre insulation, Durelis Vapourblock, external lime render. Carbon Statistics:TFA 317sqm. Form Factor 2.43 with average wall/roof U value 0.085W/m2K, floor 0.07W/m2K, Heating demand 11.1 kWh/m²a, heating load 7.3 W/m2. Final air-tightness result 0.07 ach@50Pa. PV: 7kW peak array. Overheating percentage 1%.

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mong its many great characteristics, wood has a long life, is highly durable and is easy to work with. It is also hygroscopic, which means that it has the capacity to absorb and release moisture without being damaged. It is this property that also makes wood an excellent insulation material. Inhibiting and storing is how one might sum up the function of insulation made from wood fibre. A life cycle analysis (LCA) of wood products makes the advantages of the material even clearer. Wood is an important raw material, a socioeconomic treasure. It is a renewable resource, as long as the raw material is managed according to a consciously sustainable harvesting plan with responsibility for future growth, as is the case in European forestry. Look for certification either FSC the Forest Stewardship Council or PEFC the Programme for the Endorsement of Forest Certification, or both. Buildings should be ventilated in a controlled way for the sake of the structure, the indoor environment, and for the building’s energy performance. Many homes do not suit our lifestyle every day functions, showering, cooking, central heating and laundry, for example produce significant quantities of water vapour so where the building has gaps (compounded by poor ventilation) letting air escape through the building envelope causes risk of condensation and subsequent damage or mould growth.

Inhibiting and storing is how one might sum up the function of insulation made from wood fibre Akerman Road: Certified Passivhaus. Built using Steico I Joists, wood fibre insulation, Durelis Vapourblock, external lime render TFA 371sqm. Form Factor 1.8, with U-values of roof 0.108 W/m2K, walls 0.105 W/m2K floor 0.106 W/m2K. Heating load 7.9W/m2. Predicted Heating demand 9.1 kWh/ m²a. Airtightness test results: 0.34, 0.39 and 0.4 ach @ 50Pa. Overheating frequency 1.9%.

BELOW

Older (leakier) homes were built for a very different way of living and often from locally sourced complementary materials. Naturally well ventilated they were colder and damper in the winter and dryer and warmer in the summer, but importantly often constructed form natural materials that had an inherent buffering capacity to deal with such moisture fluctuations without the threat to their structural integrity. It has been the advent of synthetic and petrochemical materials that have removed the natural capacity of the building fabric to buffer moisture with a 100% reliance on ventilation to do all the work. Obviously this requires buildings to be both designed and built to a high standard and for them to be maintained as such in perpetuity but

it also needs to accommodate the different ways in which occupants behave, in short it’s not a very forgiving way to build. No one wants to live in a hermetically sealed plastic bag, and we all want our lifestyles to be accommodated by our homes without the threat of damage to the building fabric. Older homes have intrinsic appeal to many often draughty, but none the less a pleasant house one can trust. But those houses are also no good for today’s modern lifestyle, since letting damp, warm air pass out through the building envelope may prove harmful for the building shell or the indoor environment. In addition, the operating cost, comfort and environmental impact of heating a draughty house is generally problematic. A negative experience of the indoor environment also comes down to the same issue, the inability of the constituent materials to absorb and release moisture. We simply don’t feel as well in houses that lack the ability to buffer and release a healthy amount of moisture into our living environment. Our mucous membranes, but also our skin, need moisture – a relative humidity figure (RH) of between 40 and 60 percent is optimal – to protect the body and the immune system against unwelcome attack.

RRNews - Issue 47

SIMPLICITY OF CONSTRUCTION

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The use of mineral wool (vitreous) or PUR foil backed boards requires the use of vapour barriers to prevent air leakage from the interior causing condensation in the structure. Rigid insulation boards must be cut very accurately to fit between timber structures with all of the joints taped and all junctions sealed. The security and durability of the seals and vapour control becomes more important as insulation levels increase levels meaning a corresponding increase in condensation risk.