The job of retrofitting the nation's building stock is attracting a variety of methodologies and materials. Wood fibre offers both the prospect of the material having a relatively low environmental impact but also, when applied along with complimentary materials in situations where the movement of moisture through the construction element is an important consideration, it exhibits distinctive qualities.
Applying wood fibre insulation externally and rendered with lime or open polymer render provides useful breathability in situations where trapped moisture can damage the structure.
Applying wood fibre insulation internally requires much more consideration. Under the more common conditions found in the UK where the brickwork hangs around at temperatures below the dew point, vapour passing from the room through the insulation is in danger of condensing against the inner face of the brick. At least one brand of internally applied wood fibre counteracts this by including a silicate layer within the section of the insulation which provides an effective vapour barrier preventing moisture from reaching the brickwork.
As in other applications, sections can be quite substantial compared with petrochemical alternatives, but advantages are seen in the reduction of environmental impact as well as the provision of high levels of decrement and fabric breathability.
Most of the country's buildings are made-up from brick walls, but the details below are equally applicable to stone walls.
• 215 mm existing brickwork (0.75 W/mK)
• min. 8 mm parge coat of lime / lime-cement plaster
• 100 mm rigid wood fibre insulation with integral vapour check (0.043 W/mK)
• clay / lime plaster
Approx U-value = 0.35 (subject to specification)
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