Insulation is a fundamental element in providing thermal comfort within a building’s indoor environment. Utilizing the correct, high performing insulant and the “fabric first” approach to building design allows light-frame system manufacturers to achieve low u-values through different construction assemblies. The insulation is typically placed within the framing cavity but can be placed on the external or internal framing face too.
So what are the typical and more novel types of insulation available on the market? There are four general categories: mineral wool, blown, foam, and natural fibers. In the following, generic figures have been used, but when fire mitigation and acoustic attenuation are factors, please refer to the respective manufacturer’s technical data.
Mineral Wool – Glass or Stone
Perhaps the most common insulant due to its cost and versatility is mineral wool. Whether glass or stone, it can be both non-combustible and sound-attenuating (refer to manufacturer’s technical data). Unlike blown insulation, product density comes as manufactured and is easily rolled out with minimal dust.
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Performance Data (BS-5250-2021)
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Density
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10–200 kg/m³
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Thermal Conductivity (λ)
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0.044–0.032 W/mK
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Blown – Glass, Stone, and Cellulose
Blown insulation is most commonly applied in the horizontal plane but can also be applied to sloped or vertical surfaces with the correct support. Note that the cellulose option will require chemical treatment for durability and fire resistance. The benefit of blown insulation is that it can be applied to more challenging areas where batt cannot reach, such as small or awkward spaces. Downfalls include dust production and considerations of density and coverage uniformity as drifting can occur.
Plastic Foams – Polyisocyanurate (PIR or ISO), Polyurethane (PUR), and Expanded Polystyrene (EPS) or Extruded Polystyrene (XPS)
Rigid foam insulation includes some of the best performing insulants on the market, which can achieve a thermal conductivity (λ) value of as low as 0.022 W/mK.
One benefit is that more slender sections can be used in comparison to other insulants based on their thermal performance. When site cutting for fitting is required between frames, care should be taken to avoid gaps being formed. Concerns arise around fire resistance and sustainability credentials, so these should be assessed on project requirements.
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Performance Data (BS-5250-2021)
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Density
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20–35 kg/m³
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Thermal Conductivity (λ)
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0.022–0.035 W/mK
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Natural Fibers – Wood, Lamb’s Wool, Hemp, and Straw
The most sustainable of all the insulants is natural fiber insulation. The use of this insulation type, however, does come at a cost to thermal performance, which is less than that of purpose-made product. Being bio-based means that, like the cellulose that is used as blown insulation, chemical treatment for fire resistance and durability is required. If sustainability is of high priority and these insulants are being explored, expect thicker wall assembles to account for the greater amount insulation required.
It’s impossible to cover all of the insulation types out there in the market today, but I hope this small but not conclusive article provides an overview of some of the common and not so commonly utilized insulations.
With 18 years in the timber engineering industry, working in the UK, Europe, and North America, Greg Watson currently lives in Scotland and is the Technical Manager at one of the UK’s leading prefabricated panelized light-frame manufacturers. He has a passion for large and complex timber structures and seeks to promote timber as a sustainable building material. linkedin.com/in/gregwatson87