Rock Wool Insulation Vs. Fiberglass Insulation

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Rock wool and fibreglass insulation provide thermal barriers to minimise heat loss in walls, ceiling, floors and attics. Insulation provides property owners with a cost-effective method for making structures energy-efficient. Combined with other insulating components, such as doors and windows, property owners can realise significant savings on energy costs.


Rock wool is created from basalt or diabase -- materials resulting from volcanic eruptions. The U.S. Patent Office granted a patent for rock wool as a commercially viable product in1875. The material has a wide range of applications, including insulation for pipes, vessels and industrial buildings. In the last 10 years, builders have increased the use of rock wool in residential new construction. Manufacturers make fibreglass insulation from fine molten glass fibres. Fibreglass came into its modern form in 1932. Residential Design and Build magazine cites a 2008 study by the Freedonia Research Group, which states fibreglass insulation makes up about 85 per cent of the residential insulation market in the United States.


Both products come in loose-fill or blanket/batt form. Insulation manufacturers make blanket/batt insulation faced or without a face. The faced product has a covering that functions as a vapour barrier. The vapour barrier prevents moisture from penetrating the material. Many do-it-yourself homeowners complete blanket/batt insulation jobs. The material has naturally fire-resistant qualities, but does not install as airtight as rock wool. Moisture can compromise the effectiveness of fibreglass insulation, and it has a tendency to attract rodents seeking a place to nest. Concern exists about the possible health effects of fibreglass insulation and the release of formaldehyde and tiny particles. Do not install fibreglass insulation near heat-producing appliances or fixtures. Rock wool's recyclable quality makes it environmentally friendly. It retains its thermal qualities after exposure to moisture and can come in close contact with chimneys or stoves. Mineral wool costs about 10 per cent more than fibreglass; it does not release harmful fibres or emissions. Depending on the local building codes, the project may require the installation of a vapour barrier.


The R-value measures the capacity for insulation to resist heat flow. Higher R-values slow down cold and heat flow due to greater insulation power. Rock wool has an R-3 to R-4 value per inch of material. Fibreglass has an R-3 value for each inch of insulation. Installers can purchase blanket/batt insulation that comes in R-values, such as R-11, R-22 or R-30. The recommended R-value depends on the location and the building components insulated.

Installation Methods

Batts come in lengths of 4 or 8 feet. Installers must cut blanket insulation to the desired length. The width of the material allow the installer to fit snugly in cavities between studs, joists or beams. Insulation projects with blankets or batts require opened walls, floors or ceilings. The material loses it effectiveness if gaps exist between the sheets. Follow the manufacturer instructions for installing and sealing.

Rock wool or loose-fill insulation work effectively for open new walls and between cavities of enclosed walls. One installation technique utilises an insulation blowing machine and hose to blow the insulation in place. This ensures coverage around pipes, cable, electrical boxes and other objects. Many installers simply pour loose-fill material in place for certain projects like insulating an attic floor.

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