Installing metal roof Insulation
COLORBOND® steel and ZINCALUME® steel are thermally efficient roofing materials, radiating less heat into your building as they cool down faster at night. Lighter coloured roofs, irrespective of material, reflect more heat than darker shades. The result of this is less heat available to be radiated into your building. To reduce the transmission of heat into a building, insulation can be easily incorporated during the installation of the steel roof sheeting.
There are two types of insulation commonly used during the installation of steel roof sheeting. They are:
Combined foil & glass/wool Insulation blanket
Reflective foil (or Sarking)
If we first look at the Insulation foil faced blanket, this is the proven solution for insulation under metal roofing whether it is for a residential or commercial application. It provides cost effective thermal insulation helping to reduce your buildings heating and cooling energy requirements and improve the internal comfort. The blanket is also an effective way of controlling condensation under metal roofing and helps reduce rain and hail sound. Whilst the use of metal roofing and cladding, can be quick and efficient to construct they do deliver poor performance in terms of insulation properties. An un-insinuated roof will allow up to 95% of the heat to enter or leave the building.
Correctly installed insulation, will help keep the summer heat out and improve the energy efficiency of the building. This will help reduce the cost of energy required which means that your insulation will pay for itself. The blanket should be installed over the battens with the glass/wool insulation facing up. There should be no sagging between battens to avoid air spaces between the fibreglass and the underside of the roof sheeting.
One 15 metre roll will cover 18 square metres ♦ R Value - 1.5
Available in 55mm or 75mm thickness.
Reflective Foil, or 'sarking'
Reflective foil laminates which are commonly used to provide heat insulation under roof sheeting can serve a dual function as a vapour barrier, simply by thoroughly sealing the foil overlaps with moisture impervious adhesive tapes. The laps should be about 100mm and kept in close contact when positioning the laminate so the tape can be readily applied. The laminate must be allowed to drape between the roof supports so the cold temperature of the roof sheeting will not be transmitted to the laminate by contact. If this were to happen condensation could form on the underside of the laminate and may drip into the ceiling space.
We stock and recommend Sisalation® Sisaltuff Multi Purpose Extra Heavy Duty (456) which consists of outer layers of aluminium foil bonded to the weave, then held in place with a heavy coating of flame retardant adhesive. It is installed under metal roofs, it reflects radiant heat and provides a barrier to prevent condensation on the underside of the roof sheet. Features & benefits include:
R Value - 0.7 You can cover 72sqm with one 60 metre roll
Manufactured in Australia, Sisalation® Roofing Foil is a double sided anti-glare reflective foil laminate recommended for use in the sarking of metal roofs. Flame retardant Sisalation® is suitable for use in buildings in bushfire prone areas.
Sisalation® provides an effective barrier against moisture, vapours, wind, heat and dust penetration when overlapped.
When used in conjunction with an airspace, Sisalation® is an effective thermal insulation material because of the high reflectivity and low emissivity of its aluminium foil surfaces.
Sisalation® complies with the requirements of AS/NZS4859.1. The contribution of this product to Total R-value depends on installation and environmental conditions which include the effect of dust.
Sisalation® should be installed in accordance with AS/NZS4200.2:1994 for the installation requirements for "Pliable Building Membranes". External cladding should be installed without delay. Reflective foil in roofs must be installed with a sag or drape down of approximately 40mm - 75mm between the rafters or battens. This is to allow a vapour barrier to occur between the reflective foil and the metal roof sheeting.
To achieve the stated total R-Values, a minimum air space of 40mm is required adjacent to each reflective foil face.
Condensation – things you should know:
The underside of a roof often provides conditions under which condensation of water vapour will occur. In cooler weather, roofs can become several degrees cooler than the outside air temperature. As a result, the air in the roof space may be cooled by contact with the roof. This depression of temperature is often sufficient to cause condensation as air is cooled, its ability to hold water vapour diminishes. The amount of condensation will depend on the amount of water vapour in the air and this varies with climatic conditions. Flat roofs are more prone to condensation than steep or pitched roofs.
Roofing foil provides a heat and vapour barrier and also provides a separation membrane to reduce friction between the roof sheets and the supports, due to expansion and contraction of the roofing material.
For further information on any of the products described above, please visit the insulation section of this website by clicking here.