Metal roof profiles benefit by having insulation installed immediately underneath the profile. Most often the blanket will be 55 mm of Glasswool faced on the underside with a double sided foil facing. The Glasswool offers sufficient insulation to greatly improve the ‘dew-point’ of the metal surface and this combined with the sealing of the membrane with the overlapping foil facing will prevent warmer, moisture laden air from meeting the cold surface and preventing condensation. The acoustic effect of the blanket immediately under the roof profile, also cuts out excessive rain noise.
Considerations in construction
Although there is some insulation offered by the blanket (R1.5 up to R3.0) in domestic construction, it is usually better to add extra insulation at ceiling level to effectively control the living area environment of a structure. It’s worth considering the difficulty in obtaining a trim finish if you are to be fixing a roof sheet over 75 to 100 mm of insulation. Bulging can arise and detract from the line of a nice sharp roof-line.
Section J compliance for Commercial construction has seen the development of ‘spacer’ systems such as Roof Rack that preserves the integrity of the roofing blanket up to R3.0 / 120mm ratings.
Of the various brands available, the names all tend to embrace condensation avoidance; Anticon, Vapachek, Vapastop. The Glasswool products tends to dominate the market due to their availability, competitive pricing and workability. Some of the other fibre blankets create some difficulty when screw fixing through the material. The reflective foil or captive air space types are suitable as well provided care is taken to ensure adequate air gaps are created when laying out the product.