Roof Sarking Detail

Roof Sarking, especially under metal roof cladding, plays a critical role in the buildings defense against moisture and conditions conducive to mould and dry rot.

I rarely observe sarking installed correctly, especially when the material is a combined fluff and foil product. However, like all building materials, there is nearly always a Product Installation Guide. Builder Beware, getting this detail wrong can result in the roof coming off and starting again!

Section 1.3.37 of SAA HB39 Installation Code for Metal Roofing & Wall Cladding (2015) defines sarking as "A flexible membrane designed to provide thermal reflectance and to collect condensation and moisture that may form on or penetrate a roof covering".

Section 5.3.2 (o) of SAA HB 39 Installation code for metal roofing and wall cladding (2015) states, "Sarking to enter the box gutter by 25mm".

If the sarking is cut flush (like the picture above) to allow no overhang into the gutter system, then moisture formed between the sarking and roof cladding as a result of condensation, cannot escape the building. Moisture falls short of the gutter, and ends up terminating in the roof cavity, resulting in wood rot to the perimeter roof batten, or mould and water damage to insulation and plaster ceilings and cornice.