Laying Roof Sheets for Sheds

Most of the sheds sold currently have roofing that is pierce fixed (using screws) and regardless of the Building Class (sheds are 10A) all have to be fixed according to the suppliers’ product literature) and to follow all codes set out in the BCA.

The two most common roof sheets utilised on sheds are corrugated and trapezoidal (Trimdek, TL5 etc which are all manufacturers’ trade names for this profile). Both of these sheets have a design feature formed in the side laps which is called an anti-capillary break. This forms in effect, an air break between the two sheets when laid on the roof. This prevents the capillary action of the two sheet surfaces (one under & one over) drawing moisture into the lap and into the underside of the roof sheeting. This anti-capillary break also drains water from the laps. For this feature to be effective for which it is designed – the roof sheets must be laid in the right direction with regard to the direction of prevailing weather. In effect, the anti-capillary break should be oriented always away from this prevailing weather direction.

From the start of laying the roof sheets it is important to ensure that the laying direction is confirmed prior to installation.

Qualified Roofing Contractors and Plumbers are aware of this feature due to the regulations contained in the “Installation Code for Metal Roofing and Wall Cladding” called the SAA HB39-1997 which was developed by the Victorian Plumbing Industry Board, The metal Building Products Manufacturing Association Ltd and Standards Australia. This is currently under review by Standards Australia and they will have details of expected release.

As seen in Figure 1 – the anti-capillary break is “down wind” from the prevailing weather. In the corrugated profile there remains a gap which allows moisture to drain away. In the Trapezoidal profile the gap has a larger air pocket in addition to the gap. As is obvious – if the sheets are laid in the opposite way – there is a high chance of leakage to below the roof sheeting. This simple side lapping procedure can save many hours of searching or rectifying roof leakage.


Figure 1


So prior to installation of roof sheeting – determine the direction of the prevailing weather or seek assistance from the roofing plumber. Check other roofing sheeting in your area to see and confirm the direction of laying for your particular location.

Also don’t forget to check the regulations in your state, as some states require that any work done to roofing, must be done by a licensed and qualified plumber.

For the full article go here Shedeye Science – Shed Roofing – Laying Roof Sheets