Flashings and Penetrations
The following comments are made as guidelines to be used when inspecting Dimond roofing and wall cladding systems during and after installation.
Material
Must be the same material and coating as the roof or wall cladding to give a similar durability and compatibility to the roof/wall system.
Fabrication
Flashings should be fabricated to achieve sufficient cover width and to maintain falls to avoid water ponding. They must be without noticeable micro-cracking and be fixed without damage such as dings or crushing, and should be free of scratches and swarf the same as for roofing.
Flashing joins must be sealed at both ends of the lap, and the fasteners must pass through the sealant at the leading edge. Spacing of fasteners should be no greater than 50mm apart. Laps to be 150mm min.
Fastening
Wherever possible, flashings should be screw fixed through to the supporting structure, with sufficient slope or fall to ensure ponding does not occur. Stitch screws should be the preferred means of attaching flashings to sheeting ribs. If aluminium rivets are used, the minimum size should be 4.8mm diameter.
All fasteners should be of sufficient size and frequency to withstand the loads that may be applied through wind uplift or thermal expansion, throughout the life of the roofing material. As a guide, where flashings cover the roof, use the same fastener that has been used to fasten the roof.
Fastener Frequency
As a guide, the fastener frequency for fixing flashings should be:
| Wind Zone* | Fasteners Per Metre |
| Low (32 m/s) | 1 |
| Medium (37 m/s) | 2 |
| High (44 m/s) | 3 |
| Severe (50 m/s) | 4 |
* in accordance with NZS 3604
Sensible allowance should be made to allow relative thermal expansion between flashings and sheeting if sheet lengths exceed 12m. Expansion joints in the flashings should be considered for steel flashings greater than 18m and aluminium flashings greater than 12m in length.
Flashing lapping over roofing should be in accordance with Table 2.1.O of Section 2.1.3.6 of the Dimond Roofing & Cladding Technical Manual. Where barges meet the gutter, this must be closed off to ensure wind driven moisture and birds cannot enter the building.
Profiled Foam
Profiled foam sealing strips should be installed when specified at the top end of the sheet, adjacent to the stop end. To help keep the strips in place it is good practice to position them on a bead of silicone sealant.
Notching
Best practice to notch flashing downturns around sheet profiles is to mark in-situ and use a rib-shaped template. Clearance gaps around the ribs should be just sufficient to prevent cut edge contact with the sheet surface. Gaps between 1mm and 3mm are generally considered satisfactory.
Soft edging can be used on corrugate and low rib profiles with rib heights up to 30mm and should be neatly pushed down and formed in to the profile pans to achieve a neat-tight fit.
Property boot pipe flashing
Property boot pipe flashings must not be positioned in such a way that a dam is formed across a water channel. It is preferred that Property boot pipe flashings are positioned on the 'bias' rather than square across the sheet. If the pipe and Property boot pipe flashing dam up the pan or restrict more than 50% of the water flow around the pipe and flashing, an additional cover over flashing to the ridge and sealing of the Property boot pipe flashing to this flashing should be considered. Excess silicone sealant should be avoided, as it will add to he risk of water ponding.
Penetrations
Penetration holes with their major dimension or diameter greater than 150mm must have support framing placed around the perimeter of the penetration holes.
Water diversion around the penetration must not cause an overload of the receiving channel such as the pans that the water has been diverted into, which may cause flooding. Penetration flashing shall not rely solely on the silicone sealant to achieve weather tightness of the flashing.
