Transversal junctions/expansion

When the length of the roof slope exceeds the maximum recommended length, it is necessary to join the sheets using transverse junctions. Several techniques exist depending on the pitch of the roof.

These include:

Step (or drip): for pitches of 3° (5%) or more The step height will be a minimum of 8 cm for standing seam.

Double welt: for pitches of 11° (20%) or more.
The double welt can be used for pitches of 11° and above. The minimum length of the overlap is 200 mm*The dimensions can vary due to the projected expansion and/or contraction based on the conditions at the time of installation., with a securing clip at the top. Depending on climatic conditions such as wind and rain, the overlap should be increased. The VMZINC fixed clip (#1 in diagram below) should be soldered onto the zinc sheet, not fastened to it.

Single welt: for pitches > 25° (47%) or more

The single welt or single lock cross-welt with an overlap of 51 mm*The dimensions can vary due to the projected expansion and/or contraction based on the conditions at the time of installation. can be adopted for pitches greater than 25° (42%) in the standing seam technique.

VM BUILDING SOLUTIONS recommends using the double welt over the single welt for standing seam techniques as it provides greater water resistance.

Expansion of VMZINC

Any work involving VMZINC must allow it to expand and contract freely. The linear expansion of VMZINC is 0.022 mm per meter and per degree centigrade.

Example: In Sydney, the temperature range to bear in mind is from 0°C in mid-winter to + 90°C on the surface of the metal in the sun at the height of the summer. Assuming an ambient temperature of 25°C during installation, we have to take into account an additional 65°C (expansion) 25°C less (contraction).

For a 10 meter long panel:
A. anticipate an 0.022 mm x 10 x 65 = 14.30 mm increase in length,
B. anticipate 0.022 mm x 10 x 25 = 5.5 mm contraction.

 

VMZINC Weights and Thicknesses
Thickness Gauge Weight
1.5mm 16 (10.8kg/sq. meter)
1.0mm 20 (7.2kg/sq. meter)
0.8mm 22 (5.76kg/sq. meter)
0.7mm 24 (5.04 kg/sq. meter)