Metal Roofing - General Principles
  • 1 Minute to read
  • PDF

Metal Roofing - General Principles

  • PDF

Article summary

Roofs are not waterproof – they are designed to simply collect water on the building and remove it to another location in a controlled manner to prevent water entry to the building and the associated water damage.

The design of a roof, following the roof from the highest point of the building (ridge) to the drainage system (downpipe) must:

1. have falls – no horizontal surfaces or ponding whatsoever;
2. have a system to collect and drain the water - gutters, hobs, downpipes, spitters etc.;
3. have secondary overflow in case of blockage to the primary drainage to remove the water;
4. resist pressure driven water ingress using sheet turn ups and laps to block water entry;
5. prevent condensation using insulation;
6. have** anti-capillary **protection using turndowns and drip moulds.

Penetrations in roofs must be supported and must allow the water to fall to the drainage system. The pan of the roof is
essentially a gutter. Block it and the water flow will stop causing water to pond on the high side of the roof above the
penetration. DON’T BLOCK ROOF SHEET PANS. Use a soaker flashing or dry pan.

Don’t allow any silicone over sealing to flashings junctions EXCEPT blind rivet heads and dektites (which we allow to be over-sealed – see policy for details) – the only long term failsafe method for sealing flashing joins and as recommended by the roofing manufacturers and this manual is to use correct lapping with sealant between the sheets only. Where silicone is absolutely necessary - use NEUTRAL CURE UV stabilised (Coloured) silicone ONLY. Do not use clear silicone anywhere other than for undersealing where silicone is not exposed to any UV light.

Roofing is a pre-finished product – take care of it. Clean up swarf daily and restrict access. Don’t let anyone weld, grind or drop rubbish on the roof. Install roof walk ways early to prevent damage. Kinked sheets must be replaced.


Typical Roof Section

Was this article helpful?

What's Next