Most of the people are concerned about water leakage when there is a heavy rain, especially in the large building or factories where long-length roof sheets 70-100 meters are installed at the low roof slope.
If in heavy rain, the pans (or valley) overfill, water can flow into the roof through the side-lap or flashing but the water may not leak inside the building, it depends on the roof profile and installation system because each profile has a different drainage capacity.
Main factors that affect leakage are as followings:
1. Roof profile – the width and depth of pans (valleys), ribs.
2. Roof Installation system – roof boltless system will prevent water leakage better than roof bolt systems.
3.Roof Slope – less slope with slower water flow.
4.Rainfall intensity – depends on the geographical area within Thailand, Southern has more rainwater than other parts.
5.Roof length for drainage – if the length from the roof ridge to the eaves is too long the water flow will be slower.
6.If there is an opening on the roof sheet (penetrations) which will cause nearby pans (valleys) to carry extra diverted from pans obstructed by penetration so it can cause water leakage.
Nowadays there are several steel roof profiles available in the market, each profile has a different drainage capacity feature and therefore to choose the proper roof profile and roof installation system will help to reduce the risk in terms of the water leakage.