Roof Drainage for Commercial Buildings

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Commercial buildings most commonly have low slope roofs at 2 percent slope minimum with parapet walls on all edges. These types of roof structures rely on piped roof drains. A primary drain and secondary drain are required.

Commercial Roof DrainThe secondary drain is higher than the primary drain. If the primary drain gets plugged then the secondary drain prevents water build up. If water is coming out of the secondary roof drain pipe termination then immediate action is required. It is critical that the drains be cleaned before and after every rain. If both drains get plugged, the roof structure could collapse. This happens more often than you might think.

Older buildings are especially suspect for not having secondary drains. This is a very important inspection item that almost always is a problem. If this is not addressed by the inspector, it could result in a roof collapse.

Codes sections:
• Roof drains required – CBC Chapter 15 section 1503.4 and the installation and sizing per Chapter 11 of the CPC
• Secondary roof drain required – CBC Chapter 15 section 1503.4.1 and the installation and sizing per Chapter 11 of the CPC

If you have additional questions about roof drainage for commercial buildings, give us a call at 916-606-5457 or contact us.