Maximum lengths of roofing

The valleys (or pans) of roofing have to carry water to the gutters. If the valleys overfill in heavy rain, water can flow
into the roof through the side-laps and flashings. Factors affecting waterproof and drainage capacity of the
laps of a profile include:

• the width and depth of the valleys or pans;
• the pitch of the roof—rain flows faster on a steeper pitch;
• rainfall intensity for the geographical area;
• the length of the roof from ridge to gutter; and
• penetrations that cause nearby valleys to carry extra rain diverted from valleys obstructed by the
penetration.