Technical Bulletin #19 : Mismatched Roof Pitches

PROBLEM

Some buildings are constructed with a variety of roof pitches. When roof planes that meet at a valley or hip are not of equal pitch, it is referred to as “mismatched roof pitches”.

ANALYSIS

Mismatched roof pitches affect the installation of metal roofing. When standing seam materials are being installed, the mismatched problem must be addressed in order for the valley pans and hip flashings to be bent to the right angles. When horizontally-run metal shakes, shingles, or tile are being installed, the mismatched pitches will mean that the courses of the metal roof panels will not line up with each other on either side of the hip or valley. This problem will become progressively worse along the hip line and, at some point, the course on one side might even surpass the course on the other side. In some cases, property owners will not understand why this happens until it is explained to them. This situation must be addressed particularly on metal roof systems which normally use individual hip caps at a rate of one per course that lock over the butt edge of each course. Because the courses do not align, it is difficult or impossible to use such caps.

SOLUTION

If desired, the bottom edge of the hip caps can actually be re-formed to meet both courses of shingles. While this is a good option on very short or limited hip runs, it is too time-consuming for longer hips. Whenever possible, this situation of mismatched pitches should be recognized before the roof installation is started and the manufacturer should be consulted to determine the best way of dealing with it. A common way, though, is to use ridge caps on the hip rather than hip caps. Ridge caps do not interlock with the adjacent shingle courses. Instead, the thick butts of the courses would be flattened and the ridge caps would be secured to the hip line. Some metal roofing dealers choose to do this on all of their hips because they like the look of it. In any event, metal roofing offers a great deal of flexibility and, with some forethought, issues such as mismatched pitches can be successfully addressed.

Classic Products, Inc.


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