A.Architect and roofing consultant Harrison McCampbell responds: There are several factors that may have affected the sealing of your shingles. One factor is climate: Many parts of Montana do not experience stifling heat during the summer months.

The second factor is the slope of the roof. The sun’s rays will strike the roof at different angles, depending on the roof slope. If the roof has a low slope — between 4/12 and 6/12 — then the effect of the sun on the north and south sides will be similar. But with the steeper roof slopes typical on newer houses — from 10/12 to 18/12 — the north...

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