The outer shell of a home (the envelope)is comprised of the shingles,siding,doors & windows,its what keeps us from the elements.In essence, they are one.They all work together.The chimney flashing on a roof is installed by the siding trades person who performs his work long after the roofer has completed his.
Until which time, the chimney leaks.A good Contractor bridges the gap.
A common misconception is that siding is water resistant, it is only a repellent. Installing “Ice water shield” around windows and doors before siding, eliminates any infiltration. Where a wall meets a roof, snow accumulation can melt due to heat loss, this causes water problems. Understanding the envelope of a home enables me to guarantee my work for 25 years.