A problem I sometimes find when inspecting a relatively new roof is installed on an older home is misalignment of the roofing deck below the shingles with respect to the fascia board along the lower edge of the roof or as a result of roof decking which stops short of the fascia board, resulting in a large gap at this location.  Both of these conditions can result in a lack of adequate support for the drip edge flashing which in severe cases cause the flashing to rest in the wrong position.  This creats a potential for water penetration.  In some cases, I have seen this problem along the rake of the roof at the gables, but this is not as common and does not appear to be as serious due to the layup of the roofing materials which when properly installed prevent water entry to the decking.

If the deck is severely misaligned and is installed below the top of the fascia, then the installed drip edge flashing may not match the pitch of the roof and can pitch back into the roof.  The change in pitch creates a flair in the roof at its lower edge, which can result in water leaking into the soffit.  In some cases, this can be corrected through refitting of the fascia boards to correct the alignment but could require deck replacement, depending upon the configuration of the framing and cornice details.

Deck Set Below Facia and Drip Edge

Resulting Flair at Rake

If the roofing deck is installed significantly short of the fascia so that the top edge of the drip flashing cannot lay on the deck, a similar condition occurs.  This condition is often very difficult to detect as the shingles may not provide the telltale flair unless the gap between the roof decking and fascia is extremely wide.  The lack of support for the upper edge of the drip edge flashing can allow it to tip back into the direction of the soffit, creating a back slope.  Water reaching the drip edge as a result of capillary action between the starter shingles and flashing may be directed back and run into the soffits due to this reverse slope.  This condition is normally more difficult to correct and often requires replacement of the lower roof decking or installation of a custom drip edge of sufficient width to reach the short roof decking.

Typical Flair Along First Course Due To Improper Alignment

These conditions may not always be apparent during an inspection and may only occur at a portion of the roof's perimeter making them even harder to find.  A typical inspection by the best inspector does not normally include an exhaustive review of such details of roof installation due to the time and access restrictions on an inspection whose real purpose is to determine the general condition of the property.  On most inspections many areas of the roof are not accessible to either view at an angle sufficient to detect the flair or to access the shingles to lift them safely and find this condition without potential injury to the inspector or damage to the roofing.  In some cases the first sign that these conditions exist is the deterioration caused by the water entry to the lower decking or soffit.

Consideration as to the method of repair should be should be based upon site conditions to achieve the best quality repair for the life of the roof and decking.