When buying a home, a Home Inspection of the roof and its structure is important as problems in this area can cause serious problems elsewhere leading to high cost of repairs.
We think of roofs as to what can be seen from the curb looking up. This portion is important as improperly installed shingles, flashing, capping and caulking/sealing can allow water to penetrate to the interior of the building envelope. Water can cause serious damage to the roof structure (rafters/trusses), insulation, interior ceilings, walls and anything else that is in the path of water entering the building.
The starter shingle at the base is a shingle that has been removed of tabs, reversed to allow for 1/2″ overhang at the eve line. The next shingle row goes on top of this and is laid with the bottom aligned with the bottom of the starter piece. Proper overlapping of shingles with no nail heads exposed, having a nail just above the cutout slot is required.
Care is required for all roof cutout (venting, plumbing stack or other protrusions) to ensure the hole is sealed by overlapping shingles, vent flange and roofing compound.
There is more to roofs than what is visible from the outside. On the inside the roof material can be plywood, OSB, 1×6 wooden board 3/4″ thick. These materials should never be wet.
The roof is supported by the rafters or trusses. This can look like a bunch of wood in a webbing type arrangement.
Under this is the insulation, which can consist of blown fiberglass, cellulose, foam, batts (fiberglass/Ruxol). These materials will be on top of a vapour barrier (generally 6 mil plastic) for older homes this can be a paper/tar type product or nothing.