Roof Installation, Repair and Replacement Practices
Roof Installation
Sequence
Sound installation runs: strip or repair the deck, inspect and re-nail sheathing, install eave and rake edge metal, lay underlayment, install ice-dam membrane, then apply shingles from the eave upward, finishing with ridge cap and ventilation.
Drip edge layering
At the eave, the drip edge goes under the underlayment so water sheds over the metal. At the rake, the drip edge goes over the underlayment so water running down the rake sheds off the metal. Reversing these is a common field error and a frequent exam trap.
Shingle fastening
Nails pass through the nailing strip about 1/2 to 1 inch above the exposure line and at least 1 inch from the shingle ends, driven flush - not overdriven or angled. Four nails per shingle is typical; six in high-wind areas or as the manufacturer requires. Begin with starter at the eave and rake, and offset courses so joints do not align.
Flashing details
Step flashing is woven with each shingle course at sidewalls, and counterflashing covers its top edge. Valleys are built open-metal, woven or closed-cut according to the plans and manufacturer instructions. Kick-out flashing is required where a sidewall meets a gutter to prevent water from running behind the wall cladding.
Ventilation
Provide net free vent area near the code ratio, split between low (soffit) and high (ridge) vents, and never let insulation block soffit vents.
Worked example
At a 5-inch exposure, one full shingle covers 36 in x 5 in = 180 sq in, or 1.25 sq ft, so a 100 sq ft square needs about 80 shingles - matching the familiar three-bundle-per-square rule.
Repair and Replacement Practices
Diagnose before tearing off
Leaks rarely begin where the stain appears. Trace water uphill: check flashing at walls, chimneys and valleys, pipe boots, fastener penetrations and clogged gutters. Distinguish an active leak from condensation, which shows as frost or uniform moisture on the underside of the deck in cold weather.
Repair versus replace
Local repairs work when the deck is sound and damage is isolated. Replacement is indicated when shingles are brittle, granule loss is heavy, there are multiple layers, the deck is soft or delaminated, or flashing is at the end of its life. Re-covering over an existing layer is limited by code and by warranty; many jurisdictions and manufacturers cap the roof at two total layers, and a third is never acceptable.
Common repairs
Replace torn or missing shingles by breaking the seal, cutting the nails, sliding the new shingle into position and hand-sealing it. Replace cracked pipe boots with new neoprene or lead boots. Rebuild failed step flashing rather than smearing sealant over it - sealant is a temporary repair, not a waterproofing system.
Deck and underlayment
When you strip a roof, inspect the sheathing, replace delaminated or rotted panels, re-nail, and confirm the deck thickness suits the rafter spacing.
Documentation
Photograph existing conditions before work, record the number of layers removed, and give the customer a written scope. This protects you in disputes and supports warranty claims.
Rule of thumb
If water has reached the deck, the repair is not finished until the deck and underlayment are corrected. A new shingle over a wet, rotted deck fails again within a season.