How To Re-Roof A House With Composition Shingles
Replacing a roof is one of the most critical maintenance tasks for any homeowner. Composition shingles, commonly known as asphalt shingles, remain the most popular residential roofing material due to their durability, cost-effectiveness, and aesthetic versatility. A proper roof replacement goes far beyond simply nailing down new shingles. It requires a comprehensive understanding of structural decking, underlayment systems, flashing techniques, and building codes to ensure the structure is watertight and safe.
Assessing And Preparing The Roof Deck
The foundation of a reliable roof begins with the structural deck. Before any new roofing material is applied, all existing shingles, underlayment, and fasteners should be completely removed down to the bare wood. Once exposed, the roof decking must be meticulously inspected for signs of water damage, delamination, or dry rot.
If any sections of the plywood, oriented strand board, or structural planks are compromised, they must be replaced. Standard building practices dictate that roof sheathing should be a minimum of fifteen-thirty-seconds of an inch thick, securely fastened to the roof trusses or rafters. Ensuring a solid, flat, and structurally sound deck is paramount, as new shingles require a firm substrate to achieve maximum wind resistance and structural integrity.
Installing The Roofing Underlayment
Once the deck is prepped and swept clean, the next step is applying the underlayment. This crucial layer serves as a secondary moisture barrier in the event that wind-driven rain gets beneath the shingles. A minimum of fifteen-pound felt paper or a modern synthetic roofing underlayment should be rolled out horizontally, starting from the eaves and working up toward the ridge.
In areas subjected to heavy snow and ice, building codes mandate the installation of an ice and water barrier. This self-adhering waterproof membrane must be installed along the eaves and around vulnerable penetrations. Additionally, a metal drip edge should be installed along the eaves and rakes to direct water away from the fascia boards and prevent capillary action from pulling moisture under the roof edge.
Applying The Composition Shingles
The shingle installation begins with a starter strip applied along the eaves and rake edges. The starter strip includes a line of sealant that bonds to the first course of shingles, providing critical wind resistance at the roof perimeter. When laying the primary architectural shingles, it is essential to stagger the joints according to the manufacturer specifications to prevent water infiltration.
Proper nailing technique is non-negotiable in roofing. Shingles must be fastened using the correct type and length of roofing nails, ensuring the nail head is driven flush with the shingle surface without cutting into the fiberglass mat. Nails must be placed precisely in the designated nailing zone to prevent the shingles from slipping or blowing off during severe weather events.
Flashing And Roof Penetrations
The most vulnerable areas of any roof are the penetrations and intersections, such as chimneys, skylights, plumbing vents, and roof valleys. Step flashing and counter-flashing must be carefully integrated with the shingle courses around brick chimneys and vertical walls. Plumbing pipes require specialized rubber or lead boot flashings to prevent leaks, while solar panel brackets and skylights must be sealed and flashed exactly to manufacturer specifications.
Three Key Construction Tips
Always Verify Decking Integrity Before Shingling: Never install new roofing over rotted or damaged wood. The structural sheathing must provide a solid substrate for nail holding power to meet wind uplift requirements.
Prioritize Proper Nailing Placement: A shingle is only as strong as its fasteners. Always use the manufacturer-specified nailing zone and drive the nails perfectly flush. Over-driven or under-driven nails are a leading cause of premature roof failure.
Do Not Skimp On Flashing: Roofs rarely leak in the middle of a shingle field; they almost always leak at penetrations and transitions. Always use high-quality metal flashing at valleys, chimneys, and roof-to-wall intersections to guarantee long-term watertightness.
Bonus Questions And Answers
Can I Install New Composition Shingles Over An Existing Layer Of Old Shingles?
If you are weighing the cost of a full roof replacement versus a quick fix, you might wonder about simply layering new materials over the old ones. While some local jurisdictions permit overlaying a second layer of shingles, the universally accepted best practice is a complete tear-off. Removing the old roof allows you to inspect the structural decking for hidden rot or water damage that would otherwise go unnoticed. Furthermore, the International Residential Code limits roofs to a maximum of two layers, and adding a second layer significantly increases the dead load on your roof trusses, which can compromise the structural safety of the entire home.
What Type Of Underlayment Is Required Beneath Composition Shingles?
Protecting the underlying wood is just as important as the shingles themselves, leading many to ask about the necessary moisture barriers. To ensure compliance with standard building practices, composition shingles must be installed over a code-approved underlayment, typically a minimum of fifteen-pound asphalt-saturated felt or an advanced synthetic alternative. According to the International Residential Code, in regions prone to severe winter weather and ice damming, a specialized ice barrier must also be installed. This self-adhering polymer-modified membrane must run from the lowest edges of all roof surfaces to a point at least twenty-four inches inside the exterior wall line of the building to prevent melting snow from backing up under the shingles.
How Many Nails Should Be Used Per Composition Shingle?
Ensuring your roof can withstand severe weather often comes down to the smallest details, such as your chosen fastening method. The standard fastening requirement for most modern architectural composition shingles is a four-nail pattern, with each roofing nail driven squarely into the manufacturer-designated nailing zone. However, in high-wind regions, building codes and manufacturers strictly mandate a six-nail pattern to provide enhanced uplift resistance. Structurally, all fasteners must be corrosion-resistant, such as galvanized or stainless steel, and must penetrate at least three-quarters of an inch into the roof sheathing to provide adequate withdrawal resistance against storm-force winds.
