Shingle Materials, Codes, and Deck Preparation

What This Lesson Covers

Before a single shingle is nailed down, a roofer must know the materials, understand the code requirements, and confirm the deck is solid. Skipping any of those steps invites leaks, failed inspections, and voided warranties. This lesson covers shingle types, underlayment and drip edge selection, and the deck-preparation routine that sets up every successful asphalt-shingle job.

Asphalt Shingle Types

Three-tab shingles are the traditional flat, single-layer shingle. Each strip has two slots (tabs) cut into its bottom edge, giving the appearance of three separate pieces. They are lighter, thinner, and generally less expensive than architectural shingles. Wind-resistance ratings and warranty lengths are typically lower than architectural products. Three-tab shingles are still specified on budget-driven work and repair jobs where matching existing material matters.

Architectural shingles (also called laminated or dimensional shingles) bond two layers of fiberglass-reinforced asphalt mat together with staggered cutouts. The layered construction creates a shadow line that mimics wood shake. They are heavier, thicker, and carry higher wind and impact ratings. Most residential new construction today specifies architectural shingles. Because they are heavier, verify that the roof structure is engineered to carry the added load before using them on a re-roof.

Both types are manufactured to ASTM International standards. The key physical properties to check on the packaging are: fire rating (Class A, B, or C), wind-resistance rating (miles per hour), impact rating (UL 2218 Class 1–4 where required), and the manufacturer's minimum slope requirement, which is typically printed prominently on every bundle.

Underlayment Types

Underlayment is the secondary water-resistive layer installed directly on the deck before shingles. It is not optional—building codes and manufacturer warranties both require it.

Asphalt-saturated felt is the traditional product, available in No. 15 and No. 30 weights. Heavier felt is more tear-resistant during installation. Felt can absorb moisture and wrinkle, so it should be installed and shingled promptly.

Synthetic underlayment is woven or non-woven polypropylene or polyester. It is lighter, stronger, and more slip-resistant underfoot than felt. It can be left exposed longer without degrading. Many manufacturers now require or strongly recommend synthetic underlayment to maintain their full warranty.

Ice-and-water shield is a self-adhering, rubberized-asphalt membrane. It seals around fastener penetrations and bonds tightly to the deck. Building codes in most cold climates require it at eaves, in valleys, around penetrations, and along rakes where ice dams are a risk. The required coverage width varies by code jurisdiction—always check the local adopted code and the shingle manufacturer's instructions together.

Drip Edge Profiles

Drip edge is a corrosion-resistant metal flashing installed at eaves and rakes to direct water off the deck edge and into the gutter or away from the fascia. The two most common profiles are:

• Type C (also called L-flashing): A simple 90-degree bend. Used primarily at rakes.
• Type D (also called T-flashing or drip-T): Has an additional leg that projects away from the fascia, creating a drip point. Used at eaves. The profile keeps water from wicking back under the shingles by surface tension.

Drip edge is installed before underlayment at the eaves and over underlayment at the rakes. Getting this order wrong is a common defect that allows wind-driven rain to travel under the material.

Deck Preparation

A bad deck produces a bad roof, no matter how expensive the shingles are. Follow these steps before any material goes down.

1. Visual and physical inspection. Walk the deck systematically. Probe every area with a hammer handle or your boot. Soft or spongy spots indicate wet, rotted, or delaminated sheathing that must be replaced—not covered over.

2. Confirm sheathing thickness and fastening. Most codes require a minimum sheathing thickness for shingle application; verify against the local adopted building code. Check that all sheathing panels are fastened per code spacing requirements at edges and in the field. Missing or popped fasteners must be added or replaced with ring-shank or deformed-shank nails appropriate to the sheathing thickness.

3. Check and correct gaps. Sheathing joints should have a small gap (typically 1/8 inch) to allow for expansion. Gaps larger than code allows can telegraph through the finished shingle surface and cause shingles to crack over time. Add H-clips or sister a new piece of sheathing if gaps are excessive.

4. Nail down protruding fasteners. Any nail head that is not flush will create a high spot, cause shingles to bridge, and can puncture underlayment.

5. Sweep the deck clean. Debris under underlayment creates bumps and voids that compromise the waterproof layer.

6. Snap chalk lines. Reference lines keep courses running straight and expose any rafter or truss irregularities that need correction before installation starts.

Safety Notes

Deck work is fall-hazard work from the first step onto the roof. OSHA requires fall protection at six feet above a lower level on construction sites. Personal fall arrest systems, guardrails, or safety nets must be in place before you begin the inspection. Wear slip-resistant footwear; wet or damp OSB and plywood are extremely slippery. When probing for soft spots, maintain three points of contact and position your body weight on sound sheathing. Never stand on an area you have not yet confirmed is solid.