Comprehensive Guide: How To Lay Roll Roofing For Low-Slope Structures

Roll roofing installation involves applying mineral-surfaced asphalt sheets to low-slope roof decks with a minimum pitch of 2:12, utilizing a combination of roofing nails and specialized cold-process adhesive to ensure a watertight seal. This process requires precise overlapping, careful management of thermal expansion, and strict adherence to moisture-barrier installation protocols to achieve a lifespan of 5 to 10 years.

Pre-Installation Requirements and Essential Material Preparation

Successfully installing roll roofing depends entirely on the preparation of the roof deck. Roll roofing is a flexible, cost-effective solution for sheds, garages, and carports, but it lacks the durability of architectural shingles. Before purchasing materials, verify that your roof deck is clean, dry, and structurally sound. Any rot, sagging, or protruding fasteners must be corrected before laying the underlayment.

• Essential Materials:
  
  
  • Mineral-surfaced roll roofing (typically 36 inches wide by 33.5 feet long).
  • No. 15 or No. 30 asphalt-saturated felt underlayment.
  • Plastic cement (trowel grade or caulk tube).
  • 1-inch to 1.25-inch galvanized roofing nails with large heads.
  • Drip edge flashing (corrosion-resistant aluminum or galvanized steel).
• Required Tools:
  
  
  • Utility knife with hook blades.
  • Hammer or pneumatic roofing nailer.
  • Chalk line for layout precision.
  • Trowel or caulk gun for adhesive.
  • Heavy-duty shears for trimming.
• Performance Benchmarks:
  
  
  • Minimum slope: 2:12. (Anything flatter requires a multi-ply built-up system).
  • Temperature range: Apply only when the ambient temperature is above 50 degrees Fahrenheit to ensure the bitumen is pliable and the adhesive cures correctly.

Step-by-Step Installation Procedure for Roll Roofing

Step 1: Deck Preparation and Drip Edge Installation

Begin by removing all old roofing material down to the wood deck. Inspect the decking for water damage. Install drip edge flashing along the eaves first, then proceed to the rakes (the sloped sides). Fasten the drip edge with nails spaced 8 to 10 inches apart. Once the drip edge is set, roll out your felt underlayment. Overlap the felt edges by at least 2 inches and secure them with a light tacking of nails or staples. This underlayment serves as the critical secondary moisture barrier.

Step 2: Establishing the Starter Strip

Cut a strip of the roll roofing 18 inches wide—exactly half the width of the roll—to act as your starter strip. Align this strip flush with the drip edge at the bottom eave. Apply a generous 3-inch wide bead of roofing cement along the eave, 1 inch back from the edge. Lay the starter strip over this adhesive and secure it with nails spaced 6 inches apart along the bottom edge, and 8 inches apart along the top edge.

Step 3: Laying the First Full-Width Sheet

Position the full roll of roofing material so that it overlaps the starter strip by at least 2 inches. You must apply a uniform layer of lap cement or cold-process adhesive between the overlapping sections to ensure a monolithic seal. Once positioned, nail the top edge of the sheet into the roof deck using 1-inch galvanized nails, spaced every 6 to 8 inches.

Pro-Tip: Always roll the material out completely and let it relax in the sun for 20 to 30 minutes before installation. This prevents the roofing from "bubbling" or wrinkling due to thermal expansion after it is nailed down.

Step 4: Managing Successive Courses and Overlaps

Proceed to the next course. Ensure every side lap (where the ends of the rolls meet) is overlapped by at least 6 inches. Apply adhesive liberally to these laps. Nail the overlap according to the manufacturer’s specification—typically a "double-nailing" technique where you nail the underlying layer and then the overlapping layer to prevent movement.

Warning: Never drive nails into the middle of the field of the roof unless necessary; every penetration is a potential leak point. Only nail along the prescribed selvage edges or at the necessary overlaps.

Step 5: Finalizing the Ridge and Rake Edges

At the roof peak, fold the final course of roll roofing over the ridge, ensuring it extends down the opposite side by at least 12 inches. Apply roofing cement to the underside of this overlap and press firmly. Cover the exposed ridge with a separate cap strip of roofing material, set in a thick bed of cement, to ensure complete water shedding. Finish by sealing all nail heads with a small dab of roofing cement.

Technical Material Properties and Application Standards

Common Site Failures and Field Fixes

• Failure: Large Air Bubbles or "Fish-mouths"
  
  
  • Root Cause: The material was installed while cold, or it was stretched too tightly during application.
  • Actionable Fix: Carefully slit the bubble with a utility knife, press the excess material down, apply a generous amount of roofing cement underneath, and nail the edges of the slit down, covering the nails with a final layer of cement.
• Failure: Water Seepage at Lap Joints
  
  
  • Root Cause: Insufficient adhesive application or failure to clean debris from the surface before bonding.
  • Actionable Fix: Lift the edge of the lap, scrape out any failed adhesive, dry the area thoroughly with a heat gun or dry cloth, re-apply high-quality asphalt cement, and apply consistent pressure using a heavy roller.
• Failure: Nail Pop-Ups
  
  
  • Root Cause: Improper nailing depth (overdriven nails) or movement in the roof deck.
  • Actionable Fix: Remove the loose nail, fill the hole with roofing cement, and install a new, properly driven nail slightly offset from the original hole.

Frequently Asked Questions

Can I install roll roofing over existing shingles?

While it is physically possible, it is highly discouraged. Old shingles provide an uneven surface that will cause the roll roofing to tear or puncture prematurely, and the added weight can stress the structural integrity of the roof deck.

What is the ideal temperature for installing roll roofing?

The material is best applied between 50 and 80 degrees Fahrenheit. Temperatures below 50 make the asphalt brittle and prone to cracking, while temperatures above 90 can cause the material to become too soft and sticky to handle easily.

How long does roll roofing typically last?

On a properly maintained roof with the correct slope and adequate ventilation, roll roofing will typically provide reliable service for 5 to 10 years. Its lifespan is significantly shorter than asphalt shingles because it lacks the heavy ceramic granule embedment and material thickness of architectural products.

Is professional ventilation required for roll roofing?

Yes. Regardless of the roofing material, the attic space beneath the deck must be properly ventilated to prevent moisture buildup and heat accumulation, which causes the asphalt in the roofing to deteriorate from the underside out.

Upgrade Your Roofing Maintenance Strategy

Properly applied roll roofing is a reliable, budget-friendly solution when executed with precision and high-quality adhesives. Should your structure require long-term waterproofing, consult with our local roofing specialists to explore high-durability membrane alternatives.