Roll roofing can provide a practical, relatively affordable covering for garages, sheds, porches, and other buildings with low-slope roofs. It comes in wide rolls and installs differently from individual asphalt shingles. The right method depends on the product: traditional mineral-surfaced roll roofing may use roofing cement and nails, while self-adhered products rely on a peel-and-stick backing. Before starting, check the package instructions, roof slope, local building code, and weather forecast. Correct preparation matters as much as the material itself.
What Roll Roofing Is—and When to Use It
Roll roofing is a flexible roofing material supplied in long rolls, commonly with an asphalt-based surface and mineral granules. It is generally used on low-slope roofs where conventional asphalt shingles may not be appropriate. Some products are designed as exposed, finished roof coverings; others are intended as an underlayment or part of a specific roof system. Those products are not interchangeable, so the label and installation instructions should identify the intended use.
The term “roll roofing” can refer to several products, including mineral-surfaced asphalt roll roofing, self-adhered modified-bitumen membranes, and smooth-surfaced base sheets. Each may require different primers, fasteners, laps, and application methods. Use the installation method specified for the exact product being installed. Improvising a method from instructions for another type can lead to leaks or premature failure.
Roll roofing is not simply a roll-shaped version of standard shingles. It usually has fewer seams than small individual shingles, but its seams and roof edges need careful detailing. It may be suitable for modest outbuildings and some low-slope residential applications, but appearance, service life, warranty, and code requirements vary by product. It is not automatically the best choice for every roof.
Check Roof Slope, Codes, and Product Requirements
Start by measuring the roof’s pitch and comparing it with the minimum slope specified by the manufacturer. Pitch is often described as the number of inches a roof rises vertically for every 12 inches of horizontal distance. A low-slope roof sheds water more slowly than a steep roof, so it needs a covering designed for that exposure. If the roof falls below a product’s permitted slope, do not assume that extra roofing cement will make it suitable.
Building codes and permit requirements vary by location and project. Local rules may address roof coverings, underlayment, fire classification, fastening, ventilation, and removal of existing roofing. In the United States, the applicable code may be based on a model code with state or local amendments. Contact the local building department if the requirements are unclear, and follow the product’s listed installation instructions.
Check the product label for approved substrates, temperature limits, required underlayment, and whether the material is intended to be exposed to weather. Some membranes require a compatible primer or a particular deck surface. A roof system may also need flashing, drip edge, or other components that are not included with the rolls.
Materials and Tools
Gather the materials before removing old roofing. Depending on the product and roof design, the job may require roll roofing, compatible underlayment, roofing cement or primer, corrosion-resistant roofing nails, drip edge, flashing, and a manufacturer-approved seam adhesive. Do not substitute general-purpose caulk or construction adhesive for roofing products unless the instructions expressly allow it.
Common tools include a tape measure, chalk line, utility knife with spare blades, straightedge, hammer or roofing nailer, and a broom. A roller may be required to press down self-adhered material. Use a stable ladder, appropriate fall-protection equipment, work gloves, eye protection, and slip-resistant footwear. Roof work carries a serious fall risk; wet, dusty, frosty, or windy conditions make it more hazardous.
Prepare the Roof Deck
Remove loose debris and inspect the roof surface before installing anything. If existing roofing must be removed, check local rules and the manufacturer’s requirements for installation over an existing layer. Multiple roofing layers add weight and can conceal damage. Do not cover rotten sheathing, active leaks, or loose boards.
Replace damaged decking and secure loose sheathing with suitable fasteners. The deck should be clean, dry, smooth, and structurally sound. Remove protruding nails, sharp splinters, and old material that could puncture the new roof. Repair the underlying cause of any water damage, such as failed flashing or poor drainage, rather than covering the evidence.
Install underlayment or a base sheet if the product instructions or local code require one. Follow the specified lap direction and fastening pattern. On a sloped roof, courses are generally arranged so water flows over, rather than against, the laps. However, the product’s instructions control, especially for low-slope membranes and self-adhered systems.
Plan the Layout and Make the Roof Watertight
Measure the roof and plan where each roll will begin and end. Check the roll’s coverage, including the required side and end laps; the nominal roll width is not the same as the usable coverage. Use a chalk line to keep courses straight. Dry-fit or position material according to the product instructions before applying adhesive or removing release film.
Plan how the roofing will meet eaves, rakes, valleys, walls, chimneys, vents, and other penetrations. These transition points are common leak locations. Existing flashing should be inspected and replaced or repaired if it is corroded, loose, or incorrectly installed. The membrane must integrate with flashing in the sequence specified by the roofing system, so water is directed onto the roof surface and away from the building.
Do not rely on roofing cement alone to fix poorly designed edges or penetrations. Flashing and overlapping layers provide the primary water-shedding details; sealants are used only where the product instructions call for them. For complex roof shapes or many penetrations, a qualified roofer can help determine the correct sequence before work begins.
How to Install Roll Roofing
The steps below describe a general process for exposed, mineral-surfaced asphalt roll roofing. They are not a substitute for the instructions supplied with a particular product. Self-adhered membranes and other roll products can have different preparation, lap, and fastening requirements.
- Confirm the weather and surface conditions. Work only within the temperature and weather limits in the product instructions. The deck and roofing should be dry. Wind can make a large, flexible roll difficult to control, while cold conditions can affect flexibility and adhesion.
- Install edge components and underlayment as directed. Fit drip edge, flashing, and any required base layer in the order specified by the manufacturer and local code. Edge details differ by roof design and product, so do not assume every component goes above or below the membrane.
- Measure and cut the first course. Unroll the material on a clean surface and cut it to length, allowing for any required overhang or end lap. Avoid dragging the sheet over rough decking, which can tear or damage its underside. Follow the package directions for handling and positioning.
- Align and secure the course. Position the sheet along the chalk line. Attach it using the specified fastener type, spacing, and placement. Some products call for nails along particular edges; others require adhesive or a combination. Incorrectly placed fasteners can leave exposed paths for water.
- Apply the next course with the specified lap. Measure the overlap from the manufacturer’s instructions, rather than choosing a generic dimension. If roofing cement or seam adhesive is required, use the specified product and apply it at the stated coverage and location. Avoid excessive adhesive, which can interfere with some systems or cause material damage.
- Continue across the roof. Keep the courses straight and the laps consistent. Stagger end joints if the instructions require it, and avoid placing seams where they will collect water. Press or roll seams as directed. Do not stretch the material tightly to force it into position.
- Finish edges and roof details. Complete the eaves, rakes, ridges, walls, and penetrations using compatible flashing and the product’s approved details. Cut carefully around roof openings and keep all required clearances. Inspect every seam and fastener as work progresses, because correcting a detail is easier before the next course covers it.
Self-Adhered Roll Roofing Needs Different Handling
Self-adhered roofing products usually have a release liner over an adhesive backing. The deck may need a specific primer, and the product may require a minimum surface temperature. Installers typically position the sheet carefully, remove the liner in stages, and press the membrane into place with the recommended roller. Follow the exact procedure on the product label; once bonded, repositioning may be difficult or impossible.
Keep the adhesive surface clean and avoid trapping wrinkles, debris, or air pockets. Some self-adhered products require a separate cap sheet or are intended for use as one layer in a larger system. Confirm whether the material is designed to remain exposed. A membrane intended as an underlayment should not be treated as a finished roof covering.
Common Installation Mistakes to Avoid
- Using the wrong product for the roof slope: A product with a higher minimum slope may not shed water reliably on a flatter roof.
- Skipping deck repairs: New roofing cannot correct rot, loose sheathing, poor drainage, or structural problems.
- Using unapproved materials: Incompatible cement, primer, or flashing can affect adhesion and product performance.
- Guessing at lap sizes or fastener patterns: Follow the instructions for the specific roll, not a generic online diagram.
- Working in unsuitable weather: Moisture, low temperatures, or strong winds can compromise installation and safety.
- Leaving seams or fasteners exposed: Details that do not match the required system can create leak paths.
- Covering damaged flashing: A new roof surface will not solve a failed wall, chimney, or vent connection.
Inspect and Maintain the Finished Roof
After installation, inspect the roof for loose edges, open seams, exposed fasteners, wrinkles, and incomplete flashing details. Make sure gutters and drainage paths are clear. Follow the manufacturer’s instructions for any required finishing or curing time before walking on the roof. Keep foot traffic to a minimum to reduce the risk of damage.
Check the roof periodically, especially after severe weather and before seasons with heavy rain or snow. Remove leaves and other debris that can block drainage, and look for lifted edges, damaged flashing, or signs of water intrusion inside the building. Address small problems promptly with compatible repair materials and approved methods. If a leak persists, the source may be uphill from the visible interior stain.
When to Hire a Roofing Professional
A professional roofer is a sensible choice when the roof is steep, high, structurally damaged, or difficult to access; when it has many penetrations or complicated flashing; or when the installation requires specialized heat-applied methods. A roofer can also assess whether the existing deck and roof system are suitable for the selected product.
Even on a small shed or garage, fall protection and safe ladder use are essential. If the work cannot be done safely or the instructions are unclear, pause and get qualified help. A correctly selected and installed roll roofing system depends on sound decking, compatible components, careful seams, and details suited to the roof’s slope and local conditions.