What is back-nailing and why is it done?

Direct Answer

Back-nailing is a roofing installation technique in which fasteners are installed through the concealed portion of a roofing ply or sheet so that the next overlapping layer covers them. Also called blind-nailing, it is commonly used in certain built-up roofing (BUR) and modified bitumen roofing systems to help prevent the roofing materials from slipping or moving.

Back-nailing provides additional mechanical restraint while keeping the fasteners concealed from direct weather exposure in the finished roof assembly. It is particularly relevant on sloped low-slope roofing assemblies or where the specified installation method requires additional fastening. The exact fastening pattern, fastener type, and placement depend on the roofing system manufacturer’s instructions and project specifications.

1. How Does Back-Nailing Work?

During back-nailing, the roofing installer fastens the concealed portion of a roofing ply or sheet to the appropriate substrate or supporting component. The next roofing layer overlaps the fasteners, covering them in the completed assembly.

In a multi-ply roofing system, this technique can work alongside the system’s specified adhesive or bitumen application. The mechanical fasteners provide additional restraint against slippage, while the overlapping roofing layer conceals the fastener heads.

The installation sequence and fastening location are important. Back-nailing is not simply adding extra nails wherever movement is suspected. The fastening method must follow the requirements for the particular roofing assembly.

2. Why Is Back-Nailing Done?

Back-nailing serves several purposes in roofing systems where concealed mechanical fastening is specified.

• Preventing slippage: Helps restrain roofing plies from moving downslope under gravity or other forces.
• Providing additional restraint: Supplements the specified attachment method where required by the roofing design.
• Concealing fasteners: Keeps the fastener heads covered beneath a subsequent roofing layer.
• Supporting installation stability: Helps maintain the intended position of roofing sheets during installation and service.
• Following system requirements: Provides the fastening arrangement specified for certain roofing assemblies and slope conditions.

Back-nailing is primarily a slippage-control technique. It should not be treated as a universal solution for wind-uplift resistance, because the complete roof assembly must meet its applicable attachment and performance requirements.

3. Which Roofing Systems Commonly Use Back-Nailing?

Back-nailing is most commonly associated with multi-ply low-slope roofing systems, particularly built-up roofing and certain polymer-modified bitumen assemblies.

Built-up roofing (BUR)

Built-up roofing systems use multiple layers of reinforcing felts or other specified plies assembled with bitumen. Where the installation design calls for back-nailing, concealed fasteners help restrain the relevant plies against slippage.

Modified bitumen roofing

Certain modified bitumen sheets can be mechanically fastened at specified locations in addition to being installed using an approved adhesive, hot asphalt, or another prescribed method. Back-nailing may be used where the manufacturer’s installation instructions require it.

Sloped low-slope roof assemblies

On roofs with sufficient slope to create a risk of downslope movement, back-nailing may be required at specified intervals or locations. The actual threshold and fastening schedule depend on the selected roofing system, deck construction, insulation configuration, and manufacturer’s requirements.

Back-nailing is not automatically required for every BUR or modified bitumen roof. The project specifications and system-specific installation instructions determine whether it is appropriate.

4. When Is Back-Nailing Required?

Whether back-nailing is required depends on the roof assembly and its installation requirements. Relevant factors include:

• Roof slope and the potential for roofing plies to slip.
• The type of roofing membrane or reinforcing ply.
• Whether the assembly is insulated or installed directly over a nailable deck.
• The type and condition of the deck or designated fastening substrate.
• The specified fastener type, spacing, and attachment method.
• The manufacturer’s installation instructions and applicable project requirements.

Some roofing-system instructions establish specific slope thresholds and fastening schedules. These values should not be applied to another system without confirmation. Before installation, the contractor should verify the required details against the applicable product documentation and approved assembly.

5. How Does Back-Nailing Differ From Exposed Fastening?

The main difference is whether the fasteners remain exposed in the finished roofing system.

Feature	Back-Nailing	Exposed Fastening
Fastener visibility	Fasteners are covered by a subsequent roofing layer.	Fasteners remain visible at the finished surface.
Primary purpose	Provides concealed mechanical restraint and helps prevent slippage.	Secures a component using a fastening method designed for exposed installation.
Weather exposure	Fastener heads are concealed within the assembly.	Fasteners and associated sealing details may be exposed to weather.
Typical application	Certain multi-ply BUR and modified bitumen systems.	Specified roofing panels or assemblies designed for exposed fasteners.

Neither method is inherently suitable for every roof. The correct choice depends on the roofing system design, substrate, and applicable installation requirements.

6. Does Back-Nailing Improve Wind-Uplift Resistance?

Back-nailing can contribute to the attachment of roofing plies, but its presence alone does not establish that a roof assembly meets its required wind-uplift performance.

Wind resistance depends on the complete roofing system, including membrane attachment, insulation attachment, deck connections, roof perimeter and corner details, fastener type and spacing, and the applicable design pressures.

Contractors should follow the specified assembly and its approved fastening details rather than increasing or changing fastener quantities without technical justification. Where wind-uplift compliance is required, the entire assembly must satisfy the applicable design and approval requirements.

7. What Can Go Wrong If Back-Nailing Is Installed Incorrectly?

Incorrect back-nailing can undermine the intended attachment method and may create defects that are difficult to identify after the roofing layers are complete.

Potential problems include:

• Incorrect fastener spacing: Fasteners installed too far apart or in the wrong locations may not provide the intended restraint.
• Unsuitable fasteners: Fasteners that are incompatible with the substrate or specified assembly may not provide the required attachment.
• Inadequate embedment or engagement: Fasteners that do not engage the designated substrate properly may compromise attachment.
• Improper concealment: Incorrectly placed fasteners may not be covered by the subsequent layer as intended.
• Weak substrate: Deteriorated or unsuitable material may prevent reliable fastening.
• Departure from approved details: Unspecified changes to the fastening pattern can affect compliance with the intended roofing assembly.

Installation should be inspected and documented according to the project requirements. Any identified defects should be corrected using an approved repair method before the affected assembly is covered.

8. How Should Back-Nailing Be Verified During a Roofing Project?

Because back-nailing becomes concealed after the next layer is installed, verification should occur while the fasteners remain visible.

Useful quality-control steps include:

1. Review the installation details. Confirm the specified fastener type, spacing, location, and required overlap.
2. Inspect the substrate. Verify that the fasteners engage the designated deck or fastening component.
3. Check the fastening pattern. Compare installed fasteners with the manufacturer’s instructions and project specifications.
4. Document concealed work. Take photographs and record inspection findings before the subsequent layer covers the fasteners.
5. Confirm the completed assembly. Verify that the following roofing layer covers the fasteners as specified and that the overall system matches the approved details.

For further technical guidance, consult the National Roofing Contractors Association’s roofing glossary and the Siplast Engineered Roof Systems Technical Guide, which provides system-specific back-nailing information.

Bottom Line

Back-nailing is a concealed fastening technique used in certain roofing assemblies to help prevent roofing plies or sheets from slipping. The fasteners are installed in a concealed portion of the roofing material and covered by the next layer, keeping them out of direct weather exposure.

It is particularly associated with built-up and modified bitumen roofing systems, but it is not required on every roof. The correct fastening pattern, materials, and installation locations must follow the specified roofing system and applicable manufacturer requirements.

Related Questions

• What is a slip sheet and when is one required?
• What is the difference between a seam plate and a barbed plate?
• How is fastener density verified in the field?
• What documentation proves zone-specific fastening was actually installed?

Sources

• National Roofing Contractors Association (NRCA) — Roofing Glossary: Backnailing
• Siplast — Engineered Roof Systems Technical Guide
• Canadian Roofing Contractors Association — Roofing Reference Manual Glossary
• ASTM International — ASTM D1079, Standard Terminology Relating to Roofing and Waterproofing

Last reviewed: October 2026

Commercial Skylights & Roof Access