Solar Racking Torque Specifications: IronRidge, Unirac

Last updated: November 2026

Torque is one of the cheapest controls on a solar racking job, and one of the easiest to skip. In August 2023, engineers from the National Renewable Energy Laboratory (NREL) inspected 30 commercial and utility-scale PV systems on Guam after Category 4 Typhoon Mawar. Most systems fared well. Where damage did occur, it was almost always traced to inadequate clamping of the module frame to the mount (NREL Technical Report NREL/TP-5R00-89629, November 2024).

This guide covers racking torque in practice: published values from the IronRidge and Unirac installation manuals, how to handle conflicts between module and racking specs, lag bolt basics, torque wrench calibration, and field verification. It lists only values we could read in the manufacturer’s own manual. For any other brand, the manual that ships with the product is the governing source. For the wider design picture, read the solar mounting structure design guide.

In this guide:

• Why torque matters: under-torque and over-torque failure modes
• What NREL found on Guam, with the numbers
• Torque by fastener type, and why bolt size alone does not tell you the value
• IronRidge and Unirac torque values from their own manuals
• Module clamp torque: mid-clamp versus end-clamp, and the panel-versus-racking conflict
• Lag bolts and structural screws
• Torque wrench calibration under ISO 6789
• Field verification, common mistakes and a QC checklist

Why Torque Specifications Matter in Solar Racking

Torque is the rotational force applied to a fastener, measured in newton-metres (Nm), foot-pounds (ft-lbs) or inch-pounds (in-lbs). In solar racking, torque sets how tightly a clamp grips a module frame and how well a joint resists loosening. Get it wrong in either direction and the joint can fail.

NREL’s Guam report says bolts and nuts can loosen over time if they are not installed to the specified torque (too loose or too tight), if they see repetitive loads such as wind, or if wind causes resonance in the system.

Under-Torque: The Silent Failure

Under-torqued bolts loosen over time. Wind creates vibration, vibration causes micro-movement, and micro-movement backs nuts off. NREL’s Guam team recorded inadequate clamping of the module frame to the mount as the leading cause of damage, in some cases leading to cascading failure.

A typical failure chain looks like this:

1. A clamp is installed below its specified torque
2. Wind-induced vibration loosens the bolt further
3. Grip force drops below what the joint needs to resist uplift
4. One module lifts at a corner during a gust
5. The neighboring module loses its clamp support
6. The row unzips

Loose connections can also cause electrical problems. A loose bonding or grounding connection can develop resistance, and gaps between dissimilar metals invite corrosion.

Over-Torque: The Immediate Damage

Over-torquing can deform the aluminum frame lip that the clamp grips. A deformed lip no longer spreads clamp load evenly, and the stress can transfer into the glass and cells. Cell micro-cracks are usually invisible to the eye and are found with electroluminescence (EL) imaging.

Module makers set the clamp type, the clamping zone and the torque for their frames, and their warranties generally require installation within those limits. The module’s own manual and warranty terms govern, not a rule of thumb.

The Warranty Trap

The racking manufacturer and the module manufacturer can publish different clamp torques for similar hardware. When their manuals conflict, do not pick a number on your own.

Ask both manufacturers for written confirmation of a compatible clamp and torque. Until you have it, treat the module maker’s limit for its own frame as the ceiling, because exceeding it is what damages the module and puts its warranty at risk. Record which value you followed, with photos of the wrench setting, in case of a later dispute.

What NREL Found on Guam After Typhoon Mawar

NREL’s assessment is the most useful public dataset on how racking fails in a real high-wind event. The team visited 30 systems in August 2023: rooftop, ground-mounted and carport, all commercial or utility scale (NREL/TP-5R00-89629).

Source: NREL Technical Report NREL/TP-5R00-89629, Elsworth, Van Geet, Kurnik and Salasovich, November 2024.

NREL also describes a torque audit method it cites from Schletter’s mounting system documentation: check 2% of the bolts, and if fewer than 10% fail the system passes. If not, check 10%, and if that also fails, check and tighten every bolt and torque-stripe the ones that meet specification. The report notes that regular torque checks are not always part of an O&M plan, and calls regular structural bolt torque audits “strongly recommended in high-wind regions.”

For wind-specific design questions, see our guide to high-wind zone solar mounting.

Torque Ranges by Fastener Type

Not all fasteners in a solar array do the same job. Lag bolts anchor the structure, module clamps hold frames, rail splices maintain continuity and grounding lugs make electrical bonds. Each has its own value, and the value depends on the product, not only on the bolt size.

Metric Fasteners (M8, M10, M12)

Metric hardware is common on European and Asian racking. The table shows generic engineering values for dry threads, as found in standard bolt torque charts. They are not manufacturer specifications for any solar product.

Module clamps use much lower values than structural bolts of the same size, because the aluminum frame cannot take structural bolt loads. Never apply a generic structural value to a module clamp. For ground-mount structural connections, see the ground mounted solar design guide.

Lubricant changes the result. Anti-seize and other lubricants reduce friction, so the same torque produces more clamp load. Follow the manufacturer’s instruction on whether to use anti-seize on each fastener. Where a manual gives a separate value with anti-seize, use that one.

Same Bolt Size, Different Values

Imperial hardware dominates US racking. The same nominal bolt size carries different values in different systems, as these entries from published manuals show:

The point is not that one brand is right and the other wrong. The clamp geometry, thread, material and lubricant differ, so each manual’s number belongs to its own hardware.

Lag Bolts and Structural Screws

Lag bolts anchor the racking system to the roof structure. Their holding power depends on wood species, thread embedment depth and diameter far more than on torque.

IronRidge’s flush mount manual does not give a torque value for lag bolts. It says to tighten them until fully seated. Installing to a torque value taken from a different product’s manual does not make a lag joint stronger. A lag torqued hard but embedded only an inch will still pull out.

Manufacturer Torque Specifications

Racking manufacturers publish installation manuals with the values for their hardware. The values below come from the manuals named in each section. Manuals are revised, so check the version in your hands against the manufacturer’s current document.

IronRidge XR Flush Mount

The values below come from the IronRidge XR Flush Mount Installation Manual, version 5.2 (2026), which lists bonding hardware torque values in a checklist.

Tool list in the manual: a torque wrench with a 0–300 in-lbs range, a non-impact cordless drill, and an impact driver for lag bolts only.

Thermal expansion: the manual requires expansion joints every 100 ft of continuous rail (every 60 ft when installing on the HUG attachment), and says not to install modules over an expansion joint.

IronRidge tilt mount and ground mount systems have their own manuals with additional values. This post does not reproduce them, so read those manuals for those systems.

Unirac SolarMount (SM)

The values below come from the Unirac SM Solar Mount Installation Guide (2022).

Pro Series torque table:

Standard series torque table:

The guide adds that these torques are not designed for use with wood connectors. Other notes from the guide:

• Anti-seize has been factory applied to Pro Series mid clamp bolts, and the guide says not to use anti-seize on the Pro Series end clamp, mid clamp or rail splice torque steps.
• The standard grounding lug torque is 10 ft-lbs. WEEB and ILSCO lugs vary with conductor size, so use the lug’s own data sheet.
• For the end clamp bolt, the guide says to use a low torque setting on a drill, or, with an impact driver, to stop as soon as the impact action begins.
• A thermal break is required when continuous spliced rail exceeds a maximum length that depends on temperature difference. The guide points to Unirac’s Design and Engineering Guide for the limits, and says a module must not span an expansion joint.

K2 Systems, SnapNrack and Pegasus Solar

These three manufacturers publish torque values in their own installation manuals. Earlier versions of this post listed values for them, but their current manuals were not available to read from the manufacturers’ own sites during this update, so those figures were removed rather than carried over. Use the manual that ships with your product, and keep the document with the job file.

Cross-Brand Module Clamp Comparison

Module clamps are the most torque-critical components in an array. They hold the modules to the rails, and many also create the electrical bond. They are also the most commonly over- or under-torqued.

The mid-clamp values differ by about 1.6 times (80 versus 132 in-lbs), and the end-clamp values go the other way (80 versus 60 in-lbs). Both are correct for their own hardware. Never substitute one manufacturer’s torque for another’s clamp.

Module Frame Clamping Requirements

Module frames are extruded aluminum, and the lip the clamp grips is thin. The module manufacturer’s installation manual defines where and how the frame can be clamped.

What to take from the module manual before you start:

• The approved clamping zones along the frame
• The clamp width, contact area and any required frame thickness range
• The torque range for the clamp hardware the manual approves
• Any requirement for approved clamp types and any bar on unapproved ones

Unirac’s guide lists the module frame thickness each clamp size supports (for example, B size clamps for 30–32 mm frames), which is a reminder that clamp selection depends on frame depth as well as torque.

When mixing module brands on one project, make a torque map. Label each row with the module brand and the clamp torque from its manual, and train the crew to check the map before tightening.

Lag Bolt Withdrawal and Embedment

Lag bolts transfer wind and snow loads from the racking into the building structure. The specification involves more than torque: embedment depth, wood species and rafter location all matter, and an engineer of record must verify the attachment.

Lag Screw Withdrawal Capacity by Wood Species

The reference withdrawal values below are for 5/16“ lag screws, in pounds per inch of thread penetration. They are consistent with the withdrawal equation in the National Design Specification for Wood Construction (W = 1800 × G^1.5 × D^0.75, with D = 0.3125 in), where G is the wood’s specific gravity. They are design values before adjustment factors.

Calculation: required thread embedment = uplift point load divided by withdrawal capacity per inch.

Worked example (illustrative numbers): a roof attachment in Southern Pine sees 800 lbs of uplift. At 307 lbs per inch, it needs about 2.6 inches of thread in the rafter. The real specification adds pilot hole depth, the washer and the structural engineer’s safety factors, so use the attachment manufacturer’s span and embedment tables for the actual job.

Torque Wrench Calibration: Standards and Methods

A torque wrench that reads incorrectly is worse than no wrench, because it gives false confidence. NREL’s Guam report recommends that installers use a calibrated torque wrench and are trained in its use.

ISO 6789 Calibration Requirements

ISO 6789-1:2017 and ISO 6789-2:2017 govern torque tool accuracy and calibration. The points that matter on a solar crew:

Some firms recalibrate more often, for example every 6 months. That is a company choice, not an ISO requirement, but it is reasonable for crews that use their wrenches daily.

Calibration Methods

Third-party calibration lab. Send wrenches to an accredited laboratory. They test at multiple points, issue a certificate and apply a calibration sticker. Keep the certificate in the job file.

In-house torque tester. A bench tester measures your wrench against a reference. It lets you check wrenches between formal calibrations, and it makes sense for firms with many wrenches.

Pre-use sanity check. Compare the wrench against a known load before each project. This is a check, not a substitute for formal calibration.

When to Recalibrate Immediately

• After dropping the wrench
• After overloading it (clicking past the set point under load)
• After exposure to extreme heat or cold
• After long storage
• If the wrench feels different (loose click, gritty action, sticky adjustment)

Tool Selection for Solar Work

Match the wrench range to the values in your manuals. A range that is too wide makes low values hard to set accurately.

Digital torque wrenches display real-time torque, and some log readings, which creates automatic torque documentation on high-volume crews.

Field Verification Protocols

Torque applied at installation is not necessarily torque at year five. NREL notes bolts can vibrate or self-loosen over time. Verification catches problems before they become failures.

Annual Torque Audits

NREL recommends regular torque audits of both the module attachment bolts and the racking system bolts, and an annual torque inspection. The method it cites runs in three steps:

1. Check 2% of the bolts on the system. If fewer than 10% fail, the system passes.
2. If not, check 10% of the bolts. If fewer than 10% fail, the system passes.
3. Otherwise, check and tighten all bolts, and torque-stripe each one that meets specification.

Pair this with locking hardware where the manufacturer allows it. NREL recommends locking hardware on bolted joints, and advises against split lock washers.

Suggested Commissioning Checks

The schedule below is our practice suggestion, not a manufacturer requirement. Confirm with the racking manual before re-torquing anything, because some manufacturers do not call for re-tightening.

• Day 1: verify every clamp bolt with the torque wrench and mark any that have moved
• Week 1: spot-check a sample, starting with end clamps and corner modules
• After storms and thermal extremes: inspect torque stripes and re-check marginal joints

In hurricane- or typhoon-prone regions, add inspections after major wind events.

Documentation

Document every torque-critical connection:

• Torque wrench model, serial number and calibration certificate date
• Torque setting for each component type
• Installer name and certification
• Date and weather conditions
• Photo of the wrench setting at each type of connection

This record is your defense in a warranty dispute, because it shows you followed the manufacturer’s specification.

Common Mistakes in Racking Torque

Mistake 1: Treating Impact Drivers the Same Everywhere

Impact drivers are fast, and the torque they deliver depends on battery charge, bit condition and operator technique. Manuals differ on how to use them. IronRidge’s flush mount manual lists a non-impact drill and a torque wrench for the clamps, and an impact driver for lag bolts only. Unirac’s guide allows an impact driver on end clamps only if you stop as soon as the impact action begins.

The safe workflow: use the impact driver where the manual allows it, and use a calibrated torque wrench for final clamp tightening.

Mistake 2: Ignoring Anti-Seize Instructions

Stainless steel hardware can gall against aluminum. Unirac’s guide explains the problem and calls for minimal anti-seize on specified bolts, while saying not to use it on others, such as the rail splice. IronRidge’s flush mount manual does not call for anti-seize in its torque steps. Read the manual for your system, apply anti-seize where it says to, and omit it where it says not to.

Mistake 3: Confusing Mid-Clamp and End-Clamp Torque

Within one system the two clamps often have different values. In Unirac’s Pro Series, the mid clamp is 11 ft-lbs and the end clamp is 5 ft-lbs. Torquing an end clamp to the mid-clamp value over-tightens it. Check the table for each clamp type before you start.

Mistake 4: Installing at Temperature Extremes

Aluminum expands about twice as much as steel for the same temperature change (roughly 23 and 12 millionths per degree C). A 6 m aluminum rail that warms by 40 degrees C grows by about 5.5 mm. Joints that are fully constrained then carry the stress.

This is why manuals set expansion joints and tell you not to span them with modules. Follow the manual’s maximum continuous rail length, and do not clamp a module across an expansion joint.

Mistake 5: Mixing Component Brands Without Verification

Racking components are designed and certified as systems. A clamp from one brand on a rail from another may fit and still not perform as certified. If you must mix, get written approval from both manufacturers and keep it in the job file. Do not assume compatibility because the thread matches.

Hot and Cold Weather Torque Practice

Temperature affects the materials and the tools. It does not change the torque value in the manual, and no manufacturer value in this post carries a temperature correction. Do not apply your own correction.

Cold weather:

1. Store wrenches indoors overnight
2. Follow the wrench maker’s guidance for extreme temperatures
3. Allow extra cure time for sealants and adhesives

Hot weather:

1. Install during the cooler part of the day where possible
2. Check bolt tightness after the first hot day and thermal cycles
3. Use locking hardware where the manual allows, to keep preload

Torque Quick Reference Table

Unit conversions:

• 1 Nm = 8.85 in-lbs = 0.738 ft-lbs
• 1 ft-lb = 12 in-lbs = 1.356 Nm
• 1 in-lb = 0.083 ft-lbs = 0.113 Nm

Quality Control Checklist for Installers

Use this checklist on every project, and sign and date each item.

Pre-installation:

• Torque wrench calibration certificate is current under your policy
• Wrench range covers all specified values on this project
• Anti-seize is available if the manufacturer calls for it
• Torque paint or marking pens are available
• Installation manual for each component brand is on site
• Crew has been briefed on torque values for each component type

During installation:

• Impact drivers are used only where the manual allows
• Hand torque wrenches are used for final clamp tightening
• Conflicts between module and racking specs are resolved in writing
• Torque stripes are applied right after final torque
• Photos of wrench settings are taken for documentation

Post-installation:

• Day 1 torque verification completed
• Loose bolts re-torqued and re-marked
• Torque log completed with wrench serial numbers and settings
• Annual torque audit added to the O&M contract

Conclusion

Three practices carry most of the value:

• Use the manual for the exact product. IronRidge and Unirac publish different values for similar hardware, and values change between versions.
• Resolve module and racking conflicts in writing. The module maker’s frame limit is the ceiling until both manufacturers agree.
• Verify and audit. NREL’s Guam findings point at loose clamps as the failure to prevent, and annual torque audits as an inexpensive defense.

Good torque practice starts with a clean design and an accurate hardware list. To see how a modeled array turns into a bill of materials, book a SurgePV demo or explore the solar designing workflow.

Frequently Asked Questions

What is the correct torque for solar panel mid-clamps?

Mid-clamp torque depends on the product, so use the value in the racking manual. IronRidge’s XR flush mount manual lists 80 in-lbs for the UFO clamp, and Unirac’s SM installation guide lists 11 ft-lbs for Pro Series mid clamps. If the module maker’s manual gives a lower clamp torque, resolve the conflict with both manufacturers before you tighten.

Can over-torquing solar clamps void the panel warranty?

Yes, it can. Module makers set clamp type, clamping zones and torque in their installation manuals, and damage from installation outside those limits is commonly excluded from warranty cover. Over-tightening can deform the frame lip and stress the glass and cells, so read your module’s warranty terms and follow its manual.

How often should a torque wrench be calibrated?

ISO 6789 recommends recalibration every 12 months or 5,000 cycles, whichever comes first. Recalibrate sooner after a drop, an overload or exposure to extreme temperatures. A stricter interval, such as every 6 months, is a company policy choice rather than an ISO requirement.

Do lag bolts need different torque than module clamps?

Yes, because the two do different jobs. IronRidge’s flush mount manual gives no torque value for lag bolts and says to tighten them until fully seated. Pull-out capacity comes from embedment depth and wood species, while clamp torque is a set value that holds the frame without damaging it.

Can I use an impact driver for solar racking installation?

Check the manufacturer’s manual first, because the rules differ. IronRidge’s flush mount manual lists a non-impact cordless drill and a torque wrench, with an impact driver only for lag bolts. Unirac’s SM guide says that if you use an impact driver on end clamps, stop as soon as the impact action begins. NREL recommends calibrated torque wrenches and trained installers.

What happens if solar racking bolts are under-torqued?

Under-torqued bolts can loosen under wind vibration and release modules. NREL’s assessment of 30 systems after Typhoon Mawar on Guam found that most damage came from inadequate clamping of the module frame to the mount, sometimes cascading across modules. Loose connections can also compromise bonding and corrosion protection.

Which torque spec takes priority: the panel maker or the racking maker?

Do not guess, and get written confirmation when the two manuals conflict. The module maker sets the limit for its own frame, and exceeding that limit is what damages the module and puts its warranty at risk. Racking makers design for a range of modules, so record which value you followed and why.