mounting and racking hardware

1 | RACKING TYPES

BASIC RACKING CATEGORIES

Here at ION, we use  two basic types of racking systems:

• Rail

• Railless

RAIL

Rail racking is exactly what it sounds like:

• Module mid/end clamps attach directly to rail

• Rail attaches to mounting standoffs

• Mounts bolt directly into roof members 

RAILLESS

The principle difference between rail and railless is that the modules attach directly to the mounting components rather than to rail:

• Module mid/end clamps attach directly to rail

• Rail attaches to mounting standoffs

• Mounts bolt directly into roof members

Railless systems will still require an array skirt at the bottom row for each array. This is built into the racking calculator of the Baseline Tool.

LAYOUT DIFFERENCES

Rail vs Railless racking will have a bearing on the preferred orientation of your modules. It is more efficient for mount and rail quantity on rail systems to use portrait orientation (long way up). Adversely, it is more efficient for mount quantity to use landscape orientation for railess racking.

2 | RACKING COMPONENTS

RAIL

• Rail structure is composed horizontally under the footprint of the array

• Rail is modular and can be spliced together to fit a variety of layout footprints using rail splices 

MID CLAMPS

• Two sided clamp used to secure modules in the interior of the array

• Mid clamps can also help with proper bonding

END CLAMPS

• One sided clamp used to secure modules at the end of the array

• End clamps can also help with proper bonding 

L-FOOT/RAIL TO MOUNT COMPONENTS

• Usually slotted and modular to allow for a variety of rail/racking systems to attach to mounting systems

• L-foot is the most common type of rail-to-mount hardware used by Ion Solar 

MOUNTS

• Attach the racking system to the roof membrane

• Usually bolted directly into roof members but can attach directly to roof sheathing using special sheathing mounts or directly to metal roofing 

GROUNDING AND BONDING

• Modules and Racking made of metal are required to be bonded

• Bonding is done by running a ground conductor along railing/modules usually landing in bonding lugs

• PV grounding runs continuously through the PV circuitry to the existing residential grounding system 

3 | ROOF SHEATHING MOUNTS & STRUCTURAL BLOCKING

WHEN IS IT NEEDED?

Trussed hip roofs will most likely have horizontal box trusses with vertical flat rafters running over them.

• This does not allow the 2.5” depth for the lag screws to land in.

WHAT DO HORIZONTAL BOX TRUSSES LOOK LIKE?

It can be a little confusing, so let's look at an overhead of the framing so we can see exactly what we’re talking about here:

• When looking at a truss roof, the roof sections on either side of the ridge will have vertical top chord members (green).

• The triangular roof sections have hips on either side. The trusses continue following the same grain as the main roof sections adjacent to the ridge causing the top truss member to be horizontal relative to the hip roof sections (yellow).

• Most often, the sheathing is attached to flat vertical rafters on top of the horizontal trusses which can run the full or partial span of this roof section (red). 

ROOF SHEATHING MOUNTS

This is the most common solution we will use to overcome this hurdle on hips on truss roofs. Note that this is not an available option for Tile Roofs.

• Has multiple fasteners. Because there are more threadings in the wood, the load is distributed evenly to each screw.

• Fastens directly to roof sheathing

STRUCTURAL BLOCKING

Blocking can not be done when spray foam insulation is present in the attic 

This is mainly used when horizontal box trusses are present on tile roofs.

• Vertical lumber is fastened between horizontal truss top chords.

  • This provides a sufficient depth for a standard 2.5" lag screw to secure to.

• With this solution, we can use normal mounts with the standard 2.5" lags.

WHEN ELSE SHOULD ROOF SHEATHING MOUNTS BE USED?

4 | CALCULATIONS

MOUNT QUANITY

A number of factors affect the mount quantity called out by the design tool:

• Uplift

  • Includes wind speed and wind exposure category.

• Rafter Span

• Rafter Spacing

• Snow Load

• X & Y Spacing

• Cantilevering

Most of these factors will be automatic in the Baseline Tool when it comes to structural calculations and AHJ/Code specifics. This will still rely on you providing accurate input for:

1. Rafter/TC size

2. Rafter/TC Spacing

3. Rafter/TC Span

4. AHJ

5. Wind Exposure Category

   • See example below. Notice that the spacing requirements are different when only the wind exposure category was changed.

UPLIFT

Uplift Calculations refers to the upward force that wind has underneath the PV modules. Our tool automatically completes these structural calculations based on the following:

• Wind Speed (automatic based on your input for the AHJ)

• Wind Exposure Category (your input)

• Calculations from the code (automatic in the tool)

• Uplift force in lbs (automatic in the tool)

These calculations make sure the roof attachments won’t come out of the roof due to wind.

WIND SPEED

• Varies from jurisdiction to jurisdiction:

  • The design tool will select this factor automatically based on your input for the AHJ

• Wind speed is determined using the highest occurrence of wind, usually over a 50 year period

WIND EXPOSURE CATEGORY

• Determined using Surface Roughness

• For most purposes, either category B or C will apply

ROOF WIND ZONES

These calculations will also tell us roof wind zones to avoid when using portrait orientation. Not every project will have restrictions on mounting zones but some will have restrictions on:

• Wind zone 3: 3'x3' corners of the roof.

  1. This is much more prevalent on gable roofs

  2. it is still technically required on hip-roofs but most hip roof layouts will not fit modules in wind zone 3 to begin with.

• Wind zone 2 & 3: 3' offset from the eave and 3' offset from any rake. We do not need to restrict mounting zones at the ridge.

Whenever possible, wind zone 1 should be prioritized for array mounting area.

RAFTER SPAN

• This measurement is used to determine the downward load on the home’s wall and ceiling structures underneath the roof.

• Qualifying structural supports will break up the total load in some areas.

• This input is critical to the structural integrity of the existing roof structure of the home. Just because it’s existing doesn't mean it is up to par to begin with.

RAFTER SPACING

• Roof mounts must be fastened directly into rafters/top chords.

• This input tells us how close mounts can possibly be mounted together on the X axis. 

SNOW LOAD

• Differs from jurisdiction to jurisdiction.

• Snow load indicates the amount of additional downward force on the building from accumulated snow and ice.

• This affects the structural integrity of racking which can facilitate the need for additional mounts.

X & Y SPACING

• Mount spacing usually defaults to 48” X-spacing

• The structural inputs and calculations can change the max spacing if the tool determines that more mounts are needed.

• X is the horizontal axis of the roof plane

• Y is the vertical axis of the roof plane 

CANTILEVERING

• Another figure that can affect total mount quantity.

• The measure from the edge of the module to the center of the mount.

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Design & Engineering > Design 9 - Mounting & Racking Hardware