Mounting BOS

How to specify mount, attachment layout, and more

Updated over a week ago


What will be done during these steps?

We'll be working strictly in the properties panel on the right. Starting from the top we'll specify:

  • Choice of rail

  • Choice of mount

  • Roof Wind Zone Max Rail Spans

  • Our Attachment Layout.

  • Roof Wind Zone Attachment Spacing

  • Number of Fasteners for Each Mount

  • Embedment Depth of Fasteners

  • Whether our racking system is UL 2703 compliant

Specify rail and mount

Using the drop down menus select the rail and mount.

Input span values for each wind zone

Next specify the Max Rail Span for each wind zone. These are different from the max attachment spacing, which will be specified later.

Why are these numbers important?

Correct values for these fields are critical. Everything from accurate maximum cantilever values (and thus accurate attachment layouts) to accurate calculations of racking hardware weights and quantities of racking hardware components on the bill of materials are affected by these numbers. If you use erroneous values to rush through the design process, some parts of your permit package (such as the attachment layout and racking hardware quantities and weights) may be inaccurate or missing.

How do I find the maximum rail spans for my design?

To find the correct maximum rail span values for designs use the rail manufacturer's online configuration tool for the rail product you're using.

Attachment Layout

This is specified with the next drop down menu. Attachment Layout is where mounts will be placed under the rail. By default the attachment spacing is staggered but you can change it to aligned columns and aligned columns (strict).

Max Attachment Spacing

We'll specify our Max Attachment Spacing for each wind zone with the next 3 dropdown menus.


The last two fields of the mounting BOS are the number of fasteners needed for each mount and their embedment depth.

What if I don't see the rail option I'm looking for?

Here is where you can find out more about adding new racking products that are not currently available.

Next Steps

Congratulations, you've completed your design and you can now download a complete permit package! This article will walk you through the permit package generation step.

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