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The "Story" with Snow Loads

Updated: Oct 9, 2023

Let talk snow loads. Yes we have engineered drawings in some 20 states but the state stamped versions are our baseline build which is 110mph wind and 20 pdf snow load.

What happens when the building fails? In most cases the purlins fall between the trusses which starts the failure. Todays box store lumber is not the lumber we had 40 or even 20 years ago.

Can you achieve a higher snow load rating? - Sure you can

I'm not a certified engineer so I always recommend working with someone in your local area. The local building inspectors and planners are often great resources. And feel free to give them my phone number so we can answer their questions.

So what can you do to increase snow load?

We generally start with the following list but what you end up doing might be a any number of things that best meet your needs / situation.

  • I first recommend bringing in the post spacing from 10ft to say 8ft. (Folks in upstate NY went to 6ft) This also makes it easier to use a 2x6x16 for a purlin in a brick pattern that adds even more support.

    • If you planned to bring in equipment on the sides we can discuss using our Headers to remove a post or two.

  • Next we could upgrade the purlins both in species and size. A better quality of lumber will always improve your build and I strongly recommend working with local sawmills given you often have enough planning time for them to pull together your order. Moving to a 2x8 will also reduce the sag that normally leads to failure.

  • And now the finishing touches - Bracing - We have a few opportunities for bracing but be careful not to add too much weight to the overall roof.

    • Note our lower purlins, used to keep the trusses from twisting, line up with an upper purlin so a 45 degree piece of 2x6 could be used to add support every 5 ft or so.

    • Bridging can be added, namely on green lumber, to tie two purlins together. (2ft insert)

    • Diagonal ?2x4? screwed to the bottom of the purlins, called an under-purlin, again used to tie them together and reduce building twist. This is also commonly used when building with green lumber.

So what is the snow load in my area?

Refer to local codes but a good online tool is the ASCE 7 Hazard Tool.

  • Type in your zip code or address

  • Version = ASCE/SEI 7-16

  • Risk Category = 1

  • Load Types = Snow and Wind

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