Tag Archives: risk category 1 building

500 Year Storm and Wind Exposure

500 Year Storm and wind exposure.

Allstate® Insurance has a TV commercial featuring actor Dennis Haysbert. Haysbert sits in an open field and questions why there have been 26 “once in 500 years storms” in last decade, when term alone implies they should only happen every 500 years.

View Allstate® commercial here: https://video.search.yahoo.com/search/video?fr=crmas&p=Allstate+once+in+500+years+storm+commercial#id=1&vid=b134fa05aba0ff046debaea22891c23d&action=click

IBC (International Building Code) in Chapter 16 (https://codes.iccsafe.org/public/document/IBC2018/chapter-16-structural-design) Table 1604.5 lists Risk Category of Buildings and Other Structures.

Risk Category I includes buildings representing a low hazard to human life in event of failure – agricultural buildings and most detached residential accessory buildings fit into this category.

Risk Category II would be most homes and many low risk commercial, industrial and manufacturing buildings.

Risk Categories III and IV cover buildings with high occupancies or are essential to fire, life and safety (like fire stations).

IBC offers Minimum Design Loads modified by a given factor depending upon Risk Category. For a previous article about this subject please see: https://www.hansenpolebuildings.com/2018/08/minimum-design-loads-and-risk/.

Reflect, if you will, back upon paragraph one above and a 500 year storm.

wind damageRisk Category I buildings are based upon a once in 25 year probability of minimum design loads being exceeded. Risk Category II once in 50 years, while Categories III and IV are once in 100 years.

So, what does one do to protect against a once in 500 years storm?

When planning your new post frame building, this becomes relatively easy – have it designed for greater loads than bare Code required minimums. While this sounds simple, very few clients consider asking for it and even fewer post frame building sales people offer it!

Why would it not be offered?


People are selling buildings using price rather than value.  Most are afraid to suggest increasing building price by a few percentage points, because they think it will cost them a sale!

I know there are numerous members in our post frame industry who are reading this article. To you I offer this challenge – as an option start offering to every potential client an ability to have their building designed for an extra even five or 10 psf (pounds per square foot) of snow load (in snow country of course). And, give them an option of withstanding greater wind speeds than Code minimums. Even upgrading wind Exposure B sites to Exposure C will increase ability to resist wind loads by about 20%.

A short wind exposure story can be found here: https://www.hansenpolebuildings.com/2011/11/wind_exposure/.

Now, sell your potential client benefits of having last building standing when Mr. Haysbert’s storm rolls through.

Sold itself, didn’t it?


Converting a Pole Barn to a Residence

Reader BAILEE in LARAMIE writes:

“Hi, I have a few questions about the structure of turning a pole barn to a residence in the Laramie, Wyoming area. The current project I am working on has pole spacing of about 10-12 feet. I wanted to know if this is still structurally stable with traditional framing with the wind in Wyoming? If not, would it be wise to double the sidewall girts for more support within the walls? Also, if we were to use the traditional framing with 8 foot spacing would that be stable?

Next, do you have any window diagrams that detail the insulation and wall construction within residential pole barns that your company would be able to share?

Please let me know. Thanks for any help that you can provide.”

Mike the Pole Barn Guru Answers:

As to the structural stability of any post frame building, anywhere – it depends upon the climactic conditions to which the building was designed by its engineer of record (EOR). If this is an existing building, you may have some challenges, as most “pole barns” are at best designed as Risk Category I buildings – which pose little or no threat to human life in the event of a catastrophic situation. Residential buildings are to be designed to Risk Category II, which increases the needed design wind and snow loads.

In the event you are installing an interior finish other than steel liner panels (most folks sort of enjoy gypsum wallboard taped and textured) members which support these types of finishes need to be designed for far less deflection. Back to in the event this is an existing building – the EOR should be consulted to determine which members need to be upgraded to meet with your now intended use of the building. Under no circumstance attempt to do this without the consultation of an EOR, it is not worth risking the wellbeing of yourself or your loved ones.


If you are starting from scratch – invest in a building kit package which has been designed by a registered design professional (architect or engineer) who has clearly been advised as to your intended use of the building. The plans they provide will call out all of the members and framing details necessary to give you an end resultant which you and the generations which follow you can enjoy.


For a small nominal fee, you can invest in a Hansen Pole Buildings’ Construction Guide, the price of which can be credited towards your purchase of one of our complete post frame building kits. Contact Bonnie@HansenPoleBuildings.com if this is of interest to you.