Tag Archives: Risk Category I

Steps to Minimize Snow Load Failures

The following article will appear in April 2019’s Component Manufacturing Advertiser magazine (www.componentadvertiser.com).

Early every year NFBA (National Frame Building Association) holds its annual Frame Building Expo – where thousands of post-frame builders, design professionals and vendors meet for three days filled with break-out sessions, guest presenters and of course a trade show.

In 2019’s Expo, one breakout session was, “Avoiding Common Building Failures in the Post-Frame Industry” presented by Ryan Michalek, P.E. of Nationwide Insurance.

The “trailer” for this session was, “Would you find it surprising that Nationwide Insurance’s loss experience with post-frame buildings is disproportionately represented by newly constructed facilities? The company’s loss history is full of buildings that are less than 5 years old and that fail when subjected to their first moderate wind or snow loading event or to a modest commodity-loading cycle. This presentation discusses the common oversights in post-frame building design and construction which lead to building loss and offers strategies to eliminate these oversights.”

I quizzed Mr. Michalek myself as to how many of these failures were subjected to a structural plan review by a Building Official. His opinion was few, if any, failed buildings were designed by a registered design professional RDP (registered engineer or architect), as they are nearly exclusively “agricultural” structures, exempted from Building Permit processes in many states.

My personal belief – every building should be designed by a RDP, as well as being subjected to structural review by a Building Official. Knowing Insurance Industry size, I questioned why it was Nationwide® and other insurance companies were not lobbying for stricter rules for these now permit exempt buildings. Mr. Michalek minced no words in stating United States agricultural lobby having far more power than insurance industry lobby.

I am just not grokking thought processes of those who would invest in buildings which will underperform or fail structurally, all for saving a few dollars. Considering many failures come from poultry industry buildings, it seems costs and cleanup of a million dead chickens or turkeys would trump a few dollars saved on construction.

What was surprising to me, was an analysis of actual most prevalent failures – although column size and embedment always seem to be big concerns from informed purchasers, it wasn’t a contributor to three major causes of failures: lateral bracing of trusses; purlin to truss connections and unbalanced and snow drift loads on trusses.

Typically builders, when they do install bracing, will just run it laterally from building end to building end. This results in all trusses bending together, as loads being placed upon bracing are not being transferred to a very stiff surface – like a roof diaphragm. By utilization of properly designed “X” braces, lateral loads can be transferred into roof plane, and keeping trusses where they are happiest – upright.

Many post-frame buildings, especially those designed with widely spaced single trusses rely upon nailed purlin-to-truss connections woefully inadequate to resist uplift forces. This becomes even more crucial in critical areas such as “end zones” and close to eaves or ridge. A solution would be to use appropriate engineered hangers to attach purlins.

A third common area of failure occurs from designs where drifting snow causing unbalanced loads has not been accounted for. Roof truss designers have an ability to turn off a “switch” in their engineering design programs accounting for drift loading. This results in a less expensive, although under designed truss. With no structural design review, no plan’s examiner will catch trusses being inadequately or inappropriately designed.

Not only do trusses need to support unbalanced snow loads, so do roof purlins. It’s not unusual for an engineered building to have purlins either spaced closer together, or of higher grade or larger size in roof drift areas.

Fast forwarding to 2019’s NFBA Expo – where a frequently heard topic of discussion revolved around a plethora of snow related building collapses in Wisconsin, Minnesota, North and South Dakota. A great majority of these roof failures came from buildings exempted from Building Codes.

While it is impractical, unaffordable or unfeasible to retrofit existing buildings to meet Code loading requirements, we can make changes to minimize or eliminate future failures due to snow. Every time a post-frame building roof collapses, it reflects poorly upon our industry. When prefabricated wood roof trusses fail, truss manufacturers get blamed.

Together these two industries can lobby for changes ultimately making for better and safer buildings.

In my humble opinion, these would include:

Require all buildings over 200 square feet to be constructed from plans sealed by a RDP, as well as to be subject to a structural plan review and field inspections.

Eliminate “agricultural exemptions” from permits.

Eliminate Risk Category I as an IBC option. Risk Category I reduces design loads for snow and wind. This doubles annual probability of failures as compared to Risk Category II.

Eliminate use of Cs to downward adjust top chord live loads due to roof slope and “slipperiness” of roof surfaces. Too many buildings have snow retention systems added to roofs, after completion. This would be all well and good if RDPs and truss technicians were made aware when computing their designs.

Create minimum design dead loads of five psf (pounds per square foot) for both top and bottom chords of roof trusses. Some post-frame buildings have sheathing installed between purlins and roof steel, overloading top chords. Personally, I receive numerous inquiries every week from building owners who now want to install ceilings in their existing post-frame buildings and find their building’s trusses are not designed to support this weight.

Have Building Departments re-evaluate values used for snow (and wind) loads in their jurisdictions. 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.  An increase of design snow load of only 15% cuts annual probability of a failure in half!

Hopefully we will learn from this past winter’s collapses and become proactive together to make for better and safer buildings!

Roof Collapses Due to Heavy Snow are Largely Avoidable

Roof Collapses Due To Heavy Snow Are Largely Avoidable.

Portions of this article are thanks to a February 25, 2019 article by Bill Steffan at www.woodtv.com

 

 

 

 

 

 

 

“Above pic. is the Negaunee Schools bus garage in Marquette Co., Michigan.  The roof collapsed under the weight of heavy snow over the weekend.  There were 16 buses inside the garage when the collapse occurred.  The collapsed triggered the sprinkler system and that led to a substantial accumulation of ice.  This was one of several buildings that had a roof collapse due to heavy snow in Marquette Co. 

Another collapse occurred at Shunk Furniture.  The force of the collapse blew out windows in the building.  “The first buildings to be concerned about are the pole buildings, the large-span pole buildings with truss spacings of eight foot or greater,” said Gary Niemela, Owner of Skandia Truss.”Those are usually the ones to be concerned about. Probably want to take the heavy snowload off. If the snowload is three to four feet deep on those, you’re going to want to do something,” said Niemela.”

I am going to address several issues, all of them ones leading to a better investment of a new post frame building owner’s dollars.

What, a Building permit?

In a surprising number of jurisdictions across our country, post frame (pole barn) buildings are exempted from a building permit process for one of several reasons. In some areas, there are just no actual building departments. Next step up is a “Building Permit” is issued for a minimal fee (usually in a clerk’s office) usually to get it added to property tax reevaluations.

In my humble opinion every building should have RDP (Registered Design Professional – architect or engineer) sealed plans submitted to an authority who can do minimally invasive site inspections via one of a myriad of online live chat options. Permits and payments could be obtained electronically. This type of system could even be contracted out to third-party providers on a percentage type contract with carefully worded expectations so there is not someone having hurt feelings at a later date.

But I Have to Pay for a RDP!

Yes you do and a good one will save you more money than they cost (or give you a greater value) in efficient use of materials and ease of construction. Favorite articles is on this very subject: https://www.hansenpolebuildings.com/2018/08/minimum-design-loads-and-risk/.

Do Away With Risk Category I

I can hear people screaming now about how much more they are going to have to pay to get a building designed for a once in 50 year occurrence (Risk Category II) rather than once every 25 years. For practical purposes, you cut in half risks to life and property from a catastrophic failure. In many buildings added investment will be minimal, as compared to gain in reliability.

Insurance Company Discounts

Property insurers should offer some discounts for building from RDP sealed plans, as well as a further discount for buildings designed for above Code minimum climactic loads.

Minimum Design Loads and Risk

Minimum Design Loads and Risk

Model Building Codes, such as IBC (International Building Code), offer minimum design loads for climactic forces such as snow and wind. As building permit issuing agencies adopt codes, within their scope they can establish minimum values for their particular jurisdiction.

Key word here “minimum” – least values a building may be designed for and still obtain a permit to build.

I have long been an advocate for structural designs above minimum requirements. All too often potential new post frame building owners have not had adequate consultative design recommendations enough to find out increases in structural strength are often achieved with minimal investment.

For an earlier article concerning this subject please see https://www.hansenpolebuildings.com/2015/11/bike-helmets-and-minimum-building-design-loads/.

From IBC Section 1604.5, “Each building and structure shall be assigned a risk category in accordance with Table 1604.5. Where a referenced standard specifies an occupancy category, the risk category shall not be taken as lower than the occupancy category specified therein.”

Balance of IBC Chapter 16, including Table 1604.5 may be perused here: https://codes.iccsafe.org/public/document/IBC2018/chapter-16-structural-design.

Buildings representing a low hazard to human life in event of a failure include agricultural facilities. In most jurisdictions, detached garages and shops are also considered to be a fit and these would be considered as Risk Category I. In many areas agricultural buildings are either permit exempt, or do not have to go through structural plan reviews and inspections.  Read a very expensive story about an agricultural building using minimal requirements: https://www.sbcmag.info/content/9/design-load-reductions-risk.

Risk Category I buildings are designed to allow for an occurrence greater than minimum design loads of once in 25 years (or a 4% chance in any given year). In theory, all buildings in this category should collapse within 25 years of construction.

Sobering, isn’t it?

Shopping for a new post frame building and want yours to be last one standing when a storm of a century comes to visit? If so, I would hope whomever you are speaking with offers options of increasing Risk Category from I to II. And bumping up snow loads by 5, 10 or even more pounds per square foot and/or increasing design wind speed by a few more miles per hour.

If you are not offered these options – ask for them. I’d like to have your building be left standing!

Turn a Horse Barn into a Home?

Re-purposing buildings is a popular American past time, as evidenced by the proliferation of big box lumber stores across the country. Here is a story about a new owner of an existing Hansen Pole Buildings’ horse barn, who is contemplating it becoming a home.

Tim writes:

“Hello, I just purchased a property that has a Hansen Pole barn that is new on it and I am wanting to convert to home any ideas and /or plans , I have attached a photo of barn  center section is 48×28 x14 and the 2 side sections are 48x12x10”.

Drum roll please:

You emailed me because you know and trust I am the expert and will not lead you astray. Or, this was the email address you happened to find, either one of which is totally fine.

In order to give you definitive answers I would need to know who the original purchaser of the building was, so we can pull up the plans and specifications for it, if they are available.

In the meantime, I will hope to give you my best guess answers. The existing building is most probably designed under Risk Category I of the International Building Code (being as it is used as a horse barn) which is for buildings of low risk to injure someone in the event of a catastrophic event. These would be non-residential structures. A residence is a Risk Category II structure – which has more stringent requirements for wind, snow and seismic events.

The real issues are most likely to come in designing to gypsum wallboard (sheetrock aka drywall) the walls and ceiling.

On the walls, the deflection criteria for walls which support drywall is much greater than a wall with only steel on the exterior. This can affect the size(s) of the columns and they may have to be added onto in order to provide adequate stiffness. It is likely you will use bookshelf girts on the walls to create an insulation cavity. If so, and they are properly sized, they should be stiff enough to support drywall.

The trusses, rafters and roof purlins are not designed to support the weight of a ceiling. This will require an engineered truss repair, as well as probably upgrades to the rafters on each side (addition of more members). If you are planning on attaching sheetrock to the underside of the roof purlins, more purlins will need to be added to reduce deflection – and the only real way to insulate between the purlins on the sheds is to use closed cell spray foam, which is not an inexpensive proposition.

Ventilation is going to pose an issue (which is why the closed cell insulation is the solve for the sheds). In the main portion of the building, if a dead attic space is created, it must be ventilated. I cannot determine from your photo if the building has enclosed overhangs or not. If they are enclosed and the ridge is vented, you are in luck. If not, then gable vents are the alternative and would need to be added.

My best recommendation – leave the barn and design a post frame home which truly fits your needs and lifestyle, rather than trying to fit what you want inside a preexisting box which requires a boatload of work to upgrade.