Tag Archives: metal plate connected wood trusses

A Case for Minimum Post Frame Truss Loads

A Case for Minimum Post Frame Truss Loads

Portions of this article were written specifically for Component Advertiser, a monthly truss industry publication. However I feel strongly enough about this subject to use my column to pitch it to both my employers and other post frame building kit suppliers and contractors.

In my career I have done about everything imaginable when it comes to post frame (pole) building trusses. I have been blessed to have been able to spend a better portion of over two decades working within or owning prefabricated MPCWT (metal plate connected wood trusses) manufacturing facilities. I have designed, engineered, fabricated and delivered trusses. As a builder, I raised my first set of post frame trusses nearly 40 years ago and many more have followed.

I have also been a provider of post frame building kit packages across most of my adult life. Our industry (post frame buildings) is one where low price, rather than service and quality, drives most sellers and buyers. Sellers, more often than not, have not learned well how to convey value of benefits they offer – instead they live in fear of being a five-spot more than their competitors when it comes to price.

For nearly seven years I have been writing a weekly advice column, “Ask the Pole Barn Guru™”, where I answer post frame building oriented questions from anyone. One repeatedly asked question is in regards to adding ceilings to existing post frame buildings. Most roof trusses for these buildings were not designed to support ceiling loads, generally due to a fear of increasing building price.

Many post frame buildings are constructed in areas where pole buildings are exempt from building permits, or there are little or no structural plans reviews done. This contributes to an attitude of “make it cheap” by encouraging use of minimal loads for trusses.

A great majority of post frame buildings are used as residential accessory buildings – garages, shops, RV parking, man caves, she sheds, etc. Nearly all of these buildings have truss spans of 40 feet or less, so my proposal for voluntary minimum loading requirements for post frame buildings will be directed towards these structures.

Why not apply these minimums to larger span structures? Many wider span buildings are going to be used as horse riding arenas or equipment storage for farming and are never going to have ceilings in them. Costs to design for greater loads, for spans of 50 feet and greater could result in some significant costs. Wide span buildings being used for more humanly occupied (and therefore more critical in protection of human life) purposes are likely to have a Registered Design Professional (architect or engineer) involved, who will specify roof loads based upon building use and function.

In areas of minimal or no snow, with Pg (ground snow load) values of under 20 psf (pounds per square foot) Top Chord Live Load (TCLL) should be fixed using a minimum of 20. For areas where white stuff has a greater possibility of occurrence 25 psf appears to be a reasonable minimum.

Most post frame buildings have light gauge steel roofing over purlins. Hopefully they also have some sort of minimal weight material between these to minimize or prevent condensation issues. In most instances, total dead loads required in order to support truss weight, condensation control, purlins and roofing will be less than 2.5 psf. There are folks who have ideas not always shared with truss designers – like using OSB or plywood sheathing between purlins and roofing. Also, rooftop solar panels are becoming more and more popular and find their way onto more than a few roofs not designed to support their weight.

My proposal (again for buildings of 40 foot spans and less) would be for a minimum TCDL (Top Chord Dead Load) of five psf. While this does not solve every possible case, it does allow for greater end user flexibility.

Traditionally, most post frame buildings did not have ceilings installed, so a very minimal BCDL (Bottom Chord Dead Load) has been used. Most typically a one psf loading will be selected, more than covering bottom chord lateral bracing and limited lighting. However, as post frame have moved from farms to suburbia, more buildings are getting interior finishes – meaning ceilings. I like to use 10 psf, in cases where I am designing for a drywall covered ceiling with insulation above, however even five psf would handle most ceiling loads.

Load duration – no snow, I am good with 1.25, snow areas 1.15. However, in my humble opinion, if TCLL exceeds 50 psf, chances are snow will be piled on top of these trusses for more than two months across structure’s lifetime and a DOL (Duration of Load) of 1.0 will be most appropriate.

A hidden side benefit to establishing these voluntary minimums will be stronger trusses able to withstand more abuse in handling. Some lumber members will be larger dimension or higher grade material and steel connector plates will increase in size. All of these factors increase probabilities of reduced truss damage.

Hansen VisionNow, I believe, time has come to stop selling price to post frame building clients and sell benefits. Safety becomes easiest to sell – no one wants to live with a fear of their building collapsing and injuring them, their loved ones, or destroying their valued possessions. Flexibility in future use – also an easy sell, if a future building owner decides they want to add a ceiling they can safely do so.

Minimum post frame truss loading benefits all, by raising the overall quality of finished buildings  with a negligible investment.

An Advance Article Preview for The Advertiser

Besides being a semi-regular contributor to Rural Builder magazine, I have also had articles published in several other lumber and wood truss periodicals. I’ve been asked to write an article for The Advertiser (https://www.componentadvertiser.com/), which I share with you below:

Increase Your Post Frame Sales

Nearly every U.S. and Canadian metal plate connected wood truss manufacturer has one or more clients who either construct pole barns or sell kit packages. Not much excitement though in dealing with typical orders of usually anywhere from four to 10 trusses per building.

Money can certainly be made in post frame industry sales. My 1990’s truss plant, based in Spokane, Washington, almost exclusively built pole barn trusses. It was not unusual for us to have backlogs of weeks and when it came to post frame trusses. We dominated Northwest U.S.

How we did it.

We tailored our inventory to best build to our client’s needs. By having 2×6 2850msr and 2400msr in wider widths, we could provide smaller dimension chords than our competitors, with lighter trusses. Considering jobsite manhandling involved, lighter weight trusses are an advantage! And let’s face it – those high grades have very few visual defects, resulting in some very pretty trusses!

Also in our inventory, for web stock, was msr 2×3. Many truss webs can be higher grade 2×3, rather than 2×4. Again, much 2×3 msr was much prettier wood than 2×4 visually graded material others were using, not to mention saving truss weight.

 

 

Webs requiring lateral bracing were checked to see if a larger dimension or higher grade would eliminate bracing. Installing job site bracing take both material and labor, reducing braces for a minimal investment makes for happy clients.

Be a Consultant.

Being able to be different in the post frame industry gives one a leg up, where virtually everyone does things alike. When a truss client can say, “I do things just like everyone else and also provide….” to their potential customer, it gives them an advantage.

Most post frame roof trusses will be 40 foot spans or less. Point out very small price differences to add five or 10 pounds per square foot (psf) of load to top chords. Many post frame trusses are designed with a bottom chord dead load of one or two psf. One of my most asked questions of my Ask The Pole Barn Guru™ advice column – is how to add a ceiling to post frame buildings. A five psf bottom chord dead load would solve this dilemma. Both of these are points your client can use to sell why he has a better building than Brand X.

Offer More Stuff.

Your delivery truck starts spinning dollar signs an instant a key gets close to an ignition switch. Since you are going to make a jobsite trip, why not add more product?

True glu-laminated post frame building columns are a wonderful thing – strong, light weight and straight. In most instances a product of 1650f three ply 2×6 glulam will replace 6×6, 6×8 and in some cases 6×10. Downside of glu-lams – current lack of distribution, as manufacturers are primarily in South Dakota, Wisconsin and Pennsylvania. Work with a manufacturer to bring in ¼ or ½ of a truckload of 14 to 24 foot lengths, they might even help to floor some inventory. Once builders start using them, they will never go back to solid sawn columns. This provides another differentiation for your client and it helps to tie them to you as their supplier.

Sell them msr lumber.

With 2×6 1650 msr being over 40% stronger than best commonly used visually graded #2, you can do your client some favors in helping to point out strength and quality benefits. Side benefit for you – quicker inventory turns. Buy more lumber get better negotiating power with wholesalers and mills.

Glu-lam column and selling lumber margins are not going to be as high as your truss margins, expect maybe 20%, however consider this a bonus profit you would never have otherwise had. I always felt 20% of something beat 100% of nothing every day.

Expand your post frame building industry view and increase your bottom line!

Impact of Weather on Metal Plate Connected Wood Trusses

Impact of Weather on Metal Plate Connected Wood Trusses

Proper jobsite storage of trusses has always been near top of my personal list. If in doubt, I recommend erring towards caution’s side. Hansen Pole Buildings’ Construction Manual addresses proper truss handling and storage:

“Trusses store best when standing upright.  

Shore and brace standing trusses well to keep from toppling. Trusses not stored in a vertical position can and will warp, and become difficult to use.  

Store trusses with “tails” (overhangs) so truss weight does not rest on tails.

Unload trusses in bundles and store on level ground, but never in direct contact with ground (to avoid collecting moisture from ground). Allow for good drainage at truss storage location in event rain occurs before installation. Protect trusses from damage resulting from on-site activities, environmental conditions or elements. Exercise care at all times to avoid damage to trusses due to careless handling during delivery, unloading, storage, and installation.

In warm, rainy weather, moisture regain in unprotected trusses can result in fungal staining. Wetting lumber also results in swelling. Subsequent shrinkage of framing may contribute to structural distortions.

To store trusses not being used immediately, cover with a water repellant opaque tarp for protection. Plastic may be an acceptable alternative, provided there are side openings to allow air flow. Handle trusses in such a way as to prevent toppling when removing banding from bundles. Trusses stored on black top or other impervious surfaces and continuously moved around construction site are subject to damage when they are slid along surface with equipment. As a result, galvanized coating on connector plates may be removed, allowing plates to rust and possibly reduce plate thickness.”

(Portions of this article, below, are from an August 7, 2018 article by Sean Shields and Kirk Grundahl, P.E. published in SBC Magazine)

In 2000 and 2004 Alpine (Alpine manufactures steel connector plates for trusses https://alpineitw.com/ ) undertook a weathering study entitled Durability of Plates, R&D #90-07 dated January 3, 2000 and January 22, 2004. Mr. Stu Lewis provided this report to SBCA (Structural Building Components Association) to aid SBCA with background information regarding a common notion truss plates back away from lumber under short term (i.e. less than nine months of outside storage) weather exposure. Key concepts from this report, given an Orlando exposure condition from July 1998 to December 1998 follows:

CONCLUSIONS

  1. No particular plate type in this study showed markedly different back-out performance or retained tooth holding capacity than other plates tested.  
    1. For all plates, storage under cover, even if it was just another joint, was better than direct exposure. 
  2. No excessive corrosion was noted of any type of truss plates, nor were tooth holding reductions considered significant with respect to their magnitude..
    1. …it appears some exposures, specifically top plate on horizontally oriented truss joint fully exposed to weather, experiences an average loss in tooth holding strength of about 14 percent in a 5-6 month exposure in severe central Florida climate of this study
      1. this is likely due to occurrence of plate back-out due to repeated wood shrinkage and swelling. 
  3. Typical practice of permitting trusses to be exposed to environment for a short period of weeks or even months after truss fabrication and before closing in structure is confirmed as not resulting in an excessive loss in strength and is therefore acceptable with respect to joint strength…….. 

Alpine results point us in a right direction, even though this is a limited study of truss plate performance due to weathering. However, all truss weathering studies to date have been performed on truss plates and truss plate joints, but never on finished trusses as stored at truss plant or on job site

Typical practice of permitting trusses to be exposed to environment for a short period of weeks or even months after truss fabrication and before closing in structure is confirmed as not resulting in an excessive loss in strength and therefore acceptable with respect to joint strength… 

Our (SBCA) goal is to take all background information we can find, along with our SBCA weathering testing program findings, and create a set of best practices to help maintain good truss performance during their entire service life (ideally if we can, it would be nice to see consistent trends, predictable and can be modeled)

From this work we believe SBCA will be able to provide best practice counsel with respect to storage, truss plate performance and, most importantly, define any effect on overall truss performance post-installation.