Tag Archives: lumber grading

Checks and Splits in Post Frame Timbers

Checks and Splits in Post Frame Timbers

Checks and splits in post frame timbers (wall columns) are often misunderstood when assessing a structure’s condition. There are two means where checks and splits can form in wood elements: during seasoning, or drying, and during manufacture.
Development of checks and splits after installation occurs after wall columns have dried in place. Usually these were installed green, especially after a recent pressure preservative treatment. Due to their size, it’s not practical for timbers to be kiln dried. Some are air dried for a period of time prior to installation, but mostly they are installed green, and therefore, are allowed to dry in place.
During the seasoning process, stresses develop in wood as a result of differential shrinkage often leading to checking, splitting and even warping. Wood fiber separation results in checking and splitting. Due to innate wood characteristics, it shrinks and swells differently. Generally wood shrinks (or swells) approximately twice as much tangentially to annual rings as compared to radially. Additionally, during initial drying process timber outside inevitably dries quicker than interior, causing differential stresses to develop.

Combined effects of these drying stresses in a post often, and sometimes inevitably, result in formation of a check or a split. Since wood’s weakest strength property is tension perpendicular to grain (similar to how wood is split with an ax), drying stresses can result in a check or split forming in a radial direction across annual rings. However, while these seasoning characteristics may initially appear as problematic, they likely are not. It is important to remember as wood dries, it becomes stronger. Furthermore, the development of these seasoning characteristics is, quite often, normal. Most importantly, both are accounted for in derivation of design values for timbers and are also accounted for in applicable grade rules.

A check is separation in wood fibers across annual rings of a piece of wood and a split is a separation of wood fibers across annual rings but through a piece of wood. A third type of fiber separation, known as a shake, occurs along annual rings and is generally a naturally occurring phenomenon in standing trees, not a result of seasoning. There are several types of checks and splits defined and handled in grading rules for timbers.
In evaluation of post frame timber columns normal checks and splits can often be interpreted as problematic by some design professionals with respect to allowable design values. However, in most cases they are not. There are instances, however, where a check or split may reveal an important issue or a problem. For example, a relatively large split across a severe slope of grain.

Still concerned? In many locations glu-laminated post frame building columns are available, usually at a slight premium. Individual members of glulams have been dried prior to fabrication and pose little chance of checks or splits.

Smartphone App to Test Lumber Strength

I have been a proponent of machine rated lumber since I bought my first truckload to be made into trusses at Coeur d’Alene Truss (http://www.cdabuilders.com/) back in 1978. Years later I spent five terms on the Board of Directors of the Machine Stress Rated Lumber Producers Council (http://www.msrlumber.org/).

I have opined previously on the merits on machine graded lumber: https://www.hansenpolebuildings.com/2012/12/machine-graded-lumber/.

Mississippi State University™ has taken lumber testing technologies and placed them directly into the hands of the public. Please read on in this MSU article:

The “Smart Thumper” app, available for download in the Apple Store, uses sound waves or vibrations to determine stiffness, a quality that relates to strength, for individual pieces of lumber. (Photo by David Ammon)

STARKVILLE, Miss.—Determining the stiffest piece of lumber is now easier with a new smartphone app created by scientists in Mississippi State University’s Forest and Wildlife Research Center. 

Called “Smart Thumper,” the app uses sound waves or vibrations to determine stiffness, a quality that relates to strength, for individual pieces of lumber.  

Developer Dan Seale, professor in MSU’s Department of Sustainable Bioproducts, said it will help carpenters, contractors, architects, engineers, lumber mill personnel and consumers. He pointed out that it can be particularly beneficial for the do-it-yourself market.

The Mississippi State team that has developed an app to determine stiffness of individual pieces of lumber include, from left, Frederico Franca, assistant research professor of sustainable bioproducts; Songyi “May” Han, an MSU sustainable bioproducts doctoral student; and professor Dan Seale. The team’s work is part of the university’s Forest and Wildlife Research Center. (Photo by David Ammon)

“All lumber is not the same, even though it may be graded the same. The grade is based on a range of values and characteristics,” Seale said. “Perhaps a consumer has a pack of lumber which meets the specification for No. 2 grade, but they need a couple of pieces for a header, something that might span the opening for a window or door. This app helps select the stiffest pieces that are least likely to sag over time,” Seale explained.

Frederico Franca, the app’s co-developer and an assistant research professor in sustainable bioproducts, first envisioned the app when he discovered that the equipment designed to test lumber costs around $84,000.

“The goal was to make something cheaper and more readily available to give consumers and stakeholders broader access to nondestructive testing equipment,” Franca said. “Now anyone with a smartphone can download the app to help pick out the stiffest pieces for whatever they are building.”

His love of physics, along with the desire to create something less expensive, fueled his idea for a smartphone app that would render lumber values through the use of sound and vibration. 

“With this app, I can show you which lumber pieces are stiffer and therefore stronger,” Franca explained. “This can’t always be done through visual inspection. You need vibration or you need sound.”

Lumber mills use both visual and mechanical means to grade all types of dimensional lumber. Pieces can be tested for strength and stiffness, and the numbers are crunched through an algorithm to determine grade.

“This app can help further evaluate lumber within established grades, potentially optimizing the longevity and cost efficiency of wood structures by selecting stiffer pieces for situations that demand higher performance,” Franca said.

Also a part of the code development team is Songyi “May” Han, an MSU sustainable bioproducts doctoral student whose 2017 master’s thesis relates to marketing the smartphone app.

The app is available for download in the Apple Store. Visit https://itunes.apple.com/us/app/smart-thumber/id1436858557?mt=8.

Learn more by visiting http://smartthumper.fwrc.msstate.edu/.

Prime Lumber

Prime Lumber is a grade description for a special product variation of two inch dimensional lumber intended for use where appearance is a consideration.

Prime LumberFor No. 2 PRIME, the grade is based upon #2 dimensional lumber characteristics except the holes, skip and wane are closely limited to provide a high-quality product. While PRIME lumber may “look” better, it has the same design strength values as lumber which does not classify as PRIME. (Readers – “skip” is a place on a piece of lumber that failed to surface clean when run through a sawmill planer.)

PRIME lumber is especially prized for use on outdoor members where it will be seen on a frequent basis – decks, patio covers and picnic tables would be some of these cases. Much PRIME SYP (Southern Yellow Pine) is pressure preservative treated and used for decks.

Most frequently PRIME lumber can be often found at “big box” lumberyards such as The Home Depot® where building owner/consumers are more discerning as to appearance and less concerned with price – as PRIME lumber is going to be more expensive.

Contractors are often more skilled at “making things work” as long as the materials meet the minimum structural requirements. Low price seems to become more of a driving factor than how a board looks.

In pole building construction, the use of PRIME lumber for wall girts and roof purlins, with limits on wane, makes it increasingly probable for all screws to be installed through the steel siding into the framing, without having to push or pull purlins or girts back and forth.

As mentioned in my last article, for a #2 grade (which is what is most commonly found at lumber dealers), wane is allowed to be up to 2/3 thickness and ½ width for ¼ length. On a 12 foot long 2×6, the wane could be 2-3/4” on the wide face, 1” in depth across the 1-1/2” face and three feet in length.

The very same 2×6, under PRIME requirements can only have ¼” deep or wide of wane, except an occasional piece may have wane on one edge up to 3/8” deep by 3/8” wide for a foot!

When deciding which lumber to purchase, keep in mind all of my discussions recently on wane, EE (eased edge), heat treated lumber, grade stamps – are designed to help you justify your purchase according to what you are using the lumber for. Lumber is not just lumber. It has many variations with cost considerations. Pick the right product for the right use.

Grade Stamps

Walk into your local lumber dealer – whether a big box store (aka The Home Depot® or Lowe’s®), a national lumber dealer (think ProBuild®, Stock Building Supply®, or 84 Lumber®) or the local mom and pop lumber seller and pickup any piece of dimensional lumber.

grade-stampOn it will be a grade stamp – which is a voluntary standard of marking each piece of lumber to assist the consumer in identifying the moisture content, product grade, species or species grouping, the accredited agency under who’s authority the lumber was graded, as well as a unique mill number identifier or the name of the sawmill which produced the lumber.

One of my son Brent’s first days of working with me involved placing Simpson Strong-Tie® joist hangers on rafters. The rafters were different colored wood – Brent noticed the difference between the darker, more reddish hue of the Douglas Fir rafters as opposed to the whiter color of the ones which were HemFir. I explained to him what the information on the lumber grade stamps was, including the indication of the species of lumber.

The “big giant head” for lumber grading starts with the ALSC (American Lumber Standard Committee, Inc. www.alsc.org).

The ALSC, is a non-profit organization comprised of manufacturers, distributors, users, and consumers of lumber. It serves as the standing committee for the American Softwood Lumber Standard (Voluntary Product Standard 20) and in accordance with PS 20, administers an accreditation program for the grade marking of lumber produced under the system.  This system, the American Lumber Standard (ALS) system, is an integral part of the lumber industry’s economy and is the basis for the sale and purchase of virtually all softwood lumber traded in North America.  The ALS system also provides the basis for acceptance of lumber and design values for lumber by the building codes throughout the United States.

As noted above, a function of the ALSC is to maintain the American Softwood Lumber Standard.  The ALSC in accordance with the Procedures for the Development of Voluntary Product Standards of the U.S. Department of Commerce and through a consensus process establishes sizes, green/dry relationships, inspection provisions, grade marking requirements and the policies and enforcement regulations for the accreditation program.  The ALS system as a whole is set up to give manufacturers, distributors, users and consumers a mechanism to formulate and implement the Standard under which softwood lumber is produced and specified.  Participation of each segment of the industry is an integral part of the program and provides the industry with a direct voice in the standardization and accreditation program as it evolves into the twenty-first century.

In the case of Brent’s rafters, the Douglas Fir ones were marked with the WWP® logo of the Western Wood Products Association (www.wwpa.org) which is the largest association of lumber manufacturers in the United States. The Douglas Fir ones were marked with a mill number to indicate the producer, however the others were produced by Idaho Timber (www.IdahoTimber.com).

The rafters happened to be graded as Select Structural (SelStr), which indicates a relatively smaller group of allowable defects than the more commonly seen framing material, which is normally graded as #2.

For a brief overview of allowable defects in lumber, please read more at: https://www.hansenpolebuildings.com/blog/2013/12/lumber-defects/

The species of lumber was how Brent and I originally got into the discussion of grade stamps. It was indicated by the DFir and HemFir designations on the rafters.

All of the framing lumber used on this building (as well as all Hansen Pole Buildings) is seasoned to a moisture content of no greater than 19% at time of surfacing, which was indicated by the “KD” on the grade stamps.

Lots of information contained in a little stamp – but as Brent’s older sister Allison says, “My Dad knows more worthless trivia than anyone”.

Pole Barn Lumber: Southern Pine Updates

Southern Pine lumber has been popular since Colonial times for a wide variety of applications. Favorable growing conditions, wise forest management, and efficient manufacturing ensure a continuous supply of high-quality Southern Pine products for future generations. Southern Pine consists of four main species — shortleaf, longleaf, loblolly, and slash — and has been the preferred choice for today’s design/build professionals.

Visually graded North American lumber is subject to periodic sampling and testing, to verify the product being provided to the public, meets the published design values. These design values are used by architects, engineers and Building Officials to ensure new wood construction is adequate to support the loads which will be imposed upon the structure.  If you’ve ever looked at the end of a piece of lumber – this is where you might find “SYP” stamped on it, for Southern Yellow Pine, which is the same as Southern Pine.

The most recent testing of Southern Pine lumber resulted in a technical proposal by the Southern Pine Inspection Bureau to significantly lower design values. This submittal was reviewed by the Forest Product Laboratory.

As a resultant of this review, the American Lumber Standard Committee (ALSC) has ruled the design values which apply to visually graded Southern Pine and Mixed Southern Pine sized 2” to 4” wide and 2” to 4” thick (2x2s through 4x4s) in No.2 and lower grades (No.2DNS, No. 2, No. 2NonDNS, No.3, Stud, Construction, Standard and Utility), will be reduced as much as 30% as of June 1, 2012.

What does this mean?  This would be like waking up some morning and finding out the dollar you had is now worth 70 cents.  The lumber used in your building, which sizes and grades were chosen based upon your building location and design, now possibly will not meet the building code. The issue here is the design date and your lumber need to match.  In other words – if you purchased 2×2, 2×3 or 2×4 size lumber prior to June 1st, it may not be large enough for your construction design.

Down the line, this will affect lumber larger than 2×4’s, but we don’t know when, or “how much” it will be affected.  The original SPIB proposal submitted to the ALSC included a reduction in design values of 25-30% for all grades and sizes of visually graded Southern Pine.

The wholesale lumber market has substantially adjusted pricing of Southern Pine to compensate for the lower strength values. In many markets, the now stronger Douglas Fir, Hem-Fir and Spruce-Pine-Fir have gained popularity.

For the end user, the recommendation would be to use larger dimension Southern Pine conservatively, until such time as new values are accepted and published. In using Southern Pine for critical members such as floor joists, rafters, beams and headers it would be prudent to go to the next larger size member than what is shown in span tables.

You can be sure I will have my ear to the ground.  I will again blog about Southern Pine, should I find updated information.