checks Archives - Hansen Buildings

Hart and Home YouTube – Episode III

If you missed our previous episodes, please go to bottom of this article, on left, and click on arrow twice to go to Hart and Home YouTube – Episode I. Moving forward:

For those following along at home:

Lumber Offloading Some discussion will be made here about “allowable defects” in lumber. Our main struggle with lumber quality is clients having unrealistic expectations. Lumber is chosen for strength characteristics, rather than due to “pretty looks”. If an expectation lumber will be clear, vertical grain, knot and wane-free, a severe disappointment will occur. Wood is an organic material. While produced in a “factory” environment (a sawmill), lumber is subjected to naturally occurring defects accounted for in grading rules. These characteristics are taken into account in strength values for allowable design. Minor dimensional differences in individual boards are a function of shrinkage due to moisture content, wood species and even individual tree characteristics. Shrinkage is more prominent across grain – hence variations in the board’s wide face are more pronounced. Ultimately these small dimensional differences do not affect the finished building.

All structural dimensional framing lumber used in Hansen Buildings will be at least graded as #2 (or “standard”) or better. For discussion’s sake, we will limit scope to this grade. Four inch and smaller (e.g. 4×6 and any two inch – 2×4 through 2×12, 4×4 and 4×6), are all graded under “joists and planks” rules. Characteristics listed below are unintended to be all-inclusive, but merely to be a frequently seen item overview.

In any given lumber “production run” typically 5% is allowed to be outside grading rules (to have more defects than expressly allowed) and still have a sum total declared as “on grade”.

Checks – seasoning checks are unlimited. Through checks at ends are limited as splits. Splits can be equal to 1-1/2 times board face width (e.g. 8-1/4” on a 2×6, 16-7/8” on a 2×12). Keep in mind, many times these boards will be trimmed off, especially when used as girts, purlins or rafters. A split portion may thus be removed when trimmed to be put into service.

Knots – on a 2×6, up to 1-7/8” at wide face edge, 2-7/8” at wide face centerline; on a 2×12 up to 3-3/4” at wide face edge, 4-3/4” at wide face centerline.

Holes – (from any cause) on a 2×6 1-1/2”; on a 2×12, 3”.

Wane – up to 2/3 thickness and 1/2 width for 1/4 length. An example would be on a 12’ long 2×6, wane could be 2-3/4” on wide face, 1” in depth across 1-1/2” face and 3’ in length.

Bow (or Crook) – a board size and length function. As an example: for a 2x6x12’ – 5/8” would be acceptable, with greater amounts allowable with longer lengths.

Twist – for a 4x6x16’ would be allowable up to 1-1/2” and still be within grade.

Timbers

5” x 5” and larger are graded as “Posts and Timbers” and have their own characteristics. Again, addressing #2 grade, they include:

End splits – up to twice post face are permitted: (Ex: 12” on a 6” face.)

Wane – 1/3 of face.

Bow, crook and twist are NOT limiting factors under grading rules for posts and timbers.

It is essential any suspected shortage or damage be reported immediately. Vendors become highly suspicious of possible jobsite damage, as it increases with time. An example of this is when (after several months on a jobsite) a client asked for replacement of some damaged steel – his provided photographs actually showed tire marks where it had been run over!

Construction Manual – we do frequent updates and additions to it, often several times annually. Since Kevin and Whitney’s investment, more and more of our clients have gone to wet-set brackets, rather than embedded columns. Hence, we have added several pages of wet-set bracket specific details and instructions to Chapter 5, Setting Columns.

Solid sawn vs. glulam columns. We agree totally with Kevin’s analysis, glulams are a superior product and I would highly recommend them to any client (for extended reading, please see https://hansenpolebuildings.com/2014/10/glulam-4/). One downside is distribution, as they are manufactured in limited and highly scattered locations, costs of shipping and time delays can become issues.

Watch for our final episode of this series – coming soon!

Checks and splits in lumber and timbers, especially timbers, are often misunderstood when assessing a structure’s condition. Checks and splits can form in wood by two means: during seasoning, or drying, and during manufacture. This article is concerned with checks and splits resulting from seasoning after installation.

Development of checks and splits after installation occurs after a timber has dried in place. Quite often these timbers were installed green. 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 usually they are installed green, and therefore, are allowed to dry in place. This also applies to a lot of dimension lumber.

During the seasoning process, stresses develop in wood as a result of differential shrinkage often leading to checking, splitting and even warping. Separation of wood fibers results in checking and splitting. Due to wood’s innate characteristics, it shrinks and swells differently. This is best explained in the image below. As a general rule of thumb wood shrinks (swells) approximately twice as much in the tangential direction of annual rings as compared to radial direction. Additionally, during the initial drying process outside of a timber inevitably dries quicker than interior, causing differential stresses to develop within a timber. Combined effects of these drying stresses in wood often, and sometimes inevitably, results in formation of checks or splits. Since wood’s weakest strength property is tension perpendicular to grain (similar to how wood is split using 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, development of these seasoning characteristics is, quite often, normal. Most importantly, both are accounted for in derivation of design values for lumber and timbers and are also accounted for in applicable lumber grade rules.

See Figure 4-3 from the Wood Handbook, FPL-GTR-190

Figure 4-3 from the Wood Handbook, FPL-GTR-190

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 grade rules for dimension lumber and timbers.

In use evaluation of dimension lumber and timbers 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. In the image below, ends of both timbers are exhibiting various sizes of normal checks developed as timbers dried. If these timbers were being examined in a structure they would look similar to each adjacent image.

Upper left image shows two large timbers with visible splits on both ends as a result of seasoning. These are considered normal. Each red arrow points to how these checks would look in use.Therefore, checks and splits are often not an issue with in use lumber and timbers.

In summary, normal checks and splits are often encountered when assessing a structure, but they are accounted for in derivation of design values and handled in lumber grade rules.

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Hart and Home Youtube Episode III

Checks and Splits in Post Frame Lumber

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