Log grading determines the quality of lumber suitable for building projects by measuring its strength properties and load-bearing capacities.
To grade a log, its scaling diameter inside of bark must first be estimated using a form class before measuring defect-free sections in three butt-log grading faces (Figure 8).
Low-grade logs can be used as ties and other construction products. Furthermore, their rustic appearance makes them suitable for rustic-style structures.
F1
F1 timber grade is used for logs intended to be used as wall logs or sawn round timber beams, sorted using visual criteria as an effective grading standard – this approach tends to be conservative.
This grade allows up to 30% tree defects. These could include reaction wood, small encased knots and bark-encased scars. In addition, up to 5% heart centers may either be boxed or free.
Grading begins by locating the vertical section with the highest proportion of defects. Once found, this section is divided into four equal sections called faces to determine grade; to do this effectively, two worst faces must have clear cuttings with cumulative lengths that meet standards set out for that grade (12 feet or 16 feet respectively). Figure 10 displays features of an F1 grade 12-foot section butt-log.
F2
Trees that do not produce enough high-grade wood to meet F1 field grade may be designated “F2.” This grade category is often seen when wood used to construct handcrafted log homes or large structural pieces such as ridge beams, purlins and rafters is designated this grade.
Grading logs involves creating four equal sections on a butt-log to evaluate its quality, or faces, and selecting one as the grading face; thereafter the remaining three faces are assessed against standards based on clear wood percentages.
When timber is judged against grade standards, it must be free from defects that would compromise its strength-to-weight ratio, such as shakes, crookedness and protruding limbs. Certain manufacturing characteristics are permitted as long as they don’t compromise strength – these “non-merchantable” defects.
F3
F3 grade logs are the lowest standard used to create lumber and other structural components, often reserved for large diameter, aged trees with natural tapering to their shape. The United States Forest Service established this grading rule so log buyers could estimate how much lumber will be extracted from factory-class logs of different species.
Grading rules for these grades take into account several aspects of timber quality, including strength and use. Furthermore, they specify size/number/percentage defect allowances with any deductions allowed per defect.
To determine the grade, trees are evaluated on their small end or top end with at least half of its grading face being clear, according to grading rules. Defects including reaction wood, bark-encased scars, shakes and insect damage must also be free from defects on this face of their evaluation.
F4
Logs are graded for quality using visual assessment by trained graders who follow guidelines established by various standards that outline which features are acceptable in which classification grading system. These rules aim to limit knot size, number and placement; and other characteristics which reduce strength.
F field grade timber allows a higher proportion of trees’ wood to be suitable for load bearing wall frames and other dimension lumber products, including rafters, headers and sills, timber frame floor and ceiling joists, etc.
F-graded timber can also be used in load bearing applications without too much movement, providing more budget friendly alternatives than unsorted or C24 grades and providing high levels of structural performance.
F5
Timber grades take into account more than knot holes, wavy grains and manufacturing defects when it comes to timber grades; they also consider structural integrity of components like ridge beams, purlins and rafters. If stress grades of your logs do not support your home sufficiently enough for support purposes, you could potentially encounter issues with roof settlement or even collapse of this component of woodwork.
As a way of establishing the grade of any given tree, cumulative length of clear cuttings (defect-free sections) on each grading face is used as the standard for grading. Depending on its DBH, different lengths of clear cuttings may be required in order to arrive at a specific grade.
Establishing a grade hinges upon the presence and length of clear cuttings present on each grading face. For instance, to achieve F1 status on a butt-log grading face requires three clear sections at least 6 feet long – this information helps form class and DBH estimation of grades more accurately than ever.
F6
Log grading ensures the timber you use for your building project is structurally sound and contains limited defects or flaws, making it suitable for its intended purpose.
LTHC log grading system generally divides logs into “butts” or “uppers,” with butts representing the largest and best part of any single tree that yields clear wood; uppers grades represent stem portions above butt grades that may contain some flaws that don’t inhibit structural utility.
An F1 grade requires at least two clear sections of at least 5 feet in DBH size to qualify as being defect free, while for instance a 20-inch DBH tree must have two.
F7
A licensed timber grader conducts an evaluation based on visual appearance and strength classifications to help balance aesthetics with structural capacity. They evaluate pieces used for walls, ridge beams, purlins and rafters – components which carry much stress – in your log home.
Grading a tree involves comparing its diameter inside bark of its small end (known as grading face) against specific standards outlined in Table 2, such as Table 2. Defects must fall entirely within the outer 40% of this quality zone for them to be disregarded.
Grading system accommodates various degrees of defect tolerance, which ultimately determines a particular piece of lumber’s final timber grade. F-grades indicate bending strength; higher numbers indicate stronger wood. That is why LTHC always recommends high quality timber for our clients’ projects.
F8
F-grade timber grades are defined by its strength and resistance to loading. Although in-grade testing can verify its strength, individual timbers within each grade may differ significantly in strength due to natural characteristics like resin pockets or grain slope.
To accurately grade a tree, its butt-log must first be divided into four equal sections or faces, which will then be selected as the “grading face”. Once chosen, this face should contain most knots and defects so the remaining three sides may be evaluated on their clear wood properties alone.
Structural grades are assigned for every species based on its strength, and connected to stress grades through tables in visual grading standards. For instance, unseasoned river red gum belongs to Strength Group S2, and if it meets AS 2082’s requirements it will receive a stress grade according to Table H2.1.
F9
Logs used for walls, headers, ridge beams and purlins must be stress graded prior to use in order to meet code requirements. Grading checks for defects that affect strength in order to address knots, wane shakes checks as well as manufacturing characteristics of timber products.
Appearance grades do not represent stress grades but instead consist of visual grading conducted on two or four sides; G4-2 involves 2-sided visual sorting while G5 involves 4-sided grading (for instance).
Structural grading is essential, and while you might find cheaper, lower quality lumber from a mill or log home manufacturer that doesn’t adhere to this practice, it will not meet code requirements for the structure you are constructing. Be sure to demand that every log and structural wood component you buy comes stamped with visual stress grading stamps so you have an end product with the structural integrity needed for safe building practices.