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Types of Pressure-Treated Lumber

Types of Pressure-Treated Lumber

Treated wood is available in a wide range of sizes and shapes. Pressure-treated for outdoor usage is the most common variety that a homeowner will see. Pressure-treated lumber, used for projects like wooden decks and fences, helps keep your outdoor structures looking beautiful for years by avoiding termites, rot, and fungal decay. Few people are aware of pressure-treated wood's advantages and why it should be utilized.

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Even though the substance is the same, pressure-treated lumber varies from typical wood products in various ways. Treated lumber is a product in and of itself, from its manufacture through its intended and proper application.

Continue reading to learn more about this popular but distinct building material and how to use it in your projects.

What is Pressure-treated lumber?

Pressure-treated lumber (PT) is wood that has been impregnated with chemicals and preservatives to protect it from decay and insects. The wood is maintained using an air-replacement preservative in a depressurized storage tank.

This approach is the most successful in avoiding rot and insects, but it does not protect against weathering or rust.

How is Pressure-treated lumber produced? 

First, the untreated timber is subsequently put in a massive horizontal treatment cylinder. The door is shut, and a vacuum is used to remove most of the air in the cylinder and the wood cells. When a preservative solution is poured into the cylinder and forced into the empty wood cells, pressure is created, resulting in pressure-treated wood.

Types of Pressure Treated Lumber

Pressure-treated Lumber comes in four different varieties. A tag will be attached to one end of each piece of pressure-treated timber to identify its allowed usage.

The four types of Pressure-treated lumber are as follows:

  1. Above Ground

Above-ground pressure-treated wood can be utilized in readily maintained or replaced applications. It's only allowed to be used on surfaces that are at least 6 inches above the ground. It can only be used once it has been completely aired and drained.

Above-ground wood is for project elements that satisfy all of the following requirements:

  1. isn't on or near the ground

  2. dries quickly between wet periods, and

  3.  isn't in a tropical environment

  1. Ground Contact 

Pressure-treated wood that has been in direct contact with the soil can be utilized above ground or in direct contact with the ground.

When compared to above-ground treated wood, it delivers double the chemical retention and protection.

It must be utilized if the lumber is less than 6 inches from the ground or has restricted ventilation.

It must be utilized in situations where wood replacement or preservation is difficult.

  1. In-Ground contact

Pressure-treated wood used for in-ground or critical applications has a greater retention level than timber used above-ground or in contact with the earth. Where there is a higher risk of deterioration or excessive environmental exposure, use in-ground type wood for critical structural components such as foundation posts, exposure to fresh or groundwater, or utility poles.

  1. Marine Grade

Because of the high heat and pressure lamination and waterproof glue, marine-grade plywood is more resistant to moisture. Any gaps between the layers are filled with glue to keep the layers from twisting and deteriorating. This item is also made of hardwood, making it considerably more durable.

A waterproof sealant can extend the life of a plywood pier, boat, or another submerged item. 

Additional Read:


Grades of Pressure Treated Lumber

Pressure-treated lumber comes in five grades: Premium, Select, Number 1, 2, and 3, and Number 1, 2, and 3. The fewer knots, fissures, and other faults there are, the lower the grade.

  1. Premium

Exterior Wood designed a "Premium" type of pressure-treated lumber for customers that want more. It's better for a retail lumber yard with many walk-in customers searching for a more attractive product.

  1. Select Structure

The most durable and long-lasting material is Select Structural (SS). The grain slope on a 28 is 1 in 12 with seasoning checks and 2-1/4" tight, well-spaced knots. A knothole every 4' is allowed in select grade wood, and splits cannot be longer than the board's width.

  1. Grade 1 structural

Lumber has a structural rating of 1 or 1, and the BTR is 1 in 10. It is more durable than 2 or 3-grade wood. Knots in a 28 must be spaced and tight, with no more than 2-3/4" between them, to avoid falling out. Each plank is permitted one hole every three feet, and any splits must be no wider than the plank's width.

  1. Grade 2 structural

Number 2 grade timber contains more knots and imperfections than #1 grade, even if one face is clean enough to be classified as select or premium. The wood grain may have a peeling edge or wane, with 1 in 8 slopes.

Splits up to 1.5 times the board's width are allowed, as are 3-1/2" knots and one hole every 2'. Framing, lintels, rafters, trusses, joists, beams, and fences are used frequently for second-grade wood.

  1. Grade 3 structural

More checks, cracks, wane, well-spaced larger knots and holes, and a grain slope of 1 in 4 are found in grade 3 or construction grade timber. The wood is often used for bracing, packaging, shipping, and light building or framing where it will not be visible. An SPF 3 28 can be utilized to span structural lengths of 12'-4".

  1. Construction grade 

1-grade lumber is generally referred to as construction grade. From load-bearing to trim, it's employed in all aspects of home building. Although both have almost the same structure and functionalities, still many of the applications wander around the construction grade. It is more stable than the other grade lumbers.

  1. Standard grade

The wood of the second structural grade contains more faults and knots than the first. Joists, trusses, and other load-bearing structures are typical applications. The wood is 43 percent translucent in terms of visual 'quality.'

  1. Utility grade

One of three categories of wood, the utility grade, has fewer limitations on knots and flaws than the other grades. Because it is not as strong as the other classes, it is frequently used for light frame applications such as bracing, crates, and pallets. It must be defect-free in 29 percent of its appearance.

  1. Appearance grade

Some mills and merchants employ premium and select categories, as well as the amount of clear wood. The aesthetic value has no bearing on the structural quality; it makes things seem better. It's only meaningful if the wood's appearance is visible, such as on deck boards, railings, or other exposed structural sections.


A chemical solution has been applied to preserve pressure-treated wood from insects, mold, mildew, and rotting. Diverse types of treatment and wood grades are available for various uses. Pressure-treated timber is a product in itself from its production. Few people are aware of the benefits of pressure-treated wood and why it should be used. The material is the same but differs from traditional wood products in several ways. Hopefully, this article helped you make a better choice.

Visit Florida Lumber for more information. 

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