Pressure Treated Lumber

Pressure treated lumber is a major part of building materials used in the construction industry today. Globally, it is a $6 billion per year market. It is valued for its ability to resist decay, insects and moisture, which makes it suitable for decks, fences, marine and ground contact structures and any outdoor place that needs protection from these elements. Its popularity is always growing in the US and around the world. But PT lumber as we know it today is a relatively new product evolving over the last two centuries and available for residential construction for only half a century.

Early History of Wood Preservation

The practice of treating lumber in order to protect it from moisture and insect exposure and extend its longevity goes back to Ancient Greek and Roman days. There are records of wood preservation going back to Alexander the Great’s time where bridge timber was soaked in olive oil. The Romans protected their ship hulls by brushing the wood with tar.

Industrial Revolution and the Birth of Pressure Treatment

In modern times, the Industrial Revolution brought about a need for inventing more advanced developments in wood preservation involving pressure treatment and the use of specialized chemicals for preservation. Telegraph poles and railroad ties were the items most widely used which were in need of protection from constant exposure to the elements including water, insect and fungus damage.

Starting in the 1830s, as endless miles of telegraph wires and railroad tracks were laid out across the US and Europe, it was quickly realized that the maintenance effort of replacing rotten utility poles and railroad cross ties was a major problem that had to be addressed. Inventors and scientists made great breakthroughs in developing chemicals and processes for wood preservation including pressure treatment. Chemicals like creosote, an oily liquid derived from the distillation of coal tar, were used to saturate the timbers, but the process of pressure treatment was a major development in the second half of the 19th century which helped to deeply embed the chemicals into the wood fibers for a much extended longevity.

How Pressure Treated Lumber Is Made

Pressure treatment involved the manufacturing of long metal cylinders, approximately seven feet wide by as much as a hundred and fifty feet long which can be tightly sealed to withstand great pressure. The railroad timbers or utility poles were placed inside and the air tight door tightly shut. Then a strong vacuum process was applied in order to suck out as much natural moisture as possible from deep within the cells of the wood fibers. The massive metallic cylinders were then flooded with creosote and other chemicals which were soaked up by the super dry wood timbers. Then the air pressure was pumped up to several times that of the atmosphere further driving the chemicals deep into the cells of the wood and kept at that state for many hours or even days. The pressure was then released, the chemicals drained and the wood taken out, deeply saturated with the creosote water proofing, and the other insect and fungi repelling chemicals.

This is how pressure treated wood is still manufactured today although some chemicals have been replaced due to their toxicity. For the next hundred years pressure treated wood was almost exclusively used for industrial applications including the aforementioned utility poles, railroad ties but also bridge timbers, pier timbers, docks, farm fences etc. It wasn’t until the 1970’s that PT lumber started being used residentially.

Pressure Treated Lumber Enters Residential Construction

Before the 1970’s there were relatively few decks as we know them today. Those decks were primarily built with redwood lumber which was widely used in the construction industry at that time. Cedar was another popular species used for its natural water repellant properties since antiquity. Wood siding was also largely made using redwood and cedar. But environmental concerns rising in the 1960’s and 1970’s about the extinction of redwood forests helped bring about the residential use of pressure treated lumber in the 1970s. The lower cost of abundant PT lumber brought about a great increase in its use and backyard decks soon became a big fad across the country changing our lifestyle significantly.

Today we all enjoy outdoor living and hosting barbecues on our decks accessed directly from our back doors, essentially increasing our living space substantially.

Environmental and Health Considerations

As decks were becoming ubiquitous and as the national consciousness of protecting the environment and saving the planet grew, it was inevitable that concerns about the toxicity of the chemicals used in PT lumber would become of greater concern. PT lumber used to be treated with chromated copper arsenate (CCA) with the known poison arsenic as an active ingredient, presumably to keep termites and other insects away. The Environmental Protection Agency (EPA) was naturally not too happy about that. In 2003 the toxic chemical CCA was replaced with less toxic chemicals like copper azole (CA). As copper replaced arsenic as the main active ingredient the price of PT lumber also went up significantly.

It is never a good idea to eat building materials whether it’s PT lumber, lead paint or asbestos shingles, but still we can be grateful that the EPA continues to protect us from all these toxic substances.

Evolution of Deck Construction and Materials

The structure of decking materials has also evolved over the decades. Early decks were constructed with 4×4 posts and 2×4 decking boards. The posts were usually notched to structurally bear the weight of the 2×10 band board joists and often went directly into the ground where holes were dug and filled with concrete.

Over time, innovations in material and building practices and codes changed the look of decks to what we have today. The decking boards soon became thinner and wider, from 2x4s to 5/4×6 boards which is essentially slightly thicker than one inch and 5-1/2” wide.

The 4×4 posts became more substantial 6×6 posts bearing on galvanized metal base plates anchored in a concrete footing that extends slightly above ground in order to keep post bottoms dry and out off the dirt. Modern decks usually don’t structurally rely on perimeter posts for support but have a double 2×12 beam under the deck from one end to the other with multiple posts for structural support.

At first, decking boards were manually nailed with 16 penny galvanized framing or box nails. This process was succeeded by pneumatic nail guns which came into the scene in the 1980’s. Finally, decking screws with Torx heads became the preferred method. Today many decks use concealed fasteners which usually involve the decking boards being plowed along the edges to accept these fasteners.

This fastening method is almost standard with engineered modern decking boards like Trex, which like PVC trim, Hardy board siding and other engineered building materials have steadily been transforming the construction landscape over the past few decades.

Modern Decking Choices

Today, a growing number of decks use composite lumber like Trex, while more high end decks use epee and other exotic woods, all with concealed fasteners. The posts and railing systems are also some form of PVC products for low maintenance as decks are constantly subjected to the weather and maintenance is a valid concern. PT decks need to be topcoated with preservative sealers every so many years.

Nevertheless, PT decks continue to be a top choice due to their relative low cost and ease of installation. Wood is also a more environmentally friendly product than plastics and composite products. Decks in general, show no decline in popularity and are one of the most cost effective ways to increase your living space and make a major impact on the quality of life at your home.

Outdoor living is best experienced on a deck as a flat, unobstructed area makes it comfortable to walk around. It is the best place to set up a barbecue grill for a summer cookout with family and friends. Easy access to the kitchen and home interior makes a deck a natural extension of your home. A deck is also a great place for kids and pets to play on while still being seen and supervised from inside the house. And it’s a great place to just sit back and relax while enjoying the sunshine, perhaps a glass of wine or even that occasional cigar you can’t smoke inside the house.

Ready to Build a Better Outdoor Space?

Choosing the right materials is one of the most important decisions in any outdoor project. Understanding how pressure treated lumber has evolved—and how it performs alongside modern alternatives—allows you to make informed, confident choices for your home.

If you’re considering a new deck or an outdoor renovation, the team at FineCraft Contractors is here to guide you through material selection, design, permitting, and construction with clarity and craftsmanship at every step.

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