Use pressure treated wood in any situation where there's direct contact between the wood and anything that could supply moisture. This means posts in contact or buried underground obviously, but it also includes any lumber touching concrete or masonry since it's porous and wicks water like a sponge.
In general, pressure-treated lumber is recommended in situations where there is direct contact between the wood and anything that could supply moisture: Retaining walls, which function to support landscaping projects and hold back soil. Any posts or beams that come in contact with the ground or are buried underground.
Most typically when using untreated woods outdoors you are going to run into several potential issues. Untreated wood becoming wet can be the first problem. This is going to cause the wood to decay, rot, and grow fungus over time. Wet conditions make for a nice breeding ground on untreated wood being used outdoors.
While treated wood has distinct advantages, you might decide that they aren't worth the added health risk. Yet, if you need something to last a long time and you know people won't come into much contact with it, treated lumber might be the better choice.
Pressure-treated wood should be used for all outdoor projects, assuming you're using a type of wood that is not naturally repellant to insects and rot. That said, not all pressure treatments are created equal. The two main types of PT lumber are above-ground and ground-contact.
Generally, you can use non-pressure-treated wood outside for about 2-5 years if it is not maintained or protected from high humidity, heavy rain, or prolonged exposure to sunlight. Also, untreated wood outdoors will not last as long as pressure-treated wood.
If you want to add color to untreated wood, a fresh layer of paint does the trick. However, untreated wood requires some special attention before painting. If you don't properly prepare the wood, moisture damage could destroy the wood, or natural tannins may bleed through the paint.
Naturally Resistant
To deter the pests, homeowners can obtain heartwood-grade lumber for construction projects. Termites also tend to avoid specific species of trees such as redwoods, yellow cedar, Laotian teak, and cypress. However, these types of wood are not as long-lasting as treated lumber.
If you're looking for a durable, long-lasting material that's resistant to rot and decay, cedar is a good choice. Cedar is more expensive than pressure-treated wood. Cedar has a more natural look that many people find appealing.
Pressure treatment is a process that forces wood preservatives or fire-retardants into the wood. These processes are considered the best and most effective method to extend and preserve timber life. Preservatives protect the wood from attack by wood ingesting insects; like termites, and wood rot caused by fungal decay.
Pressure treatment helps protect wood from rot and insects with the help of high pressure and preservatives, helping to extend its life. Generally, pressure-treated wood can last anywhere from 10 to 40 years, depending on a few factors.
In certain conditions, even pressure-treated wood can rot and decay. Moisture and pooling water on decks can lead to rot and decay. Because dry rot is a fungus, it can spread like a cancer throughout a deck.
Pentachlorophenol-treated posts exhibited durability in excess of 60 years, whereas lumber specimens treated to standard ground-contact retentions had no failures after 39 or 45 years.
Ground-contact lumber is, as the name suggests, suitable for contact with the ground. It's commonly used for pressure-treated posts and some framing. Containing a greater amount of chemical treatment, these wood products can last much longer than aboveground lumber, and up to 40 years, in some cases.
When it comes to comparing treated wood vs. cedar, pressure-treated wood is the sturdier and more weather-proof of the two. It's highly resistant to insect attack and rot, and special versions rated for “ground contact” can be buried in soil and will continue to shrug off decay for decades.
These may not give you specific information about their safety, but some countries are known to produce safer pallets than others. Newer British, Canadian and American pallets, for example, are largely safe as most are heat- or pressure-treated rather than being fumigated with chemicals.
It typically costs less than cedar or redwood, and it is a totally natural, untreated wood. On top of all that, it also happens to be gorgeous. Juniper is commonly used for raised garden beds, retaining walls, outdoor steps, fences, decks, and many other exterior applications.
Once treated, green and brown timber are usually labelled with a UC3 or UC4 rating. The latter is a more harsh treatment than the former and is for use on wood that is in permanent contact with the ground (such as fence posts). The former is for wood that is not in contact with the ground such as fence panels.
Pressure-treated wood may be protected for a while, but if it stays damp enough for long enough and starts to rot, termites can feed on it.
Recycled Plastic Lumber and Plastic/Wood Composite Lumber
The plastics are rot- and corrosion-proof and don't crack, splinter, or chip. Even in exposed and sub-grade conditions, plastic lumber has a long life expectancy. It will not leach chemicals into the ground, surface water or soil as treated wood can.
Which Wood Lasts the Longest? Teak wood easily lasts the longest when used for outdoor furniture or decking. When properly maintained, it can last for the entirety of your life and years after.
Characteristics of Redwood and Cedar
When you're looking for the best wood for outdoor use, both of these types of wood are naturally resistant to rot and decay, along with being termite and insect-resistant. Redwood and cedar are also known to: Resist warping and twisting.
The difference between the two is that pressure treated lumber will resist the elements better than untreated due to chemical preservatives added, and so will maintain its integrity in conditions that would cause normal wood to rot.
A combination of untreated wood that is exposed, with warm temperatures, and constant moisture will inevitably cause wood rot to occur. If you have wood siding, painting it with quality exterior paint every 3-6 years should extend the life of your siding from any rot.