Your Guide to the Most Durable Wood Species for Outdoor Use

If you want to talk about a building material that's stood the test of eons, look no further than wood. In an era dominated by metal and fossil fuel-based composites, utilizing wood is a refreshing and rewarding experience. Wood can be used outdoors for various applications from siding, fencing, decking, trim, furniture, gazebos, barns, sheds, and more. It's a versatile and renewable resource that adds character and warmth to your building or property. However, not all species of wood are created equal. Millions of years of evolution have created thousands of woody species, all with their unique properties. This article will focus on domestic wood products native to North America that exhibit a high degree of water, fungal, or insect resistance for outdoor applications.  

What Is Naturally Durable Wood?

Naturally durable wood comes from tree species with inherent properties to resist decay caused by water, fungus, molds, or insects. Wood moisture content between 20-30% is prime for fungi to colonize. Fungi prefer temperatures between 21°C and 32°C to grow. Once fungi are established, insects and termites start to move in. Certain species of trees have evolved complex and efficient chemical defense systems to increase their resilience to these threats. Species of wood that exhibit natural durability to water, fungus, molds, and insects will vary in their ability in each specific defense. 

Environmental Impacts of the Forestry Industry

Wood products are renewable resources that can be replenished indefinitely if the entire ecosystem, including the soil, plants, animals, and aquatic resources, is cared for and considered before logging. Look for Forest Stewardship Council (FSC) certified wood to ensure your wood products come from sustainably managed forests. 

The harvesting, transportation, milling, and drying of wood products is an energy-intensive process. Wood products themselves are considered carbon neutral and can delay the release of carbon that occurs when wood products decompose in the forest. But, the process to get wood products to the consumer is anything but carbon neutral. Wood is heavy and takes a lot of energy to move around, so sourcing wood products from as close to you as possible makes a sizeable impact. The United States, in particular, has some of the most stringent environmental standards in the world, much more so than developing nations, and all proposed logging must undergo a comprehensive environmental assessment. Exotic woods from developing countries likely come from poorly managed forests. In many cases, the global industry is clearcutting large swaths of virgin timber in a far from transparent supply chain that the consumer knows very little about.

Durability and Sustainable Harvesting

The main issue with naturally durable wood is many species have durable properties in the heartwood, while the younger sapwood often has less inherent durability without additional surface treatment. Heartwood is the darker wood near the tree's center, and the sapwood is the lighter wood toward the outside. Older trees tend to have greater ratios of heartwood than younger trees. However, after centuries of excessive deforestation, we must leave old-growth trees intact to maintain the forest's ecosystem and promote diversity and resiliency. Old-growth trees are often defined as being at least 120 years old, but this age varies depending on the region. Since 1600, over 90% of the old-growth, virgin forests across the United States have been logged. Canada has more old-growth remaining but continues to log some tracts of old-growth forests, particularly in British Columbia, where 54,000 hectares of old-growth forest are logged annually. Old-growth forests are relics of our past that we must protect and treasure.

What Are the Most Durable Wood Species in North America?

Species of natural durability found in the Eastern US and Canada include:

• black cherry
• black locust/honey locust
• black walnut
• cypress
• eastern red cedar
• red mulberry
• southern yellow pine, and
• white oak. 

Below, we take a look at some quick facts for each of these species.

Black Cherry (Prunus Serotine)

• Range – Eastern US and Canada
• Growth Rate: Fast growing, pioneer species
• Decay Resistance: Sapwood - Moderate. Heartwood – Very High 
• Sustainability: IUCN's red list of threatened species ranks this as a species of least concern. All around a very sustainable option.
• Notes:  Straight-grained, stable, and machines well
• Common Uses: Furniture, veneer, and trim, flooring and deck planking, cabinets.

Black Locust (R. Pseudoacacia) and Honey Locust (G. Triacanthos)

• Range: Eastern and the Central US
• Growth Rate: Fast growing pioneer species
• Decay Resistance:  Black locust sapwood - high. Black locust heartwood – very high; Honey locust sapwood – moderate. Honey Locust heartwood - moderate.
• Sustainability: IUCN lists as a species of least concern.
• Notes: These hardwoods are not widely available as sawn timber. Typically found as rounded fence posts. Honey locust is easier to machine than honey locust. 
• Notes: These hardwoods are not widely available as sawn timber. Typically found as rounded fence posts. Honey locust is more accessible to machine than honey locust.
• Common Uses: Fence and decking posts

Black Walnut (Juglans Nigra)

• Range: Eastern US 
• Decay Resistance: Sapwood - Moderate. Heartwood - Very high. Susceptible to insect attack.
• Sustainability: Not listed by IUCN
• Decay Resistance: Very high
• Notes: An expensive, premium hardwood 
• Common Uses: Furniture, cabinetry

Baldcypress (Taxodium Distichum)

• Range: Southeastern US
• Growth Rate: Moderately Fast
• Decay Resistance: Sapwood - moderate. Heartwood - high to very high
• Sustainability: IUCN lists as a species of least concern.
• Notes: Great workability and accepts finishes well
• Common Uses: Siding, furniture, trim, veneer, docks

Eastern Red Cedar (Juniperus Virginiana)

• Range: Eastern US and Canada
• Growth Rate: Medium
• Decay Resistance: Sapwood - moderate.  Heartwood – Very high  
• Sustainability: IUCN lists as a species of least concern.
• Notes: Highly aromatic – often called aromatic red cedar. Widely available
• Common Uses: Furniture, fence posts, birdhouses, trim 

Red Mulberry (Morus Rubra)

• Range: Eastern US
• Growth Rate: Fast
• Decay Resistance: Sapwood -  Moderate. Heartwood - Very high 
• Sustainability: Not listed by IUCN 
• Notes: Not commonly found as sawn timber
• Common Uses: Fence posts, furniture

Southern Yellow Pine (Pinus Palustris) 

• Range: Southeastern US
• Growth Rate: Fast
• Decay Resistance: Low.  Heartwood - Moderate
• Sustainability: Listed as vulnerable on the IUCN red list due to a population reduction of over 20% in the past three generations. This was caused by overexploitation and a decline in its natural range. The old-growth trees of this species were largely cut and replaced by plantations of loblolly and slash pine across the southeastern US.
• Notes: Due to being on the IUCN red list, this species is best avoided for now.
• Common Uses: Fence posts, decking, structural members

White Oaks –True White Oak (Quercus alba) and Bur Oak (Quercus Macrocarpa) 

• Range – Eastern and Central US and Southeastern Canada
• Growth Rate: Slow to medium 
• Decay Resistance – Sapwood – High. Heartwood – very high
• Sustainability: Not listed by IUCN. All around a very sustainable option due to higher resistance in the sapwood.
• Notes:  A heavy and strong wood type. Exhibits moderate to high shrinkage during drying but stable after drying. It can react with iron, potentially causing discoloration similar to Western Red Cedar. Moisture is not quickly absorbed by its end grain. Widely available
• Common Uses: Windows, doors, fine furniture, wood flooring, structural members

What Are the Most Durable Wood Species In Western North America?

In the western US and Canada, douglas fir, redwood, western red cedar, western larch, western juniper are highly durable.

Douglas Fir (Pseudotsuga Menziesii)

• Range: The western US and Canada
• Growth Rate: Medium
• Decay Resistance: Sapwood - Moderate. Heartwood – Moderate to high
• Sustainability: IUCN lists as a species of least concern. All around a very sustainable option if it is from second-growth logging. However, old-growth Douglas fir is still being logged in British Columbia.
• Notes: Strong mechanical properties. Standard construction lumber is often labeled as "Fir/Larch."
• Common Uses: All outdoor needs, structural lumber.

Redwood (Sequoia Sempervirens)

• Range: Northern California, Southern Oregon
• Growth Rate: Fast
• Decay Resistance:  Sapwood - Moderate to high. Heartwood – High to very high. Second growth is moderate to high.
• Sustainability: Listed as vulnerable on the IUCN red list due to a population reduction of 40% in the past three generations caused by over exploitation and a decline in its natural range.
• Notes: More expensive wood type due to historic overharvesting. This continues to be a very common wood used for exterior applications. The fast growth of the species and the fact that all of the current redwood harvested is second-growth improves its sustainability rating but it is still listed by IUCN and is best avoided if there are other wood species available. Not prone to shrinkage and warping. Exterior applications require very little maintenance beyond sealing every 3-5 years.
• Common Uses:  Furniture, decking, veneers, trim

Western Red Cedar (Thuja Plicata)

• Range – Pacific Northwest Region from California to Alaska, including British Columbia. 
• Growth Rate: Slow to medium
• Decay Resistance: Sapwood – moderate. Heartwood – very high.
• Sustainability: IUCN lists as a species of least concern. However, old-growth western red cedar is still being harvested in coastal British Columbia and Alaska. FSC-certified lumber will help ensure you are not supporting old-growth logging. Red cedar does not regenerate as fast as redwood and can live to be 1000 years old.
• Notes: A soft and lightweight wood with weaker mechanical properties than most species. If it's painted, use a stain-blocking oil primer so that the resins don't bleed through the paint. Tannins in cedar can stain fasteners, so use stainless steel, galvanized, or aluminum. Cedar tends to be a stable wood with straight grain. Western red cedar is widely available but expensive.
• Common Uses: Siding, shingles, trim, furniture, deck planking, fencing, aesthetic members.

Western Juniper (Juniperus Occidentalis)

• Range: Western US
• Growth Rate: Medium to fast
• Decay Resistance: Sapwood - High. Heartwood - Very High.
• Sustainability: IUCN lists as a species of least concern.
• Notes: Not a standard sawn lumber. Species have become widespread due to fire suppression. They are commonly cut down for fire fuel reduction treatment but not always processed for lumber.
• Common Uses: Fence posts, trim.

Western Larch (Larix Occidentalis) and Eastern Larch (Larix Laricina)

• Range: The two species have distinct ranges, but together they cover the majority of Canada and the northern US
• Growth Rate: Fast
• Decay Resistance: Sapwood – Moderate. Heartwood – Moderate to high
• Sustainability: IUCN lists as a species of least concern. All around a very sustainable option.
• Notes: Strong mechanical properties. Typical construction lumber is often labeled as "Fir/Larch."
• Common Uses: All outdoor needs, structural lumber.

What Are Some Tips For Installing Wood Outdoors?

Wood will last longer if you can limit ground contact and minimize pooling water. Wood that touches soil will degrade faster than wood that is above ground. To minimize pooling water, slightly slope the topside of the wood for water drainage – a flat surface will collect water. Any wood product outdoors will last much longer with a roof over it, so a deck with an awning will last much longer than a deck without cover. If you plan to make outdoor furniture, shelter it, if possible, and bring it inside during the winter.

Where Can You Buy Naturally Durable Wood?

Start by looking into species that are more local to you. Some species are more common than others. The best places for local lumber are neighborhood lumberyards or small private operations that selectively log their own property and mill their own boards. Because old-growth heartwood is so challenging to come by these days, you might have luck sourcing reclaimed wood from old structures being torn down. 

How Do You Maintain Wood Outdoors?

The key to making wood last a long time outdoors is to allow it to dry out. Water is most readily absorbed through fastener holes and end grains. Surface sealants can resist water absorption and range from breathable exterior paints to plant-based oils or synthetic varnishes and polyurethanes. If you use a surface treatment, make sure it's a breathable product and allows moisture to escape the wood. For any exterior wood product, surface treatments are advised and are best reapplied every couple of years or as needed based on your local environment. Drier climates tend to be friendlier to wood longevity than moist, humid climates. 

How Long Does Wood Last Outside?

Durability will vary widely by species used, your application, and your local environmental conditions. There are wooden structures that are hundreds of years old still standing and structurally sound all over the world. The key is maintenance and allowing the wood to dry out. You can expect to get 50 years out of a properly maintained piece of wood for exterior applications, which is very similar to pressure-treated lumber. Expect much less if you don't plan to maintain it.

What Are Other Options There For Outdoor Wood Use?

Thermal modification of wood is a process that superheats wood products to improve durability and can be used on any species. It is an expensive option but uses no toxic chemicals and can last up to 25 years with little maintenance and much longer if you maintain it with surface treatments.

Metallic-based pressure-treated wood and carbon-based pressure-treated wood are standard options for exterior wood. If maintained, pressure-treated lumber can last up to 50 years. Other options include shou sugi ban, a traditional Japanese technique that chars wood planks with fire and finishes with natural oils. This technique can work on species of wood like pine that aren't naturally durable by themselves.

What Are The Pros Of Choosing Naturally Durable Wood?

• Renewable Resource - Trees can be grown indefinitely if the forest ecosystem remains resilient and healthy through sustainable forest management practices. 
• Healthy and non-toxic – No added synthetic chemicals. Any finish applied is of your choosing.
• It doesn't have to end up in a landfill – Wood can be recycled or composted. Wood without synthetic chemical treatments is a biodegradable product.
• Aesthetically appealing – Take pride in your wood products. Maintain them, and show off the beauty!

What Are the Cons To Naturally Durable Wood?

• Sourcing can be trickier and pricier to source naturally durable species than non-durable species like pine and spruce. Species such as locusts, western juniper, or red mulberry are not commonly available commercially. If you have access to any species on this list, they might likely contain sapwood which is not as durable as heartwood. However, you can improve sapwood’s durability with surface treatments.
• Maintenance – Even with naturally durable species, you will want to maintain wood products to extend their lifespan. Care will involve applying surface treatments every 3-5 years to maximize the service life of the wood. Naturally durable wood species can last a considerable time with neglect. Still, long-term, you're better off keeping up with maintenance.  
• High energy footprint for transportation – Wood is heavy. Choose local options as close to you as possible. Use the species native to your regions that have evolved chemical defenses to your local environmental conditions.

If you are looking for wood products for your next outdoor project, consider non-pressure treated naturally durable wood. Wood products have a lower impact lifecycle than composites and metals, especially when sourced from FSC-certified forests. Always remember to source wood as locally as possible since domestic wood products are the most sustainable options.