Natural wood adds character and warmth to your outdoor spaces, from benches and bridges to garden beds and gazebos. Unfortunately, some fungi and insects love wood as much as you do.
It’s important to choose a durable, weather-resistant wood for exterior use. Some lumber is treated with chemicals to protect the wood and prevent or delay rotting, and some are just naturally more resistant to rot. Here are 10 woods that stand up best to rot.
No wood is entirely rot-proof, but there is a good number of species that have superior rot resistance and can be used outdoors without chemical treatment. Others are moderately resistant and may require regular or semi-regular treatment to extend their strength against rot.
How Does Wood Get Rotted in the First Place?
Wood lovers must know thine enemy: Fungus. Yes, insects can do some damage, too, but insects are only attracted to wood that is wet and already rotting. Usually, the fungi move in first, then the termites and other wood-destroying insects come along.
The fungi that destroy wood are decay fungus, or wood-decay fungus. They are basically plants that don’t contain chlorophyll. They can’t produce their own food by photosynthesis so, in order to live, they must take their food from other materials. In this case, their food is wood. Decay fungi settle into the wood and their eating habits destroy the wood’s substance and reduce its strength.
Decay fungi, like most other organisms, require four basic conditions to survive.
The 4 Conditions That Rot Needs to Occur
|Moisture||A moisture content within the wood of 20-30% They can’t survive much outside of that range.||Wood is porous and can really soak up water. The fungi need some water to survive, but if the wood has soaked up too much water, the fungi can’t breathe. It needs to be able to access oxygen to live.|
|Oxygen||Air needs to contain at least 20% oxygen||Fungi is a living thing and requires oxygen to grow.|
|Warmth||70°F and 90°F||Fungi like it moderate. Most decay fungi will die at temps above 130°F and will become dormant at temperatures below 40°F.|
|Food||In this case, wood||Wood serves double duty for fungi, being both a food source and a place to live and be insulated from extreme temperatures.|
For comprehensive information about wood rot, check out the website of the International Association of Certified Home Inspectors (NACHI).
Some woods are no match for the life-crushing decay fungi. Some soft woods are naturally absorbent, which makes them more prone to be a welcoming home for fungi.
Non-resistant woods include:
While some of these woods are harder than others, none of them are a good choice, especially in their natural state, for outdoor furniture or projects that are kept in a humid or damp environment. Beech, for instance, is very unsuitable for outdoor use. It reacts severely to humidity changes and gets nasty black mildew very easily. No amount of coating or oil can make it as durable or resistant to rot as any of the resistant woods.
Fortunately, there are options for woods that hold up much better to the threat of fungus and rot.
Why Some Woods are More Resistant
Why do some woods last well on your porch, while others seem to rot after one season? It has to do with the composition of the tree.
- Amount of sapwood: the wood closest to a tree’s bark is a called its sapwood. On a cross-section of a tree, it’s that light-colored layer, right before the bark. Sapwood generally does not have much decay-resistance, no matter what type of tree it’s part of. So, if a piece of lumber has a lot of sapwood, it’s going to have low resistance to decay. And it won’t last long out there.
- Amount of extractives: Extractives in wood are what give it its color, scent, and other physical and mechanical properties. They are the waxes, fatty acids, resin acids, and terpenes of a tree. Typically, if a tree grows slowly, it has more extractives and higher decay resistance. So older-growth trees tend to have more natural protection against rot.
Fortunately, you don’t have to be a tree specialist to know which woods to use for the most durability against wood rot. At your local lumber mill or hardware store, it’s likely that an employee familiar with woodworking will be able to point you in the right direction.
Before you head out to shop for rot-resistant lumber, it’s good to have an idea of what kind of wood you want. After all, each wood will have different properties aside from resistance and durability, like color, texture, grain, how easy it is to work with, its availability and, of course, its cost.
The World’s Most Rot-resistant Woods
Not all naturally resilient woods are widely available. For instance, some tropical woods are very decay resistant. The warmer temperatures and higher moisture levels in the tropics have primed them to withstand decay. These more exotic woods are more expensive and not as easy to pick up at your local store as their more common domestic counterparts.
In order of most-to-least, these are the woods that are resistant to decay and rot damage, along with information about the ease or difficulty of working with it and other physical characteristics of the wood which may make it desirable for particular projects.
Extremely Rot-Resistant Wood
Its extreme density and hardness make mahogany stand up very well to water and insects. It is one of the most resistant woods to rot and known for its superior strength, stability, and durability.
Appearance: Mahogany has a fine, visible, sometimes spiral grain. Colors can range from gray to brown to red to orange, or a blend of all four. The bulk of the Mahogany timber that is commonly used in the United States comes from three different countries, Mexico, Honduras and the Philippines.
Working with Mahogany: As one of the most workable woods, it is relatively easy to cut, sand, route and stain. It is beautiful when finished natural. Due to its workability, ability to withstand wear and water, and as its rich, natural colors, it is an expensive option.
Uses: Popular uses include furniture, floors and doors, as well as luxury items like yachts, boats, musical instruments and writing pens.
|Spanish Cedar |
Very dense and decay resistant, Spanish Cedar stands up well to weathering, is very durable and costs less than mahogany. It is mainly grown in Ghana and Ivory Coast.
Appearance: It has uniform, light pink to reddish-brown colors that tend to darken with age. Grain patterning can be somewhat bland.
Working with Spanish Cedar: It is easy to work with both hand and machine tools. Slightly softer, and less durable than mahogany, it can leave fuzzy surfaces and may require extra sanding to obtain a smooth wood surface.
Uses: Because of its ability to withstand weather, it is often used for windows and exterior trim. It is also commonly used for cigar boxes and humidors, as well as the lining of closets and chests.
Teak has been referred to as the gold standard for decay resistance. It is also very durable and resistant to termites. Prized for its appearance and durability and is quite expensive. Widely grown on plantations in tropical regions of Africa, Asia, and Latin America.
Appearance: Usually a golden or medium brown, with color darkening with age. The grain is straight, though it can occasionally be wavy.
Working with teak: Very easy to work with and finished well. Teak contains a high level of silica which can cause cutting edges to blunt over time
Uses: Furniture, exterior construction, carving, small wood carvings and wooden objects, boatbuilding.
|Moderately Rot-resistant Wood|
Cypress is moderately durable for decay resistance. It is grown in the U.S. and tends to be very affordable.
Appearance: Color is usually a light, yellowish-brown. Sapwood is nearly white. Straight grain and medium texture to coarse texture.
Working with cypress: It has great workability and accepts stain and paint very well.
Uses: Commonly used for interior trim, veneer, exterior construction, small wood objects, some furniture, docks and boatbuilding.
Old-Growth Cypress – The old-growth version of this resistant wood has so much more heartwood, causing it to be harder and have much greater resistance to rot and insects.
Redwood is rated as moderately durable to very durable regarding decay resistance. It is somewhat expensive and is grown along the coastal northwestern U.S.
Appearance: Heartwood color can range from a light pinkish brown to a deep reddish brown, with pale yellow sapwood. Grain is generally straight, though figured pieces may be wavy or burled.
Working with redwood: It is typically easy to work with hand tools or machinery. Curly, wavy, or irregular grain can be a challenge. Finishes well.
Uses: Redwood is favored for construction lumber, beams, posts, decking, exterior furniture, veneers and trim. Small, burled pieces are used for specialty pieces, turning and musical instruments.
Old-Growth Redwood – Once again, the old-growth version of this wood is very resistant to rot and insects.
|Cedar (Western Red)|
This variety of cedar grows in the Pacific Northwest of the U.S. and in Canada. It has been rated as durable to very durable for decay resistance and mixed resistance to insect attack. Other varieties of cedar are similar. Check wood-database.com for specifics.
Appearance: Reddish to pinkish brown, often with random streaks and bands of darker areas. Narrow sapwood is pale yellowish white. It has a straight grain and medium to coarse texture.
Working with cedar: Easy to work with both hand and machine tools. Because of its relative softness, it dents and scratches very easily and can sand unevenly. If you plan to paint, make sure you use a stain blocking oil primer because the resins in cedar will easily bleed through paint.
Uses: Cedar is a great wood for exterior work, such as shingles, exterior siding and lumber and boatbuilding. It is also popular for boxes, crates, and musical instruments.
White Oak is a very hard, wood that is readily available and grown in the U.S. It is rated as very durable and resistant.
Appearance: Light to medium brown in color, commonly with an olive cast. Often displays prominent ray fleck patterns when sawn. Grain is straight, with a coarse and uneven texture.
Working with white oak: Easy to work with hand and machine tools. Has moderately high shrinkage values and can react with iron, sometimes causing staining and discoloration.
Uses: Windows, doors, fine furniture and wood flooring and in boatbuilding.
This wood is grown in Eastern North America and is rated as being very durable and resistant to decay. It is a moderately expensive wood.
Appearance: When freshly cut, it is pinkish brown and darkens to a medium reddish brown with time and exposure to light. The grain is usually straight and easy to work—with an occasional curly grain pattern. It has a fine, even texture.
Working with black cherry: Cherry is known as being one of the best all-around woods for workability. It is stable, straight-grained, and machines well. When being stained, as it can sometimes give blotchy results—using a sanding sealer prior to staining or using a gel-based stain is recommended.
Uses: Cabinetry, fine furniture, flooring, interior millwork, veneer, turned objects and small specialty wood items.
Grown in the Eastern U.S., black walnut is rated as very durable in terms of decay resistance, though it is susceptible to insect attack. Very popular and considered a premium domestic hardwood in the U.S. An expensive wood.
Appearance: Color is a light pale brown to a dark chocolate brown with darker brown streaks. It can sometimes have a grey, purple, or reddish cast. Grain is usually straight, but figured grain patterns such as curl, crotch, and burl are also seen.
Working with black walnut: Typically, easy to work, unless grain is very curled or patterned. It stains, bends and finishes well, but rarely needs staining.
Uses: Extremely versatile and popular for a variety of projects: furniture, cabinetry, gunstocks, interior paneling, veneer, turned items, and other small wooden objects and novelties.
How to Stop or Prevent Rot
Even rot-resistant woods can become vulnerable over time or with extreme conditions. So, how do you stop wood rot in those cases?
If you’re using a wood outside, starting with a rot-resistant wood is the most important step. From there:
- Limit ground contact. When a wood is in direct contact with the ground, it opens the wood to mold and fungus because it allows moisture to penetrate the wood.
- Pitch the wood so that water does not collect on the surface.
- Remove plants and vines that grow over the wood. They accelerate rot due to moisture.
- Use chemical wood preservatives to deprive fungi of its food source and make wood inedible to decay fungi.
- Keep it painted or stained to help keep out water.
- Remove any standing water.
The more you can keep wood dry, the better you limit the chance of fungus getting a hold on your exterior wood and outdoor furniture. Preventing rot is much easier than stopping it once it gets going.
Pressure-treated lumber is wood that has undergone a process that forces a chemical preservative deep into the wood. The “pressure” part is when the wood product is placed into a large holding tank which is depressurized to remove all air.
A preservative is added to the tank, under high pressure which forces it deep into the wood. The tank is then drained and the remaining preservative reused. The wood is removed from the tank and prepared for shipment to your local lumberyard.
This chemical makes the treated lumber resistant to fungus and insects, which makes the wood more durable. It can then be purchased as lumber, boards, posts and plywood.
A Wood for All Seasons
Pressure-treated lumber makes a great building material for the outdoors all year long. If you’re building or buying a deck, mailbox, swing-set, picnic table or any other exterior wood project or product, you can count on long life from a piece made from pressure-treated lumber.
Is Chemically-treated Wood Safe?
The words “chemically-treated” may make you wonder if this wood is safe for pets, children, for garden use, for interiors and more.
The EPA is currently reevaluating the type of pesticides pumped into pressure-treated woods. These chemicals are chromated arsenicals, which includes chromated copper arsenate (CCA), a type of arsenic – and a carcinogenic. Many uses of CCA have already been limited by the EPA.
Pressure-treated wood is now treated with Alkaline Copper (AC) and Quaternary Ammonium Compounds (ACQ). These compounds are much less toxic and have shown to not leach into soils the way CCA and Creosote have. This does not eliminate health risks, but significantly minimizes them.
General Safety Tips for Chemically-treated Wood
- Wash children’s hands after they have been in contact with treated wood
- Do not put food directly on a treated wood surface, like a picnic table.
- Do not use treated wood where it may come into contact with edibles, such as in a garden
- Never burn treated wood – indoors or outdoors. Burning this type of wood releases chemicals in the ash and smoke.
- Do not use treated wood near livestock, feed, or food-producing animals.
- Do not use treated wood where it may come into contact with drinking water.
- Do not place treated wood or sawdust in a compost bin, and do not use it as mulch.
- Do not use bleaching or cleaning agents such as sodium hypochlorite, sodium hydroxide, sodium percarbonate, citric acid or oxalic acid on treated wood. These can cause the wood to release chemicals that may be inhaled or come in contact with skin.
To learn more about CCA, visit the EPA website.