The Most Durable Woods for Outdoor Use
Some Tips on Lumber Choices for Outdoor Construction
How to Source it
Read this before your next outdoor project!
Before you build anything out of wood for occasional or prolonged use outside, whether it is a fence, deck, outdoor furniture, treehouse, performance stage, outdoor bar, boat, pergola, screening, raised garden beds, landscape stairs, edging or retaining walls, it is imperative to learn some basics about the durability of different types of lumber. Not all species can handle the elements and those that can, still have different qualities and climate sensitivities that may or may not be appropriate for you project.
These days when most people take on an outdoor project, they run to their local big box store for some lovely green pressure treated lumber. Don’t get me wrong, there is certainly a place for pressure treated material but for most outdoor projects I am not a fan, and just because lumber has been pressure treated doesn’t mean it will be the most durable choice either. If you look closely at those little tags on the pressure treated material taking up most of the shelves at your local big box, much of it will say “not suitable for ground contact” or something to that effect. We will explain some of the reasons you may select pressure treated material below, but the main purpose of this article is to introduce you to some other species of lumber that can be as good if not better for your outdoor projects, with the additional benefits of added character, increased longevity and reduced exposure to toxic chemicals frequently found in pressure treated lumber.
Availability of different species of lumber is still largely a commodity dependent on your geography, demand, scarcity and regional trends and it is not something that is easily shipped if you can’t find your chosen material locally. One of the reasons there are many skilled masons coming from Mexico, is that lumber there is scarce and expensive there but rocks, sand and stone are plentiful, so locals get accustomed to building with the materials they have available to them. Big box stores throughout the United States don’t stock many of the species best suited for outdoor construction so you may not be aware that there are other options besides the treated stuff. On the West Coast of the U.S. and even parts of the midwest, some big box stores sell roughsawn Redwood, a very durable wood for outdoor construction, but Redwood is not even available for special order at these chains on the East Coast.
Let’s forget about the big box stores though for now though, as most of the species we discuss below are not going ot be available there regardless of your location. What follows is a list of lumber species available in various parts of the U.S., that have better than average outdoor durability and decay resistance and may be suitable for your next outside building project. Keep in mind there can be great differences between the durability and decay resistance between the heartwood and sapwood of these species, even on a single board from the same tree, so just because a board is of a certain species, does not mean it will withstand the elements. If someone tells anectdotally that you they’ve seen that material rot, there may be more to the story so do your research. In most species, the heartwood (the older center core of the tree) is going to be more durable than the sapwood (the outer younger layers of the tree). Sapwood eventually changes into heartwood as the tree grows and new growth rings are added each yeat. The thickness of these different layers will vary from tree to tree. In species where heartwood is durable and sapwood is not, you can even see sapwood decay after a short period of time, on say a post in the ground, but the decay may slow or almost stop altogether at the heartwood. Depending on the species, the line separating the sapwood from heartwood may or may not be easily identifiable.
The following species are native North American timbers that are suitable for certain outdoor applications where withstanding the elements and decay is important to longevity.
Cedars in general are a durable source of lumber as long as the milled lumber has a chance to breathe and dry out from time to time. In other words, cedar is a great choice for outdoor applications above ground or with very little ground contact. The material will hold up better than some woods when touching the ground, but overtime can decay with prolonged ground contact, especially in most of the material available today.
Eastern Red Cedar
The Eastern Red Cedar Juniperus virginiana, is also known as the juniper and pencil cedar. In spite of its geographic name implying “eastern”, this species can actually be found throughout the US and Canada though is more prominant in the east. The heartwood is light red or pink in color and typically has small knots. The sapwood is lighter colored and distinguishable from the heartwood. This wood is very durable and has great resistance to decay and boring insects. It is commonly used for fence boards, gardens, coffins, ship and boat building and outdoor posts.
Eastern red cedar trees are easily found in the wild as birds eat the blue juniper berries and spread the seeds in their poop. This species grows realtively quickly in the wild but finding large trees can be a challenge. This type of cedar will definitley have more knots than the western variety but the knots themselves add character and can be quite beautiful. Occasionally you can find a stand of wild eastern red cedar trees growing near a forest and as the other trees in forest mature, the cedars die off but remain standing, leaving lots of dead material that is perfect for using as durable outdoor lumber, or even posts without doing anything other than using a chainsaw to cut the poles to length.
Western Red Cedar
Western Red Cedar, Thuja plicata, is a durable wood that weathers very well but like most cedars, generally needs to breathe. The name can also refer to trees known as giant arborvitae, giant cedar, Pacific red cedar or shinglewood. The heartwood of the Western red cedar varies in color from brown to pink to dark brown but ages to a beautiful silver gray color over time with exposure to the elements. Sapwood on the Western Red Cedar is whitish colored and easy to differentiate from the heartwood. It does have a mild aromatic cedar smell but the Western Red Cedar is actually not a true cedar. The wood is quite durable but can be attacked by the common furniture beetle. Western Red Cedars are less prone to splitting than Eastern Red Cedars and frequently have far fewer knots. This lumber does not take preservatives well. It is commonly used for cedar shake roofing, fence boards, exterior cladding, siding, beehives, sheds and greenhouses. Some Native American cultures along the Pacific coast make rope from the bark of Western Red Cedars. If you’re even in Squamish or Whistler, British Columbia, Canada its well worth a visit to the Squamish Lil’wat Cultural Centre where you can learn how to make traditional cedar rope.
There are actually several types of tree commonly referred to as “white cedar”. The Port Orford Cedar (sometimes called the Lawson Cypress or Oregon Cedar) which grows along the Pacific Coast and the Southern White Cedar, also known as the Atlantic White Cedar or False Cypress.
The Port Orford species has a light colored heartwood with a straight and even grain but it is not a true cedar. It is typically used in boatbuilding, oars and paddles, construction, decks, mine timbers and even for concrete forms. It is very decay resistant and also resists acid to some extent. The heartwood and sapwood are hard to differentiate except that the heartwood does not take preservatives well, whereas the sapwood is penetrable and treatable.
The Southern White Cedar grows along the North American East Coast, and also has a light colored heartwood. This is a true cedar, giving off the common “cedar aroma” when freshly cut. The grain is also even and straight but the wood is softer and more prone to cracking than the Port Orford White Cedar. The wood is very durable outdoors and resists boring beetles and other insects better than the Port Orford Cedar.
Various types of cedar are frequently used for roofing shingles sometimes called “cedar shakes”. Traditional hand split “royal” cedar shake roofing shingles are approximately 1/4″ thick at their thickest part of the wedge, and have an expected lifespan of 20-30 years. A newer cedar shingle style is called “tapersawn”, as they are sawn instead of split, and are more uniform and thicker, closer to 7/8″ thick. Tapersawn cedar shingles have a service life expectancy of 50 years and make for a beautiful roof.
You may have seen cedar roofs or siding covered in moss, usually on the north side of a building. The moss is not necessarily an issue for the cedar but the appearance may bother some people and if it is thick enough, can prevent the cedar from breathing. One very cool trick, that will work for some other species as well, is to add a thin strip of copper, either copper sheeting or wire to the ridge of the roof. When the copper gets wet in the rain, the very slight acidity of the rain water droplet will actually react with small molecules of the copper strip, and bring these moleules with them, washing over the cedar shakes as the water drains to the gutters. This “copper wash” is actually a form of copper sulfate which forms cehmically when copper and acids react. The copper sulfate will prevent moss from growing on the cedar roof and is actually one of the chemicals use to created pressure treated lumber.
Locust (Honey) AKA Mesquite
Honey Locust, Prosopis julifora, is also known regionally by a variety of other names including Mesquite, Ironwood, Algarroba, Honeypod and Texas Ironwood. The heartwood typically has darker wavy lines running through a golden to reddish brown, fine to medium grain when freshly cut. It weathers to a nice gray color, but the weaterhing process can take longer than some other woods. Sapwood is paler and only covers a small portion of the outer layers of the tree, maybe 1″ thick. This wood is durable outdoors but not nearly as durable as Black Locust in terms of ground contact, as Honey Locust lumber is sometimes targeted by termites. Honey Locust sapwood is permeable to treatment but the heartwood is not. In some parts of the country you can find Honey Locust or Mesquite railroad ties, but the material is also used for poles, piles and farm equipment. The wood is very heavy, even when dried and moves very little in service once it is dried, though it can check when air dried.
You can sometimes find these trees growing near steambeds and the moist soil of river valleys. The Honey Locust can be distinguished from the Black Locust by long thorns growing along the trunk (both have thorns but Honey Locust are much longer) and a smoother bark that can crakle a bit and take on a look similar to Hickory as the trees age. Honey Locust trees also produce seed pods that are 12″ long, nearly twice the length you will find on Black Locusts.
Black Locust, Robinia pseudoacacia, is a very strong and durable wood but also very heavy. Black Locusts also go by the names of Yellow Locust, False Acacia, Robinier and Akazie. The heartwood can range from yellow to dark brown but usually has a distinct greenish tint to it and it is among the most durable woods for outdoor use. It is not hard to find fence posts made out of Black Locust that have been in service for over 100 years! There is a marked contrast between the heartwood and sapwood, and the spawood is not as durable. The century old fence posts usually have evidence of sapwood decaying around a solid heartwood core that is still usually quite strong. Other common applications are boat decking and planking, gates, fences, propellers, bearings & bushings, weatherboards, boxes, pallets, truck decking, farm euipment, pulleys and wooden gears.
Black Locust trees can be differentiated from Honey Locusts as they have fewer and shorter thorns along the trunk that are more spread out and less than 1″ long. Both Black and Honey Locusts have seed pods, but Black Locust pods are less than 7″ long and Honey Locust pods can be closer to 12″. Black Locust is more durable than Honey Locust for outdoor use but both can be good in the right application.
One odd thing about both locusts is that these trees tend to grow very quickly. Usually fast growing trees are not great for lumber but in this case, the lumber is quite durable, dense and heavy.
American White Oak, Quercus alba, can be a good choice for outdoor projects. The heartwood ranges in color from light tan to yellow and dark brown. The sapwood is lighter in color and easily differentiated if looking at the end of a log or plain sawn board. White oak has straight grain patterns and closed cell structure making it much more durable than Red Oak. White Oak is slow drying and can be difficult to season without twisting and cracking but the heartwood is very durable for outdoor use.
Typical outdoor uses for White Oak are outdoor furniture, boat and ship building, paneling, fencing, shingles, coffins, railroad ties, and whiskey barrels. Keep in mind that Red Oak and White Oak are very different species and Red Oak has an open cell structure that will not hold up nearly as well outdoors, especially with ground contact or anywhere it cannot breath well. Many fence suppliers will sell “oak fence boards” that are made from both White Oak and Red Oak lumber. The boards are generally all mixed together and tough to differentiate. If you want your outdoor project to last, we’d recommend using only White Oak in outdoor applications. We’ll discuss the difference between White and Red Oak in more depth in another article.
Osage Orange, Maclura pomifera, is the most durable wood found natively in North America. The heartwood has great color variation but typically has a greensih tint when freshly cut. Sapwood is lighter and will be clearly differentiated. Osage is another very tough and heavy hard wood, that is difficult to work with tools because of its toughness. Osage is an outstanding wood though for ground contact and will last literally forever, put it in the ground and you’re grandkids will never have to worry about it.
Common outdoor applications are posts, stakes, farm equipment and machinery parts, railroad ties, wheel and hubs. Osage was a preferred choice for Native American Bows. The only challenge with Osage these days is finding trees large enough for dimensional boards or beams, but smaller and shorter logs are not hard to come by.
Cypress, Taxodium distichum, is a beautiful wood from trees growing in the swamps of the southern Unisted States. Common names of trees used for cypress material are red cypress, yellow cypress, southern cypress, gulf cypress, bald cypresss and swamp cypress. These needle bearing trees loose there all of there needles each year and can appear dead in the winter but emerge each spring with beautiful evergreen like foliage. They grow in lowlying wet areas, in swamps and and near streams and have neat looking offshoot knuckles that can grow into new trees.
Cypress trees produce an oil in the heartwood that makes it very durable to moist conditions. It can be tough these days to find boards with the desired heartwood, and much of the production lumber grows quickly. For this reason, ground contact durability on the material is variable. It can be very good but it may also decay faster than desired. Cypress does however tend to hold up very well in above ground applications. Freshly cut Cypress logs will have a high moisture content and may take longer than average to season. Once the material is dry it has very good dimensional stability. These naturally occuring oils make the wood somewhat resistant to preservative treatment. Cypress lumber is variable hardness, strength and stiffness but is a joy to work with tools.
American Chestnut, Castanea dentata, was once one of the most important lumbers in North America and the tree comprised large percentages of forest tree populations along the East Coast roughly along the Appalacian Mountain corridor. However by the middle of the 20th century, this species had been wiped out nearly to extinction by a fungal disease discovered in 1904. There are a few remanant populations where the disease did not strike for whatever reason and there has been recent success in producing disease resistant varieties of the American Chestnut. It is unlikely you will find an American Chesnut still standing today but if you do, please do what you can to protect it and consider sharing the location with the American Chesnut Society for study.
Chesnut lumber was widely used and is a beautiful wood for all sorts of applications and it is an excellent material to reclaim, resaw and remill from old beams. Due to the price premium it may not be the best choice for outdoor applications but the wood does have good durability and a high resistance to decay. It does not take preservative well thought and the heartwood will be more durable than the sapwood. The heartwood will be brown with gray tones and the blight is pronounced by worm holes in much of the material which itself can be attractive. Ferrous metals will cause the wood to stain but can add character. If using reclaimed chestnut, the worm holes and bluing effect from nail holes is even desireable by some.
Redwood, Sequoia sempervirens, also known by the names California Redwood, Coast or Coastal Redwood, grows to throughout California and Oregon and can live to be over 800 years old! These beautiful trees are the centerpieces of conservation efforts and parks including Giant Sequoia National Park, Redwood National Park, Kings Canyon National Park, Muir Woods and others. The trees are beautiful and the size of mature trees is truly astonishing, don’t miss any opportunity to enjoy a forest of these trees.
The heartwood ranges in color from light red to dark brown. The sapwood is easily distinguished as it is pale yellow to nearly white. The strength properties of this material are varible and the wood is very wet when freshly cut but dries quickly and with minimal defects. It moves very little in service but joinery is commonly used as it does not hold screws and nails as well as most wood. Redwood is a very durable wood that is resistant to insects and fungi and the heartwood is durable in moist environments. It also take preservative treatment so large redwood timbers can make for beautiful outdoor construction. Look for naturally fallen or otherwise sustainably harvested timbers to reduce demand for the giant specimen trees. Remember you’re voting with every dollar you spend.
There are several types of Hemlock commonly used for lumber and there are notable differences in the outdoor durability between different species of Hemlock. The variation in durability becomes problematic in exposed outdoor condition as most lumber yards don’t differentiate between the different species. In fact, hemlock and fir are commonly used as framing material and in dry applications they have similar structural properties and strenght ratings so they are simply milled and graded together and labeled as hem-fir. Inside of a protected wall this is not an issue but the durability for outdoor applications becomes problematic. So we recommend avoiding the use of the hemlock you may find in your local lumber yard unless you can be sure it is of a variety suitable for outdoor use.
Western Hemlock, Tsuga heterophylla, for example, also goes by the names of Pacific Hemlock, Alaska Pine, Hemlock Spruce, BC Hemlock and West Coast Hemlock, has very little resistance to insect attack, and is generally not considered to be durable for outdoor applications, especially for ground contact.
Other Resources for Outdoor Building:
Pete Nelson from Treehouse Master’s has some beatiful books on his craft and well worth checking out. In particular we like his 2014 book called Be in a Treehouse – Design / Construction / Innovation.