Oak is one of the most popular woods used in furniture, flooring, cabinetry, and many other applications. Its attractive grain patterns and natural durability make it a go-to choice for indoor and outdoor projects. But not all oak is created equal when using oak in outdoor environments exposed to the elements. So how suitable is oak for outdoor use?
The type of oak, its inherent properties, proper finishing and maintenance all play a role in determining how well oak will resist weathering, rotting, and decay when used outside. By understanding the characteristics of different oak species, their relative durability, and using the right protective treatments, oak can be a sensible option for your next outdoor furniture or landscaping project.
Types of Oak for Outdoor Use
Two main oak categories are commonly used in woodworking – white oak and red oak. Within each group, numerous species and sub-species have their distinct traits. However, some general differences between white and red oak are important when choosing wood for outdoor applications.
White oak derives its name from the light color of the wood. But more importantly, white oak exhibits certain properties that make it the preferred choice for outdoor use.
Some of the most common species of white oak include:
- White Oak – The classic white oak species found throughout North America. It has a straight grain and medium texture.
- Bur Oak – Similar to white oak but with a coarser grain. Often found in the Midwest.
- Chestnut Oak – Named for its resemblance to chestnut but maintains the white oak properties.
- Swamp Chestnut Oak – A moisture-loving white oak variety.
- Live Oak – A sturdy evergreen oak native to the southeastern states.
White oak has a closed pore structure thanks to cellular structures called tyloses. Tyloses block the wood’s pores, preventing moisture and decay-causing agents from easily penetrating the wood. This makes white oak naturally resistant to rotting and fungal damage.
The dense, straight grain of white oak also makes it quite strong. All these innate characteristics mean that white oak holds up remarkably well when exposed to outdoor conditions including rain, snow, moisture, UV rays, and temperature fluctuations.
Due to its weather-resistance, white oak has been used for centuries in applications like wooden water pipes, boatbuilding, barrels, and more. It’s easy to see why it remains a popular choice today for structural outdoor wood components like:
- Retaining walls
While not completely impervious to moisture, white oak will last longer outdoors than most other domestic hardwoods before needing replacement.
In contrast to white oak, red oak is more susceptible to rot, warp, and decay when used in outdoor projects. Some common species of red oak include:
- Northern Red Oak – The most prevalent red oak species, naturally found from Canada to the Appalachians.
- Black Oak – Named for its dark bark, it shares many red oak traits.
- Pin Oak – A popular landscape tree with a conical shape.
- Scarlet Oak – Similar to red oak but with distinctive fall colors.
- Shumard Oak – A tall tree native to southern states.
Red oak has a more open pore structure than white oak, allowing moisture to seep into the wood faster. This makes red oak more prone to cupping, splitting, swelling, and rotting when exposed to the elements. Red oak also contains tyloses like white oak, but fewer, resulting in less natural water resistance.
While stains and protective finishes can help compensate for some of red oak’s deficiencies, it will generally need frequent maintenance and refinishing to retain its integrity outdoors. Red oak should not be used for structural outdoor applications where strength and moisture resistance are paramount. It’s best reserved for non-load bearing exterior projects like:
- Decorative trim
- Planter boxes
Red oak’s aesthetic qualities still make it a popular wood species for accent details outdoors. But it’s important to understand its limitations in terms of weather-resistance compared to white oak.
Durability and Resistance of Oak Woods
The natural durability and longevity of oak in outdoor settings depends on a variety of factors:
- Oak species (white vs. red)
- Temperature and climate
- Level of moisture exposure
- Ultraviolet light exposure
- Required structural strength
- Outdoor wood preservatives used
- Frequency of finishing/refinishing
Under ideal conditions, white oak can last over 100 years when used structurally in covered outdoor applications. Even when used in direct sun and moisture, white oak exhibits excellent resistance to decay thanks to its dense composition and tyloses. It rates very high on decay resistance scales compared to other domestic hardwoods.
For example, white oak decking boards can often last upwards of 25 years before needing to be replaced, even with minimal finishing. On the other hand, red oak deck boards may show signs of cupping, cracking, and rotting after less than 10 years.
When selecting any oak for outdoor use, Going with lumber heartwood – the central part of the tree – will provide better results than the sapwood. The heartwood contains more tyloses to guard against moisture absorption. Picking boards with the straightest grain also improves performance.
Oak should not be used in direct contact with soil, as it can still suffer decay from ground moisture saturation. Elevating oak off the ground with stone, concrete, or pressure-treated posts will extend its lifespan outdoors.
Undercover applications like porches, sunrooms, and pergolas provide added protection for oak by limiting moisture exposure. For the best durability, white oak is the ideal choice. But even red oak will fare better in a protected setting versus direct outdoor exposure.
Finishing and Treatment for Outdoor Oak
Another key factor when using oak outdoors is choosing an appropriate exterior wood finish. Unfinished oak will weather quickly from exposure to the elements. The right outdoor finish helps slow down moisture absorption, UV damage, staining, and mildew growth.
Recommended Outdoor Finishes for Oak
- Spar Varnish – Provides excellent protection for outdoor oak while allowing the natural color and grain to show through. Requires periodic recoating.
- Exterior Paint/Stain – Opaque finishes block UV rays to minimize damage. Offer moisture resistance when applied properly. Need regular touch ups.
- Penetrating Wood Sealers – Soak the wood pores without creating a thick film. Allow wood to breathe while repelling water. May need yearly reapplication.
- Bleaching Stains – Contain oxalic acid to stabilize oak tannins and prevent dark staining. Provide moderate UV protection.
- Teak Oil – Penetrates into oak providing water repellency. Needs multiple coats and annual re-oiling.
- Epoxies – Offer superior moisture resistance. Can leave a plastic-like surface and require stripping for refinishing.
Clear film-forming finishes like varnish or polyurethane for white oak provide the best combination of protection and longevity before reapplication is needed. Painted finishes also perform well.
Red oak benefits from penetrating oils and stains that can be refreshed annually. Clear finishes may need to be reapplied more often to compensate for red oak’s inherent lack of moisture resistance.
To Paint or Not to Paint Oak?
There’s debate on whether exterior paint provides adequate protection for oak over time. Paint can crack and peel as the wood expands and contracts, allowing moisture intrusion. Repainting can help counteract this, but also requires completely stripping the old paint for proper adhesion.
Unfinished, weathered oak takes on a gray patina over time. Some prefer this aged look to painted wood. Others appreciate paint’s ability to prevent staining or match other colored elements.
For white oak, a clear film-forming finish is generally a better choice than paint from a durability standpoint. But paint is still an option if you don’t mind higher maintenance. For red oak, a painted finish limits moisture exposure into the vulnerable wood.
Proper surface preparation, primer selection, top coat application, and maintenance are key to any painted exterior wood finish. Understand paint has limitations on exterior oak, especially horizontal surfaces like railings or benches that see more abuse.
Alternatives to Oak for Outdoor Use
Although oak has many positive traits, white oak may not offer the ultimate weather-resistance needed for some exterior applications. Several alternative woods naturally excel when used outdoors:
- Teak – Contains oils that make it highly resistant to water, decay, insects, and weathering. No finishing required, but will gray without maintenance.
- Cedar – Heartwood has excellent decay resistance. Red cedar commonly used for decks, furniture, and landscaping.
- Redwood – Dense grain fights off moisture and insects. Used for decking, siding, and outdoor projects on the west coast.
- IPE – An extremely dense Brazilian hardwood that lasts for decades
- Cypress – Displays good moisture and insect resistance. Stays relatively stable in outdoor settings.
- Mahogany – Certain species have natural oils that help resist weathering and decay. Used for outdoor furniture and boats.
- Douglas Fir – Has good strength and resistance to swelling and shrinking. Best performance when properly finished.
These woods and certain treated lumber options contain high levels of natural oils, resins, and extractives that boost their longevity outdoors. They resist swelling, checking, and rotting better than most oak varieties.
However, most exotic hardwoods cost more than domestic oak. And some species like teak and IPE are becoming less available due to overharvesting and deforestation concerns. This makes oak look more attractive to use sustainably from a cost and environmental standpoint.
Cost Considerations for Oak
Oak is generally cheaper than many exotics used for outdoor projects. Here are some typical price ranges:
- White Oak – $3 to $6 per board foot
- Red Oak – $2 to $5 per board foot
- Teak – $15 to $30 per board foot
- IPE – $7 to $12 per board foot
- Cedar – $3 to $7 per board foot
- Redwood – $4 to $9 per board foot
White oak boards for outdoor use command a small premium over red oak. But oak’s cost savings generally outweigh the added maintenance required to keep it looking good outside. This makes oak a budget-friendly option for large outdoor projects like decks, pergolas, and fencing.
Using oak for smaller pieces of outdoor furniture or accent items means the higher cost of woods like teak, IPE, or mahogany has less impact on the total budget. On a per board foot basis, the cost looks high. But since less wood is needed, the numbers are not as skewed.
When deciding between oak and other woods for your specific outdoor project, always compare the full installed price. Consider long term maintenance costs in addition to upfront lumber expenses.
Sustainable and Eco-Friendly Oak Options
With environmental issues like deforestation and climate change a growing concern, using domestically sourced oak is one way to reduce the environmental footprint of outdoor projects. Fortunately, oak is not considered an endangered species and manages to regenerate faster than it’s harvested in most regions.
Other tips for sustainable outdoor oak use include:
- Source oak lumber from suppliers of responsibly managed forests.
- Use oak salvaged from old barns, factories, or demolitions rather than new lumber.
- Choose oak certified by the Forest Stewardship Council (FSC) as sustainably harvested.
- Consider using oak cutoffs or smaller scraps creatively.
- Use water-based, low VOC finishes to reduce environmental impact.
- Maintain oak properly to maximize its functional lifespan.
- Compost oak scraps or recycle at end of useful life rather than sending to landfill.
Following environmentally responsible practices allows us to enjoy the benefits of durable, attractive oak for outdoor living while also doing our part to protect nature for future generations.
- White oak is the best species for outdoor use thanks to its density, tyloses, and natural decay resistance.
- Red oak has less resistance to moisture and weathering. Requires more maintenance outdoors.
- Proper finishing and maintenance are mandatory for optimal oak performance.
- Teak, cedar, and redwood naturally resist weathering better than oak.
- Oak is generally cheaper than most exotic woods used for outdoor projects.
- Responsible sourcing and care of oak allows sustainable use for eco-friendly projects.
With the right considerations for wood species, finishing, and maintenance, oak can be a great choice as an environmentally responsible and budget-friendly outdoor material. Its natural beauty, versatility, and durability make oak suitable for everything from patio furniture to back decking. By matching the oak type with its intended use and location, you can enjoy the benefits of this classic American wood for generations.