The Difference Between Treated and Untreated Wood

Learn when you must use pressure-treated wood and when untreated works just as well.

Pressure-treated wood is treated with copper salts and other chemicals to resist rot and insect attacks, making it indispensable for outdoor structures that come into contact with soil or moisture, such as carrying beams and deck posts. Untreated wood, on the other hand, is raw spruce or pine and is excellent indoors or in well-protected places outdoors, provided it is painted and maintained regularly. If you use untreated wood incorrectly outdoors, it can rot in just a few years, while pressure-treated can last for decades.

Environmental Aspects

While pressure-treated lumber is essential for structural longevity outdoors, it does contain chemicals. Therefore, you should never burn treated wood scraps in your fireplace or use them to build raised garden beds where you plan to grow edible vegetables. For garden beds, cedar or heat-treated wood are much safer, natural alternatives that also offer excellent rot resistance without the chemicals.

Cost Differences

Untreated lumber is significantly cheaper than its treated counterpart. This is why framing a house or building indoor furniture is always done with untreated wood. However, trying to save money by using untreated wood for an outdoor deck frame is a false economy. The cost of tearing down a rotten deck and rebuilding it far exceeds the initial premium you pay for properly treated lumber.

Summary

Choosing the right type of wood is the foundation of any lasting project. Use treated wood for ground contact and outdoor structures exposed to rain. Use untreated wood for indoor projects where it will stay completely dry. By understanding this simple rule, your DIY projects will stand the test of time.