When building a foundation for a home or structure, choosing the right materials is crucial to ensuring structural integrity and preventing rot and decay. Pressure treated wood is a popular choice for many exterior construction projects, from decks to fences. But can you use pressure treated lumber for the foundation? There are a few key factors to consider when deciding whether pressure treated wood is an appropriate choice for a foundation.
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What is Pressure Treated Wood?
Pressure treated wood has been forced to absorb chemical preservatives under high pressure. This process helps protect the wood against rot, fungi, termites, and other pests. The preservatives used include chromated copper arsenate, alkaline copper quaternary, copper azole, and Micronized copper. The chemicals are forced deep into the cellular structure of the wood where they won’t easily wear or wash away.
This process extends the lifespan and weather resistance of pressure treated lumber. It’s a popular choice for projects like decks, fences, retaining walls, and outdoor furniture. The lifespan of pressure treated wood depends on the level of chemical treatment measured in retention levels. Higher retention levels indicate more preservative in the wood.
Benefits of Using Pressure Treated Wood
There are several potential benefits to using pressure treated lumber for foundations:
- Rot resistance – The chemical preservatives help prevent rot, even when exposed to soil and moisture.
- Insect resistance – Treatment makes the wood unappetizing to termites and other wood destroying insects.
- Affordability – Pressure treated wood is typically less expensive than natural rot resistant woods like cedar or redwood.
- Availability – Pressure treated lumber is widely available at most home improvement stores.
These benefits make pressure treated a popular choice for many exterior projects. But foundations have some specific requirements that may make other material options better suited.
Drawbacks of Pressure Treated Wood Foundations
While pressure treated lumber works well for above ground projects, using it for home foundations has some potential downsides:
- Strength – Pressure treated wood is not as strong as concrete or concrete masonry units. Over time, it may crack, warp, or compress.
- Permanence – While treatment extends lifespan, pressure treated wood will still eventually rot. It does not offer the extremely long lifespan of concrete.
- Moisture wicking – Being exposed to soil, pressure treated wood can still absorb moisture from the ground which can lead to rot over time.
- Termites – While treatment repels termites, they can still potentially get through to untreated interior sections of a wood foundation.
- Off-gassing – Some newer pressure treated lumber uses chemicals that can initially off-gas fumes into a home.
These cons don’t necessarily prohibit using pressure treated wood altogether, but they require taking additional precautions to reinforce the foundation and prevent moisture exposure.
Requirements for a Pressure Treated Foundation
Because pressure treated wood has drawbacks for foundations, builders need to take steps to reinforce it if using it as a foundation material. Here are some requirements to keep in mind:
- Use only ground contact rated pressure treated wood, with a retention rating of 0.60 pounds per cubic foot or higher.
- Create a moisture barrier by sealing around the foundation with a waterproof membrane or coating.
- Elevate the wood off the ground using a gravel base or foundation frames to prevent moisture wicking.
- Use engineer approved beam sizes and additional supports like pilings or pillars to provide added strength.
- Ventilate crawl spaces under wood foundations to prevent moisture buildup.
- Use termite shields and metal flashings around posts and wood in contact with soil.
Following these best practices helps account for the vulnerabilities of pressure treated lumber when used for foundations. Proper installation is key to performance and preventing problems.
Alternatives to Pressure Treated Foundations
Although it’s possible to use pressure treated lumber for foundations when properly reinforced and elevated, concrete and masonry alternatives provide some other options:
- Poured Concrete – Poured concrete foundations offer extreme strength and permanence. Concrete resists moisture, pests, and degradation far longer than wood.
- Concrete Block – Concrete masonry units allow building below grade foundations with moisture resistance and strength.
- Insulated Concrete Forms – ICF blocks made of foam and concrete provide insulation and moisture resistance.
- Brick – Solid brick foundations stand up well to moisture and offer lasting structural integrity.
These alternatives do cost more than pressure treated wood but may be worth the investment for enhanced durability and performance. The foundation is a critical structural component, so using the optimal materials can prevent problems.
Pressure Treated Wood Foundation Cost
One advantage of using pressure treated lumber for foundations is the lower cost compared to other options. Here is a comparison of estimated costs per square foot for pressure treated wood foundations vs other common foundation types:
| Foundation Material | Cost per Square Foot* |
|---|---|
| Pressure Treated Wood | $15 – $25 |
| Poured Concrete | $4 – $8 |
| Concrete Block | $10 – $15 |
| ICF | $10 – $20 |
| Brick | $25 – $30 |
*Costs vary based on location and site conditions
As the table shows, a pressure treated wood foundation can provide significant cost savings over other foundation materials. Though over the full lifespan, the additional maintenance and replacements required for pressure treated may make the other options more cost effective overall.
Conclusion
Pressure treated wood can technically be used for residential foundations when properly engineered and reinforced. However, for many homes concrete, masonry, or insulated concrete forms may provide a better overall value through greater strength, moisture resistance, and longevity. Ultimately, the optimal foundation type depends on budget, longevity expectations, soil conditions, and other factors. Consulting with an architect or structural engineer is the best way to determine if pressure treated wood is suitable for a specific home foundation project.