Extending the Life of Utility Poles with Remedial Treatment

Despite newer developments often opting for underground wiring, utility poles remain the most common means of supporting wiring. There are roughly 120 million utility poles in service, owned by utility companies, rural electricity associations, telephone companies and railroads.

The vast majority of utility poles are made of pressure-treated wood, often derived from Southern Yellow Pine. The manufacturing process results in a stronger, preservative-treated pole with a naturally long life compared to raw wood, but the life expectancy of utility poles can be extended even further through the implementation of inspection programs and remedial treatment.

Remedial Treatment is Key to Pole Life Extension

Utility asset managers would be wise to investigate how utility pole life expectancy can be increased by adopting an inspection program followed with remedial treatment. Typical inspection programs often go into effect within 7 to 15 years post-installation, varying by region. After the initial inspection, many companies adopt a 10-year cycle.

Remedial treatment is an additional step and is done post-inspection when needed.

Inspection Programs vs Remedial Treatment


According to authorities, the practice of lumping together inspection and remedial treatment is common but has faults. Though both tasks are very similar, from an accounting perspective they should be separated. Remedial treatment should be considered a preventative measure rather than a repair following the inspection.

The Federal Energy Regulatory Commission only considers inspection, testing and reports on poles to determine a need for repair or replacement as an identifying factor. Applying a treatment product on utility poles is therefore not a maintenance expense, but instead a capital expense.

There is plenty of documentation and research to back the importance of remedial treatment extending the life of utility poles.

Deterioration Zones and Projected Service Life

To understand the impact of remedial treatment plans, it must first be understood what the current project lifespan of a pole is within the appropriate deterioration zone.

There are 5 Decay Zones defined by the American Wood Protection Association, which include:

  • Decay Zone 1 - Low Hazard with 49.8 years Expectancy

  • Decay Zone 2 - Moderate Hazard with 56.8 years Expectancy

  • Decay Zone 3 - Intermediate Hazard with 44.5 years Expectancy

  • Decay Zone 4 - High Hazard with 43 years Expectancy

  • Decay Zone 5 - Severe Hazard with 40.3 years Expectancy

The average life expectancy of a utility pole in the United States is right around 45 years, without any type of remedial treatment. These figures are calculated by testing the strength of the utility pole. If 50 percent of the pole in question does not meet the strength needs outlined by the National Electric Safety Code they are labeled as rejects, have met their life expectancy, and must be replaced.

By adopting a remedial treatment plan following normal inspections, companies can raise the life expectancy of their utility poles significantly.

Utility Pole Life Extension with Remedial Treatment


According to research done by Osmose, utility poles given remedial treatment when needed will have a 60 percent increase in life expectancy, bringing the average 45 year lifespan up to 73 years. Another study done by Quanta Technology found that a combination of regular inspections and a treatment program could extend life as far as 96 years in certain Decay Zones, with 80 percent being more typical throughout the United States.

Remedial treatment plans can vary, but typically involve the application of a preservative treatment every 8 to 15 years. Pressure treated wood utility poles are most likely to experience decay at ground-level and below. Fungus is the leading reason for decay and will most often occur at ground level and up to 18" below. Surface decay can actually be incredibly damaging as it's the outer 3” of the pole that makes up 90 percent of its strength.

Exact remedial treatment plans and preservatives can vary, but the most successful treatments will include these four factors:

  • Primary active ingredient must penetrate a minimum of 2" of the pole, with 3" being a better goal. Other active ingredients do not need to penetrate this deep, but the primary preservative that attacks decay should.

  • Preservatives must be active and offer prolonged protection based on whichever remedial treatment cycle is in effect. This will vary based on Decay Zones and regions as well.

  • Preservatives must fight against growth of both soft rot and brown rot, the two most common fungi that cause decay on pressure-treated utility poles.

  • Preservatives with multiple biocides aren't required, but are highly recommended. This ensures that other microorganisms, moisture and insects will be kept at bay, in addition to the common fungi mentioned above.

Determining which preservatives are best for your company and region will require some research, but is well worth the effort. By ensuring your product(s) meets these four factors you'll be well on your way to better protect your utility poles.

The old practice of installing utility poles, practicing inspection-only, and simply waiting until the poles can no longer perform is a waste of resources, in terms of manpower, finances and natural resources. It is in the best interest of contractors and utility asset managers to develop a remedial treatment plan in addition to their current inspection program.