Pressure treated lumber marking codes (C) Daniel Friedman Treated Wood Lumber Life & Warranty

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Preservative treated wood life:

This article gives the life expectancy of treated wood or preservative-treated lumber, lists typical treated wood warranty periods, and provides a list of factors affect the life of treated wood.

This article series discusses treated lumber processes, properties, and use in construction of decks, porches & other outdoor structures and provides a Guide to Pressure Treated Framing Lumber Methods, Chemicals, Durability, and its Health Concerns.

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Life Expectancy & Warranty Period for Treated Wood in Various Applications

Data tag on treated wood deck board, Two Harbors MN (C) Daniel FriedmanQuestion: how long does pressure treated wood last

2017/07/01 Anonymous said: how long does pressure treated wood last ?

Reply: Treated wood life expectancy, warranty periods, & factors affecting treated lumber life

Good question, Anonymous.

Shown at left, data tag on treated wood deck boards on a ground-level deck in a shaded location in a damp and freezing climate - Two Harbors, in Northern Minnesota.

[Click to enlarge any image]

Typical in-use life span of treated lumber used in swing sets, decks and deck posts is 10-20 years. Keep in mind that actual useful life and "warranty period" for any product may be quite different, and that warranties are usually limited in scope and conditions. Interestingly there are two different "life expectancy" issues for treated wood:

  1. The service life of treated wood while it is part of a structure
  2. The remaining life of chemicals used in wood treatments that may create a disposal issue. Vick (1996) discusses the problem of safe handling of the tremendous volume of demolition materials that include CCA-treated lumber.

The actual service life of preservative-treated wood, like that of many other building materials, is often shorter than its design service life. (Vick 1996).

However a look at the warranty period offered for treated wood products tells us how long the manufacturer expects their product to last, provided you used it and installed it properly. Companies and researchers typically expect properly-treated wood used outdoors, properly-installed, to have a life extension of 25-50 years. My own field experience shows that actual life of wood outdoors can vary considerably.

18 Factors Determining the Life of Treated Wood Decks, Porches & Other Outdoor Structures

The warranty period for treated lumber varies considerably depending on at least the factors listed alphabetically below. Naturally above-ground use and soil-contact or below ground use of treated wood product means very different exposures and environments.

  1. Application (proper use) of the treated or preservative-treated wood product, such as above-ground vs. below ground use, structural vs. non-structural;
  2. Drainage details such as post top cuts, facing cupped deck boards arch-up, providing for drainage gaps between floorboards, and use of flashings and air gaps at deck ledgers as well as flashing over built-up beams all increase the life of decks and other outdoor structures made using treated lumber.
  3. Elevation: beyond above-ground vs. ground-contact, depending on location and climate, wood structures built above ground but close to it are less ventilated, retain more moisture, and are likely to have a shorter life.
  4. Lumber species & quality; most treated wood used in deck structures is #2 or #3 SYP, often knotty, prone to twisting, and lower quality than other more costly species & wood selections.
  5. Manufacturer or wood treatment processor: companies use different processes, chemicals, quality control procedures, lumber grades; some warranties extend as long "lifetime" of the customer
  6. Maintenance - keeping above-ground wood clear of algae, organic debris; use of preservative coatings or stains. Preservative coatings increase the moisture resistance of wood, treated or not, thus improving its rot-resistance as well as its resistance to photo-oxidation.
  7. Shade exposure: in some climates, a deck located in high shade or always-shaded areas may be prone to rot, algae, wood-rotting fungi
  8. Shipment & storage conditions of the treated wood before use (possibly)
  9. Sunlight exposure (for above ground applications): high sun-exposure is a factor in photo-oxidation, checking, warping, color loss, & life of preservative coatings;
  10. Soil moisture level and moisture level variation
  11. Soil chemistry and composition, including soil drainage properties
  12. Structural integrity: inadequate supporting footings, piers, connections, missing or improper fasteners contribute to early structural failures; combining rot, movement, and poor connections invites a deck collapse.
  13. Treatment method & chemistry: borate vs copper derivatives, &c. have different treatment efficacy, lifetimes, & applications; also important are the extent of pre-drying, use of & level of pressure, moisture content of the wood at time of treatment, concentration of treatment chemical and extent of chemical treatment up-take in or penetration throughout the wood
  14. Weather variations & weather exposure, temperature, sunlight, wind, rain, snow, ice, algae & mold growth on surfaces
  15. Wood hygroscopicity of the particular wood species or wood product at the time of treatment; importance varies by treatment method
  16. Wood density, moisture-level when treated, and similar factors (possibly)
  17. Wood destroying insects, presence of
  18. Workmanship of the wood-construction product including cuts, treatment post caps, accuracy of joints between connected members, fasteners, drainage (cited above), use of flashing, wood orientation, & other factors such as placing walking surface or deck boards with the arch of cupped boards facing upwards all affect life of the treated wood as well as the structure. (Haapio 2008)

Also see FIRE RETARDANT PLYWOOD where thermal degradation is discussed

Examples of Treated Lumber Warranty Periods - 2 years to "lifetime"

Watch out: all of these treated lumber or treated wood product warranties have limitations and exclusions such as warranting only to original owner, construction details, degree of avoidance of ground contact, &c.

Actual Field Experience with Treated Wood Life for Posts, Steps, Decking

Depending on the efficacy of treatment, I've found older copper-arsenate-treated wood to show a wide range of actual lifetimes from 20+ years above ground to less than 15 years for ground-contact and below-ground use. Failure patterns I have observed are particularly interesting and include:

Watch out: for faux-treated wood. Some garden supply companies, landscape companies, and possibly some lumber yards sell a (usually softwood) "landscape tie" that is green and makes you think it has been treated with wood preservative; the preservative, if any, is a topical spray of very limited durability.

When buying "treated lumber" for outdoor, above ground or ground contact use, look for the plastic tag stapled to the lumber as that gives information about the lumber treatment type, intended use, source, company, and warranty.

Research on Life Expectancy of Treated Lumber or Treated Wood Products

Deck & Porch Wood Treatment Companies

This article series discuss best porch & deck construction practices, including choice of framing materials, decking or flooring choices & installation, how to select and use deck and porch structural and flooring fasteners, actual deck & porch framing construction details & connections, deck joist & beam span tables, how to build leak-proof rooftop decks, construction of covered & screened porches, deck & porch railing construction & materials, choices of finishes and stains for decks & porches, and past & current deck lumber preservative treatments with related health & environmental concerns.


Continue reading at DECK FLASHING LEAKS, ROT Case Study or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see New Preservatives and Corrosion where we describe structural fasteners designed for use in pressure-treated lumber.

Or see ROT-RESISTANT Deck Lumber & Flooring for a disucssion of lumber and flooring alternatives to preservative-treated wood.

Or see ROT, TIMBER FRAME for tools and approaches to assessing the extent of wood timber rot or insect damage.


Or see FIRE RETARDANT PLYWOOD where thermal degradation is discussed

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PRESERVATIVE TREATED WOOD LIFE at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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