Timber Bulkheads: Treatment, Marine Borers and Upkeep

Timber is the traditional bulkhead material across much of the country. The Virginia Institute of Marine Science notes that most Chesapeake Bay bulkheads were historically built of wood, and USACE's coastal design manual describes well-designed, well-built timber structures as long recognized as viable and economical for marine use. Timber is also the material most dependent on correct treatment, because wood is an organic material that organisms can attack.

This page covers how timber bulkheads are built, what degrades them and how treatment and maintenance affect their service life. For a comparison with the most common non-wood alternative, see Timber vs. Composite Bulkheads.

How timber bulkheads are built

Many timber bulkheads are post-supported walls, which USACE describes as regularly spaced piles or posts with attached facing material that retains the backfill. In a typical timber version, horizontal wales are bolted to the piles and vertical sheeting or planks behind them hold the soil. Tie rods run from the wales back to deadmen or anchor piles. Timber sheet pile walls, built from tongue-and-groove planks, are another form. USACE's sheet pile manual, written for its own floodwall and retaining wall projects, restricts wood sheet pile walls to short-to-moderate heights and temporary use, a reminder that timber's structural range is narrower than steel's.

USACE's coastal manual is specific about two details: at marine locations only treated timber should be used, and hardware and fasteners must be corrosion-resistant or protected. It recommends minimizing joints in the sheeting and using a filter behind it.

See bulkhead components explained for the role of wales, tie rods and deadmen.

What degrades a timber wall

Marine borers

The USDA Forest Products Laboratory describes marine borers as able to attack susceptible wood rapidly in saltwater harbors, where they are the principal cause of damage to piles and other wood marine structures. Borers include shipworms, pholads and the small crustacean Limnoria. Borer pressure differs by region, which is why treatment standards, described below, assign the most severe category to southern waters.

Decay and the tidal zone

USACE's Coastal Engineering Manual says wood components are susceptible to biological attack everywhere except below the mudline, and that most deterioration occurs in the wet and dry tidal range. Untreated wood decays rapidly in contact with soil or seawater.

Fasteners and hardware

Metal connectors are subject to rapid corrosion in water and damp air, and some metals corrode galvanically in seawater. The Coastal Engineering Manual notes that abrasion from sand, debris or mooring lines can strip protective coatings, and that any metal protection has a limited life in the marine environment. In practice, failed bolts, rods and hardware can end a timber wall's useful life even when the wood is sound.

DiagramSimplified illustration — not an engineering drawing

Treatment: matching preservative to exposure

Treatment is what makes timber viable in water. The Coastal Engineering Manual states that correctly treated wood can increase service life by a factor of four to five over untreated wood, and that piles subject to borer attack need maximum creosote penetration and retention, with a waterborne preservative added where infestation is severe. USACE's bulkhead manual lists creosote and creosote coal-tar solutions or waterborne salts, sometimes in combination, as borer protection.

The American Wood Protection Association sets use categories by exposure. A USDA Forest Service summary describes the marine categories this way:

The same Forest Service publication states that for marine or brackish construction, only creosote, CCA and ACZA are approved. Owners do not need to specify chemistry themselves, but they can ask a contractor which use category and preservative the material is certified to and whether it matches the local water.

Field cuts

Cutting or boring treated wood exposes untreated interior. USACE advises avoiding field cuts where possible and treating any cut surfaces with a similar preservative.

Environmental considerations

NOAA's living shoreline guidance notes that treated wood bulkheads may contain chemicals that can leach into the coastal environment. EPA reports that manufacturers voluntarily stopped producing CCA-treated wood for most residential uses at the end of 2003, while CCA remains used for products such as pilings and poles under approved labeling. Permitting agencies in some areas have their own rules on treated wood in water; check with your regulator through the bulkhead permit guide.

Maintenance outlook

The Coastal Engineering Manual describes timber maintenance as reapplying protective coatings where used, replacing deteriorated members and replacing members damaged by vessels, waves or fire. It notes that re-treating deteriorated pressure-treated wood is usually not practical; those members should be replaced. Owners can watch for:

1. Soft, eroded or hourglassed piles in the tidal zone.
2. Gaps or missing boards in the sheeting, often with soil loss behind.
3. Corroded or missing bolts, rods and plates.
4. Wales pulling away from piles, or the wall leaning outward.

For repair approaches, see timber bulkhead repair and the bulkhead maintenance checklist.

Where timber tends to fit

Timber is commonly considered for sheltered residential shorelines with moderate wall heights, where treated material suited to the local water is available and the owner accepts periodic hardware and member replacement. It may be a weaker fit in warm waters with aggressive borers, where treated-wood restrictions apply, or for tall walls with high loads.

Final suitability depends on local conditions and professional design. Compare timber with other materials in the Material Comparison Explorer.