Deck Ledger Boards – Part II

Deck ledger board flashing is used in the construction of a deck to help prevent or deter water intrusion, rot, and potential structural damage from occurring at the area behind or at the mounting bolt penetrations at the ledger board . When a ledger board is not properly flashed, water can infiltrate behind it, causing a range of issues. Understanding the construction of a ledger board and the use of flashing at this location can encourage or inform better quality construction and installation.   In turn, better quality construction and installation result in safer structures that last longer.  These effects lead to overall lower lifecycle costs.

deck ledger boards

Deck Ledger Board Construction:

A ledger board is typically a horizontal framing member attached to the exterior of a building to support one end of the deck. It is crucial to a deck’s structural integrity, serving as a point of attachment for joists. Ledger boards are often attached to the building’s rim joist, secured using lag screws or bolts. In the case of attachment to a masonry wall, like brick, it is important to consider potential water entry points.

deck ledger board construction

Water Intrusion and Its Consequences:

When a ledger board is not flashed, water can find its way behind the board, leading to a cascade of problems. In a masonry context, water can penetrate the joint between the ledger board and the brick. It may then follow the path of least resistance, seeping into the interstitial space between the ledger board and the exterior wall. This water can further penetrate the bolt holes, reaching the interior of the building.

water intrusion in deck ledgers

Flashing is the primary defense against water intrusion. In brick constructions, flashing can be integrated into a reglet or raggle in the mortar joint. This creates a barrier against water penetration and directs any water away from vulnerable areas. Proper flashing should not only cover the top of the ledger board but also extend over at least a top portion of its face, providing comprehensive protection.

Elastomeric Sealant Application:

In addition to flashing, applying an elastomeric sealant in each anchor or lag screw hole enhances water resistance. This sealant can help create a waterproof barrier around the fasteners, preventing water from entering through these points. This additional layer of protection is especially crucial in regions prone to heavy rainfall or where decks are exposed to the elements.  Elastomeric sealants represent a category of materials specifically designed to endure dynamic movement, temperature fluctuations, and exposure to environmental elements. The term “elastomeric” stems from their unique ability to maintain a high degree of elasticity or flexibility over extended periods. The scientific principles behind elastomeric sealants involve the molecular structure and composition of the material.

At the molecular level, elastomeric sealants often comprise a polymer matrix, commonly based on synthetic elastomers or silicone. The molecular chains within these polymers are inherently flexible, allowing them to stretch and contract without losing their structural integrity. This flexibility is a result of the chemical bonds and molecular arrangements that enable the material to absorb and recover from stress, including movement and deformation.

One critical attribute of high-quality elastomeric sealants is their resistance to ultraviolet (UV) radiation. Exposure to sunlight and UV rays can degrade many materials, leading to brittleness and reduced flexibility over time. In elastomeric sealants, UV-resistant additives or stabilizers are often incorporated into the formulation. These additives act as a shield, mitigating the detrimental effects of UV radiation on the molecular structure of the sealant.

The scientific resilience of elastomeric sealants lies in their ability to withstand various environmental stressors. When applied in the context of a ledger board installation, the sealant’s elasticity accommodates the natural movements and contractions associated with temperature changes, ensuring a continuous and effective barrier against water infiltration.

As the deck and ledger board experience thermal expansion and contraction, the elastomeric sealant remains pliable, preventing cracks or fissures from forming. Additionally, the UV resistance helps the sealant’s molecular structure remains intact, preserving its flexibility and sealing properties even in a degree of exposure to sunlight.  This chemical resilience translates into durable protection against water intrusion, making elastomeric sealants a crucial component in the construction industry, particularly when securing ledger boards to prevent potential water-related damage.

sealant application deck ledger

It should be understood that even though there is significant scientific improvement, in recent years, in the molecular structure of elastomers, polymers, and other synthetic type materials, their ability to withstand exposure to ultraviolet rays is significantly limited. Almost without exception, exposure to ultraviolet rays will deteriorate these materials in an accelerated manner.

Insidious Nature of Water Entry:

Water entry may seem somewhat innocuous, but its effects can be insidious. Over time, continuous exposure to moisture can lead to rot, compromising the structural integrity of the ledger board and adjacent components. Water infiltration behind the ledger board poses a risk to the building’s framing, sheathing, and potentially the interior spaces.

Water intrusion poses a significant threat to various building materials, and its effects can be particularly detrimental over time. Understanding how water causes damage to both organic and inorganic materials is crucial for implementing effective preventive measures.

nature of water entry deck ledgers

Water’s Affect on Lumber and Wood Sheathing:

Water, especially in the form of persistent leaks or prolonged exposure, can lead to rot in framing lumber and wood sheathing.  Moist conditions create an ideal environment for fungi, such as mold and mildew, to thrive, accelerating the decay of organic materials.  Rot compromises the structural integrity of wood, weakening its load-bearing capacity and posing safety risks.

Water’s Affect on Drywall and Cellulose Paper Face:

Drywall, composed of gypsum and paper, is highly susceptible to water damage.  Water exposure can cause the cellulose paper face to delaminate, creating a breeding ground for mold.  Mold growth not only compromises the aesthetics of drywall but can also contribute to indoor air quality issues.

water affect on drywall

Water’s Affect on Brick and Mortar Joints:

Water can lead to the deterioration of both brick and mortar joints in masonry constructions.  Freeze-thaw cycles, common in colder climates, exacerbate damage as water within the masonry expands upon freezing, causing stress on the materials.  Efflorescence, the white, powdery substance on masonry surfaces, indicates the presence of soluble salts brought to the surface by water.  While efflorescence itself may not be harmful, it signals moisture-related issues that, if unaddressed, can lead to spalling (flaking or chipping of the surface) and other structural problems.

water intrusion in deck ledgers

Masonry Deterioration Over Time:

Excessive exposure to water can accelerate the weathering of masonry overloads, including deterioration of concrete elements.  Water carries dissolved minerals and salts, promoting chemical reactions that contribute to the breakdown of the masonry.  The long-term impact can include surface erosion, loss of structural strength, and aesthetic degradation.

In summary, water intrusion can have varying effects on building materials, ranging from rot in organic materials to deterioration and efflorescence in masonry. Recognizing the signs of water-related damage is crucial for implementing timely repairs and adopting preventive measures to safeguard the structural integrity and longevity of buildings.

Understanding the intricacies of ledger board construction, potential water entry points, and the importance of proper flashing and sealant application is vital for anyone involved in deck construction. These measures are not about selling a product; rather, they are fundamental to the science and engineering of building to ensure durability, safety, and the prevention of long-term damage caused by water intrusion.  Use a contractor who understands and cares about doing things right.  Always come up feel free to reach out to us here at Dupont Decks and Patios.  You can contact us or email us through the website!

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