Over the past few weeks we’ve looked closely at a few topics related to structural connectors used in wooden decks. Wooden decks are basically made of wood, but they building code requires that steel connector plates, brackets, and fasteners are used at several key locations and deck construction. Most of these connection points are at the joints between one type of framing member and another. In the part one of this three-part series, we looked at a litany of different types of connectors used at these different types of joints and connection points, and then last week we took a look at some of the building code requirements and threats facing decks such as seismic forces and storm and weather related uplift and wind related forces.
Today though we’re going to take a look at the long term threat of corrosion to these steel connectors. In most cases these steel connectors are made with a steel base, steel is extremely strong. Steel one of the strongest materials abundantly commonly used in building construction. Steel the, I’ll be it very strong in terms of both tensile and compressive strength, does not have a high resistance to oxidation and deterioration and in fact we’ll fail very quickly over just a few years if left to rot in optimal conditions for oxidation.
In the image below, we show a gazebo roof above a patio area. The framing members of the gazebo roof are connected with zinc coated galvanized structural connectors. This structural hardware works both as a joist hanger and a rafter hanger.
Importance of Corrosion-Resistant Hardware in Deck Construction
When considering deck construction, selecting the appropriate hardware and fasteners is important for ensuring the long-term structural integrity of the deck. One of the primary considerations in this selection process is the level of corrosion resistance exhibited by the connectors and fasteners. The outdoor environment presents unique challenges, as structures are exposed to elements that can accelerate corrosion, compromising the stability and safety of the deck over time.
Similar to a backyard deck system, the picture below shows the ridge of a gazebo type canopy roof rystem, the roof system is connected between framing members with structural hardware at many connection points.
Steel and it’s associated corrosion and oxidation is also compounded and/or exacerbated by the chemicals used in many types of wood preservatives and treatments.
Corrosive Nature of Outdoor Environments
Outdoor environments are inherently more corrosive to steel due to exposure to moisture, oxygen, and other environmental factors. Decks located in areas prone to high humidity or frequent rainfall, such as coastal regions or areas near bodies of water, are particularly susceptible to corrosion. The presence of saltwater in coastal areas further exacerbates the corrosive effects, as salt can accelerate the oxidation process of steel.
Chemical Treatments in Wood Preservation
In addition to environmental factors, the chemical treatments used in wood preservation can contribute to accelerated corrosion of connectors and fasteners in deck construction. Pressure-treated lumber, commonly used in outdoor decking, undergoes treatment processes to enhance its resistance to decay and insect damage. These treatments typically involve the infusion of chemicals such as chromated copper arsenate (CCA), alkaline copper quaternary (ACQ), or copper azole (CA) into the wood.
The picture below shows another rafter hanger with two carriage bolts installed below to connect a corner brace. Both of these carriage bolts and associated nuts and washers are made from hot dipped zinc galvanization coated steel.
While effective in prolonging the lifespan of the wood, these chemical treatments can have adverse effects on metal fasteners and connectors. The corrosive properties of the chemicals, combined with the high moisture content often present in treated wood, create an environment conducive to corrosion. As a result, the fasteners and connectors used in conjunction with pressure-treated lumber must exhibit superior corrosion resistance to withstand these harsh conditions.
Factors Contributing to Corrosion Risk
Several factors contribute to the heightened risk of corrosion in outdoor deck environments. Exposure to fire retardants, present in some treated lumber formulations, can accelerate the degradation of metal components. Fumes emitted from nearby industrial zones or agricultural activities, such as fertilizers and pesticides, can also increase the corrosive potential of the environment.
Additionally, soil composition and moisture levels play a significant role in corrosion risk. Decks constructed in areas with high soil acidity or exposure to acidic rainwater may experience more rapid corrosion of metal hardware. The accumulation of organic matter, such as leaves or debris, on the deck surface can trap moisture and promote corrosion over time.
In the case of this zinc coated steel hardware, the zinc provides resistance to oxidation from exposure to the moisture. In this particular case though the hardware is covered by a makeshift type clear corrugated poly roof system, that roof system is not 100% water like a building or home roof, but it keeps the majority of rainwater off of the hardware. In other cases though, at most deck assemblies, hardware of this type is left exposed.
Selection of Corrosion-Resistant Hardware
Given the multitude of factors contributing to corrosion risk in outdoor environments, selecting corrosion-resistant hardware is paramount in deck construction. Stainless steel, galvanized steel, and specially coated or treated fasteners are commonly employed to mitigate the effects of corrosion. Stainless steel, in particular, offers exceptional resistance to rust and corrosion, making it an ideal choice for deck hardware in corrosive environments.
The selection of corrosion-resistant hardware and fasteners is essential for ensuring the longevity and structural integrity of outdoor decks. By understanding the corrosive nature of outdoor environments and the impact of chemical treatments in wood preservation, builders can make informed decisions when selecting hardware for deck construction. Stainless steel and other corrosion-resistant materials provide reliable protection against the detrimental effects of corrosion, ensuring the safety and durability of outdoor deck structures for years to come.
This moderately thorough explanation covers the importance of corrosion-resistant hardware in deck construction, the corrosive nature of outdoor environments, the impact of chemical treatments in wood preservation, and the selection of appropriate materials to mitigate corrosion risk. The scientific chemical elements at work with both exposure to moisture and bonding of materials and the reaction of metals with exposure to the natural elements are a complicated confluence of different factors. We will touch on more of these details and analysis in future blogs as well
Use a contractor who understands and cares about doing things right. Always, feel free to reach out to us here at Dupont Decks and Patios. You can find us online at https://dupontdeckspatiosdc.com/ and you can email us there as well!
