A common denominator for deck collapses is a special family event, such as a graduation, wedding, birthday party, or family reunion. A properly designed and constructed 14-ft x 24-ft residential deck floor, designed for a 40 psf uniform live load, should safely support 84 occupants based on an average occupant weight of 160 lbs. Knowing that a deck has been safely used for years by as many as 10 occupants, the practical question for the homeowner might be is the deck safe for a special event when 15, 25, 35, or more family and friends could occupy it? Absent an inspection by a qualified person, a homeowner would not know if their deck was safe for more than 10 occupants. Past “experience” alone can lead to an unfounded assumption that the deck will safely support more than 10 occupants during an upcoming “special event,” when in fact, it is not safe. [For all photos, See PDF or View in Full Issue.]
Applied occupant load is only one side of the structural safety equation. The load capacity of critically important deck connections can be reduced due to decay of the wood components and/or corrosion of steel fasteners made with nails, screws, lag screws. or bolts.
For an example of red rust corrosion, a ½-inch diameter carriage bolt removed from a 4x4 guard post connection is shown (Photo 1) next to a new bolt for comparison purposes. In this case, the bolt had been in service for 13 years. The homeowner was aware of coastal saltwater corrosion and attempted to remove the bolt when it broke. Without removing the bolt from the connection, the homeowner would not have known that the shank had been reduced to less than ¼-inch (or about 25% of the original area) and could not be relied on to secure the 4x4 guard post to the deck floor framing.
Further complicating the matter, a deck that seems to be new or cosmetically repaired (freshly painted) for appearances may not be safe. Some decks are built without a permit from the local building department and not inspected at the time of construction. Even when permitted and inspected, the deck code requirements adopted by the applicable state or local jurisdiction vary widely. For example, some jurisdictions require the deck guard post to be connected to the floor framing using a structural connector (Photo 2) to meet the IRC requirement of 200-lb concentrated load applied on the top rail. Other jurisdictions do not require a structural connector (such as depicted in Photo 3), allowing the deck contractor to use their judgement on how to construct the connection.
The guard connection in Photo 3 is made with two ½” bolts and washers and would appear to be strong and safe, but in fact, it is not because the rim joist was not adequately secured to the floor framing system. For this test, the rim joist was screwed to the end grain of the joists as is typically done in the field. When the top of the guard post is loaded in the outward direction, the screws are loaded in withdrawal from end grain, which is the weakest direction for fasteners in wood. [It should be noted that loading wood screws in withdrawal from end grain is not permitted by the National Design Specification for Wood Construction (NDS).]
Given the numerous uncertainties about your deck, from its construction through its time in service, existing decks should be inspected by a qualified person on an annual basis for safety. Do you know which codes and practices were used to construct your deck? Do you know the extent to which its wood framing and connections may have deteriorated due to outdoor moisture and rainwater? Have its fasteners and connectors experienced corrosion? For occupant safety concerns, an inspection of a deck for appearance alone should not be considered a meaningful deck inspection.
The purpose of this article is to recommend two deck construction and inspection educational resources that a homeowner, deck contractor, or design professional can use to learn about conducting a meaningful safety inspection of an existing deck. The primary objective of a meaningful safety inspection is to identify safety-related deficiencies that may lead to an occupant injury event.
Inspecting an Existing Deck for Safety
As stated by Bruce Barker in Deck Codes + Standards (2024, 2nd Edition),
“If you don’t know what a safety defect looks like, you will not find it.”
Because an existing deck (or even a new deck) may not be safe, a meaningful deck inspection requires the inspector to be knowledgeable about all deck elements that are critically important for occupant safety, deck construction details that are based on the current residential code (IRC), and good industry deck construction practices. Having this knowledge base about construction details that are considered “safe” for occupancy, the inspector has a standard or benchmark for identifying and evaluating potential life-safety deficiencies of an existing deck.
Safe Deck Construction Details and Requirements
DCA6-2015 Prescriptive Residential Wood Deck Construction Guide, published by the American Wood Council (AWC), is an excellent (free) resource for a homeowner or deck contractor to learn about safe deck construction details. DCA6-2015, hereafter DCA6, is based on the 2015 IRC deck code requirements and good industry practices.
Presented in 22 sections, DCA6 gives the structural design requirements for joists, cantilevers, beams, decking, connections, support post, footings, bracing and lateral load requirements, guards, handrails, stairways, and detailed drawings that show the recommended type and size of fasteners or connector type and load rating. For example, DCA6 gives two safe options (Figures 8A and 8B) for connecting a deck beam to support posts.
Anyone may download the complete DCA6 in English or DCA6 in Spanish from the AWC website.
Unsafe Existing Deck Details, Defects, and Recommendations
An excellent, one-of-a-kind resource for learning how to inspect an existing deck for continued safe use is Deck Codes + Standards (2024) by Bruce Barker, a longstanding American Society of Home Inspectors (ASHI) leader who has inspected decks for over thirty years. Available from Amazon, the author shares his inspection experience by boldly addressing myths about deck construction, common defects observed in the field accompanied by code-conforming requirements and details, why a permit and inspection is critically important for deck safety and the homeowner, and tips for homeowners (Appendix 2) on how to select a good and qualified contractor for deck repairs or replacement.
Deck components and elements as well as related code requirements are presented and explained in layman’s language supplemented with detailed illustrations (such as Photo 4). The applicable code requirements for different deck components and elements are presented and discussed using example photos of details that are proper and code conforming, and others that did not work and why.
The 127-page 8.5”x11” book includes a detailed Residential Deck Inspection Checklist that could be extremely helpful for a homeowner when addressing the reported deck deficiencies given in the inspection report, serving as a third-party assessment of the risk involved for different deficiencies. The Checklist is designed to document the condition of an existing deck and includes specific deficiencies and recommended actions for each condition/deficiency that may be indicated by the inspection. The recommendations for addressing specific defects range from:
- Recommend,
- Strongly recommend, to
- Do not use deck. Strongly recommend professional evaluation.
The standard practice for residential home inspectors when reporting a deck defect is to recommend further evaluation by a “qualified” or “licensed” contractor, or “design professional.” Homeowners should know that home inspections, per standard practice, are based on visual observations only. For example, a home inspector (by standard practice) is not required to remove a nail, screw, lag screw, or bolt to inspect for corrosion of the shank or to investigate potential defects beyond what is visually apparent. If a home inspection report indicates a deck defect, homeowners are strongly encouraged to heed the advice given for “further evaluation” by a licensed contractor, engineer, design professional, or other qualified professional.
Concluding Remarks
DCA6 and Deck Codes + Standards (2024) can help an inspector gain knowledge of current deck code requirements, know what to look for and where to look for potential deck deficiencies, and report the results of the inspection in a manner that communicates the importance of the noted deficiencies with corresponding recommendations for the homeowner. Inspecting an existing deck for continued safe use is challenging because of potential deterioration of materials (lumber, decking), fasteners (nails, screws, lag screws, bolts), and connectors (joist and stair stringer hangers, beam to post or post to footing). Wood decay and/or corrosion of fasteners and connectors may not be visible and can reduce the strength of the critically important deck elements.
A unit on “Deck Inspection—Focusing on Life Safety Issues” will be presented at the April 2025 Virginia Tech short course, Structural Design of Wood Structures, being held on April 16–17 in Blacksburg, VA. For more information and to register, visit the Virginia Tech short course website.
Frank Woeste, P.E., Professor Emeritus, Virginia Tech (VT), conducted wood engineering research and taught wood design courses throughout his 26-year tenure at VT. In cooperation with other faculty and wood industry professionals, he has developed and participated in VT continuing education programs for more than 30 years.
Joseph Loferski is a retired professor from the Department of Sustainable Biomaterials at Virginia Tech, where, for 45 years, he taught classes and conducted research on wood, wood construction, and durability of wood materials.