Make Safety a Priority: Key Considerations for Residential Deck Design
As we head into the fall, families across the country have been spending more time in the backyard, often on their porches or decks. This fact serves as a good reminder of the importance of ensuring the safety of the outdoor spaces we enjoy so much. Unfortunately, deck collapses all too often occur in the summer and fall seasons. According to recent industry reports, 6,500 people have been injured from collapsing balconies and decks in the United States since 2003. Complicating matters for existing homes, the North American Deck and Rail Association (NADRA) estimates there are 40 million decks in America that are more than 20 years old. This means they were installed prior to today’s building codes. Amidst this reality, homeowners and builders alike are encouraged to evaluate older structures to make sure they are renovated and compliant with current safety standards.
To help address this issue and encourage compliant deck design and construction, the American Wood Council recently published updates to its Design for Code Acceptance #6 – Prescriptive Residential Wood Deck Construction Guide (DCA 6) – reflecting new requirements found in the 2012 International Residential Code (IRC) and other new provisions pertaining to single-level residential wood deck construction.
The guide provides an overview of several design considerations for residential decks in accordance with recent building code changes and updated industry practice, including new requirements for lateral hold- down tension devices; shorter deck length (length must be equal to or less than the overall deck width); limits on post heights; the addition of 2×6 deck joist spans; additional footing options; and, the addition of a new table for glued laminated timber beams (glulam). All of these updates, along with ongoing minimum requirements and limitations for wood deck construction, are important for builders to know to ensure safe deck design. A few special areas for attention with regard to new minimum requirements include post heights, deck length to width ratio limits, and the use of glulam for beams:
- Post Heights: Post heights are tabulated along with footing sizes in the new DCA 6. The 2012 IRC requires residential decks to withstand a minimum of 40 pounds per square foot, in addition to the weight of the deck itself. A minimum post size of 6×6 is specified, but options are available for 4×4 posts in the Commentary.
- Deck Length to Width Ratio Limits: New to the 2012 DCA 6, the overall deck length must be equal to or less than the overall deck width. This 1:1 ratio limit is similar to open-front structures defined in AWC’s Special Design Provisions for Wind and Seismic. Larger aspect ratios may be permitted when designed by a registered design professional.
- Glulam: A new table for glulam timber beam spans is incorporated in the 2012 DCA 6 allowing for up to 18 foot spans. Note, all lumber and glulam used should be a naturally durable species – such as Redwood or Western Cedars having heartwood for 90 percent or more of the width of each side – or be preservatively treated with an approved process in accordance with American Wood Protection Association standards. Aside from understanding basic minimum requirements, the International Code Council and NADRA also suggest inspecting existing decks for tell-tale points of failure, including split or deteriorating wood, loose or missing nails, screws or anchors where the deck is attached to the building, and wobbly handrails or guardrails.
Whether you are a builder or homeowner, deck safety needs to be a priority. Builders should stay up-to-date on the latest building code changes, keeping in mind there are usually updates reflected in the IRC and the DCA 6 guide at least every three years, in addition to state and local amendments. Homeowners should work with qualified inspectors to ensure their decks are compliant with today’s building code.
Stay safe during the outdoor season by ensuring your decks adequately meet all current codes and requirements.
The full DCA 6 Construction Guide and other resources related to code-compliant residential design are available on the AWC website, www.awc.org.
John “Buddy” Showalter is vice president of Technology Transfer at American Wood Council. Find more information at www.awc.org.