Should I use 2x6 or 2x8 joists for my deck in Fredericton?

Use 2x8 joists for your Fredericton deck in almost every scenario because the additional span capacity, stiffness, and resilience to long-term moisture exposure make them the superior choice over 2x6 joists for the modest cost difference. A 2x6 joist is only appropriate for very small decks or very short spans, and even then, the money saved rarely justifies the trade-off in structural performance.

The fundamental difference comes down to span. A 2x6 SPF joist at 16 inches on centre spans a maximum of approximately 8 feet under standard residential deck loading of 50 pounds per square foot combined. A 2x8 at the same spacing extends that to 10 feet. In Fredericton, where most residential decks run 10 to 16 feet deep from the house, a 2x6 joist cannot cross the distance without adding an intermediate beam and additional footings. That intermediate beam with its posts and footings sunk to Fredericton's 1.2-metre frost depth adds far more cost than the price difference between 2x6 and 2x8 lumber. At current New Brunswick lumber yard pricing, a 12-foot 2x8 pressure-treated board runs roughly $18 to $24 while a 12-foot 2x6 is $12 to $16. On a 16-foot-wide deck requiring 13 joists, the upgrade from 2x6 to 2x8 costs approximately $80 to $105 in additional lumber. A single concrete footing sunk to 1.2 metres in Fredericton's soil costs $150 to $250 installed, and an intermediate beam requires three to four footings minimum. The 2x8 pays for itself immediately by eliminating that beam.

Beyond span, stiffness is the quality you feel underfoot every time you walk across your deck. Engineers measure this as deflection, the amount the joist bends under load. Building code limits deflection to the span divided by 360, meaning a 10-foot joist can sag no more than about a third of an inch under full load. A 2x6 at 8 feet meets this requirement on paper, but in practice, Fredericton homeowners with 2x6 joist decks frequently report a noticeable bounce or springiness underfoot. This is because the code represents a minimum standard, and a joist at its maximum span is working at the upper boundary of acceptable deflection. A 2x8 spanning the same 8 feet deflects approximately 40 percent less, producing a deck that feels solid and confident rather than soft and bouncy. If you plan to place heavy items on the deck like a large ceramic planter, a full outdoor dining set, or a barbecue island, that extra stiffness is not a luxury but a practical necessity.

Fredericton's climate introduces a long-term consideration favouring the 2x8. The city experiences temperature swings from minus 25 Celsius in January to plus 30 in July, combined with Maritime humidity that keeps wood moisture content elevated for much of the year. Over 15 to 20 years, this cycling gradually weakens wood fibres through repeated expansion and contraction. A 2x6 at its maximum 8-foot span has less reserve strength to absorb that degradation than a 2x8 at the same distance. Building inspectors in the Fredericton area generally prefer to see 2x8 as the minimum joist size on new deck permits for this reason.

The one scenario where 2x6 joists make sense is a very small attached deck or landing, such as a 6x8-foot platform at a back door that primarily serves as a transitional space rather than a living area. At a 6-foot span, a 2x6 has ample capacity and the low profile helps when you need to keep the deck surface close to the door threshold height. For any deck larger than about 80 square feet or spanning more than 7 feet, the 2x8 is the right call.

Regardless of which size you choose, all joists should be pressure-treated SPF with MCA treatment, connected using 18-gauge minimum joist hangers such as the Simpson Strong-Tie LUS26 for 2x6 or LUS28 for 2x8, with stainless steel or exterior-rated coated fasteners throughout.

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