I'm building a large deck (16x30 feet) in the northeast and I've already dug 10 holes for 10-inch sonotubes to ensure they reach below the frost line, which is currently 44 inches deep. My main question is whether I need to add footings at the base of these tubes. Is the 10-inch concrete pier at that depth enough, or should I be using a larger footing, like 14-16 inches wide, beneath the sonotube?
2 Answers
Since you're building a big deck, it's definitely wise to consider footings. The larger the deck, the higher the chance of frost heave. It's generally a good idea to have solid footings to anchor it well, especially in areas prone to frost.
You need to think about the point load on each pier based on your soil type. Without calculating that, I doubt 10 tubes will suffice for a deck that size. I'd recommend planning for footing pads or using bell end tubes at the very least.
Do I need a form for that, or can I just dig out the hole wider at the bottom, raise my tube 8 inches, and fill it to create a footing that’s about 14 inches wide and 8 inches deep? The footing pads sound like a great option too! According to some online calculators, the point load per pier is estimated around 2500 lbs, especially since the deck is attached to the house.