I'm a new homeowner with DIY enthusiasm to improve the outdoor living space. Recently completed build my fence now planning to do a pergola first and then add deck to it so we can enjoy some outdoor space. I have a question about pergola post where instead of concrete footings can I lay 6×6 or 4×6 lumber on the ground with gravel underneath and secure them by driving 12 or 24 inches rebar through wood into the ground and attach the 4 pergola posts to them using bolts. Our winters temperatures generally get down to -5f maximum and we see winds with maximum speeds to 60mph. I have seen videos on YouTube doing this using some fancy connection hardware but I thought using bolts should work. I ask this question as later when I do the deck after pergola it would be a bit easier to build deck. The size of pergola will be 10×10. Any thoughts would be appreciated.
Here is a link to one of the videos I saw on Youtube
Pergola Post attached to ground lumber
Best Answer
You say you get winds up to 60 MPH but you don't see a need to have a tall structure anchored in concrete? Sure, most wind will likely whistle right through an open(ish) pergola, but all it takes is one good gust, square on the flat side of the roof joists, and it'll blow right over.
Even if you were to thread the top of the rebar and use nuts & bolts to hold the lumber to the top of the rebar, a 24" piece would pull right out of the ground with a 60 MPH wind pushing on an 8-10 foot tall lever. Additionally, rot (even with pressure treated lumber) will enlarge the holes in your sleepers and the fit between the wood and the steel will get sloppy. The rebar will rust, exacerbating the issue.
I've used rebar through holes in treated landscape timbers as edging for my gravel driveway. I've had to replace the lumber 3 times in less than 30 years. The timbers laying on the ground (granted, they weren't carefully installed with gravel for drainage, but still) rotted out to the point that there was not much left of them. After picking up chunks of rotted wood, it just took one or two hits with a 2 pound hammer to loosen the rebar enough to pull it out of the ground by hand. A perfectly acceptable installation method for something at ground level, but I sure wouldn't want to visit your house knowing that this was all that was securing hundreds, if not thousands, of pounds of lumber over my head.
There's a reason you see people using "fancy connections": A) it's required by code, and B) it's safe. Note that code is often "written in blood" - accidents have happened; engineers have studied what caused the failure; code was updated to require a minimum construction to prevent that kind of failure from happening again.
Frankly, renting a powered auger to drill a few holes for footings (be sure to check for buried utilities before drilling), getting them drilled to below the frost line (again, be sure to check for buried utilities before drilling), inspected (if necessary in your locale), filled with concrete and setting post anchors in them is far cheaper and simpler than the potential damage to people and property if this should fall over. Think of the hospital bills on top of the house repair, and possible lawsuits from people you thought were your friends, should your short cut method fail.