Planning to add a pergola to my deck for shade and growing grapes and need help deciding if I should extend the posts of the pergola to the ground on a concrete base or if I can just attach it to the deck by replacing the existing corner posts used by the deck railing and just beefing it up with additional blocking.
Some project specs:
- Deck is 12x10’; attached to the house and supported by two 6x6 posts set on 16”(?) concrete pillars; the posts at the base of the stairs are set in the ground which presumably provides a small amount of additional support for that corner
- I will use 4x4s for upright posts (expecting some warping and cracking) because in my opinion the 6x6’s look too beefy for my small deck and I'm trying to keep the added weigh down
- I will use 2x6s for the cross beams and rafters
- This will be about 800lb of added weight, including the weight of the grape vine and any accessories, so 200lb per post
- The pergola will not be attached to the house, but will be ~2 inches away from the house at the closest point
Location: Greater Philadelphia Area
UPDATE (05/26/2020): Decided I'm comfortable with skipping the concrete base. For the four corners I will be using this style of blocking and tying everything together with plenty of structural screws. Its might not be necessary but I am also considering adding a sister board to strengthen the cantilevered portion of the outer joist. The outer joists did not have joist hangers connecting them to the ledger board for some reason so I will be adding that as well as securing the joists under the posts with DTT ZMAX Galvanized Deck Tension Tie Kit.
I am sticking with 4x4 upright posts and 2x6's for everything else, the trellis top will get covered with shade curtains and later grapevines so I don't care too much if they look "puny" as long as they are solid and strong. Toja Grid makes extensive use of 4x4s in their pergola kits so that gives me confidence in the strength of (properly secured) 4x4s.