This is my first post to this forum. I am building a pergola over my existing deck. The deck construction itself is made up of 6 x 6 vertical support posts, topped by 6 x 12 horizontal support beams and then 2 x 8 deck joists running 16" OC. It is currently topped with redwood 2 x 6 deck material. The pergola I am constructing consists of 6 4 x 6 Doug Fir vertical support posts (3 front / 3 back). The 4 x 6 posts are sandwiched by 2 x 8 Doug Fir beams which are through bolted on the 4 x 6 vertical posts. The maximum span on the doubled 2 x 8's is 12'. On top of the 2 x 8's I am running 2 x 6 rafters which are placed 16" OC and have a span of 9'. Hopefully that gives everyone a baseline on the bones of the current design. My question is if how I am connecting to the existing deck is sufficient. I have gone underneath the deck and mounted six 4 x 6 beams between the 6 x 12 main support beams of the deck. These 4 x 6 beams have a max span of 9'. I removed the deck boards above the new 4 x 6 support beams and dropped the vertical posts onto the beams below it, strapping and bolting the posts to the beams using Simpson Strong tie accessories. In addition to that, I aligned the 4 x 6 horizontal support beams so that one side of the vertical pergola posts would sit flush against one of the existing deck joists. I then bolted each vertical pergola post to the existing 2 x 8 deck joist structure. So each vertical pergola post is bolted to own 4 x 6 horizontal support beam distributing the load to the existing 6 x 12 deck beams and is also bolted to the existing 2 x 8 deck joist structure. Lastly, I "boxed-in" each pergola post between the deck joist system using scrap 2 x 8 material for added stability.
Can anyone comment on whether this sort of set up should be sufficient or should I consider placing additional support beneath the deck? Based on my calculations, the pergola weighs about 1500 lbs. The weight should be pretty evenly distributed across the 6 vertical posts which would be about 250 pounds per vertical support carried by the 4 x 6 horizontal beams and the 2 x 8 deck structure below it.
Thanks and sorry for the lengthy explanation.....hopefully it makes sense.
OK, haven't heard from anyone so I assume I have confused some folks. I added four pics, one of the Pergola and deck (work in progress) and three photos of the underside of the deck showing the 4x6 cross members set perpendicular on the main 6x12 beams and two other pics which show the vertical 4x6 pergola posts notched and seated on top of the 4x6 cross beams as well as lagged into the existing 2x8 deck joists....any comments on strength of this design....sufficient or should I consider dropping 4x4 posts under the 4x6 cross members and taking them all the way to the ground? Other ideas?
Last edited by cpfullback; 08-12-2011 at 10:56 PM.
Reason: Adding Pictures