How We Built a Pergola Over Our Existing Deck
For years my wife and I had been talking about how a pergola would be so nice over a portion of our backyard deck but I just couldn't figure out how to properly secure and integrate it into the existing deck structure without running into a huge amount of tearing out and redesign. Finally, a warm spring Saturday morning out on the deck with a fresh hot mug of coffee provided the inspiration for how to "get `er done"! Oh, the blue window box was an additional spice we added. Let your imagination roam!
Living near the coast in southeastern North Carolina we're very accustomed to occasional high winds, i.e., hurricanes. So my main concern was a secure foundation for any structure built on top of the existing deck. As I had built the deck with a very solid foundation of doubled up 2x8's for the girders on which were placed the 2x8 joists I simply needed to plan the corners of the pergola to be located near the intersection of a deck joist and girder. You do want to make sure though that your vertical posts extend all the way to the ground for additional stability. I recommend placing a concrete paver under each set of posts as well.
The photo below shows one of the four corner holes cut in the deck near the intersection of a joist and girder (the girder is barely visible below the deck surface, but it is there).
3/8" diameter carriage bolts were used to bolt the posts of the pergola to both the joist and the girder supporting the joists. In this design, I used two posts at each corner to add a bit of oriental design flair. This design also served to securely hold the support beam for the overhead rafters. And this brings us to the next step; building and mounting the two rafter support beams.
Rafter Support Beams
The photo at right shows one of the two rafter support beams. It was constructed by nailing and bolting two 2x8s together. Spiral decking nails were first used to nail them together. Then 1/4" carriage bolts were placed in pairs (one pair is shown in this photo) every 18" down the length of the beam. I don't have construction in process photos but I placed the support beam (they were very heavy!) by nailing a scab board onto the vertical post just below the height to which the beam was to be set. Shims between the scab and the support beam were used for final leveling before bolting the beam in position. 1/2" carriage bolts were used for mounting the support beams. These support beams carry the weight of the rafters and anything hung from them so for safety you must use bolts for attaching the support beams. Never use nails for attaching the support beam to the posts as they will not hold. Large C-clamps are also really handy for temporarily holding pieces for drilling the bolt holes. Once both of the rafter support beams were secured with the 1/2" carriage bolts we were ready to mount the rafters.
Mounting the Rafters
This was by far the easiest part of the whole job. 2x6's were used for the rafters. They were place on 16" intervals. They were also spaced so that one could be attached to each pair of vertical supports to give the structure stability in all directions. At this point we had a finished pergola and were ready for the fun of placing plants, lights and whatever else suited the fancy, ie a blue window!
And that's it! You can be creative and add all sorts of decorative plants and outdoor ornamentation. Make it yours and enjoy!