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Building A Pergola On A Deck

A pergola is a structure built to provide overhead shade. It is usually supported on four sides by vertical posts that hold in place a lattice of wooden members. Some pergolas are attached to the house at one side with a ledger board. If you plan to do this, make sure you take all the same precautions to maintain a watertight connection using flashing and caulking. The sizes of the overhead members can vary but the lowest boards in the assembly will be the heaviest. Beams attached to posts will support one or more layers of cross members. The spacing and size of these members or louvers will dictate the amount of sunlight that is allowed to penetrate and the visual mass of the structure. Sometimes vines are trained to grow through the latticework to provide a lush natural canopy.

Pergola Design Ideas

This cedar pergola is supported by vinyl columns with a decorative capital.

This is a wood arched pergola. The rafters were probably cut from 2x12 material.

This white vinyl pergola kit was attached to the house wall with a ledger board. There is an extra layer of 2x2 slats installed over the rafters for extra shade cover.

This ipe pergola is designed with an asian influence. Notice the decorative knee braces.

This curving pergola uses a zig zag rafter tail design.

This formal white pergola features classical dentils along the frieze. Also notice the curtains.

This is a unique pergola post to header detail with decorative bracing.

This polynesian themed pergola uses a quad post detail built from (4) 4x4 posts accented with trim.

This cedar pergola uses bidirectional rafters to suppert a concentric square 2x2 canopy.

This hip style pergola is built up from cultured stone columns.

This SouthWest style pergola uses a heavy timber beam and adobe column bases.

This sea side pergola uses billowy fabric to create a light weight shade cover.

This pergola has trained vines draped across the canopy to create a natural vegetative shade over a hammock.

This classical pergola uses doric columns and a coffered 9 square open roof.

This wood pergola is installed above an octagon deck.

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For pergolas and other overhead structures, they are certainly subject to building codes. While intended only for shade, these structures often support hanging swings. Depending on the design, slats overhead intended for shade, may be close enough to support bridging snow. Due to the structure of some snowflakes, snow is able to bridge over gaps as big as 4 inches or more. Snow piling up on a pergola likens it to that of a roof. Even without snow bridging possibilities, many building authorities will assign a minimum 20 psf live load for the structure to support. 

It is very important to properly attach pergola posts when installing a pergola over a deck.   The main concern is how the structure will react under high wind conditions.  Most deck builders bolt pergola support posts to the frame of the deck using (2) 1/2"x6" lag screws with washers per post.  This technique is the same as attaching a rail post.  Pergolas are top heavy and can sway in the wind without lateral bracing and can act experience strong uplift forces as the pergola acts as a sail.  Attaching sections of rail in between pergola posts will strengthen the pergola.  Installing 45 degree bracing in between the post and header beam will also increase stability.  Using 6x6's for support posts will further strengthen the structure.  Deck Lok brackets are an option for extremely windy areas and hurricane zones. 


Comments, Questions and Reviews


I also saw this under gazebo construction. "We recommend using continuous 6x6 posts to support the deck and roof structure. In order to do this you will need to notch out the posts to accept the deck beam and roof header." I would have thought the deck beam notch in the 6x6 would make the upper pergola posts less stable but perhaps I am mistaken and this is the ticket.

posted by markhusbands at 12/4/2014 3:20:43 PM

I''m interested in building a ground level or near ground deck with a pergola. In this case is it better to mount the 6x6 pergola posts directly to the deck footings, and attach the deck beams to the sides of the posts with carriage bolts, or mount the deck beams to short notched posts (on footings) and then mount separate pergola posts on the deck surface?

posted by markhusbands at 12/4/2014 3:06:49 PM

Mark, better to two two sets of posts, one for the deck and one for the pergola. Carriage bolts connecting beams to sides of support posts bear the entire load of the deck, which you want to avoid. They work that way on ledgers when you put in lots of them between every joist you can''t do that where there are only a few posts.

posted by GaryShanno at 7/4/2015 8:37:34 PM