Expert: Dan Griffin - 7/18/2011

Question
I just completed a pergola over my existing patio.  It has some unexpected sway that I am trying to determine if is normal.

The pergola is constructed out of red cedar.  It is attached by a 2x8 ledger to the house.  2x6 stringers on 22 inch centers then span about 14 feet to a double 2x8 beam which is supported by two 4x6 posts.  The posts are supported on two 8 inch piers and are attached to the piers using post-brackets.  The post-brackets are attached using eight 1 3/4 inch screws.  The beam is attached to each post with four 3/8 inch x 3 1/2 inch lag screws, two from each side.  There are two 26 inch braces on either side of each post going upward at 45 degrees (looks kind of like an upside "Peace" sign).  These braces are attached to the beams by two 3/8 inch x 3 inch lag screws, one lag screw from each side of the beam, and are also attached to the posts by one 3/8 inch x 4 1/2 inch lag screw holding each brace to the side of the beam (e.g., there three lag screws supporting each brace).

There are two levels of 2x6 stringers; the lower level perpendicular to the house and a second level on top of the first which is parallel to the house.  The upper level is on about 20 inch centers.  Overall width is 16 feet.  The posts are about 11 feet apart.  The pergola is assembled using notches and stainless steel screws.  It was not from a kit (I cut all of the lumber).

My issue is that the front of the pergola kind of sways slightly side to side if pressed.  It is very solid if the posts are pushed towards the house; however, if the posts are pushed parallel to the house it gives slightly; visually apparent.

My question is whether this swaying is normal for a pergola attached to the house, or if this is something I should be worried about and if so if you have any suggestion as to what I should do about it.

Thank you.

Answer
David, if this had a roof on it, it would be quite rigid.  The loose pergola design never creates a diaphragm.  The knee braces you describe should have stabilized the outside beam, but you note that there is still some movement.  Each connection has a little give and then you notice a larger total move.

The easiest way to create the rigidity you want is to install an x brace in your base set of rafters.  This can be done with a sawn in metl wind brace like this:
http://www.strongtie.com/products/connectors/WB-WBC-TWB-RCWB.asp
look at the TWB brace.

You could also use aircraft cable with turnbuckles or all thread with turn buckles.  I hope this solves your problem.