The Problem
To understand why the attachment of the column is more difficult than one would expect, we need to recall one of our basic science lessons from elementary school. When the column is pushed from the side it acts like a simple lever. The column is the effort arm and the point of attachment is the pivot point or fulcrum. A very small force applied at the top of the column will become very large at the base. Likewise a tiny movement at the base will be magnified greatly at the top of the column. This will vary depending on the column length and type of attachment, but is significant in all.

One solution that works very well is to use bracing. Diagonal braces attached to the columns will increase the stability for most pergolas enough that little or no post attachment to the floor surface is needed. The problem with bracing is aesthetics - they just don't look right on most pergolas. They are fine for casual or rustic structures but totally inappropriate for more formal pergolas particularly those with round columns. Therefore we need to find a secure way to attach to the surface in a way that minimizes movement and most of all, prevents the structure from collapsing.

Surface Type is a Major Factor
Not all techniques will work with any surface. Although there are many types of surfaces that a column may be attached to, we will address the most common: wood decks, concrete with or without stone or brick, concrete pavers, and grass.

Wood or Composite Decks.  The good news is that it is easy to securely attach a bracket to wood and most composite decking. The bad news is that the decking is almost certain to deflect or bend if pressure is applied to the side of the column, unless the pergola is also attached to the house or other structure. For this reason it is best to have an attachment method that has a structural member of the column extend through the decking and attach to the framing of the deck. If the column can only be surfaced mounted then additional framing should be added below the decking to minimize deflection. In either case blocking should be added between all of the floor joists. This will help spread the load. We strongly recommend the use of 1/2" carriage bolts or threaded rod to secure the brackets to the framing. Lag screws are not a good long term fastener for this application.

Concrete. A concrete slab with or without a covering of stone or brick is a common surface for pergolas. Steel and heavy aluminum mounting brackets work well on these surfaces because they do not move at all if the concrete and any surface covering it is sound. Some movement should be expected especially if the pergola is freestanding. Remember even a tiny movement at the base will be multiplied as you get higher on the column. Not all columns will work with these brackets. In that case, the most common approach is to cut a hole in the concrete and use a wood post or other ground mount.

Grass or Earth. Probably the easiest to deal with, mounting a column in the ground can be with a wood post, aluminum or steel ground mount, or surface brackets with concrete piers.

Concrete or Stone Pavers. Generally speaking this type of surface should be treated as a ground mount because the pavers will move when pressure is applied to the side of the column. Simply remove the pavers, install the mount and column and replace the pavers cutting them as necessary to fit. The one exception to this is when the pergola is attached to the house or other structure. The attached structure may provide enough lateral stability that none is required from the column attachments.

There are Several Techniques to Attach Pergola Columns.

Column Concrete Mount:
Mount is bolted to concrete on top of leveling plate with masonry bolts.  Smaller bolts are used to level mount by compressing against leveling plate. The column, which has a matching aluminum structural tube, is slid over the aluminum pipe of the mount. This mount has the advantage of four point attachment rather than a single bolt. Also, the leveling bolts allow the installer to get the column plumb without having to use shims which are inaccurate and time consuming. Backyard America offers this type of mount for our 8" and 10" round columns. It will not work with other types of columns.

Column Concrete Mount - Modified for Wood Mount:
Using the column concrete mount outlined above, installation with threaded rods and wooden blocking will allow for attachment to a wooden surface, such as a deck.  A wooden board will be added under the decking surface and secured to the existing decking framing.  In addition, blocking should be installed between all of the floor joists to help spread the load and reduce deflection. The decking, as well as the new board will be drilled out to accept the threaded rods.  Each end of the threaded rods will have a washer and nut installed on them.  Then, the entire mounting assembly is tightened down to compress the mount to the decking and bracing.

This type of mount has the advantage of easy placement without concern over existing blocking or framing placement.  You can simply add the blocking and the mount where you need it.  In order to have this mount remain as secure as possible, attachment of the wooden blocking is critical.  There will be some movement, especially if the pergola is freestanding, however it should be acceptable if installed properly.

Column Threaded Rod Installation:
Threaded rod is available in lengths of 8' and longer. It is commonly used to secure columns of all types as long as there is a hole through the center from end to end. The rod is epoxied in a hole that is drilled into a concrete slab or pier. The column is slid over the rod. At the top of the column a nut is threaded on the rod and tightened against a custom made adapter.

The rod does not keep the column from moving at the base so a base plate is required. The picture at right shows the rod passing through the base plate that is available with our 8" and 10" round columns.

The threaded rod technique works well if the column is designed for it and if the top attachment hardware is available. It is often used with fiberglass columns because they typically are not designed to work with pergolas.

Column Ground Mount:
This is a mount made specifically for our 8" and 10" round vinyl columns. An aluminum pipe is put 30” into the ground, and set in a minimum of 8” of concrete. The column has a matching structural aluminum tube inside of it which is dropped down over the ground mount. Backfilling the hole completely with concrete will reduce movement even more.

The advantages of this type mount is that it is fast and relatively inexpensive. The disadvantage is that it only works with the columns it was designed for.

Steel and Aluminum Post Mounts:
Originally designed for railing and fence posts, post mounts will also do an adequate job for square columns when attached to concrete. We have them in 4", 5", 6" and 8" square sizes with lengths of 24", 36", and 37". Typically, they are installed by inserting four threaded rods into pre-drilled holes in the concrete. The rods are secured to the concrete with epoxy. A leveling plate and the mount are slid over these rods and tightened down by nut and lock washer.  Bolts are tightened against leveling plate to plumb the mount.

This type of mount works well with square vinyl columns. The mounts must be designed for the columns so that there is a tight fit to minimize movement of the column. There will be some movement, especially if the pergola is freestanding, however it should be acceptable if installed properly.

Steel and Aluminum Post Mounts with Wood Mount Adapter:
Using the standard post mounts outlined above, an optional wood mount adapter kit can bee added to the post mount to increase the versatility of the mount.  The wood mount adapter kit consists of two heavy metal plates and the needed attachment hardware.  A wooden board will be added under the decking surface and secured to the existing decking framing.  The decking, as well as the new board will be drilled out to accept the bolts for the wood mount adapter kit.  The entire mounting assembly is then tightened down. 

This type of mount has the advantage of easy placement without concern over existing blocking or framing placement.  You can simply add the blocking and the mount where you need it.  In order to have this mount remain as secure as possible, attachment of the wooden blocking is critical.  There will be some movement, especially if the pergola is freestanding, however it should be acceptable if installed properly.

Aluminum Ground Mount:
This extruded aluminum mount is designed specifically for vinyl 5" post sleeves.  The mount is put 36” into the ground, and set in a minimum of 8” of concrete. The mount will snuggly fit the inside of the 5" vinyl sleeve. This mount is available in multiple lengths depending on both the height of the post sleeve, as well as the desired depth in the ground.   Backfilling the hole completely with concrete will reduce movement even more.

The advantages of this type mount is that it is fast and relatively inexpensive.

Treated Post Ground Mount:
If the column is a hollow wood or vinyl sleeve, one of the lowest cost and easiest ways to mount it on the ground is with a pressure treated post. The pressure treated 4 x 4 or 6 x 6 is put at least 30” in the ground with at least 8” set in concrete. Backfilling with concrete will add additional stability to the column. For most sleeves, the post will have to be padded out to keep it from moving from side to side. If a cedar wood sleeve is used, care should be taken to keep it out of contact with the soil to minimize the chance of rot. This can be done by attaching the sleeve to the post with stainless steel screws.

The treated post mount is easy and relatively low cost. It can be the most stable mount as well, particularly if a 6 x 6 post is used.

Treated Post Framing Mount:
This technique is used on decks and porches with vinyl or wood sleeves. In this case, the 4 x 4 or 6 x 6 is attached directly to the structure's wood framing using carriage bolts. Additional blocking should be added to increase the stability of the connection.

Surface Wood Post Mount:
A wide range of mounts for attaching wood posts to concrete and wood surfaces are available. Simpson Strong Tie and other manufactures make code approved connectors and fasteners for a wide range of applications. The drawing at right shows a typical "boot" type mount. The mount is bolted to concrete using a masonry anchor or screws.  The wood post is inserted into boot, plumbed, and attached with 4 screws on each side. The installer will typically cover the mount with matching trim.

Wood post mounts are a good choice for attaching wood columns to concrete or to decks when the framing is not accessible.