A Pergola on Existing Retaining Wall



A Pergola designed atop a Unilock stacked wall, (glued together). This very substantial and rigid pergola will stay put for decades even though the wall was not designed to support a pergola. This pergola would sit directly on a patio without fastening and would not move. When you have a complex or challenging pergola project, get in touch with Gardenstructure!

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Pergola in Existing Retaining Wall

Can you install a pergola on our existing retaining wall?

  Yes, you can, however, the interlock retaining wall needs to be well constructed and the pergola needs to be designed to do it!

We hear it all the time. This was a unique case. They wanted a pergola to sit on a stacked wall of Unilock Stone. These are basically interlocking stones that are glued together. Not much lateral strength to something like that. You can’t just build your typical pergola and expect it to last beyond the first windy day.  In this case, we had to create a self-bracing pergola that would be heavy enough to stay put, and structurally rigid enough to not rack the block apart. The large braces are made of marine plywood.

Designing a Pergola on Existing Wall

Designing a pergola on an existing stone wall was not easy in this case. The builders of this interlock retaining wall didn’t consider past the need to rough in pockets for 4×4 posts and we were not keen on rebuilding what they built. The patio and interlock retaining walls were just too pretty. So, we designed around it.

The wall was fairly sturdy, lots of glue was used. We only had a 4×4 pocket, so we used 4×4 PT posts at the core, and built them out to a more substantial 8×8 post. For this pergola on retaining wall to stay put, we had to make sure it would not rack in any wind. This was a fairly sheltered location as well. I am not sure I would attempt this in the middle of a field in Florida, but for this inner city Toronto home it worked fine.

As long as the Pergola would not wiggle within the retaining wall, it would not work the stones loose. Giving the pergola enough mass would also prevent movement. We opted for massive marine plywood braces. The braces were laminated 3 layers thick and are equivalent to the transom of a boat for strength.

Details for this pergola are available in plan form–just click the link!

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