Learning how to cap your pergola posts will keep them lasting longer and prevent swelling and splitting.
Exposed wooden posts tend to split over time. The sun beats down on the wood (even when stained and sealed), drying it out and shrinking the wood fibers. Then rain, snow, and ice penetrate the post, causing swelling, warping, and weather damage.
Here’s the good news – topping your exposed posts with plastic post caps will keep them pristine.
How to Install a Pergola Post Cap
As a recap, here are the steps we’ve already covered:
- How to Install Pergola Post Brackets
- Staining and Sealing Pergola Wood
- How to Install Pergola Posts
- Wall-Mounting a Pergola Frame
- How to Frame a Pergola
- Installing Pergola Rafters
Installing your pergola post caps is the simplest part of building a Pergola. Here’s what to do.
Step 1: Measure for Your Post Cap
Post caps are available in a variety of sizes. You need to measure the true size of your beam – in this case, a 6×6 cedar beam measures just shy of 5.5”x5.5”. Pay attention to the interior measurements of your post cap, especially if you’re ordering online.
The underside of the cap looks something like this. Pretty straightforward.
Step 2: Fit the Cap on the Post
Before you do anything else, place the cap on the top of your pergola post. If your post is at the height you want, and the cap fits, you’re done. You don’t need to glue or screw it as long as the cap is a snug fit.
But if you want to trim down the height of your pergola post, it’s time to measure and mark the height you want.
Step 3: Measure and Make Your Posts
When measuring, make sure there’s enough space on your remaining pergola post so the cap can slide down over it. Now connect your marks with flat, level lines across two sides of your pergola post – the side you’ll be sawing from and the side you’ll be looking at as you saw.
Step 4: Cut the Posts with Reciprocating Saw
You’ll need a reciprocating saw blade large enough to cut through the width of your pergola post. Remember to account for the back-and-forth movement of the blade while sawing; this will require a few extra inches on either end. Consider the diagonal distance as well. A 4×4 post, for example, will cut just fine with an 8” saw blade. But a 6×6 post, as shown in this example, requires a much longer blade of 12” in length.
Line up your reciprocating saw blade with the first flat, level line you’ve marked.
Hold it at this level firmly as you begin sawing, making sure you stay level on both ends of the saw.
As your saw blade gets further into your pergola post, your second drawn line comes into play. Do your best to maintain the level on the far side of the saw (since you can’t see over there), and be sure to follow along your second-level line. Doing so will maintain a flat, even cut for your pergola post.
Set your pergola cap on top of the pergola post, pressing it down as tight as it will go.
The caps complete the look for a modern pergola frame, with the added benefit of being a protective final step.