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How To Build a Pergola On an Existing Deck

Have you ever seen a pergola on a deck? If you have a large deck, but lack shade, adding a pergola is an attractive option. You may have seen a pergola, arbor, or gazebo in a neighbor’s yard and wondered if you could add one to your deck. The short answer is…probably. Today, we will investigate how to add a pergola onto your existing deck.

What Can I Build?

The design of your pergola will be limited only by the design and size of your deck, and where it will go. Below is a sample list of questions you will need to answer before beginning your pergola project:

  1. Will your pergola be free standing? 
  2. Does your design require the pergola to be attached to the home? 
  3. What will the pergola cover?

Tools You May Need to Build Your Pergola

You will need a few carpentry tools, as well as safety gear. Below is a list of common tools required for this project, but your design may require others as well:

  • Circular saw
  • Ladder
  • Bar clamps
  • Drill and bits
  • Level
  • Carpenter’s square or speed square
  • Handsaw or reciprocating saw
  • Jigsaw (if your design includes curves)
  • Hammer
  • Tape measure
  • Pencil or marker
  • Wood chisel
  • Socket set or wrench
  • Sawhorses (2)

Steps To Build a Pergola On an Existing Deck

Safety First

As with any home improvement project, avoiding injury is the most important step. Make sure that you have eye and ear protection, gloves, and any other safety gear you feel is necessary to do the job safely. We also recommend having help available.

Step 1: Location

The location of your pergola is important to both the quality of the project and its usefulness. For example, many do-it-yourselfers attach their pergola over an exterior door, usually one that leads to a deck or patio. Regardless of the location of your new pergola, get any approvals you may need before beginning your project. Some local jurisdictions will require a permit, while others may not.  Also, we advise consulting your architectural committee if you live in a restricted subdivision, as some prohibit any outdoor additions.

Step 2: Layout

When you have your location selected and your required approvals, you can lay out your project. An important consideration when laying out your pergola is what it will be covering. In the design phase, try to envision how the pergola might be used. Many will place a swing or bench under the pergola.

Pro Tip. If you plan to just have seating under your pergola, you probably won’t need to strengthen the deck. However, if you plan to cover a hot tub or other heavy feature with

your pergola, you will likely need to add joists and/or braces to support the weight. 

Step 3: Install the Posts 

After you have your footprint, you’ll need to locate where your posts will be attached to the deck. In most cases, using widely available hardware to connect your pergola is your best option. We’ll assume you are building a four sided pergola. Many deck mounted pergolas are attached to the house, but if yours will be free standing, you will simply add two additional posts in a similar manner. 

Starting from a corner on the house side, measure out away from the house and mark the dimension of your design. Do the same for the other side. Now, with a helper, measure diagonally from corner to corner, and make a mark on the deck. If your layout is accurate, the lengths will be exactly the same. These two marks will be the locations of your posts. Ensuring that you have adequate support underneath, connect the bottom of the posts to the deck using galvanized post connectors. 

Next, nail two small 2” x 4” boards to the deck, one of each side of the post, and attach a full 2” x 4” to it, allowing it to pivot. Plumb your post in both directions and nail the braces to the posts about halfway up. Do the same for the other side.

Step 4: Install The Beams

At this stage, you are ready for the beams. These will connect the posts to the house and support the rafters. To make this connection, first clamp a beam to the post and drill at least two pilot holes all the way through the beam and post. Bolt these together using galvanized carriage bolts and repeat for the other side. 

To make the connection to the house, you will need to install a ledger board. This will serve as support for the roof rafters and will require a modification to the house, depending on the exterior. If your home has siding, the ledger board is mounted to the framing underneath. If your home has stucco, the ledger board will be attached through the stucco into the wall framing. However, if your home has brick, the installation becomes much more involved. 

To attach a pergola to a brick exterior, a long piece of steel angle iron called a lentil will likely be required. This is done by removing a small section of brick and bolting the lentil to the wall framing. Attaching your pergola to the brick is not an option, because should your deck move, it will likely take the brick with it. The ledger board can now be attached to the wall framing below the lentil and the brick replaced. The ledger board will hold up the pergola, and the lentil will support the weight of the brick.

Step 5: Set The Corner Braces

Your pergola design will have rafters to support the roof and will likely involve bracing to add support to the beams. To install these braces, cut four short sections of lumber the same dimension as your beam. On each end, cross cut a 45 degree angle. Connect a brace to the two outer sides of each post and then to the beams using galvanized lag bolts.

Step 6: Set The Rafters

Depending on your design, you may have gable rafters, shed rafters, or even hip and valley rafters. The rafter layout will determine the shape and style of your pergola, so select it carefully. A shed style rafter design remains very popular due to its durability and ease of installation.

The rafters will get most of the attention, so taking extra time to make them attractive is important. Most pergola builders will cut decorative curves or angles into the ends to improve the overall appearance. If you plan to do the same, make these cuts on sawhorses before installing the rafters. Attach your rafters to the ledger board with weather-resistant screws, spacing them evenly to reduce material waste. If your design will have louvers, install them on top of the rafters. 

Your New Favorite Spot

Many of us long for a peaceful spot to watch a sunset, listen to music, or just get away from it all. Building a pergola yourself is a rewarding project that can add not only value to your home, but great enjoyment. You might find that your new pergola becomes the preferred gathering spot for the whole family.

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