How to Build an Attached 16 X 20 Pergola

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(Image: tape measure 1 image by Martin Grice from Fotolia.com)

A pergola built onto the backyard of a home can be an attractive and inviting addition to any landscaping project. When a pergola is attached to the home, it becomes an extension of the home itself. Attached pergolas are often used to cover patios or decks, and in this way provide shade and help to cool a sunny deck. An attached pergola also needs fewer support posts and requires less work to anchor the supports than a fully detached pergola.

Things You'll Need

  • Rubber mallet
  • Mason’s string
  • L square
  • Measuring tape
  • Stakes
  • Hurdle
  • Post hole diggers
  • Gravel
  • Carpenter’s level
  • Cement
  • Garden hose
  • Wheel barrow
  • Trowel
  • 2 redwood cedar boards, 4X4 inches each
  • 11 cedar boards, 2X4 inches each
  • Jig Saw
  • Hammer
  • Nails
  • Drill
  • Half-inch drill bit
  • Carriage bolts
  • Phillips head screwdriver bit
  • Wood screws
  • Hurricane clips

Drive two stakes into the ground at the foot of your building just below where the pergola will attach to the home. Tie a mason’s line to a stake and place an L square on the ground beneath the line so that one ray of the square is parallel with the house and another is perpendicular. Tie the mason line to a hurdle, and place the hurdle so that the mason’s line aligns with the L square. Repeat this process for the other side of the pergola. Tie a mason’s line to two more hurdles, and place them at the 20-foot point at the end of the pergola. Use the L square to ensure that the corners are all perfectly 90 degree angles. The point where your mason lines intersect is where your posts will attach.

Measure your 4X4 posts. Dig holes at the two intersecting mason lines that are as deep as one-quarter of the posts with your post holes. Add 2 inches of gravel to the bottom of these post holes, then insert the two posts into the holes. Prop the posts upright with the 2X4-inch boards. Ensure that the posts are vertical with a carpenter’s level.

Mix cement in a wheelbarrow with water from a garden hose until the cement is the consistency of a mud pie. Using a trowel, transfer the cement to the hole in the ground. Allow the cement to dry and cure before removing the 2X4-inch braces.

Measure and cut three of your cedar boards so that they are 16 inches wide. Attach one of your boards to the side of your home as an anchor board using a hammer and nails. The board should be level with the tops of your pergola posts.

Drill a half-inch hole, oriented toward your home, into the center of each post. Drill similar holes into the ends of your two remaining 16-inch-wide boards. Lift each board to the top of your posts, and sandwich the posts between the boards. Line the boards up with the posts so that the drill holes match up. Slip a carriage bolt between each set of drill holes and fasten securely. You’ve now created a beam for your pergola.

Lift one of your remaining 2X4 boards to the top of the beam and the anchor board to use as rafters. The rafter boards should rest on top of the beams and abut the anchor board. Angle the rafters so that they rest on their sides on the beam and attach them to the beams and anchor boards using hurricane clips.

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