How can I attach privacy lattice to a fence?

Nail support posts onto your side fence posts, then attach the extension, but a solid piece is going to take a lot of support due to wind load. Why not just plant fast-growing evergreens? Why would neighbors be so intetested in your yard?

Really hard to add to existing without replacing the fence posts with taller post to hold the addition. Will just blow over with a strong wind. Better just to rebuild a taller fence or as suggested plant hedges.

Hi Sam, How high is the current fence? How high a piece of lattice do you want to attach? We live in Maine and we have topped a board fence (4' high) with 2' of lattice. It has been up for years and is fine. (ignore lattice leaning. . . that came from our porch)

https://homeguides.sfgate.com/fence-lattice-extensions-83049.html

https://www.google.com/search?q=add+lattice+to+top+of+fence&tbm=isch&source=hp&sa=X&ved=2ahUKEwjcicmptenjAhVOJKwKHSGaCboQsAR6BAgEEAE&biw=1536&bih=740&dpr=1.25

Privacy lattice is available in wood or plastic, but both need to be set in a frame. Most often the frame is two 1x4s that sandwich the lattice. Sometimes a groove is cut into a 2x4 and the lattice is set into the groove. Here is a link to the first method. https://www.practicallyfunctional.com/simple-diy-trellis-screen/

The framed lattice is then connected to your existing post tops using metal L-shaped brackets and screws. Place a bracket atop a post so that the upright will be on your side of the fence, so it will be easier to attach to the lattice frame. Mark the position of the holes on the post. Pre-drill those positions, replace the bracket and screw it securely into place. Set the next bracket on the next post so it lines up exactly with the first. You want the lattice panels to be straight atop the fence. You will need to connect the top of adjoining panels with a straight bracket.Lattice panels are most often 8 ft long and 4 ft wide. High winds could stress such a tall structure, so use plenty of brackets. Most people add only 2 ft tall lattice to existing fences. See the links below for hardware.

https://mobileimages.lowes.com/product/converted/031107/031107508007.jpg

https://mobileimages.lowes.com/product/converted/081942/081942063650.jpg

Use Screws or nails to do the job.

Make a wood frame and cut slats in the frame for the lattice work to fit in tightly. This would help keep the lattice from bending and warping in the heat.