There are several reasons why you might need to extend your fence post but the most common is wanting more privacy or security with a taller fence.
Most municipalities allow you to have a fence 8 feet tall without needing a permit for a taller fence. Some people that have a 6 foot tall or less fence realize their neighbors can see into their yard.
If you have a 6 foot fence you could extend it 2 more feet with lattice or other fencing material. Second reason is if your post rotted midway up or something hit it and broke it.
You need a way to cut off the broken/rotten post and install a new one on top to keep the same height. Either reason will work with the methods below to extend your existing fence post.
Fence Extension Types
There are three different ways to extend your wooden fence post. The two easy ways are adding metal tie fastener to both posts on the front and back or adding a wood face board on the front and back of both posts.
The third way is a bit more difficult since you have to create a half lap joint on each post and then connect the posts with through bolts. Let’s dive into each method.
They may be called heavy duty tie plate or mending plate or tie strap but it’s essentially a wide piece of thick metal that goes across both front and back sides of the posts to reinforce the joint and transfer tension loads.
This one from Simpson is 12 gauge which is thicker than the ones you find at the local lumber store that are 20 gauge. The lower the number, the thicker the gauge of metal for future reference.
I also like that it is 16” long which allows 8” on each post to help transfer the load. I would install this strap with structural connectors rather than regular nails or screws to give it more support.
I have used structural nails
and structural screws
and found the screws easier to install and less injuries from stray hammer blow to the thumb or knuckle from holding the nail.
Nails will also find the random wood knot and go sideways on you. Either are considered structural, which is what you want to keep both posts together.
Just like the metal connector you are attaching a 1×4 piece of lumber (actual dimensions are ¾ x 3½) to the front and back of the posts.
Where as the metal may only be 16 inches long, you could do the same length in wood or you would use an even longer piece of wood to completely cover the front and back of your adjoining posts.
Many times a wood face board is used on a fence to the post to cover the uglier pressure treated post. So if you already have a face board on the other part of your fence, you would simply need longer face boards to extend your current post with another post.
My recommended attachment method for the face board is the same structural screws as above. Structural screws are made from stronger steel and are heat-treated for maximum strength. Depending on the type of wood, you may need to pre-drill the face board so you don’t split it and compromise it’s strength. Most soft woods such as pine, cypress or cedar will all need to be pre-drilled.
Half-Lap joint with through bolts
Creating a half-lap joint is not difficult but you do need to pay attention to your measurements. The old saying measure twice, cut once is always right. I sometimes measure things more than twice and still make a bad cut every once in a while.
You want your half-lap joint to be the same on both posts and generally 6-8 inches down on your first post and the same on the post going on top.
It’s called a half lap because you are cutting half of the material from each post a certain distance down from each post. When you attach them, it will form a joint that is the full thickness across both posts.
In this case a picture helps explain what it looks like on two vertical posts that are then connected with two or more through bolts. This article from This Old House shows how to create a half lap joint with a circular saw and sharp chisel.
The key is cleanly getting rid of the leftover wood between the saw kerfs. A wood rasp will help clean up any bumps from the saw kerfs. You need at least a ⅜ thick 4 inch long galvanized bolt to connect the posts properly.
This video also shows a hybrid method of cutting with a circular saw on both sides and cutting the rest of the wood with a hand saw.
This is my preferred method and faster than cutting a bunch of kerfs, but when I was first starting out using a circular saw, the kerf method was very easy with little skill.
I hope this article explained in detail the three different methods you can choose to extend your wood fence post.
I think choosing the specific method may boil down to your current fence style and the style of the extension you will be adding or if you’re joining two posts for something other than a fence.
If you currently have face boards over your posts, the second method would blend in seamlessly. If you don’t have face boards already, the quicker method would be with the metal hardware plates.
Finally, if you are extending two posts for something like a deck, then the strongest most structurally sound method is the half lap joint.
To our readers from Great Britain, apparently there is a metal sleeve that you can use to extend wooden fence posts. I really wish this product was available in the United States but I’ve searched everywhere and can’t find it.