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Build a Colonial Williamsburg style picket fence to last

By Paul Stevens

We have tried the ready made picket fences sold at the lumber yards but quickly realized those two narrow boards they use to staple them together are not much more than a temporary spacers to hold them together until you get them home, they are not even a full 2x4 what’s up with that? Like many we took them home set my post and nailed them up, and in about a year we had a crooked fence falling apart.

After visiting Colonial Williamsburg and admiring the white picket fences, we decided that design would be perfect for our next garden project. This design uses a strong back design as the top rail, a "strong back" is used in wood frame structures where another 2 x 4 or 2 x 6 is turned and nailed to the side of the top rail. As you are looking at the fence with a strong back, you will see the typical top rail where the pickets attach. Now imagine another 2 x 4 laid flat and nailed across the top of the rail. This helps strengthen the top rail from sagging as well as moving side to side during strong winds. This is a strong back and will make a fence last for years. It is best especially using treated wet wood to turn the growth rings where they curve outward up, so that as the board dries out it will take a natural curvature and shed water instead of curving inward and holding water.

The Colonial Williamsburg fences have tall corner post with decorative tops, and then the top rails are mortised into the post with the strong back laid on top and nailed between the posts. Some use a second strong back as the bottom rail, but most use just the top, with the bottom rail mortised into the post as well. The line post are cut off so that the flat board used on top of the rail to make the strong back runs continuously across the top of the line post, or that is where the joint is made. You can 45 that joint to make it even stronger.

This type of construction does require at least the top rail to be motorized into the post as setting it on the outside, would mean your top board used for the strong back would stick out 1-1/2” at each post. The bottom rail can be mortised as well or it can be laid flat in between each post and nailed into spacer blocks. The mortise cuts are really pretty easy to do; using a skill saw set at 1-1/2” depth scored a few times in the mortise, and knocked out with a wood chisel. It doesn’t have to be as precise as building furniture. I set my corner post first with the mortise cuts, and then I use one string to align my post holes. Once those are complete I place strings at my top and bottom rail placement, as well as the top of the post. This way I can plumb the post mark them and take it out to lay the post down cut my mortise joints, cut the post to length and then set it in concrete.

A larger 6 x 6 post used as the corner post, and 4 x4 used for the line post makes the most attractive and lasting fence. Especially when the corner post are topped with an 8” x 8” x 1-1/2” cap followed by another smaller size to form a stepped up cap, or other ornament, then use trim around the bottom of the cap to make it look like a porch post.

On our first project to duplicate the Williamsburg look we used the 6 x 6 post, made our strong back rails and hand cut decorative pickets then nailed them on to the rails. On our second project I actually used 4 x4 posts as the corner post, and used the ready made picket fence sections. I left the rails on that came with the fence, but mortised them into the post and then used treated 2 x 4 as the top and bottom strong back. Sure this takes more material, but I’m not replacing fence every few years either.

We go back and visit where I did the 1st project and that fence looks as good as it did when we built it over 15 years, the one we currently have around our garden in the pictures has been in place eight years. I occasionally have to nail some of the pickets where the staples have pulled through. I also see on the 4 x 4 corner post the mortise on two sides does not leave much post left, they have not broken through but I wish now that I had used the 6 x 6.

Both fences were sprayed with two coats of a good water based primer and then two coats of latex white paint. I choose water base because of the high water content in the treated lumber. I could of left it cure and used oil base paint, but after all this time, I’m pretty sold on the water based products, especially the primer with the stain blocker as the knots will bleed through if you don’t prime first.

Always use galvanized nails or nails coated that will not rust, I ended up with a couple of regular nails in the nail pouch and they rust and bleed through very quickly.