Installing posts for deck handrails. Deck Framing:

Installing 4x4 Posts
For Synthetic Handrails
Around A Deck

Part 1 In A Series Of 3 Articles


In This Article:

4x4 treated posts are lag-bolted to the rim joists of the deck. Additional blocking is added to prevent the posts from flexing too much. Post spacing problems are discussed.

Related Articles:
Skill Level: 2-3 (Basic to Intermediate) Time Taken: About 8 Hours

By , Editor


While building an extension for an existing deck, I was asked to install a new synthetic handrail product around the perimeter of the new and improved deck. The original deck had treated wood deck boards, which had already been replaced prior to the installation of a hot tub.

This synthetic PVC handrail system uses post sleeves that slide over an ordinary 4x4 treated post. The steps shown in this article should also apply to any handrail method that employs 4x4 posts to support railings or guards.

Deck framing before installing handrail posts. This is the deck extension after the framing was complete.


For the handrail posts I used 4-foot-long treated 4x4's.

I clamped the post to the rim joist, then inserted plastic-composite shims to make the post plumb. I didn't want to use ordinary shims because they may rot eventually, allowing the posts to become loose.

Installing 4x4 posts for handrail, corner post.


Fastening Handrail Posts To Deck Framing:

I drove a pair of GRK 5/16 x 4" lag screws through the rim joist into the post. On the corners I used 4 lag screws.


Two of the handrail posts were installed on the part of the deck that already had the new deck boards installed. I had to remove one piece of deck material.

Since the post landed right on the gap between boards I made a notch with a jig saw.


I clamped the post to the rim joist, used shims to make the post plumb, and drove in a pair of 4-inch lag screws.


I noticed that the post could wiggle inwards and outwards, because the entire joist was flexing. To remedy this, I wedged a piece of 2x8 blocking between the joists and secured it with 3-inch deck screws. This made a big difference.


Post Spacing Problems:

The 24-foot long side of the deck needed 4 sections of handrail, and 5 posts. I installed the corner posts first, then measured the distance between the posts. But simply dividing this distance by 4 does not give me the proper post spacing, because there are 3 intermediate posts (each 3½" wide) included in this distance. So I deducted 10½" (3½" times 3) from the measurement, and then I divided by 4 to determine the spacing between posts.

I marked the handrail locations on the rim joist. All of the post locations landed on an open space between the joists... except one. One post overlapped a joist by one-quarter of an inch. That post needed to have a 1/4" deep notch made in the side.

The Joy Of Expensive Power Tools:

In the past I've done this with a circular saw, but now I have this expensive slide miter saw, which makes short work of this task.

This photo shows me making the deep longitudinal cut all the way through the 4x4 post.


Then I made the shallow cross-cut to lop off the thin slab.


This is what the post looked like after being installed.


One of the other posts landed midway between the ends of the joists. This post could flex a bit more than the others, so I added a piece of blocking behind it.


The deck framing after all the posts were mounted to the rim joists.

The 24'-long edge is on the left side of the picture.


Another photo from a different angle.


This is the 18-foot edge of the deck, which had 3 sections of handrail and 4 posts.

After I installed the posts I turned my attention to installing the new composite deck boards.


I slipped a couple of post sleeves over the posts to see what they looked like.

Continue to: Installing Synthetic Handrails, Part 2.



Tools Used:

  • Cordless Impact Driver
  • Basic Carpentry Tools
  • 12" Bar Clamps
  • Miter Saw (Slide Miter Saw Is Optional)
  • 4' Level

Materials Used:

  • Treated 4x4, 4' Long
  • Treated 2x8 Blocking
  • Synthetic (Composite) Shims
  • 3" Deck Screws

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Copyright © 2005

Written June 4, 2005