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4×4 Cedar Deck Posts Installation – Step by Step Deck Building Part 6

4×4 Cedar Deck Posts Installation – Step by Step Deck Building Part 6
This entry is part 6 of 10 in the series Building My Deck Step by Step
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Installing The Cedar 4×4 Posts

This step of installing the cedar deck posts is fairly simple to do and needs to be done before I start to lay the deck boards and treads on the stairs.

The first thing I had to do was to figure out the length I needed to cut my posts to. Then I counted the amount of posts I needed and at what length since I had two different lengths on the upper deck, one length on the landing and then a miter cut on the post at the bottom of the stairs for the angle of the stairs.

View my Railing Detail and Post Height Detail Drawings Below.


So my required post length for my deck has to be long enough so the top of my railing meets code specifications for my deck height. (Again please check your local building codes for these dimensions before designing your deck) My required railing height for a deck of 42 inches above grade is 36 inches.  For my area if my deck was over 48 inches off of grade then the railing needed to be 42 inches in height above the deck boards, I am happy I did not need one that high. Also if my deck was 24 inches or lower above grade then a railing was not required.

Calculation of The Post Length

To calculate my cedar deck posts length to meet code I needed to know the width of the joists, the thickness of my decking material, and also the thickness of my top railing. These measurements are:

  • Joist Width – 7 ¼”
  • Deck Board Thickness – 1”
  • Thickness of My Top Railing – 1 ½”

My calculation for the post height is as follows:

  • Railing Height (36”) + Deck Board Thickness (1”) + Joist Width (7 ¼”) – Top Railing Thickness (1 ½”) = Post Length (42 ¾”)
  • Total amount of posts at 42 ¾” is: 11ea
  • Total amount of posts at 72” for my lattice is: 2
  • Total amount of posts at 48” for my stairs is: 1

zzzz-IMG_0850Cutting The Cedar Posts To Length

After measuring and cutting the 3 longer posts, I took the time to make a quick jig to cut the 11 others.  First I cut one post to the length of 42 ¾”, clamped it onto my deck to double check the measurements. Now that I know that this one is cut correctly I made my jig by using stop blocks on my cutoff saw. This really makes things go fast and also increases accuracy and stops measuring errors.

The posts are now ready to be installed and I will get my tools and other supplies ready.

Things I required:

  • Cedar Shims (For plumbing the posts)
  • 3 ½” Coated Deck Screws (Longer is better here)
  • PL Premium Construction Adhesive (Screws loose their grip after years go by)
  • 48” Level
  • Power Drill
  • Clamps

installation-4x4-cedar-railing-postsI started out clamping the posts in place one at a time, gluing to the rim joist and then shimming it plumb using shims if needed. Once the post was plumb, I screw nailed it through the rim joist. On the corner post I could glue and screw two sides. After installing the posts I went back and added blocking between the joists that was up tight against a second side of the posts, and also on the third side as well when the post was in a corner. These were also glued and screwed to the posts and fastened to the joists. Doing this little bit of extra work, and block around the posts really adds a ton of strength to the lateral stability of the post, which when you have a whole lot of people leaning on the finished railing it is never going to move.

Some times when installing posts for a railing you want to use carriage bolts instead of screws, this is a personal choice and there is nothing in the building code for my area that requires it. (You may want to check your local building codes for what is needed in your neck of the woods) For this deck I would have had to countersink the heads of each carriage bolt into the rim joists so I could add my finish fascia on top of the rim joists so this is why I elected to use screws and glue.

Finally The Last Post

For the very last post which was the one at the bottom of my stairs I had to install it over length by a bit.  Why?  I did this because then I could very easily figure out what angle I needed to cut the top but I did have to measure the height to the top of the post from the top of the tread. This is easy as it is the same measurement as all the other posts.

closeup-cedar-railing-posts-stairsSo what I did was take the precut cedar post and clamp it in place where it was going to be fastened.  I then measured where the top of the post would be on the outside of the post and marked that. Next I took a nice straight piece of wood that was long enough to span the distance from this post at the bottom of my stairs to the first post on the landing.

Using A Straight Edge To Figure Out The Cut Angle

Taking this piece of wood I can now clamp it in place, lining it up with my mark on the first post and then lining up the other end with the top edge of the post on the landing.  I then drew a line along the side of the post that needs to be cut.  I unclamped the post, took it to my cutoff saw, setup the angle and then cut the post.

The post was then ready to be installed just like all the others.

My post installation is now complete. It is time to start installing the fascia in the landing and then I can install the cedar decking.

Series Navigation<< Deck Stair Stringers – Deck Building Step by Step Part 5 .... Cedar Deck Board Installation – Step by Step Deck Building Part 7 >>
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Warning: The topics covered on this site include activities in which there exists the potential for serious injury or death. DOES NOT guarantee the accuracy or completeness of any information contained on this site. Always use proper safety precaution and reference reliable outside sources before attempting any woodworking or home improvement task!

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