So you're ready to get started? Watch our how-to tutorial before you start your build.

Before you begin any DIY project, make sure to wear the appropriate personal safety equipment. Eye protection, ear protection, gloves, long pants, a long-sleeved shirt, and reinforced toe shoes are recommended. Always make sure that you have a first aid kit nearby. For any home project, be certain to follow local code and permitting requirements. 

Guardrail post installation is a critical connection and dictated by code.  The guardrail will have requirements for lateral loads from multiple directions.  Check with the local municipality for code requirements.

Step 1

Start by attaching a scrap piece of lumber under the deck frame to support the guardrail post while fastening. Attach to both joists adjacent to the guardrail post. Use 3” exterior grade wood screws to fasten the scrap block to the underside of the deck frame. Install this block at every location where a guardrail post will be installed. This block will be removed once the guardrail post is completely installed.

Step 2

The materials needed to install a corner guardrail post are as follows:

• Treated wood 4x4 post for the guardrail post
• Treated wood 4x4 post block measuring the same width as the deck joist material
• (2) 2X joist material cut to fit in between the adjacent joists
• (12) Simpson Strong Tie SDWS 8” Timber screws, 4) other screws are shown in the diagram and they were installed during the front rim joist installation.

Step 3

The corner guardrail post attachment is shown below in Simpson Strong Tie fastening guide. To learn more about multiple guardrail post attachments, check out this guide by Simpson Strong Tie.

Step 4

Cut the post blocking to length.  Measure the distance between the adjacent joists and mark the pieces of joist material to be cut.  Cut with a circular saw and treat all cut ends with a wood preservative.

Step 5

Place the 4x4 guardrail post and plumb the post. A post level or a standard level can be used. Use a 3” exterior grade wood screw to tack the post to the frame. Fasten the screw into the bottom of the post on one side.  This will let the post stand and still move on the other side so that it can be plumbed.     

Step 6

Using a post level or standard level, plumb the post and install a 3” exterior grade wood screw through the top of the frame and into the post.               

Step 7

Measure and mark for the fasteners that will hold the guardrail post blocking behind the post.  These fasteners will be the Simpson Strong Tie SDWS 8” Timber screws.  The blocking is 1 ½” thick joist material and will fit tight to the post.  The fastener needs to be in the middle of the blocking so measure over from the edge of the post ¾” and make a mark.  The second block will be tight to the first block and is 1 ½” thick so measure from the first mark 1 ½” and make a mark.  This will be the center of the second block. 

Step 8

Transfer the marks down the side of the joist using the speed square. 

Step 9

To make sure the fasteners on the side do not hit the fasteners coming in from the front, mark 1 ½” down from the top and 1 ½” up from the bottom.  The front fasteners are marked at 2” so now they will not hit each other.

Step 10

Mark the center of the post on the front rim joist and transfer the line down the joist. 

Step 11

The marks are already there for the fasteners at 2” down from the top and 2” up from the bottom so where they intersect is where the fasteners will go. 

Step 12

Mark the center of the 4x4 blocking and transfer that line down the front of the front rim joist.  The fasteners will be located where the lines intersect. 

Step 13

Repeat the markings for the side rim joist on to the next adjacent joist. 

Step 14

Set the 4x4 post blocking in place next to the guardrail post and against the front rim joist. 

Step 15

Fasten the two post blocks together with (2) 3” exterior wood screws. Make sure that the tops of the blocks are flush with each other.

Step 16

Fasten a scrap piece of lumber to the top of the two post blocks.  Use (1) 3” exterior grade wood screw and attach in the middle of the scrap piece of lumber.  The scrap should overhang each side by at least ¾” and flush with one side of the post blocking.  This will allow the block to sit inside the two adjacent joists so that it does not need to be held.  It will also allow the post block to fit sunggly against the post.

Step 17

Drop the block in place between the joists and tight to the guardrail post. 

Step 18

Predrill through the joists and into the blocks. 

Step 19

Insert the fasteners through the joists and into the blocking.  Make sure the head of the fastener indents into the lumber and is flush with the outside edge of the joist. 

Step 20

Remove the top scrap piece of lumber to complete the install.