Deck Rail Post Attachment

The best approach to ensure a strong connection is to install unnotched rail posts flush to the inside or outside of the deck frame. We recommend spacing your rail posts 6' apart or less.  Most builders use (2) 1/2" through bolts to attach 4x4 wood posts to the deck rim. Do not over tighten fasteners because it can crush wood fibers in the posts and greatly diminish the strength properties of the post. Some deck contractors have switched to structural screws in the place of bolts for rail post attachments. Such fasteners must be properly designed for your intended use and are approved by your local building department. The only code requirement states that the guard rail must resist a 200 lb. load along it’s top.

Lateral bracing brackets are available for rail post connections attached inside the frame. The bracket does a fine job of transferring the normal or perpendicular stress into parallel shear loads that work particularly well with bolts and can increase the load capacity from 400% to over 1500% over a notched rail post installation. Two brackets will be required for corner rail posts. Using this method will require you leave enough vacant space in the frame for the rail post and bracket to fit.

Generally, it is not recommended to notch posts guard posts where connected to the deck framing. This end of guard posts is subject to the greatest bending force, and cracking of the post at the notch is a common result. Fastening 4x4 posts at their full cross-section is proven to provide the best results and is strongly encouraged. 

Stair Rail Posts

This particular rail post will function as a corner post and a top stair railing post. This is why the post is oriented on the angle and not perpendicular to the house. Use a quick clamp to hold your 4x4 post in place while drilling.

Through Bolt Hardware

Use a 1/2" x 6" galvanized through bolt with washers on both sides to attach the 4x4 rail post to the deck rim.

Never notch rail posts.

Use a hand ratchet, box wrench or impact gun to install your through bolts. You may need to use shims between the rim joist and the post to plumb the post.

Stiffen the rail with blocking.

Install side posts using blocking to strengthen the perimeter rim joists. You may use scrap framing material for blocking or bridging. Posts installed on the end of the deck parallel with the ledger board do not require blocking.

Rail post must be less than 4" from the house wall.

In this case we installed blocking between the ledger board and the end post to set the post 3" from the house wall because the ledger bolts were protruding (drilled 1-1/2" holes to avoid the bolts) and to avoid touching the siding.