How to Install a Deck Flush Beam vs. Drop Beam

Step 1: Access How Much Space You Have Under Your Deck

The amount of space under the deck can be one of the determining factors in which beam style to use. A drop beam can be used where more room is available under the deck. A flush beam must be used when the deck is lower to the ground and there is not enough room under the joists to fit a dropped beam.

Step 2: Determine How Much Flexibility Your Deck Design Needs

A drop beam can give a little more flexibility with the frame as the joists will cantilever over the beam, meaning they run past the beam. This can help to enlarge the deck while keeping the posts away from certain items in the yard.  It can also give the ability to change the joist length after the beams have been installed.

A drop beam can add an appealing visual to the deck by having the beam back from the edge and creating a shadow effect. It can also give a floating effect when trimmed out with lattice or skirting.

Beam Mounting Differences

Mounting the beam directly on top of the post with mechanical brackets is one way of installing the beams. This method can be done with either a drop beam or a flush beam.

Mounting the beam in a notch of the support post is another method.  This is usually done on the drop beam scenario and not on the flush beam. If this notch were done on the flush beam, the joist could come into the support post and not be able to attach to the beam. The notch is used to keep the beam straight and not twist over time. The flush beam has joists attaching to it so the joists will keep it from twisting and the notch is not needed.

Attaching Joist Hangers Differences

A flush beam will use more joist hangers as both sides of the joist will have a hanger attached to it. A drop beam installation will only have hangers on the ledger. The drop beam will require hurricane ties attaching the joists to the beam. 

A drop beam will require blocking over the beam between the joists.  This is to keep the joists from twisting.  A flush beam will not require this as the joists are attached to the beam with joist hangers.