How to Install Flush Posts Top Mounted Railing
Flush Posts Top-mountedNot your standard wooden rail. This style railing has the strength of side-mounted posts, the look of top-mounted and no visible connectors. All screws and hardware are hidden. Originally the railing was going to be installed on the sides of the fascia. After completing the decking, the customer requested a change order for the upgraded railing.
LayoutThe post layout involved tracing each end of the 4x4 post on top of the already installed decking. We began by marking 3" setbacks from the deck edge at all post locations.
Each post would slide through the cut-out then anchored to the frame from the inside. The three-inch set back was to account for the thickness of the fascia and rim board.
Some of the lumber had slight variations in thickness. So when marking the setback, sometimes we would use 3 1/16". Measuring the two layers was more accurate. It's subtle but helps with levelling the posts.
When tracing the bottom, it was essential to use the exact post for that location for a tight, seamless fit.
Notching the deckingFor the post-cut-outs in the decking, we used pilot holes, a jigsaw and a file. The 4x4 post corners had a slight curve, so pre-drilling pilot holes helped match the corners and provided a starting point for the jigsaw.
After knocking out the cut-out piece, a little bit of filing around the pilot hole areas, then dry-fit the post before cutting the next one.
Looking back at this step, a router with a premade template may have been much faster with good enough results. Something like a 1/2" top bearing bit and some 3/4" plywood probably would have done the trick.
Another option at this stage. Hiding the post hole cut out by making it slightly smaller than the post thickness. Then plane the section of the post that slides in for anchoring. The larger post dimensions resting on top would hide any cut-out gaps. Waterproofing would need to be added to the planed area so that it doesn't rot.
Anchor and level postsFirst, we pre-drilled two holes in the 4x4 for the structural screws to help keep it from splitting. Then sink the post in the cut-out until it was flush with the bottom of the framing. The deeper it reaches, the more leverage it can take from someone leaning up against the railing. Maximum leverage support.
Two people made it easier for levelling and setting. One up top with the level. The other underneath the deck, ready to sink the screws. Once the post was close to level, we added one structural screw, but not all the way. It allowed some fine-tuning before adding the second anchor to set the post permanently.
Most of the screws were 6" in length. Occasionally some eight or nine-inch were necessary when the framing was to tight, and the screws needed an angle.
BracingCorner posts are the strongest; the other 4x4s and railing support them in both directions. With inline and end posts, it is especially important to add blocking perpendicular to the railing. We used scrap joist cut-offs and sandwiched the 4x4s. Back nailed from joist to block end and toe-nailed.
Cut the tops
The posts have a finished height 36" above the decking, so our total railing height was 1 1/2" larger than the minimum height requirement. We scribed a cut line around the posts with a speed square and finished the tops with a skill saw.
For a tight-fitting top and bottom plate, I like to trace rather than measure. We stacked two 2x4s on top of each other face side down. Then placed them on the decking up against the posts for tracing.
Each cut line was marked using a square hooked on the plates with the protruding end touching the inside of the posts.
CuttingWe carefully held the lumber together and pulled it far away enough to use a skill saw after scribing. Still stacked, the first cut finishes the top board and goes 1" into the bottom plate. By partially cutting the second board, it helps keep a consistent length, and you don't need to measure twice.
After cutting the plates, we dry-fitted to guarantee a snug fit.
CuttingThere were over three hundred balusters in total to cut. So we set up the chop saw. With a post height of 36" minus the plates and four-inch bottom opening. Each one would be 2' 5".
To reduce the amount of measuring, we set up the saw beside the deck stairs. The idea was to place the saw exactly 2'5" away from the steps to the blade. That way, the 2x2s didn't need measuring. Just slide four at a time into the stairs and chop.
Spacer TemplateEach baluster was spaced three inches from its neighbour and centred on the top plate for the railing design. That's two measurements per end, so 4 x 300 = let's make a template. We ripped a simple 1" strip to get the 2x2s centred consistently. And attached a bunch of 3" wide blocks for spacing.
Drawing a 3" line from the chop saw blade makes quick work of these spacer blocks.
Attach to platesThe deck had many different lengths of railing sections. The jig was sometimes too long or too short. To keep spacing even on the ends, we worked from the center out.
To keep the screw heads out of sight, install from the plates' outside face into the 2x2s. The bottom plate faces the decking, and a 2x6 covers the top plate.
Install Railing Section
Once a railing section was complete, all we had to do was lift into place and fasten to the posts. All the screws are installed on the underside to keep them hidden. And set at a 45-degree angle to capture as much material as possible. On larger sections, we also installed a block under the bottom plate to prevent sagging.
Layout / CuttingThe top rail is a 2x6 finishing piece with mitred joints and overhangs evenly on both sides of the railing sections. We used long 18' pieces for the straight runs, so the only joints are the corners and deck angles. To find the mitres, we placed two 2x6s in their final position. And then added a third overlapping the others.
The inside and outside of the overlap edge on each board are the points for the angle cut. We marked these and joined them with a line for cutting. A chop saw works best for clean angle cuts.
InstallThe top rail serves as a decorative piece and the final structural component. We applied a generous amount of glue to the top plate and clamped the 2x6 (top rail) in place. For the next piece, the same process plus a bit of glue for the mitre face. When the seams were tight, and the overlap was perfect, we added screws from the top plate up into the top rail. You can run your hand along the railing without being interrupted by indentations.
After this step, the railing takes on a whole new level of sturdy. All the sections and posts work together.
It's a big deck at a little over 900 sqft added to the already existing 12x12 decks. Our favourite parts are the railing and walkway. We are thrilled with how sturdy the railing feels and glad the customer chose this style for their home.