My near-ground level deck is quite large (20x16) at one side and its end is a one-step stair. But at the edge, one end is flush with the last deck board (Trex 5.5") but the other end is like 1" short, showing the below beam.

Flush side:

enter image description here

Short side:

enter image description here

This happens because over the number of boards, the gaps could be slightly different between each board and the bottom frame could have some off measurement.

My question is how to fix this? If the below beam showing like 3-4" then I can put on another board. In this case, it's only 1".

I am thinking of two options below so please let me know:

Option A:

Cut the last board by 1" along the length (on table saw). So the new width is 4.5" (Green bar). Then get another 16' long board and cut it so the new width is 3" (Purple bar) only instead of 5.5". The read line is the below beam lumber. Then on the side of the beam, I can install 1" fascia board. This way there will be 1-2" of overhang. If I follow this option, do I join the two new cut boards closely or do I leave gap in between them? They are no longer having groove at the gap. So I will screw on top instead of using Universal Trex Fasteners.

enter image description here

Option B:

Create custom build trim pieces. This is harder (Trex doesn't sell the 90 degree trim pieces for Enhance version). So basically I need to create an L-shape using 1x8 for the long side of the L and 1x2 for the short side. But on the short side of the L, I will have to cut it so that one end is exactly 2" while the other end is 1". Then I can slap this trim on and stain same color of the deck.

At this point, it's too late to move the stair below or change the frame. I have many more 16" Trex boards. So I am tempting to go with Option A.

What are your suggestions?

5 Answers 5


My first choice would be to see if you can get a wider deck board (~7.25") and then rip that to the appropriate width.

If it's the first board above the stairs, expect it to see a lot of traffic. Of the two you mention, I'd go with Option A. I would join the two pieces together, rather than leave a gap (because there's not much bearing for that small edge piece to fasten to the deck top). Best approach would be to rip a tongue and groove, and consider putting a layer of construction adhesive below the lip piece.

  • I saw Trex has 7.5" fascia board but it is thinner than regular boards. But I like your suggestion on using adhesive. Do I need to glue on the side of the boards together too?
    – HP.
    Aug 1, 2016 at 17:05
  • Even if it is thinner, I'd still be tempted to go with a wider board if you can layer it on another piece of some kind. Depending on the difference in the thicknesses you could use a planed-down, primed 1x or strapping to buy you the thickness. This assumes a riser or some trim on the top stair. I'd go with PL 400 or similar for adhesive. T and G joins aren't usually glued so that the material can expand and contract, but you're using a composite (which will so do less) and the adhesive would likely limit squeaking. Aug 1, 2016 at 21:20
  • So the thickness of fascia board is only 0.7" vs. 1". What can I use for the 0.3" thickness? Can you elaborate more on "primed 1x or strapping" as I am not familiar.
    – HP.
    Aug 1, 2016 at 23:18
  • Hmm, yeah, .3" will be tricky to get. Not sure my previous suggestion is the way to go in that case. By "primed 1x" I just meant a primer coated 1x4 (or 6 or 8) board. Strapping usually = 1x3. Two options not yet mentioned: 1) plane down the beam so that you have consistent alignment, 2) pull up a few pieces of decking and reapply, spreading out the space. Aug 1, 2016 at 23:33
  • Well, the beam has footing and nails / brackets from the stair. So plane is not an option (I have thought of that). Also composite decking is very tricky to adjust the spacing since Universal Trex Fastener is somewhat fixed. I might be able to pull 0.5" but the higher risk is that the actual framing below is off. So pulling the decking boards which taking tons of time would not be an option either. At this point, I am leaning toward Option A to glue 2 pieces. So when I use PL 400, do I need to glue the edges of the two boards together?
    – HP.
    Aug 2, 2016 at 0:57

. Put the last boards down but don’t use the universal clip on the rim joist side. screw the side toward the rim joist but do it at an angle and bury the screw inside the groove So that the board looks normal and is securely attached (the screw will be hidden). Secure a board the length of the underlap (or whatever you want to call it) next to the last board so it looks normal. Get underneath the board and snap a line right next to the rim joist. Take the board off and rip it for the final piece. Screw it down from the top knowing it will get covered by whatever railing system I use. I think that will work just fine and I don’t have to add material.


Can you just extend the deck frame far enough to support another full deck board? Add another rim joist to that side with maybe a one inch block behind it at the end that’s showing, and a two or three inch block at the end that’s shorter. Should give you enough extra frame to attach decking into.

  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know how better to contribute here. Jun 18, 2019 at 23:54

You could look for wider board but i do not think they make one .Add a new framing board. rip a piece of decking .Glue into grove to make one width, and glue it to frame and screw it also. round it over as a nosing.


Get another thin rim board and shim one side accordingly then install a ripped edge that's even

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