How to fix deck board at edge not lined up with beam

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My near-ground level deck is quite large (20×16) 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:

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Short side:

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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.

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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 1×8 for the long side of the L and 1×2 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?

Best Answer

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.