Should I try to avoid butting 2 deck boards on 1 joist?

13 years ago

I am replacing my existing PT 2x6 deck boards with 5/4 PT, and am thinking about trying to avoid butting boards against each other on the same joist.

A deck book got me thinking about this because it tends to weaken the boards by having the screws so close to the ends, and it invites rot by having the ends over a solid board underneath, which doesn't allow for drainage or air circulation. This seems to make a lot of sense.

So the book suggests having a parallel joist, separated by a 1/2" spacer, to screw the next board in line to. With a wide deck, and a random arrangement of board ends, this adds a lot of parallel joists.

I'm trying to figure out if I have a valid construction concern, or if I'm just being neurotic. It seems the standard method for building decks is to just randomize the ends as much as possible, butt the boards on a single joist, angle the screws a bit into the joist, and be done with it. It seems a bit half a$$ed, but if it works and lasts, why not?

Help, experiences, and ideas appreciated!

Thanks,

David

In a previous message:

http://ths.gardenweb.com/forums/load/porch/msg060940437221.html?2

...I asked advice on an idea for replacing my deck boards, dividing the deck into three sections separated by perpendicular trim boards. The only reason for doing so was this concern about two boards on a joist.

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Comments (5)

john_hyatt
13 years ago
Its a good idea to add sister joists when butt joining composite 5/4. With pt 5/4 it hardley matters. J.
brooklyndecks
13 years ago
David,

As John said, you shouldn't overthink a pressure treated deck, as it won't look good for very long anyway. That said, you can still build it well and be proud of it when you're finished.
I build higher end, using Ipe for decking, and this is how I frame for butt joints. I stagger the joints, and create a repetitive pattern. I sister joists wherever a joint happens, so each board lands on it's own joist. Butt joints are always problematic...I work with a caliper and a table saw to make sure that I butt 2 boards that have exactly the same width. You'll find out that 5/4x6 really means 1"x5 3/8 or maybe 1"x5 1/2". I rip the wider board to the same width of the smaller. Then there's the cut...the 2 boards need to meet at a tight joint. It's not easy, so I round over the tops of both cuts. It's more forgiving. If there's a slight gap, you won't notice it.
Anyway, there is a lot to deck building that you can obsess about, but do you want to? I do, because I like to...I need to.
Back to your question...I sister the joists together...no 1/2 gap.

steve
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David B
Original Author
13 years ago
Thanks for the advice. When you guys sister joists, do you run it full length, or just as a short nailer under each board joint?

David
brooklyndecks
13 years ago
david

I sister full length. Since I repeat the pattern every 2 or 3 rows, it makes sense to sister one time, instead of many.
If I used a random pattern, I might do random sistering, but that would really slow down the job.
If you sister full length, you get another benefit...a stiffer deck...better than viagra.
If you already have a stiff deck, you could sister a 2x4 instead of a larger board. Make sure it's well fastened, and coplane at the top with it's sister. It's also a good idea to cover the double joist with vycor to seal out the moisture and tree trash.

steve
David B
Original Author
13 years ago
Thanks, Steve. The boards I'm removing are all 2x6 PT, and I'm thinking about using some of them as these sisters, since I have them, and most seem pretty solid.

Went to Lowes yesterday to buy some framing lumber to shore up the previous bad design, and browsed through the 5/4 PT deck boards. Man, they are crummy! Full of knots.

David