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When laying the planks for a patio, is there any advantage to keeping them at 16 ft, and adding the extra few feet, as in the first image, or is it a better idea to splice them every 8 ft, as in the second image?

patio 16 ft vs 8 ft -long planks

They need to be held down to the joists, and so either way there is no economy in the number of screws.

To state another obvious factor, transportation is a lot easier if they're cut down at 8 ft before moving, and the installation of 16 ft-long planks may be a tad more difficult, but I'm wondering if there are other (structural) factors, such as water ingress at the additional cuts.

Does, for example, ease of subsequent access underneath matter?

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  • For a floor it does not matter much, use the size easier for you to work with. Any cut end you will want to treat and any wood on wood points(planks on joists). Have you looked at the newer composite/plastic type planks?
    – crip659
    Commented Jan 11 at 16:49
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    Transport them whole. If you're paving a rectangle and you take the waste from the last deck board cut to start the next line every time, then you'll get a pattern with the cut moving diagonally. Think about it. First line has waste x. Starting the next line with a fresh board, then, has waste x too, shifting it to make room for last line's waste, now it's 2x waste. Same logic at next line yields 3x waste. Etc. Disruptions in joist spacing will probably break the pattern.
    – popham
    Commented Jan 11 at 19:33
  • Technically the stiffness next to a cut deck board is about 1/2 the stiffness of the board spanning without a cut at either end. 185/384 = 48%. Technically the deck boards act as a diaphragm, bracing deck supports opposite from the ledger board (in a common deck construction pattern, anyway). Interrupting them more frequently weakens the diaphragm.
    – popham
    Commented Jan 11 at 22:42
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    @FreeMan I see your point. I was expecting there is common wisdom on this topic. I suspect, for example, that in addition to the chipmunk entrance in my garden there is another entrance under my deck. So far I've simply let them be. If this were to be a raccoon or (gasp) a skunk, I would hire someone to solve the problem, and then I wouldn't want to be told that I should have designed easier access through the planks.
    – Sam7919
    Commented Jan 12 at 15:04
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    @Sam7919 Access through the planks seems like it would be a source of significant weakness to the platform. I don't think any standard deck or porch would favor a trapdoor through the floor rather than a door through the side. Commented Jan 12 at 15:53

6 Answers 6

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It's entirely an aesthetic and practical decision. It doesn't affect the integrity of the deck in any meaningful way, and moisture will collect at the joist-decking interface regardless.

I prefer fewer and randomized joints rather than dashed lines across a deck. You do you.

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  • Do you design plank randomization? In other words, do you use intent in it, or is it enough to pick up the nearest (random) piece and install it (which, I'm guessing, could mean many more cuts)?
    – Sam7919
    Commented Jan 11 at 18:44
  • Randomization in this case isn't truly random. You would want to maintain some minimum separation in adjacent rows for best visual appearance. Using cutoffs to start the next row does not inherently add cuts. We're talking about random position, not random length.
    – isherwood
    Commented Jan 11 at 18:56
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    Nope. The question was whether that's not the case. It's meta. It's not about what to do assuming that's the case. It's specifically asks about structural concerns.
    – isherwood
    Commented Jan 12 at 14:28
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    @Sam7919 I couldn't help recall an old project of mine when I read your comment about designing randomization and the followup answer about "best visual appearance". There is of course research behind this! What you generally want is "blue noise" which is randomness that looks pleasing to our vision system, possibly because it mimics how the receptors in our eyes are laid out. Basically random but without the clumping you get from true randomness.
    – pipe
    Commented Jan 12 at 15:49
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    @pipe Nice hint! But applying blue noise to the patio planks problem does not seem exactly like a trivial problem: 1- the y-coordinates are constrained, since the planks must be adjacent with uniform gaps, and 2- the x-coordinates must lie on joists. Please add an answer, even if the answer to 1 & 2 is not immediately obvious to you either.
    – Sam7919
    Commented Jan 12 at 16:51
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I agree transporting and working with 16' lengths of anything can be difficult. The key is to really plan out various layouts and cuts based on your joist spacings and keeping wastage to a minimum. Then maybe cutting them into 10' and 6' is better or all 8' or some other combination of different sizes.

When I redid my baseboards in my apartment the 16' boards would not fit in the elevator. After some careful measurements and planning I found 10/6 was the best way to get them cut before I brought them home.

You said the amount of screws is the same but actually the more joints you have the more screws you need because you need double the screws at each joint. I also agree with isherwood that staggered joints look better than if they are all lined up.

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It might depend on what material you're using for the deck boards, and if you ever intend to take them up for maintenance underneath, which it sounds like you are. I've put new planks on a couple different decks, and used the 5/4 pressure-treated deck boards from a big box store. They came quite "wet", and I didn't feel like waiting a couple weeks for them to dry out, so I put them down soon after I brought them home. What happens is that the wood then shrinks. Not really a problem when they're screwed down while wet as the screws will keep them from shrinking significantly length-wise. However, if you take one (or more) up for maintenance, you'll find that they've gotten a bit shorter, and no longer are as long as they were initially, leaving screw holes that might not line up with your joists, and extra gaps between the ends of boards. I used 16' pressure treated on my current deck, and although it looks fine now, I know as soon as I take up any long ones, I'll get lots of 1/2" to 3/4" gaps between the ends of the boards, especially on the long pieces. Using shorter boards would help minimize this to some extent.

If you're using wood decking and have the patience to wait for it to dry out for a few weeks on the job site before installation, then this will be minimized and won't make as much of a difference, other than ease of handling and the difference in cost-per-foot of different lengths of planks, if that's an issue for you. Though if you wait a few weeks, some boards might start twisting and warping as they dry, leading to a less-smooth deck.

If you're using a decking that's manufactured (i.e. composite or something similar that doesn't have any shrinkage issues), then this won't make a difference.

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    The absence of length-wise shrinkage is a material property of wood. It's not caused by the restraint of screws. The shrinkage from 30% to 0% moisture content is something like 0.1% to 0.2% (moisture content doesn't cause dimensional shifts above the 30%), where my understanding is that the softwoods tend to shrink less than the hardwoods, so I've always assumed that they're on the 0.1% end of that range. Conservatively, though, (0.002)16ft = (0.002)192in = 1/32", where the framing supporting these boards are so flexible that the screws will pull the framing along for the ride.
    – popham
    Commented Jan 12 at 5:28
  • There is a problem with the other direction's shrinkage, though. I forget the strain numbers for radial versus tangential, but the average is something like 5%. If the boards are installed swollen with that 5%, then the screw spacing at 4in implies shrinkage between the screws of (0.05)4in = 3/16". Couple that shrinkage with the stiff framing between two screws, the wood can split between screws.
    – popham
    Commented Jan 12 at 5:34
  • Yeah, length-wise movement in boards is, for all intents and purposes, nonexistent. It's never a consideration when building furniture, whether out of softwood or hard.
    – FreeMan
    Commented Jan 12 at 14:27
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    That's not true. You don't build furniture with 16 foot boards. Shrinkage is absolutely a concern with decking and siding. I intentionally overlap cedar siding boards slightly for this reason. The gaps on my home from the original installer show why.
    – isherwood
    Commented Jan 12 at 14:33
  • Dang it. My mind treated 0.384 from the above 0.002*192 computation as 0.0384 because I was expecting a very small value. The shrinkage value is 3/8" total, not my BS 1/32". The PT lumber at the hardware store might actually have 30% moisture content, making that 3/8" the actual shinkage (15% => 1/2(3/8")). The 3/8" and item 7 from fpl.fs.usda.gov/documnts/fpltn/fpltn-234-1942.pdf confirm the wisdom of this answer. Sorry for the down vote and BS misinformation dragging down your totally legit answer, Milwrdfan. If you bump your answer with an edit, I'll be able to switch my vote.
    – popham
    Commented Jan 12 at 20:44
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Fewer boards is better. Every deck I've had looks the worst at the joints as it ages. There is no practical difference.

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    This seems to be an opinion on appearance and not an answer to the question about the practical implications of splice location.
    – isherwood
    Commented Jan 11 at 17:23
  • Do you mean they look worse at the joins when new, or that joins suffer more with age?
    – Chris H
    Commented Jan 12 at 9:48
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    @ChrisH they age worse
    – Tiger Guy
    Commented Jan 12 at 13:53
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The exact dimensions that I would use would depend on a number of factors, not least joist spacing.

However, this example seems to be approx 21 feet wide, so I would cut half the boards to approx 14 feet, and the remainder to approx 7 feet, and ensure that the joists matched the two joints that this would make. Note that this is less work than one of the other suggestions of starting each row with the offcut from the previous row.

Though of course I would measure in millimetres...

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  • I blame whoever made it one foot longer than what is at the extant of being commonly available. +1
    – Mazura
    Commented Jan 13 at 2:10
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adding the extra few feet

No. You don't want any of them only on like three joists. You can get away with that doing hard wood flooring because it's all T&G, and on pieces two feet long you put nails like every 8" into the subfloor... or more.

If it's a 19' long deck, you buy 10' planks and have a butt seam down the middle on a doubled up joist you sistered for the purpose of landing them all there.

If it has to be weaved, they shouldn't be shorter than spanning 4~5 joists. Which might make for a lot more wastage. But the primary concern should be the finished product; not getting it LEED certified.

It's all going to depend on how long the deck is and how long of planks that you can get. If you can get 20' delivered, then obviously do that.

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  • Agree that ideally if you're using PT lumber, you'll want to try and double up where you have ends to give more screw area and not having to screw so close to the ends of the boards, at an angle, to hit the single joist.
    – Milwrdfan
    Commented Jan 13 at 2:00

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