Submitted by OrangeYouGlad100 t3_yhx353 in DIY
I have researched joist spans and found that the max span for 2x6 deck joists is about 9 feet. However, even after extensive searching, I can't figure out whether this number is specific to joists that are not supported in the middle. If a 2x6 joist is supported in the middle (and on either end) by a deck block, can it be longer than 9 feet?
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Yes, if you support in the middle you can go further. 9' would be the max unsupported span. So if you had multiple deck blocks you could go 45' or even further.
Side note spans are not the same across all regions. Make sure to confirm with your local building codes
There are also different span guidelines based on the species of wood being used.
46' feet maybe?
Span is support to support But it is different for decks depending on the distance between joists, the type of wood used (treated wood can be made of several species depending on where you live), and is reduced in northern areas that get heavy snow loads.
Your deck blocks should be under your beams (dbl 2x6) and the middle deck blocks would need a beam. Supporting 1 joist midway, but not the next one is not proper.
This is it. Span tables vary depending on joist spacing, type of lumber and snow load.
"Your deck blocks should be under your beams (dbl 2x6) and the middle deck blocks would need a beam. Supporting 1 joist midway, but not the next one is not proper."
For both of those things, I took inspiration from these plans:
https://gardenplansfree.com/furniture/deck-plans-free/
which have essentially the same setup for a 12x12' deck with 2x8's.
Are those plans no good, or are my deviations from those plans no good?
Page 5 has illustrations and a chart of beam sizes. Your local codes may vary but this municipality is known to use national best practices for building codes. Page 4 shows differences for supports at the ends vs supports with overhang.
https://www.rockvillemd.gov/DocumentCenter/View/528/Construction-Requirements-for-Decks?bidId=
If it’s supported in the middle then it’s not spanning 9’-0”, it’s spanning 4’-6”.
Why use 2x6's? These will deflect more than 2x8s or 2x10s. This means the deck will be bouncy instead of firm.
What decking material will you be using?
If SYP, your maximum span is 9'. Your drawing shows some spans are not supported and are 10' long.
I can't use 2x8's because I need to keep the deck low to the ground since I'm building it as a "step down" from another deck next to it.
"Your drawing shows some spans are not supported and are 10' long"
I used the strategy from these plans in which only every-other joist has blocks:
https://gardenplansfree.com/furniture/deck-plans-free/
It seems overkill to have block(s) under every joist.
Those plans are 2x8's which have a maximum span of 11' 10" if SYP. The plans say the joists are 141" which is 11' 6", so there is no span problem. A 2x8 has less deflection than a 2x6. You can't change to a 2x6 without changing the design.
One thing I do not like about those plans is that there is no positive connection to the ground. By this, I mean I could stand on the side of your deck and lift it up (if I were strong enough). That's because the blocks are not attached to the ground, and the deck is not attached to the blocks. Also, if you're in an area with frost heave, the soil moves with changes in temperature. The deck blocks will move up and down, and eventually (maybe in the first few years, depending on how well you prepare the site), you will have uneven and wompy deck footings, leading to a deck that is not evenly supported.
You can solve both of these problems if instead you use 2x8 lumber and pour footings that support the perimeter of the deck. You need a footing at each corner to support the short side. And then since the outside joists are too long at 16-18' each, you need a support at the midpoint of each of these. The footing has a metal fastener in it when you pour it (or attached after with bolts when it has cured), and then the deck is bolted to the fastener.
You also need to calculate the load to make sure you have enough footings. If the deck is 18'x10', that is 180 sqft. The rule of thumb is 40 pounds of live load (a person walking or an object on the deck) per square foot plus 15 pounds of dead load (weight of the deck materials) for a total of 55 lbs per sqft. If you have a footing at each corner and one at the midpoint, this creates six sections of 30 sqft each, and each footing must support 55*30 = 1650 pounds. Use this footing chart to determine what size footing to pour based on your soil type:https://www.decks.com/how-to/articles/deck-footing-size-chart
I would add 2x8 joist blocks (short pieces) between the joists as well:https://www.decks.com/how-to/articles/deck-blocking-and-bridging
All lumber should be rated for "ground contact" treated wood, because you are so close to the wet soil that it is subject to rot due to poor air circulation. "Ground contact" has additional protection compared to normal treated lumber.
Here is an image of my deck plans to help visualize the setup in question:
https://drive.google.com/file/d/1Zs97wA_hXPqVcCFDbkHZ_RisW3bhXe7K/view?usp=share_link
This link doesn't work for me.
I added the image to the original post.
That's too much over kill on the pierpads/ deck blocks. For 16' you should have 3 pads/ blocks on each doubled up 26, 2 towards the end and 1 center. I would add a double 26 beam in the middle for added support/ to help bounce or defection. So imagine the beams going the 16' length, two where you have them at the top and bottom, one in the middle. So 3 -16' " beams" or double joist, and 9 pads total for a rock solid foundation.
Also if you add butyl tape/ window flashing that comes in rolls, on top of the joists where the decking meets ( on top of the 2*6 where you screw the decking) your joists will last a whole lot longer.
That 3 beam setup would be strong enough for most environments/ weight.
Here in WA if the deck isn't over 30" off the ground you don't need railing.
Also they sell concrete blocks/ pierpads with an adjustable 4*4 metal bracket so if you mess up a cut or the ground settles, you can use a wrench to adjust it up and down. Good luck..
Thanks for the suggestions! Unfortunately, I already bought like 20 deck blocks that have a space for a single 2x and therefore can't fit a double beam (this kind https://www.lowes.com/pd/Common-7-in-x-11-in-x-11-in-Actual-7-125-in-x-10-375-in-x-10-375-in-Concrete-Deck-Block/50113084 ). I suppose I could return them all.
Alternatively, could it make sense to use 3 beams like you suggested, but put the blocks under joists instead of beams like in my picture? I got that idea from these plans:
https://gardenplansfree.com/furniture/deck-plans-free/
What's the load/ weight your putting on this? Usually the load is supported by beams running 90 degrees to the joists.. I can't speak to this plan, I've never built one like this but it doesn't mean it's wrong..
Unless your installing on concrete you'll want to make sure all 20 blocks are level and even with each other. That can be a pain but depending on skill and terrain. But if you're going for a low profile look than this might be better than buying and burying adjustable pierpads. Good luck!
Thanks. Aside from the weight of the deck itself, it will only need to support a few deck chairs and a few adults. And yes, it will be low profile. The joists will be just an inch off the ground and the surface of the deck around 8 inches high.
Gotcha. Make sure you use treated lumber, not much ventilation under there. Good luck.
Also here in WA, I believe you don't need a permit for a deck not attached to the house. If that were the case I'd negate the first beam. If you're, worried take a detailed drawing to a builder and they might give it a once over for you.
Make sure you're considering all of the factors in designing this and see if you can get some sort of plan review from somebody with experience.
For example, if you frame the deck with 2x6 only, you will generally not be able to attach the safety railings strongly enough to meet the 200 pound midpoint all directions force resistance requirement according to the testing done by some reputable engineering journals.
You also have to think about snow loads, springiness from using minimum code spacings and spannings, how to attach it to the house securely, type of lumber used on the various components, strength of the staircases (if any), etc.
It will be very low, almost sitting on the ground, so I don't need rails or stairs. I'm trying to place enough blocks to avoid springiness.
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The span, is the distance between supports.
What this person said. If you've got a deck block in the middle, you cut your span in half.
Do I need a deck block under every joist? In these plans, they use a deck block under every-other joist:
https://gardenplansfree.com/furniture/deck-plans-free/
but they're using 2x8's, so maybe they don't exceed the max span for 2x8s if the beams on either side count as support?
Correct about the 2x8 spans. Those are shit plans and there are a few things wrong. The most obvious being their materials list having errors.
But yes, they are using 2x8s and in theory those are supported by the rim joists and the span is allowable. They just have some extra supporting deck blocks in there for good measure.
But the way they have the joist hangers set up in there the joists are not actually being supported. I wouldn't follow those plans to the letter.
Anyway, if you're dead set on using 2x6s with questionable spans just use more deck blocks than you need and you don't have to overthink the framing so much.
Thanks, that makes sense. Those plans might be shit, but my impression is that all the regulations and suggestions I'm reading are overkill for an unattached deck that sits at ground level and only supports a few patio chairs. Like, do I really need to dig a 4 foot deep hole and dump in bags of concrete for something this size?
There will always be better ways to do a thing. Does your area freeze? If so you would want to pour footings deeper than your ground freezes, as the frost will move the footings up and down and make your deck unlevel. Google "frost heave."
But, frost heave or not, you can get away with deck blocks if you're trying to go cheap and easy and accepting that the platform will end up moving.
And certainly if this deck is elevated you want to pay really good attention to beam spans and hardware and making sure you're not going to kill anyone.
But if you're putting down a platform on the ground for a few chairs and want to cut some corners, go ahead. There will always be people (on this forum) who will poke holes in your project and point out all the errors (and there will almost always be errors.) But there's also something to be said for learning by doing and not getting bogged down under the weight of perfection to the point that you never build anything.
You might find your deck spongy. Or unlevel. Or you might have to replace it in a few years with something better. But if you don't mind sacrificing a little time and money for the sake of learning some lessons, do it. Build some confidence and competence and make some mistakes to better learn what to do (and what not to do) next time.
It's easier to start putting together the pieces of how to do things the right way by doing, rather than learning just the theory.
My two cents. I sell build plans and have built a ton. I stand by the sentiment. Don't kill anyone. Do some research. But feel free to make some mistakes and learn by a little trial and error if you are willing to accept the consequences.
Thanks for the input. Yes, it does freeze where I'm at, but I'm thinking frost heave won't be a big deal for a deck that sits a few inches off the ground.
The deck is indeed just for a few deck chairs and doesn't need to be built like a tank. I honestly don't even care if it becomes a little unlevel or wobbly after a few years as long as it continues to support two adults and their beers.
One thing I've heard engineers say is: "Any idiot can build a bridge that stands, but it takes an engineer to build a bridge that barely stands."
The point is that to make something truly economical that will last takes a lot of experience. And what counts as "barely stands" to an engineer is not the same as what it means to you.
Yes if you just slap up a deck it'll be ok for a few years. But I wouldn't get carried away trying to lighten designs and skimp out on footings without a good working understanding of what time, water, and gravity will do to the ground and materials you are using for the deck.
Or if you are ok with things starting to get shitty in a couple years... Go for it I guess.
Here's some information on deck blocks. Just remember it might feel like going backwards to return items/ rework your plan but in the long run a solid built deck will be worth it.
https://decksbye3.com/are-deck-blocks-a-good-idea-and-bad-plus-installation/
This one of those local building code things you should check into. Just because it works doesn't mean it's within code. It can't hurt to ask.
Figure out what standards are in place for you locally. Last time I built a deck, I used this reference guide. It will have the table in here to answer your questions.
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https://awc.org/wp-content/uploads/2022/02/AWC-DCA62015-DeckGuide-1804.pdf
jet_heller t1_iug6b8h wrote
The span goes from support to support.