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A few freestanding deck questions

DerekR | Posted in General Questions on

Hey it’s me again, first of all thanks for the info in my last thread about attached decks, you saved me a costly mistake

now, I want to use these titan foot anchors for my free standing deck, they drill 2 feet into the ground https://titanbp.com/pages/deck-foot-anchor/
im waiting to hear back from the manufacturer about this question but I thought I’d ask to see what everyone thinks here while I wait

The footings for my house foundation are 1 foot in the ground, this Titan anchor puts a large bolt 2 feet into the ground, will that be ok to drill into the ground right beside my foundation footing or 1 foot away from it at most since the footing is 1 foot deep?

other question is since it’s freestanding is setting it off from the house 1 inch fine or should I go more or less than 1 inch

last question, I find mixed results when I search for this online, I see cantilever is supposed to be 1/4 or 1/3 the total span of the joist, what determines wether it’s 1/4 or 1/3?

thanks again

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Replies

  1. jamesboris | | #1

    On cantilevers for decks, check your local code. 1/4 is considered best practice most of the time even if code allows 1/3. It is, however, a deck, so if you can guarantee that no one is ever gonna enclose it or put roof columns on that cantilever or something, I don't think 1/3 is unreasonable. Note that I am only saying this because you sound like an owner-builder. It's common, good practice to overbuild decks and porches on the assumption that they may be changed into buildings later.

    Keep the hole 1' away. Here is a quote from an email I had with an engineer on a similar project: "... deck loading will be minimal, so we are not going to be *overly* concerned with the performance of the footing at the pier locations. We will want to get the deck piers spaced minimally 12” from the house pier, but you should be closer to 24” since we are centering the house piers on the strip footing. I think it would be best to [...] give you two pier diameters between [deck and house] piers."

    I would use a longer anchor/helical if it was me. The soil was disturbed during the initial excavation, and is not going to have much shear strength for those titan anchors. Unless you can guarantee that the excavation went no further than 12".

    As for your 1" question... if you're referring to the gap between the house and the deck, I think 1" is plenty. Even 1/2" would be, in my opinion, but I'd like to hear others' opinions too. Note: I am assuming that you won't allow the gap to get clogged with leaves or debris, and that your deck will be either level, or slightly pitched away from the house.

    1. DerekR | | #2

      Ok when you say piers are you talking about the foundation footing? So the 2 foot bolt needs to be 1 foot from the very edge of my house footing or 1 foot from the foundation wall

      Because my foundation footing is probably 6 to 8 inches past my foundation wall

      The ground around my footings were undisturbed, my ground is also very hard so I don’t think the 3 foot bolt would make it to the bottom

      I was mainly concerned about the bolt being 1 foot below my foundation footing since the footing is only 1 foot deep, it doesn’t sound safe to me but I don’t know how else I would do it otherwise if I use these

    2. Expert Member
      MALCOLM TAYLOR | | #5

      James,

      "1/4 is considered best practice most of the time. It is, however, a deck, so if you can guarantee that no one is ever gonna enclose it or put roof columns on that cantilever or something, I don't think 1/3 is unreasonable."

      The maximum cantilever is based on what the building code allows, not best practice or what might seem reasonable.

      1. jamesboris | | #7

        Of course. I will edit my response to reflect that -- but it could be applied to 90% of the questions posted here. When I worked in the midwest, I saw 1/3 for decks often on projects that had plans -- but we'd often change it to 1/4 for reasons I implied above. In Texas, I've seen it vary.

        1. Expert Member
          MALCOLM TAYLOR | | #10

          If you look at the link I provided in post #3, the allowable overhangs are all under 1/4 of the span.

          I made a point of mentioning code requirements because Derek seems to be relying on the advice he gets here for guidance - with no apparent appreciation that it may get him into real trouble once his BI gets involved.

  2. Expert Member
    MALCOLM TAYLOR | | #3

    Derek,

    Does your foundation have perimeter drains? If so the piers need to be far enough from the footings so they do not disturb the pipe or rock.

    The maximum allowable overhangs (cantilevers) for various wood species are shown in table #2 of this link: https://www.nnva.gov/DocumentCenter/View/523/Residential-Wood-Deck-Construction-Guide-PDF

    When a deck is freestanding you no longer have to worry about lateral loads on the ledger, but have to brace for those loads on the posts. The requirements for bracing are in whatever building code covers where you are.

    1. DerekR | | #4

      I don’t have any drains around foundation, house is on a slight slope though

      I was concerned about the 2 foot bolt being 1 foot below my footings, a 1 foot footing vs a 2 foot bolt right next to each other

      1. Deleted | | #6

        Deleted

    2. DerekR | | #8

      So the overhang is determined by the size of the joist not it’s span, according to that link you sent

      I could have a 5x5 deck with 2x12s and the cantilever could be 3 feet?

      Edit: Nm I didn’t see the small text below that chart

      1. jamesboris | | #9

        No... "1/4" here means that Cantilever Length = Backspan Length x 1/4. See p. 33-34.

  3. DerekR | | #11

    If I want the side deck to be able to cantilever to my door so that my footings are 2 feet away from foundation I’m going to have to make the deck 8 feet long, that’s going to look pretty horrible for where this is going to be located

  4. steve41 | | #12

    I'm not 100% certain but I believe it would need to be even more than 8ft if you have an overhang on the side furthest from your house (ie. two overhangs on opposing sides). The span used for determining overhang would be the span between the supports. So, you would need: 2ft overhang + 8ft + second overhang (max. 2ft) = total deck length. Maybe an expert could chime in to confirm or correct this.

    Perhaps start with your preferred deck design size and work backwards to determine what overhangs/supports will be workable. Good luck with your project.

    1. DerekR | | #13

      Over hang can be 1/4 the joist span so 8 feet would be 2 foot overhang

      So the deck would have 2 foot over hang then 4 feet between the posts, then another 2 foot overhang

      If what your saying is true I don’t even have room for the deck and I’ll have no way to get into my house

  5. steve41 | | #14

    I'm saying that IF you believe you need a 2 foot overhang adjacent to your house, then the distance between supports would be 4x that (= 8ft). This excludes any 2nd overhang, if there is one. I'm sure there are design options/engineered solutions, it'll likely just need more exploration.

    1. DerekR | | #15

      Could I have the overhang on just 1 side? So 2 feet then 8 feet? I’m approaching my neighbors property line at this rate

      If I have 2 feet 8 feet 2 feet I think I will be within 5 feet of his line

  6. steve41 | | #16

    Yes, you could do that. And again, note the qualifier on my previous input: I would definitely suggest getting confirmation from an expert source.

    If your getting a permit I would suspect your code guy would confirm setbacks and review your drawing for any obvious code violations.

  7. walta100 | | #17

    I think you should reconsider your deck “foundation plan”. The screw in the link seems total useless to me it appears to more or less float on the surface and your deck is expected to have seasonal movement relative to house of several inches. I am not so sure that I believe the deck is that likely to return to its original location after a dozen or so freeze thaw cycles.

    How hard could it be to dig a 12 inch deep hole and put in the concrete?

    What is the local zoning set back requirement from the property line for your deck most places it 10 feet and it does not sound like you have that much room.

    Walta

    1. DerekR | | #18

      No it doesn’t float, a large 2 foot bolt pulls and holds the plate down, you screw it into the ground with an impact wrench, it has more wind up lift resistance than a 1 foot concrete footing

      1. walta100 | | #21

        "HOW DOES FROST AFFECT THE ANCHOR?

        The Deck Foot Anchor™ does not heave up from the ground like a fence post that is literally popped out of the ground a little bit each year. The Deck Foot Anchor ™ remains anchored to the ground and moves with the soil as it expands up or settles down during freeze or thaw cycles.

        The Deck Foot Anchor is not a frost footing and falls under Section R403.1.4.1. Exception 4(IRC) and Section 9.12.2.2.(7) (NBC). Therefore it is recommended for use with freestanding decks, unless the soil does not freeze in your area."

        The above quote is from the web site you linked to. It was next to an animation showing the deck jumping up and down when the ground freezes and thaws.

        Walta

  8. Expert Member
    NICK KEENAN | | #19

    Derek --

    Do you get frost where you are? It sounds like you don't since the house footings are only one foot down but I want to make sure.

    1. DerekR | | #20

      Frost line is at 4 inches

      Do you think I can drill this 2 foot bolt into the ground like 1 foot away from my house footings?

  9. ddrake | | #22

    Hi Derek,
    I have somewhat similar freestanding deck project permitted and ready to go, so have been following the discussion on this and your previous post with interest. I wasn't previously aware of the Titan Deck Anchor product, and was curious to see if it would make a difference for my project. In my case, the reason for designed a freestanding deck is to avoid having to attach a ledger through 4" of continuous exterior foam insulation and into studs, rather than a rim joist.

    In my area, frost line is 30" and soil bearing capacity is 1500 psf. For my deck, I'm using (10) 8" diameter cast-in-place concrete columns extending 12" above grade, each with integrated spread footing 14" in diameter by 6" thick. Each pair of columns supports a 5'-10 1/2" doubled 2X6 beam running perpendicular to the house, and the beams in turn support 2x8 joists 16" OC, running parallel to the house. This allows me to run decking perpendicular to the house (primarily for aesthetics).

    Looking at the Titan Deck Anchor literature, it appears max spacing between anchors is 6'-0" OC. For my project this would require using (16) Titan anchors, rather than (10) concrete columns. Titan Deck Anchors w/ 36" augers look to be about $80 ea; my cost for concrete columns is about $60 ea, including concrete, rebar, sonotube forms, post bases, and rental for the machine to drill (10) 14" x 36" holes.

    Titan seems to claim labor savings as the big advantage to their system. I assume their ad copy ('finished before lunchtime') means about 4 person-hours to install the (16) anchors my project needs. That's only 15 min. each—hard to see how it could be any faster. By contrast, I'm estimating 2 days labor (16 person-hours) to drill holes, set forms, and mix and pour concrete for columns.

    Bottom line: taking everything into account (materials + rental fees + labor), using Titan Anchors for my project would cost $460 more than concrete columns. And that's assuming the city building inspectors would sign off on the system without requiring engineering.

    Of course, in an area with a shallower frost line, and/or higher soil bearing capacity, concrete columns could be considerably smaller, requiring less excavation and labor, and making the cost differential between piers and and Titan anchors even greater.

    Finally, I'd be concerned that over time, the vertical movement allowed by the Titan system would result in a deck surface that was no longer flat, and that this condition would be quite obvious, given how the deck runs next to the house.

    1. DerekR | | #23

      Yes I’m thinking about doing 12 inch diameter concrete tubes just 12 inches deep, so that I can get closer to my foundation, atleast on the side of the house where I have limited space, then I’ll use the titans on the front deck

      Really want my cantilever to only be 1 foot at the side of the house and have the concrete tubes 10 inches from my house footings

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