Framing for 'floating' deck stairs

Forums › Home Workshop DIY › Framing for 'floating' deck stairs - advice

saxtimnew

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Wannabe Geek

#317976 3-Dec-2024 09:21

Hi all,

I'm currently planning some floating deck steps and had some questions about the framing. Here's a basic drawing of what they'll look like to match the slope I'm working with:

r/diynz - Framing for floating deck stairs

The bottom 5 stairs are 1134mm square (8 x 140 decking boards with 2mm gaps). Pictured below is how I'm planning to frame them (I've included a picture of the decking layer on the right) (the upper stairs are a little smaller but framing principals will be the same)

My questions are - do I really need the bearers to be double 100 x 50s, or will I get away with a single 100 x 50? And, do I need to use joist hangers on the 3 inner joists, or will I get away with end or skew nailing them in pace? I think joist hangers might be overkill for this short a span?

eracode

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#3315439 3-Dec-2024 10:28

IANA chippie but am an experienced DIYer and have built many decks and associated steps. I find your drawing a bit hard to follow because it's difficult to tell which pieces support which - or maybe all the brown lines are in the same plane? - in which case they're not really differentiated as bearers and/or joists?

In your green drawing, the bearers are shown as running top/bottom on the left and right - but they don't appear to be supporting the joists which presumably run left/right. I feel we need more info to be able to answer your question.

If all the 100x50s are in the same plane, you would need to double-up the 'bearers' at the sides. Normal span for 150x50 joists sitting on 100x100 bearers is ~400/450mm.

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johno1234

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#3315440 3-Dec-2024 10:43

What is the highest drop from a step to the ground?

saxtimnew

5 posts

Wannabe Geek

#3315446 3-Dec-2024 11:13

To add some clarity -

The steps are going up a bank, so are not all in the same plane but rising in height one on top of the next (first picture). This means that each subsequent step is resting on the previous. Riser height is around 180mm. The back of each step is basically at ground level, so the front of each step will be a max of 300mm off the ground.

In the second diagram - the framing members running vertically in the picture are the bearers, those running horizontally are the joists. Because the steps are close to the ground, the joists won't sit on the bearers but hang off them in the same plane (hence the question can I get away with end nailing, or do I need joist hangers)

Here's a picture of something similar to what I'm trying to achieve:

wellygary

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#3315448 3-Dec-2024 11:27

Irrespective of the position of the steps, make sure there is a direct path through the steps you can take without having to break your stride.

... having to change direction, particularly on garden steps where you might be carrying objects is just an accident waiting to happen,

eracode

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#3315449 3-Dec-2024 11:34

In each step frame, are any of the 100x50s shown in your green drawing supported by/sitting on, any of the others?

Normally joists are supported by/sitting on, bearers. I suspect that's not the case here - and each frame is a flat rectangle made of nine pieces of 100x50 (plus two spacers)? (That's what I meant by 'in the same plane' - no piece resting on or supported by any other piece, apart from the posts.)

If that's the case, then there are no bearers - all pieces are joists. But that's just my pedantry - it doesn't really matter what we call them but using the word 'bearers' was confusing.

Then IMO:

you will need to double-up the side 'bearers' - one 100x50 won't go your span without sagging
don't bother with hangers - if you use good-quality galvanized nails of appropriate length, you'll be fine.
if you assemble the frames in the correct order, you won't need to do any skew-naiing. All joints can be end-nailed - which is better than skew.

Sometimes I just sit and think. Other times I just sit.

saxtimnew

5 posts

Wannabe Geek

#3315453 3-Dec-2024 12:00

If I understand your question correctly, no, none of the 100 x 50 framing members sit on top of each other (my diagram is for a single step, each subsequent step will have the front resting on the rear of the one below if that's what you mean). I haven't got my computer on me but I did a quick sketch (sorry not a great drawer) - hopefully it might make it a little clearer (not to any scale). It's basically just a square frame:

Most images I'm seeing online don't look to use traditional bearers in steps, just a basic square/rectangle frame all built from the same size lumber. Basically what I'm asking is can I get away with a simple frame like the picture below, no bearers (so in my sketch above I wouldn't double the framing over the posts), no joist hangers, supported by 100x100 posts concreted into the ground? My inclination is I'm overthinking it a bit!

Building Box Steps and Stairs for Decks – Tanzite StoneDecks

saxtimnew

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Wannabe Geek

#3315456 3-Dec-2024 12:05

Sorry, re-read your reply and I think you were specifically asking about if each individual frame rests on the next, to which the answer is yes, in the same way as the second picture above. So not all frames will have 4 posts supporting them, the first will have four concreted posts, then most of the others I was planning on doing either 2 or 3 (2 at the back, and some with one at one of the front corners depending on how far it is offset/cantilevered from the step below)

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mdf

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#3315458 3-Dec-2024 12:18

Disclaimer: DIY only.

NZS3604 has the rules for all the spans. For decks, table 7.1(b) on p 147 is your friend: https://www.standards.govt.nz/shop/NZS-36042011

If I'm reading your plans right, you're looking at a ~1.2m joist span at ~600mm centers. In which case, 4x2 / 100x50 / 90x45 SG8 timber is fine.

However you don't really have bearers with your in-plane design. 32mm decking is okay for 600mm joist centers (NZS3604 again, 7.4.3), but I would use joist hangers. Skew and end fastening is not that strong and I suspect that the middle of your step would be springy. I'm not sure that double 2x4s would add anything in this scenario?

And it looks like you're intending the picture frame the decking. Again if I'm reading the plans right, you've got a triple wide joist-block-joist to catch the outsides of the decking board. This will stop it cupping but this will need extra joist hangers. Personally I've found picture framing decking neatly to be a real b'arch though since almost none of it will be straight. If you're dead set on hiding the end grains (which fair enough) you could also consider a vertical facing board of more decking on the sides of your boxes.

mdf

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#3315459 3-Dec-2024 12:33

saxtimnew:

If I understand your question correctly, no, none of the 100 x 50 framing members sit on top of each other (my diagram is for a single step, each subsequent step will have the front resting on the rear of the one below if that's what you mean). I haven't got my computer on me but I did a quick sketch (sorry not a great drawer) - hopefully it might make it a little clearer (not to any scale). It's basically just a square frame:

This drawing shows things well I think.

The joists (the three inner horizontal bits of timber) are carrying all the weight of the decking that will run vertically, plus whoever is standing on it. You need to transfer that weight to the posts (or the posts of the step under it). A few nails/screws aren't going to transfer that weight to the doubled up vertical bears nearly as well as a proper joist hanger (or putting the joists on top of the bearers).

An alternative (if you wanted to give up the picture framing) would be to put the top and bottom joists directly on the posts. Your bearers are then only carrying the weight of the middle joist, not the whole platform.

In your other picture, the joists are carrying all the weight and are sitting directly on either the concrete or other joists. The "bearer" is really just a facing board to hide the ends of the joists, it would be carrying minimal weight even if it weren't on something solid.

saxtimnew: ... My inclination is I'm overthinking it a bit!

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neb

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#3315473 3-Dec-2024 13:22

saxtimnew: Here's a picture of something similar to what I'm trying to achieve:

Broken ankles?

Seriously, I would definitely not try and mimic that layout.

saxtimnew

5 posts

Wannabe Geek

#3315474 3-Dec-2024 13:28

Haha - yes, there is definitely an element of form over function. Seriously, I will at least make sure to take Wellygary's suggestion and rearrange the design a bit so that there is a clear line the entire way up the stairs you can walk without having to deviate.