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I have an alfresco area which I'd like to deck. The joists (Green lines) will most probably fix straight into the concrete and ideally, I'd like to go 1500mm beyond the concrete (Red line). I have a storm water pipe (White line) about 800mm out from the concrete. 800mm out from the concrete, the ground is at its lowest point, which is about 200mm lower than the alfresco. With regards to the footings and bearers, what are my options?
Community manager's note: Check out How to build a low-level deck for expert advice.
OK, so I'll do 90x45. Let's assume I raise the joists by a minimum 25mm (the lowest of a minifoot pedestal). I'll have 25mm off the slab, plus 90mm for the joist and leaving me 25mm to play with for the boards, which will either be 19mm timber, or 23mm composite.
...and the actual thing:
Depending on where I take an actual measurement from, it can vary a few mm here or there which is no big deal.
I'd use a bunch of pedestals to lift and level the joists (depending on the board I use) to the height needed so the boards finish flush with the brick. Angle brackets will be used to fix the joists to the concrete.
For some strange reason, my wife is fixated on a step-down onto the deck. But by step-down, it would be only about 20 mm. Assuming I raise the joists off the slab by a minimum of 5mm using https://www.bunnings.com.au/macsim-fasteners-5-0-x-75mm-window-packer-200-pack_p1040470 and screw the joists directly into the slab, a timber board (19mm) would result in a 26mm lip and a composite board (23mm) would be a 22mm lip, which I don't think is suitable. That little 22/26mm lip might be a tripping hazard.
Hi @IronStan001
You're absolutely correct, that little lip will become a tripping hazard. You and your family in time could get use to the little step outside, but if you ever have guests over, they will not notice that step and get caught. I suggest thinking about lifting the frame up all the way to the top of the brick and have the decking panel as close as you can to the sliding rail height. In this manner there will be no mini steps to trip over.
I've placed a sample image below to give you an idea of what I'm suggesting, but please let me know what you think.
Please note that the depth measurement for your brick lip is just a guess and you'll need to adjust it to your needs.
If you need further assistance, please let me know.
Eric
Hi @IronStan001
At this point of your journey, I suggest drawing up a complete plan with timber framing put into place. I propose thinking about spacing the brackets at 800mm apart and positioning them alternately from one side to the other. If for example using the 3240mm length and placing a bracket at the very start, you will be putting in at least 5 brackets.
At the end of the concrete slab, it is possible to reduce the distance between the bracket and first pedestal so that you can have a 360mm overhang. I'm a bit conservative when it comes to overhangs and recommend reducing it down to 200mm. This means that the first pedestal will be placed 800mm after the last angled bracket. The last pedestal can be pulled back in so that you'll have the 200mm overhang. But this all depends on how you'll be building your frame and if you're putting in a picture frame and breakers.
I strongly suggest having a look at Low-level composite deck by @oninpena. It's an excellent example of a decking frame going over a sloped concrete base and over soil. Plus, it is built for picture framing and breakers included.
Please make sure to share your plans with the community and any questions you might have.
Eric
So this is where I'm at, at the moment:
5 angled brackets fixing each joist to the concrete is fine. Then I have the 1400mm jump over to the bearer. What should the joist be fixed to, or sitting on before it leaves the concrete? A bracket? Or pedestal?
Hi @IronStan001
I suggest a combination of Brighton Masonry 400 x 400 x 40mm Charcoal Mypave Paver and Builders Edge Pedestal Foot. This will save you from having to put any timber pieces making contact with the ground. the full length of the timber piece can be supported by pavers and pedestal. I've placed an image below to give you an idea of how it can be done.
If you need further assistance, please let me know.
Eric
I can't do that.
The white line is the storm water. At this point, its about 300mm below the concrete. The green line is roughly about where the bearer would be. This is maybe about 200mm below the concrete. The ground is both too low and too loose to use pavers and pedestals, hence why I need something more stable like a bearer.
Hi @IronStan001
My apologies, I forgot to mention that the area must be first levelled and compacted so that you have a nice flat area to place the paver and the pedestal. Please keep in mind that the area has to have a slope so that any rainwater flowing in that area goes towards the drain. By levelling the area first, it will solve the issue of whether you can use pavers and pedestals together.
In regards to the storm water, you can bypass that area by placing the paver right after it. You also have the option of having one right after the concrete base if you want extra support for that area.
If the area is not levelled and compacted, any footing you place there will eventually settle into the soft ground and your deking frame will sink and bend along that spot.
The other option is to to dig into the ground at 500mm deep and put in H4 100x100 treated timber posts and concrete them into place. This will provide stable footing for your low-level deck.
If you need further assistance, please let me know.
Eric
"The other option is to to dig into the ground at 500mm deep and put in H4 100x100 treated timber posts and concrete them into place. This will provide stable footing for your low-level deck."
This is my intention. There is too much loose fill / building rubble right next to the concrete. It would require a reasonable amount of scraping away before I get to something that I'd consider firm ground. And if I do get to that point, I've now probably created a drainage problem. Hence, the preference to go with a double 120x45 bearer at 1400mm, supported by 4 posts. The end posts would be 200mm in from the end, the 2 middle posts would be 1450 to 1500mm apart. If the 120mm height of the bearer is a problem, I could still go with a twin 90x45 bearer and 4 posts since that still fits within the parameters of spanning guidelines (according to https://www.demak.com.au/wp-content/uploads/2013/08/tabma_span_tables_v1_0_june_2007.pdf).
So based on that, what option do I have for supporting the joist before it leaves the concrete?
Hi @IronStan001
If those are the conditions, I suggest using pedestals at the very end instead of an angle bracket. You'll be able to adjust the height of the pedestal should you need it to be higher. My only other suggestion is to add more footings in the middle of the 1760 length to prevent a bouncy frame.
If you need further assistance, please let me know.
Eric
