Apologies for posing another thread on low level decking. I have read through number of discussions available and gathered most of the required information. Just got few last items that I need expert advice on.
I am planning to build deck over existing exposed aggregate concrete with 1.2m overhang on the grass area. The concrete are is 4.5m x 2.4m with 120mm depth from the house floor level. The deck I am planning to build will be 4.5m x 3.6m (2.5m concrete + 1.2m overhang).
My plan is to:
- Use 90 x 45 H3 structural timber with joists spaced at 450mm. This will allow me 11mm offset from existing concrere if 19mm decking boards are used (120mm - 90mm - 19mm = 11mm)
- Use galvanized L brackets fastened with dynabolt every 1m of the joists on alternative sides
- Use 4 Pryda Post Anchor Stirrups along the long edge of the deck to support overhang area
The advice I am after:
- Would 90 x 45 H3 be adequate considering the overhang area? I am constrained by the height, but can use 90 x 90 if required.
- Would 4 stirrups be sufficient to support the 1.2m overhang area, or should I install stirrups every second joist or so?
- 11mm height offset from the concrete is good enough for ventilation under the deck?
- When installing the deck board, how frequently should I be screwing the boards on to the joists?
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I'm afraid my knowledge of decking is not as in depth as Mitchell's. Let me tag @Adam_W to see if he can give us some possible advice to your query.
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Welcome to the Bunnings Workshop community @Sham. It's wonderful to have you join us, and many thanks for your questions.
Fantastic work reading through the previous discussions, as it looks like you are well on your way to getting started on the project.
You'd need to check a timber span table to see if Treated Pine Outdoor Timber Framing 90 x 45mm could stretch 1.2m unsupported. I'd suspect that 900mm would be more within the realms of what it could achieve. However, you can counter-lever the end of the deck and having your supports at 900mm instead of 1200mm would be an option. Once again, you'd need to check span tables, but I believe 90 x 45mm would be suitable for a 300mm overhang.
Four stirrups would only be suitable if all your joists are joined together into one structure. If a joist is not supported by a stirrup, then it needs to be supported by the joists on either side of it. Did you intend on framing at the end of the joists so they are all joined together? Perhaps you might like to draw a quick diagram to illustrate.
11mm of height for airflow and drainage under a deck would be considered the bare minimum over concrete. However, you'll need more clearance than that over the grass/soil, and I'd recommend at least 50mm, so you'll need to remove some soil. In the helpful guide on how to build a low-level deck by @Adam_W, you'll find some details on how to prepare that area to be decked over.
Decking is laid perpendicular to the joists. So if you are spacing your joists 450mm apart, then you'll be screwing the decking downing every 450mm along its length.
Please let me know if you need further assistance or have questions.
Thanks @MitchellMc for your prompt response on my queries. As you have identified my idea was to frame the joists at either ends using joist hangers, so that the load can be distributed evenly.
I have managed to complete the structure of the deck over the easter weekend.. Might need good couple of days of sun before decking board is laid. I was planning to picture frame the deck, therefore had to install the additional joists close at left and right side of the deck.
It looks like you've achieved some significant progress over the long weekend! As you've mentioned, with a couple of sunny days, you'll be well on your way to relaxing on your new deck and being able to admire your work.
I'm excited to see your finished result. Please keep us updated and shout out if you run into any difficulties.
Just calculating the decking board required for the deck. My plan is to picture frame the deck using 140 x 19 boards and fill the middle using 90 x 19 merbau boards.
the question is when I am butting up two boards together, do I have to connect them on a joist, or can they be joined in between two joists?
my joists are approximately 500mm apart. If I have to connect them on joists ill be wasting fair bit of timber, so your advice will be greatly appreciated.. cheers
You need to butt the two boards together over a joist as their ends need to be nailed off to it. If not, their ends will bend when weight is placed on them. It will pay to spend some time sorting out your timber to ensure minimal wastage; it's a bit of a jigsaw puzzle. Whether going with mixed lengths or using all set 4.8m lengths, there is still a certain amount of wastage.
You could use set lengths like the SpecRite 90 x 19mm 2.25m FJ Merbau Decking - 5 Pack. However, you'll end up with a straight line of joins down the middle of the deck, and this is not generally considered pleasing to the eye. You could turn this into a feature if you widened up that central joist allowing you to nail off a breaker board and the decking boards.