Great community here. I've been reading a lot about building a low level deck. But still have a few specific questions just to make sure before I buy the materials.
I plan to build a low level decking on top of my concrete floor and will span around 1.8m across the grassy part to the right of the photo.
I plan to use 70x35mm for the joist as it has enough height to just level with the floor of the house after decking is installed.
1. for the 1.8m joist that will span the right side, do I need to double up the 70x35mm joist? or single is ok?
2. for the bearer, I'm planning to use 140 x 45 mm how far from the concrete floor can I position it? Can I have just one bearer positioned 1.8m from the concrete floor? or do I need to put 2 bearers 0.9m apart?
3. Joist spacing should be 450mm? is this the same if I will use pine?
Welcome to the Bunnings Workshop community @archerwinmakes. It's fabulous to have you join us and great to hear about your deck project.
Could we please know the height from the concrete slab to the house's floor and the overall dimensions for the deck? I can then recommend timber sizes for you to use and will provide a plan of how you need to set out your decks bearers and joists.
The concrete slab is 145mm lower than the house floor. The soil is around 80mm lower than the top of the concrete slab.
The total area is 7.34 m x 5.20 m. Area in concrete is 7.34 m x 3.20 m and area in soil is 7.34 x 2.0 m.
Thank you for your help.
I'd recommend using Treated Pine Outdoor Timber Framing 90 x 45mm for the joists. The 90mm joist plus 19mm decking will then allow 36mm for airflow and drainage. You'll need two supports over the soil area, one being the midpoint. It would be a great idea to lower that soil and lay some drainage matting and gravel over the area.
I've included a basic diagram below.
How many supports do i need for the bearers? Also, what bearers do I need to use?
Do I need to put noggins on the joist that are on the concrete?
For the joist sitting on top of the concrete, do I need to lift them up a bit or can they stay direct on the concrete? The concrete part is fully roofed and graded so water flows out from the concrete floor. thanks
You don't have enough room over the soil area to use a traditional joist over bearer layout. It will just be a continuation of your joists on the concrete, which then have noggins in between them. Supporting every second joist should be sufficient, but I'd encourage you to check the relevant timber span tables and construction codes.
You don't need to put noggings between the joists over the concrete as they with be Dynabolted to the concrete with brackets. They need to be lifted to allow airflow and drainage.
What's the recommended amount of lift for the joist? and how many brackets per joist do you recommend?
Also, I'm willing to remove soil to allow for bearers. What is the recommended size for the bearers to use so I can plan how much soil to remove.
thanks a lot.
You'd need at least 10mm, but as you'll be using 90mm joists and 19mm boards, it makes sense to lift them 36mm for a deck that is flush with the door sill. Bearers generally start a 140 x 45mm, so you would need 140 + 90 + adequate space between the bearer and soil. You'd be looking at around 330mm below the height of the concrete. Generally, low-level decks don't utilise a joist over bearer system. You should find this article helpful: How to build a low-level deck by @Adam_W.
@MitchellMc Thanks for your replies.
I have a product question for this build.
I think I'm going with your 1st suggestion on supports directly to the joist.
I plan to to follow @Adam_W suggestion to dig the holes, build up the frame, level it and concrete in the support.
How big does the hole need to be?
What type of stirrups do I need to use?
Is the Australian Builders quick set concrete ok for the job?
Also, for lifting up the joists over concrete, how many supports (L-brackets) do I need per joist over the concrete to ensure it's stable?
So many questions... thanks!
Footer sizes are determined by the type of soil you have in your location, and your local council might be of some assistance in determining this. As a general rule of thumb, a 300 x 300 x 450mm hole would be a good starting point.
You can use anchor stirrups, and the product you use will be determined by how much of the soil you intend to remove. Australian Builders 20kg Quick Set Concrete would be suitable for setting the stirrups in place.
Since you'll be lifting the joist 36mm, I'd suggest the Builders Edge Pedestal Foot Smallfoot 35 - 60mm would be perfect to use instead of L brackets. You'd place them every meter along the joist. Alternatively, a bracket similar to Carinya 100 x 100 x 50 x 4.5mm Hot Dipped Galvanised Angle Bracket would be suitable.