How to build stairs and low level deck on concrete slab?

Nath1

Dear Bunnings Community,

I am planning two small deck projects for which I wanted to seek your input - thanks in advance.

Great to see the existing support available here: https://www.workshop.bunnings.com.au/t5/How-To/How-to-build-a-low-level-deck/ba-p/45715 and https://www.workshop.bunnings.com.au/t5/How-To/How-to-build-a-deck/ba-p/102739 

Project 1. Low level deck on concrete slab of my front porch:

The porch is 5.2m x 1.5m. The height from the concrete slab to door frame is 135mm. I wanted to have a composite deck (140 x 24mm) on the concrete slab to have the deck level to the door frame. Leaving the deck board thickness of 24mm out, I would have only 111mm for the deck frame.

Questions:

- Is this a good plan to have a deck here (wife really wants to have one 🙂 )?

- If possible to have a deck, can I please pick your brain on selecting the frame timbers' dimensions, and how to create a gap between the frame timbers and the concrete slab?

Project 2. Deck stairs:

From footpath to my front porch is 4m long and 1m in height. I want to have deck stairs about 2m wide. The natural ground is sloped from porch to the footpath. I am planning to have 7 treads @143mm rise each of composite deck (140x24mm), each tread supported on a box, which is connected to a post dug in ground (please see diagram). The two sides of the stairs have existing brick walls for landscaping.

Questions:

- Any issues with the plan? 🙂

- How many posts per box (I planned 6 @0.5m spacing - see diagram) - sufficient, or overdoing it or there are better alternative plans?

- What size bearer, joist, and blocking to be used in each box?

Thanks heaps.

Regards

Nath

JacobZ

Hi @Nath1,

A big welcome to the Bunnings Workshop community, it is fantastic to have you with us.

Project 1 certainly looks feasible, although you are working with a fairly tight amount of space, having only 135mm of height available.

The smallest timbers recommended for deck framing are 90x45, so with the 24mm decking boards, this leaves only 21mm of space to the concrete below. If you had 4 extra millimetres of space, you could use these Builders Edge 25-40mm Minifoot Pedestal Feet. If you were flexible with materials, this could be achieved by using merbau decking instead of composite. 

If you were set on using the composite decking, you would have to set your bearers on Packers and bolt them to the concrete using angle brackets. If you went with this set-up, due to the close proximity to the concrete, I'd encourage you to use H4-treated timber, such as this 90 x 45mm H4 Treated Outdoor Structural Pine as it will be far better at handling any moisture that can become trapped when there is not a lot of airflow.

Project 2 also looks good, and the design for the stair box is pretty much bang on; the only change you would need to make is how far your joists are spaced apart. Most composite decking, including our Ekodeck Classic, requires joists to be spaced no more than 450mm apart. Over the 2m length, you've drawn the right number of joists, I just thought it important to clarify.

For your stair boxes, you would once again need to use 90x45 to fit within the height requirements. The allowable span for a 90x45 bearer is 900mm, so you will require 6 posts per box, as you have already planned. You can use the same size timbers for your joists and blocking.

Overall, your plan looks good, and I am excited to see how it progresses.

Let me know what you think.

Jacob