How to build composite deck fascia on concrete slab?

[matdiy]

I'm placing a low lying ekodeck on a concrete patio on timber joists. The patio is raised above the yard height so I am planning to add a single step in. I'm trying to determine where to finish my deck relative to the slab which depends on how I install the fasica for the first step. My options so far are:

(a) Install fasica on timber subframe only and trim it so it finishes before the concrete. Therefore it can be flush to the side of my house. This isn't viable as my deck is only 75mm height this would cause a very small first step.

(b) Deck overhang concrete by around 25mm and then install bottom of fascia basically directly onto concrete. 25mm comes from 23mm fascia thickness plus 2mm gap. Main downside is attaching the bottom of the fascia directly into concrete. 

(c) Deck overhang concrete by around 50mm and then install bottom of fascia onto a 25mm thick batten installed on the concrete + spacer. This would be my preference as that overhang also allows full deck boards all the way to the house. However, I am unsure if this is not advisable for some reason. I've attached a quick illustration with this setup where grey is concrete, blue is packers. Yellow is joist/batten and brown is deck/fascia. 

Thanks in advance!

[JacobZ]

Hi @matdiy,

I'm sorry to say, but I have some concerns about the design of your deck.

Building decks low to the ground reduces airflow beneath the deck, which allows moisture to build up and adds to the risk of rot. 

Having your deck this low to the concrete massively increases the risk of rot and adding a fascia board to cap the end of the frame closes off the one spot where air can flow.

Unfortunately, I don't think a timber deck is a viable option unless you can increase the clearance from the concrete.

You may be better off looking at something like outdoor tiles for your patio.

Allow me to tag @Dave-1 and @Jewelleryrescue to see if they have any ideas they could add.

Let me know what you think.

Jacob

[matdiy]

@JacobZ 

Thanks very much for the reply. I understand it isn't perfect and the risk of rot is higher. However, it is under cover and it is fairly common. For example:

https://www.workshop.bunnings.com.au/t5/Featured-Projects/Low-level-deck-over-concrete/ta-p/77402

https://www.workshop.bunnings.com.au/t5/Featured-Projects/Low-level-composite-deck-over-concrete-sla... 

Its mainly the fascia and overhang I'm curious for any advice on. 

[JacobZ]

Hi @matdiy,

If you're happy to accept the risk, then I'd go with option C.

It will look the nicest of the three options.

Jacob

[Dave-1]

Afternoon @matdiy 

In reference to the look you are asking about I would suggest option C as well. 

As to the height of steps I would set up a test area with some different height opjects and see how it feels. Nothing worse then a short step then a long height step to make someone trip.

As to low decks, I had a look at the two links you posted and while they look great remember that they were done back in 2021 and 2022. Maybe ask some questions from the projects posters to see if they would recommend anything different and how the decks are holding up?

Having the timber so close to the concrete with no easy path of draining or drying concerns me and as @JacobZ has said its your choice to build your deck the way you want I belive the same with "your choice" but it would be remiss if I didnt state my concernbs as well. I have seen timber styled square tiles from Ikea that have been made to sit on concrete taht may suit but that is about all. You could still do your edge you want with the ikea timber squares. 

Dave