How to build a low-level deck with limited clearance space?

[ragebison]

Hi All,

We've just moved into our first home, which has an ugly covered concrete outside our living area measuring 5600mm x 2020mm. I'd like to cover the concrete with a composite timber deck. I've never built anything to this scale before so it would be a big job but I'd really like to give it a go.

The main issue I've identified in doing the planning is that I only have 80mm of space from the top and bottom of the bricks pictured. I have 90mm if I go to edge of the sliding door frame, but neither of which would give me enough space to install a 23mm deck board on top of a 70mm joist, and have enough space underneath for airflow. 

I'm wondering what my options are. I had wanted to use something like tuffblocks underneath but they're 50mm to the bottom of the joist slot. 

I've seen a video on YouTube of a guy who used packers and bolted the joist to the concrete, can I potentially use more timber laid on it's side so it is only 45mm high instead?

Cheers.  

[MitchellMc]

Welcome to the Bunnings Workshop community @ragebison. It's wonderful to have you join us, and many thanks for your question about creating a low-level deck.

I'd encourage you to have a read through some of our many low-level deck projects on the community. At a minimum, you'd typically want 90mm for the joist, 22mm for the decking and then space under the joist for some type of airflow. In your situation, you can certainly bolt through the face of 90 x 45mm timber spaced with packers directly into the concrete. However, there will be next to no airflow under the deck, and you should expect the early onset of decay to some extent. Depending on how exposed the deck is to the elements, you might not see any adverse effects from the lack of airflow, or the deck materials could deteriorate quite quickly.

Please let me know if you have any questions.

Mitchell
 

[ragebison]

Hi @MitchellMc and thanks for your speedy reply.

To avoid the potential issue of rotting, could I use steel bolted to the concrete instead of timber? 

Something like this with the decking boards screwed into the top?  

If a viable option, would I still need to space it at 450 between the joists, or would I need to shorten the distance between?

I have a Kamado Joe BBQ in a quite large Merbau caddy, which combined weighs over 150kg, which I would like to have sat on the deck, so perhaps using steel might be a better, stronger solution?

Thanks again. 

[MitchellMc]

You could potentially use steel @ragebison. However, although it's galvanised, you potentially still see it rust. It could last longer than timber, though. 

Constructed with the required timber joist spacing, 150kg (that's not even a couple of people) doesn't even come close to what the deck can easily support; so, no worries there.

You always need to have 450mm centres on your joists as that is as far as decking can span before it becomes bouncy. No need to have the joists close because you're using steel.

Mitchell