How low can a floating deck on pavers be?

Mick0

Hey peeps! I have been reading and taking inspiration (thank you) for a while but first time actually posting.

I have been thinking for quite some time about building a (very) low deck for my alfresco area, roughly 7m x 4m.
I say "very" low because I must have the lowest clearance in the whole country, with only 60mm from the top of the pavers to the level of the door/house floor. Now I could take the pavers off, and that would give me an extra 6cm only, so a total of 120mm/12cm, which is still not great but I believe it'd be workable. 
But since the pavers are actually super solid, perfectly levelled and flat, I have also been toying with the idea of just going over the pavers with an extremely low deck. 
Has anybody ever done or heard of a decking that low? Do you think it would be a bad idea?
I was thinking I could maybe build the framing using some H3 70x35 laying them on the 70mm side so that the height would only be 35mm, using 5mm PVC board cut offs as spacers, placed at regular intervals between pavers and sleepers to allow for drainage and air flow (water would be minimal since the area is undercover). This would give me a total height of 40mm, and then just use 20mm decking boards on top to get to the total of 60mm/6cm.
Crazy? Dumb? I'd love to hear your thoughts and experience.

Thanks, regards.

MitchellMc

Welcome to the Bunnings Workshop community @Mick0. It's fantastic to have you join us, and many thanks for your question about decking over pavers.

Great topic which is certainly worth discussing.

In answer to your question, it has been done before, and if the area has a roof over it, you'll probably get a satisfactory life span out of the deck. Is it commonly done in Australia and to code? Likely not. This is something you'll find being done in America, where construction codes are much more lenient. I'm not sure about your local council, but mine won't approve a deck any lower than 300mm in height as visual inspection of the structure must be done from underneath.

In saying this, though, I'm sure if any builder 20 years ago saw the low-level decks being constructed today, they would think people were out of their mind, giving a ballpark figure of five years before they'd rot out. We know this isn't the case, and with adequate drainage and clearance, we even see professionals pushing the limits of how low a low-level deck can be. A couple of issues that can arise from having no airflow are cupping of boards and premature rot. This can be somewhat mitigated by oiling the underside of your decking before installation and at regular intervals afterwards and using a wider gap on the boards.

You certainly won't find any decking manufacturers (even synthetic) that recommend or warrant their product under your proposed plan, even if you lay your joists on their 35mm side. It's all a bit of a gamble, really. It would be my recommendation that you at least remove the pavers to give you some extra working height.

Let me mention @ProjectPete, @Brad and @TedBear to see if they'd like to join the discussion.

Please let me know if you have any questions.

Mitchell