What is the minimum height for a deck over a tiled alfresco area?

[LAM80]

Hi there

I have seen quite a few questions about this kind of project before in the community, and most talk about the gap between the tiles and the deck not being big enough.

With a standard deck:

- what sort of gap do you need between the tiles and the deck

- what is the total minimum clearance height that you need to deck over tiles?

Also, a lot of the answers refer to other projects where people have decked over concrete - is this the same in principle as decking over a tiles alfresco area?

I just want to say thank you at the start for this community, I think it is a wonderful initiative.

[JacobZ]

Hi @LAM80,

A warm welcome to the Bunnings Workshop community and thank you for your question.

The National Construction Code (NCC) Part 3.4.1 Subfloor ventilation is the main document for reference that relates to the clearance between the bottom of a deck frame and the substrate beneath. The principles stated in this part of the NCC are to ensure newly built decks have a life expectancy of 25+ years, which is important if you are a paying customer of a licenced builder. The minimum recommended clearance stated in the NCC Part 3.4.1 is 150mm when no termite inspection or management system is required.

Unfortunately, due to the design of concrete patio spaces in a lot of new construction, it is often not possible to create this amount of clearance and allow a seamless transition with no change in flooring height from indoors to outdoors, which is incredibly desirable. 

When this is the case, we always try to make people aware that by building a low-level deck, you are increasing the risk of moisture buildup beneath the frame, which can reduce the life expectancy of the deck. As long as you are aware of this fact, unless your deck requires building approval, there's nothing stopping you from going lower than the recommended 150mm, but where possible, you should allow as much airflow as possible and take steps to reduce the risk of premature rot.

There are relatively new structural timber products coming to market from Woodhouse TerraFrame which are H4-treated for close proximity and contact with the ground. I have started to recommend using these as much as possible as they will extend the life of your deck greatly when low clearances are expected.

As long as the tiles on your concrete patio are well supported, then there is no great difference and there shouldn't be any issues.

Let me know if this has answered your questions and please let me know if you'd like any assistance designing a deck. I really enjoy these projects and am more than happy to help.

Jacob