How to build a low-level deck using composite boards?

[KHyde]

Hi, I am about to start building a deck and have chosen Ekodeck as the boards, I would like some assistance with the framing.

I have 75mm clearance from a concrete slab I am building directly onto, minus the 23mm for the decking board I have 52mm for joists. What is the best way to install the joists for this project?

[JacobZ]

Hi @KHyde,

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

Any deck built with very little clearance will have limited airflow beneath, meaning any water that finds its way in there will not be able to dry sufficiently well, causing mould, rot and the eventual degradation of the deck frame.

Ideally, decks are built with a minimum of 400mm ground clearance, but this can be reduced assuming the builder understands the risks. Read through how to build a low-level deck for some guidance.

Unfortunately, there's insufficient clearance to build a timber deck following the generally accepted principles of deck building. 

You'll note in the Hyne Deck Joist Span Table that the smallest timber acceptable for use as a joist is 90 x 35mm H3 Pine Outdoor Framing with the 90mm side being the height of the joist.

In theory, you can use a 90 x 45mm H4 Treated Pine on its side, but it would need to be supported almost continually along the span, meaning it would more or less sit directly on the concrete. Being treated to H4 level, this is less of an issue than with H3 timber, but it is still not a generally accepted way to build a deck.

Let me know what you think.

Jacob

[KHyde]

Thanks for the information, what would be the best way for me to secure the timber to the concrete?

Also, for further information, the deck will extend beyond the concrete which drops off around 200-250mm.

[JacobZ]

Hi @KHyde,

Do you have some photos or a basic plan you can share? This will help me understand what we're looking to achieve and offer my best advice based on the specific circumstances. Seeing the bigger picture will often reveal ways around tricky situations.

Generally speaking, you can attach deck framing to concrete with galvanised angle brackets, batten screws and masonry anchors such as an AnkaScrew or DynaBolt.

Let me know if you have any further questions.

Jacob