How to build a 6x7 tiled deck?

tonicoulson

Hello and thanks for all the info you post.  I am building a low level deck to be tiled on tile cement underlay instead of decking boards (30 cm above ground) which is 6 meters by 6 meters and I have tried to use the span table but just can get my head around it.  I want to use the h3 treated pine 140x35 h3 for the bearers and 90x45 h3 treated pine for the joists and my posts will be 100x75 h4 ( is this size allowable for posts or do I need to go to 100x100).

I want it safe, but also want the most cost effective way with timber you supply. So my question is as follows

1: how far apart do my post need to span with posts listed above

2: how far apart can my bearers span apart with the h3 140x35 listed above

3: how far apart are my joists using the timbers I have listed above

4: Would tiling and using cement sheet 6 mm tile underlay on top (which I figure would make it even stronger) would this effect the span rules ? If so how and by how much. Thank you for using your brain for me, mine seems to have gone on holidays since I turned 50 and has not returned.

MitchellMc

Welcome to the Bunnings Workshop community @tonicoulson. It's wonderful to have you join us, and many thanks for your question about tiling an outdoor area.

For what you’re planning, there’s an important distinction to make. If your intention is to tile over a low-level deck, you can’t simply put tile cement underlay on a standard timber frame and expect it to perform safely. Tile underlay is not structural, and it won’t carry the load the way a proper subfloor needs to. You would need a solid, compressed or structural flooring material like Secura Flooring designed to be tiled over, and then your timber frame beneath must be built to support that flooring material according to its span requirements.

Because of this, the span tables for your 140×35 bearers and 90×45 joists only apply if you’re using them to support standard timber decking, not a tiled surface over underlay. Tiling adds point loads and a different distribution of weight, so you really need the frame and subfloor designed for that system. For a safe result, I’d recommend reviewing the Secura flooring installation guide, then sizing your posts, bearers, and joists according to that, rather than just the timber deck span tables.

Just a heads-up that building a frame to support compressed flooring is far more involved than creating a deck, as not only do you need to work with span tables, but the frame needs to be designed as per James Hardie's recommendation in the guide.

Please let me know if you have any questions.

Mitchell