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Hi, photos attached as you can see I have a deck which appears to be floorboards tongue and groove on 90 x 45 treated pine laid straight onto concrete slab, the 90 x 45 is rotting and allowing boards to come apart. This was how it was when we bought the house and over the last 7 years it is getting worse at coming apart and needs replacing.
Size is 1.785 width x length 9.290
I am open to suggestions on how to replace this, I cannot go to high, what is the minimum gap underneath as it appears I will have to lay the 90 x 45's sideways for minimum height.
All suggestions are welcome as to timber to be used for top boards and underneath.
Welcome to the Bunnings Workshop community @pano. It's fantastic that you've joined us, and many thanks for your questions.
Any less than a 10mm gap under the timber structure is inviting water to get trapped and encouraging rot to set in. The enclosed sides of your deck wouldn't be helping airflow and circulation either. I'd recommend using 90 x 45mm outdoor H3 framing timber for the joists raised 10mm on plastic packers. Given the low profile of the deck, a hardwood decking similar to Merbau would be best.
As an extra preventative step, you could spray the joists' underside closest to the concrete slab with TWA Woodcare 300g Ecoseal Tanalised Timber Treatment. This would increase their H rating and hopefully give you many years before replacing any timbers again.
You should find this guide useful: How to build a low-level deck by @Adam_W.
Please let me know if you have any questions.
Mitchell
Hi Stephen (@pano),
Since you'll be placing the timber on the 90mm face, it will flex slightly more than the 45mm side. I'd be fixing it to the concrete every 800mm with Ramset 10 x 100mm Countersunk DynaBolt Plus Masonry Anchor. Plastic packers can be placed next to the bolting locations; you might like to place them in between the bolt locations as well, so every 400mm. You can create box sections of framing if you wish, and that's a good way to construct the structure.
Mitchell
