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.
Please let me know if you have any questions.
Quick Answer: with such low clearance wood is out, but composite decking or hardie deck. For joist something like "Alyspan" which is aluminum and have wall thickness of 3+mm.
Hi thanks for your insight, I gather 450 spacing width as I will be running the 90 x 45 length ways on it's side with a half lap joint to reach out to 9.290 metres.
10mm spacers at what spacing along the lengths?
At the moment the 90 x 45's are just sitting loose on the concrete with wood spacers underneath to level out.
When I replace, will I need to frame up in box sections? Also will I need to tie down to the concrete and at what spacings with ???
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.