Thread: Decking On Concrete

Hi Richard,

I did a similar thing with a concrete landing. I covered the landing and then continued on to a timber frame. Having completed this, I would never attempt it again. Several reasons for this:
1. The existing landing or concrete will be quite uneven and this becomes far more obvious as you start putting timber on it. I had a great deal of grief getting the joists or supports true and flat.
2. No matter how good the drainage is, water still sits underneath breading mozzies!
3. Rubbish spilt on the deck also ends up on the concrete and is hard to get rid of - no solution for this.
4. There isn't a great deal of room available between the current sill and the deck which can bugger up step heights.
5. Did I mention what a sod getting everything true was?

As for treated pine, I wonder if it will be durable enough. I know Jamie Jury uses it for everything on TV but I'd like to see it in 6 months! Also, while the nail space is good (I tried to use it) the timber is not uniform enough to have exactly a nail space. Use it as a guide.

If I did it again I would hire a jack hammer for a few hours and get rid of the concrete, but not the supports as I could have used these with the timber deck. My situation was probably a little different in that I had half the deck on concrete and half on new frame. I would also hire a nail gun with the appropriate stainless nails for a day!

Ribbed or not, make sure the rib on any timber faces down. It isn't actually for grip but to allow moisture to dry. The plastic spacers is probably a good theory but I don't know how it would go in practice.

I would find a book on decking and see if you can find the standards for joist sizes etc. Your local council might have these. I suspect 70 X 45 treated pine would have to be spaced very close together.

My two bobs worth anyway, it all sounds negative but it looks damn good when finished! I only had 50mm to play with so you might have a better run with the extra space.

Have fun!
Anthony

I did this over a small area (about 10m2) when the deck I wanted to put around my pool overlapped an exisiting concrete landing. I wanted to keep it low, so I just used T/P decking as a batten and then screwed the deck to it using gal timber screws.

Apart from the obvious problems associated with getting it all true before laying the deck, the biggest problem I found afterwards was the inaccessibility of the sub-deck area after it's built. Make the gap too wide and anything you drop down there is gone forever. I've got little kids and they love sticking stuff down gaps. Things like credit cards, money, food, you name it. This may not be a problem for you.

Also, any leaves and other crap blowing around finds its way down there and sooner or later any gap under your joists that you leave for drainage is going to be clogged up with it. Another related issue is access for termite inspections. If the deck butts against your house and there's any path for them to get up into the deck timbers and then into your house, you could have a problem.

I've got another one of these situations to deal with and this time I'm going to demolish the old concrete patio and start from scratch.