Minimum thickness of decking

[alisonol]

I am making a small deck for beside my pool. It will be 3300(L) x 1700 (W).

I am going to use 90? x ? treated pine decking.

What is the minimum thickness I need to span the 1700mm distance as I have no way of getting any extra support?

Cheers Dave

[oohsam]

Hmm...
Ok so your bearers will be 1700 apart? Your joists go ontop of your bearers and the deckboards ontop of that. The thickness of the deckboards wont matter, as it will be your joists that will be bouncing, not the deck boards. Joists will be 450 apart...

Im not sure about 1700 span between bearers, they reccomend no more than 1500, but i would assume you would need thicker bearers and joists to support the weight.

Ur decking will be 90x19 by the way.

Why cant you put suport in the middle? Stirrup? Stump?

[alisonol]

I hope this makes sense.

I have an old aviary next to the pool and the foundations are brick. It is 3300 x 1700.

I was simply hoping to be able to just put some decking across the top of the existing brick work to create a simple deck. Its not a show piece.

Maybe I should just use some thicker timber that will handle the 1700 span.

[alisonol]

If I was to use 70 x 45 joists would that be ok for the 1700mm distance?

[strangerep]

I hope this makes sense.

Well, er, no. What you've said doesn't make very much sense, at least not to me.

I have an old aviary next to the pool and the foundations are brick.
It is 3300 x 1700. I was simply hoping to be able to just put some
decking across the top of the existing brick work to create a
simple deck. [...]

??? A deck that people will walk on? You surely don't mean ordinary
90x19 decking boards laid joist-less right across over the full 1.7m, do you?
Nooooo.

Maybe I should just use some thicker timber that will handle
the 1700 span.

If it's a load-bearing deck that you want, you'll need proper joists with
decking laid on top. The precise details of the joists depends on total
load, as well as the "F"(stress) grade of the timber.

Perhaps you should post a drawing or photo of what you're
starting from?

If I was to use 70 x 45 joists would that be ok for the 1700mm distance?

That sounds too narrow to me. In my copy of Staines book, a span of 1800 needs 100x50
in F17 unseasoned. For F7 treated pine, it's probably more like 140x45.
If you're serious about this, it's probably wise to buy a copy of his book "The Australian
Decks & Pergolas Construction Manual".

[alisonol]

Thanks for your help so far. Please forgive my lack of knowledge on this subject.

This deck will be lucky to have two adults on it at any one time. The current bearers? (70 x 45 treated pine)are dyna bolted to the brick foundations. The bearers are only 200 mm above the ground.

What is the minimum grade bearer and joists I would need?

[pawnhead]

If there's solid support at both ends, then get some treated pine sleepers @ 200x100x1800 and fix them down on the flat. They're cheaper than decking per m2 but it will look a bit rough and chunky. You might like that though. My brother has built a decent sized deck out of them at his place, along with sleeper retaining walls, and I reckon it looks pretty good.

[strangerep]

This deck will be lucky to have two adults on it at any one time. The current bearers? (70 x 45 treated pine)are dyna bolted to the brick foundations. The bearers are only 200 mm above the ground.

What is the minimum grade bearer and joists I would need?

Since you said "it's not a show piece", Pawnhead's suggestion of simply
laying sleepers on the flat is probably the easiest.

If you decide you really want a conventional deck, the necessary engineering
parameters for bearer and joists are influenced by how far apart the
dynabolts are which hold your existing bearers to the brick. My guess is
they're probably ok, unless everything is badly rusted/rotted already.
As for grade/dimensions of joists, TP is usually F7 stress grade, so the
joists should be around 140x45 in that case if you go that route.

But like I said, Pawnhead's suggestion of sleepers will be much simpler
(though you might need help to carry them, depending on whether they're
dry or wet, and how fit you are).

[ian]

I hope this makes sense.

I have an old aviary next to the pool and the foundations are brick. It is 3300 x 1700.

I was simply hoping to be able to just put some decking across the top of the existing brick work to create a simple deck. Its not a show piece.

Maybe I should just use some thicker timber that will handle the 1700 span.

If I was to use 70 x 45 joists would that be ok for the 1700mm distance?

That sounds too narrow to me. In my copy of Staines book, a span of 1800 needs 100x50 in F17 unseasoned. For F7 treated pine, it's probably more like 140x45.

Dave,
Just to check that you've understood the advice you've recieved so far

If you intend (or need) to span 1700mm with the deck, then your "decking boards" need to be about 100mm thick if you use F17 timber. However, if the timber is only F7, the "boards" will need to be about 140mm thick, maybe a bit less.
to get the look of standard 90mm wide decking, using F7 timber, you will need to buy what in the old money is known as 6 x 2s (I don't think you can buy 5 x 2s and 4 x 2s will likely to spring too much as you walk across them) and stand them on edge.

These sizes, in the quantity you will need for a deck, are seriously expensive compared to using standard 90 x 19mm decking on bearers and joists.


ian