Help needed with a New Deck

[freeplay]

Howdy all.

My project will be a new deck 10m x 5m freestanding.
It will be butting up against a pool on the 10m side, however it will not be fixed to the pool.
I would like the decking boards to run towards the pool edge ( 90 degrees to pool face ).

One end of the deck will be 3m above ground and the other end will be approx 30cm off the ground. ( from bottom of the bearers ).

Stumps will be set into concrete.

My question is, how far should my stump centers be? and will 100 x 100 stumps be ok.

regards
freeplay

[builderwally]

G'day freeplay

The span between your stumps should not exceed 1500mm

Your bearer spacing will depend on the size of your joists
100 x 50 depending if its pine should not exceed 1800 but that may now have changed to 1500mm someone in the forum will confirm this

And yes 100 x 100 for your stump is sufficient BUT it is a bit worrying that one end is 3m high the height at this end may need diagonal bracing back to another stump

Hope i helped in anyway

[freeplay]

What would I need to do in order to make my stump span 2500 apart.

[Yonnee]

What would I need to do in order to make my stump span 2500 apart.

Depends which way...

If the 2500mm is along the bearer, you'll need much bigger bearers to span that gap and still provide the support needed. If the 2500mm gap is between bearers, then your joists will have to be as big if not bigger than your bearers!!

You'd just about have to build your deck's structural framework from Galvanized steel I-beam.

Usually, the maximum is around 1800mm for bearer span for 100x100 timber bearers, and 1500mm for joist span using 90x45 F7 joists. But this can also depend on the type of timber used.

[Burnsy]

What would I need to do in order to make my stump span 2500 apart.

A floor load width of 4800 would require bearers of 2/290x45 to have a span of 2300 if the deck was over 1m off the ground. To have the same distance between your bearers (2300) you would need 120 x 45 joists at 450 centres.

Much cheaper to go with more posts and smaller joists and bearers.

[freeplay]

ok
so if I go back to the two million stump option... do these roughs look right?
Attachment 57763
Attachment 57764
Attachment 57765

I think i'm on the right track.
but I would appreciate all input.

[Burnsy]

At your current spacing of posts at 1500mm you will need to use 2 170x45mm sticks for each bearer, and buy them as single lengths of 4.8m, don't join them.

With your joist spacing being over 1700mm and your length requirement meaning you can't go single span, you will need to use 120 x 45 at 450mm centres. This size joist would actually allow you to span out to 2300mm with 450mm centres with up to 400mm cantilever on the ends. This means you could drop off two sets of bearers and set your 5 rows up at 400mm 2700mm 5000mm 7300mm and 9600mm.

Use the longest lengths of timber you can and avoid joins where possible.

This is all from AS1684.2

[oohsam]

That looks good. However you'd want to ensure the side where the posts are 3m high that they are stable. How far down are your holes going to be?. I would make sure they are nice and deep and put plenty of cement in them for support, extra bracing wont hurt either.
I probalby over do the support on the decking, but I'd rather have it rock solid than wobble.

What size joists are you using?>
I recentl built a deck with 40 stumps in total, but it was not high off the ground, your plan looks pretty much spot on.
With the last 2 bearers (the right most), you will not have the third row to nail your deck boards in. You may want to try and move the row in a little so you have enough bearer to put the joist on. Just an observation..
With mine, we had the same issue, but we stopped the row of stumps half way, and started a new row 50mm out. Works fine.
Cheers.

[pawnhead]

At your current spacing of posts at 1500mm you will need to use 2 170x45mm sticks for each bearer, and buy them as single lengths of 4.8m, don't join them.

Are you sure that's right. It sounds like overkill to me. I'd just use 150x75mm F14 bearers. They'll easily span half his width, so you'd only need one row of piers in the guts. Cheaper than F7 TP, and no poison injected in it either. (a lot of people don't like TP anymore) And $aving a whole row of footings, posts, and sweat.

With your joist spacing being over 1700mm and your length requirement meaning you can't go single span, you will need to use 120 x 45 at 450mm centres. This size joist would actually allow you to span out to 2300mm with 450mm centres with up to 400mm cantilever on the ends. This means you could drop off two sets of bearers and set your 5 rows up at 400mm 2700mm 5000mm 7300mm and 9600mm.

Use the longest lengths of timber you can and avoid joins where possible.

This is all from AS1684.2

That still only gets him to 10m, and he needs 10.8. I wouldn't be putting a cantilever on the end either. It's way up in the air, so I'd be putting my posts at the end, and continuing them up for a nice solid handrail. And 120x45 is an odd size that would have to be milled. You'd have to use a 140x45.
I'd use six rows (5 bays) @ 2.16m for each bay. Then I'd use continuous 100x50 F14 joists @ 450 crs. It would end up being much cheaper with all those lineal metres of joist.

Span tables:
http://www.fordtimbers.com.au/dpr_span_tables.htm
Hwd Pricing :
http://www.barrenjoeytimber.com.au/price.cfm?CatID=8
TP Pricing:
http://www.barrenjoeytimber.com.au/price.cfm?CatID=5
Shop around in your area and you may get a better price, especially for a reasonably large single order.

Edit: I'd also buy a roll of Alcor, and use it as a bearer capping, turned down (on a 45 degree angle as a drip groove) over the edges. And I'd buy some rolls of plastic joist capping for the joists. The extra time and expense is worth the investment for a lifetime without rot in the sub structure, especially since it's around a pool.

Edit 2: After a bit more thought, you can't get a continuous joist with five bays, so it would be better to put your bearer spacing @ 2.050 crs, so you can use standard 4.2m length joists with no waste. This makes the last span about 2.525, and I'd use a single span 150x38 or 150x50 (or 125x50 if you can get it) for that.

[freeplay]

MMM,

Well now you guys are getting all technical on me.
I went to the local library this morning and got Allan staines book.

My size can be flexible.. around 4m - 5m x 9m - 11m
One half, approx 4m x 4m I am looking as using the underneath to house
my pool filter and garden tools etc..
So I am looking at trying to have as little piers as posible in that area.

I don't mind paying a little extra to have more underneath working area.

I'm also not sure if Gal pipe posts would be better than wood stumps.

appreciate all the help

[pawnhead]

One half, approx 4m x 4m I am looking as using the underneath to house
my pool filter and garden tools etc..
So I am looking at trying to have as little piers as posible in that area.

I wouldn't go across it in a single span, or you'd have to use a big heavy galvanised piece of steel, or a heavy, engineered stick of timber. If you follow my layout, then you'll have an area under one half of your deck, that's 4.5m square, with just one post in the middle. The other half will be 4.5m x 5.3m, with two posts.

I'm also not sure if Gal pipe posts would be better than wood stumps.

I wouldn't be casting the posts into the concrete. There's more chance of rot than mounting them in brackets.
I'm not sure if Unipiers are suitable for exposed decks, but you could make inquiries.

What sort of handrail are you contemplating, and will it be integrated with the supporting posts?

[freeplay]

If you follow my layout, then you'll have an area under one half of your deck, that's 4.5m square, with just one post in the middle. The other half will be 4.5m x 5.3m, with two posts.

Are you suggesting that i put the posts with 2200 centres?
Or did I not understand your layout?

[Burnsy]

Are you sure that's right. It sounds like overkill to me.

Yep straight out of AS 1684.2, Table 49 - Deck Bearers more than 1m off the ground for a floor load width of 4800 using single span. Joist specs are off Table 50 - Deck joists more than 1m off the ground.

[bpj1968]

Floor load width (FLW) of 4800 means that his bearers will be 4800 apart. i.e. FLW is 1/2 the distance to the next bearer, either side of the bearer. 2400 (one side) +2400 (other side)

Have a read of Allan Staines book and figure out different combinations. At present you are digging 28 holes. 28 loads of concrete, 28 stirrups etc.

[pawnhead]

Yep straight out of AS 1684.2, Table 49 - Deck Bearers more than 1m off the ground for a floor load width of 4800 using single span. Joist specs are off Table 50 - Deck joists more than 1m off the ground.

Yeh, I was looking at floor load tables which were alright in the old days. They've toughened up a lot since a few decks have collapsed.

What does the code say about F14 or its equivalent? e.g.100x50 joists.
And what sized continuous F14 bearer would he need to span half the width of 4.5m?
It would be good if he could eliminate a row of piers and just have one row in the guts I reckon.