Deck... what joists and bearers...

[fixa24]

Hi all;
I'm in the planning process of designing a 7m by 5m deck, buit around 300mm from the ground. Planning on using h3 treated pine for joists and bearers.

Couple of questions;

1: I don't want to put posts in the ground (expense, complication), can I use the metal brackets that you would ordinarily use to mount the posts, to place the bearers on?

2: There will be no roof on the deck, maximum distance between the bearers 1400mm, max distance between footings the same. Would a H3 F7 190 x 45 bearer be suitable? There will also be a small spa on the deck.

3: And for joists i was thinking 90x45 H3 F7 with 500mm centres, using hardwood decking. Does this sound reasonable?


Cheers and thanks for your help.

[Dirty Doogie]

Hi , this sounds like another low deck. see "diagonal decking" thread by WA decker.

Yes you can use off the shelf brackets stirrups etc - but not if design live load on deck exceeds 350 kgs per metre 2. A spa knocks knocks it into a differnent category of deck.

My span tables (revised August 2007)

Bearers 2 x 190 x 45

Joists 140 x 45 @ 500 centres for 19 mm hardwood decking
140 x 45 @ 400 centres for 19 mm treated pine decking.

They have recently retested all the H3 pine they were selling as F7 - the strength has been downgraded to F4 in most cases. My information is that H3 will only be available as F5/F4 in coming months. It may be a cunning plan by timber companies to sell more wood!!

[fixa24]

Cheers mate.
So you can't use the stirrups then? The spa is 2m diameter, 1000litre capacity. I was thinking i could double the bearers, so 2 x 290 x 45 on the 2 bearers the spa would sit on. I also figured since the posts are close together this wouldn't be a problem?
Is the 350kg limit for the gal posts only, so if i do put 90x90 H4 posts in it's better?

[Dirty Doogie]

Hi Fixa,

the problem with the saddles or stirrups is that they can shear off when overloaded and they dont transfer live loads to the ground well.

You could just add extra bearer and joist depth in the spa area but you would have to extend the heavier timbers (including joists) to the next bearer all around the foot print of the spa.

Is the 300mm height you mentioned to the top of the deck? With 190 deep bearers and 140 deep joists there would be no room for stumps.

[fixa24]

Hi Fixa,

the problem with the saddles or stirrups is that they can shear off when overloaded and they dont transfer live loads to the ground well.

You could just add extra bearer and joist depth in the spa area but you would have to extend the heavier timbers (including joists) to the next bearer all around the foot print of the spa.

Is the 300mm height you mentioned to the top of the deck? With 190 deep bearers and 140 deep joists there would be no room for stumps.

Thanks.

The 300mmm height is to the top of the bearer... so looks like it'll have to be stumps then.. bugger... Thanks for your help...

[Chumley]

My span tables (revised August 2007)

Bearers 2 x 190 x 45

Joists 140 x 45 @ 500 centres for 19 mm hardwood decking
140 x 45 @ 400 centres for 19 mm treated pine decking.

Hi DD,

Something you wrote started a train of thought... -- re the 400 centres for 19mm treated pine decking: what would happen if you used 660mm centres instead - I mean would it all come crashing down, or would it get a bit bouncy?

Also, where would someone get a copy of span tables?

Cheers,
Adam

[pharmaboy2]

search span tables on here and you will come up with a few - my favourite design program is Hyne. go to their site and download =design in hyne - will do anything you please - working through the threads here will come up with a lot of links also. one just a week ago or so.

[Dirty Doogie]

Hi Chumley,

With a normal floor load the decking would just be bit springy when walked on by a heavy person and may break if two heavy people decided to jump up and down on the same spot -- who knows what party games happen on decks LOL!

Remember the sizes given above are for a deck capable of supporting 600 kg live load per metre (5.5 heavy people) and 350 kgs continuous dead load (350 litres of water) or a combination of both.

I get my span tables from a subscription site for building designers (actually I use someone elses subscription) that covers steel, concrete timber etc. I've also got a collection of older framing manuals for wind classes etc.

Some span tables are online - but otherwise you can usually pick up timber span tables at larger timber retailers. Bluescope steel publish span tables for steel but they are really complex.

Doog

[TermiMonster]

Hi DD,

. -- re the 400 centres for 19mm treated pine decking: what would happen if you used 660mm centres instead -

at that span, you would definately get breakeages with TP.
Cheers
TM

[Dirty Doogie]

Hi TM,

LOL !! If a 120 kg ballerina (mind boggles) decided to demonstrate her points (balancing on tip toes) midspan on single piece of decking at that spacing - I would be phoning my insurance company for sure! LOL!

Doog

[Chumley]

Hey thanks everyone, I'm not a ballet dancer but I'm probably close to 100+ kilos (I think gravity is definitely not a constant, seems to have a greater affect on me as I get older ). I'll have to make a few changes -- design 2.3 coming up and I'm only up to floor level ('tis a gazebo - I know I owe a few people some pictures... they're being taken as I go, but I only get Saturdays so I'm saving them up in batches). So, joists at 400mm centres it is.
Thanks again for the advice.
Cheers,
Adam
PS. And I'll do some searches in here for span tables - did a bit of (sloppy) internet research but didn't think to check the number one woody site!