Deck joist span question

[Mick666]

Hi All,

I'm currently planning a deck and am trying to decide on bearer and joist width with regard to spans etc.

The part of the deck I am referring to is a rectangle that is roughly 4.3mtrs wide x 4.5mtrs long.

As it stands, my plan is to run 4 bearers 4.5mtrs long with 3 gaps of 1400mm using 190x45mmTP. Here's where I need the advice on joists - what size joist will comfortably span that width without any bounce? Usually, like any home handyman, I tend to over engineer everything I build so I thought this was a good opportunity to garner the opinions of those far more experienced than I and perhaps do it right.

I'm perfectly willing to up the bearer size if the need be but it's the joists that I'm most interested in at this point.

Any and all advice is greatly appreciated.

Mick

[SilentButDeadly]

100x50 @ 450 centres - assuming F7 OB hardwood

Or you could just forgo the joists & decking and lay 200x50 red gum landscape sleepers instead.......worked for us.

[thebuildingsurv]

Without checking the tables I think you will find most joists upward from 90x45 will span 1400 providing they span over to or more bearers. I assume you are putting some stumps under those bearers as 190x45 wont span 4.5

[Mick666]

Yep there'll definitely be 4 stumps under each bearer. Upwards from 90x45 I assume means that 90x45 is too small and will be bouncey? So 120x45 would be ok?

Sorry SBD but I'm not super keen on hard wood subs as I don't want to think too much about possible degradation over time. I know TP is still susceptible but it will help me sleep a little better at night.

Thanks for the help chaps. Much appreciated.
Mick

[thebuildingsurv]

90x45 would be ok to span 1400 120x45 would be even better

[UteMad]

Treated pine 90 x 45 spans 1300mm for continuos span thats over 3 or more bearers (TABMA DECK SPAN TABLE ) I am not a fan of 90 x 45 pine joist where it can be avoided as they do bounce when asked to much of..
I would prefer to delete a bearer and up joist to 6x2 pine which goes 2800 for continuous span .. Once again 2400 is a nice spot to stop with 6x2 joist to lessen bounce

100 x 50 hwd joists will do your 1400 with no real bounce but you will need to deal with there differing nominal size which can vary up to 8mm in heights

cheers utemad

[SilentButDeadly]

Sorry SBD but I'm not super keen on hard wood slabs as I don't want to think too much about possible degradation over time. I know TP is still susceptible but it will help me sleep a little better at night.

...degradation?

With all due respect to treated pine.........those hardwood slabs will outlive your children (mainly because I don't have any)

In my experience, treated pine decking will be fortunate to outlive your dog.

[thebuildingsurv]

AS 1684.2 DECK JOISTS TABLE decks above 1m in height 90x45 spans 1400mm continuous span.

[UteMad]

AS 1684.2 DECK JOISTS TABLE decks above 1m in height 90x45 spans 1400mm continuous span.

1kva floor load or 2 kva.. decks in sydney are 2 kva and the spans are read off F5 not f7 anymore as pine has been respecced to f5 in the last 6 months...My suppliers issued us with the latest TABMA tables when the switch happened

Which are titled "Floor joist for domestic balconies and decks REVISED LOADING "

I checked my old as1684 and it says f5 90 x45 will do 1500
My NSW framing code doesnt go below 1800 centres

i could still be wrong though

cheers utemad

[thebuildingsurv]

Utemad,
I was referring to F5 and the table is in AS 1684.2. - Decks above 1m in height. This table is based on a 2 kPa floor loading. Decks below 1m only require 1.5 kPa (same as houses floors). AS 1684.2 is called up in BCA same for Vic as NSW, I would not see why you could not use it in NSW so I am unsure why TABMA would bring out tables that are different or more conservative. F5 would be F5 regardless of what state you live in.

I am unaware of any recent amendements to AS 1684.2 that have changed these tables. The 2 kPa floor loading used to be 3 kPa but changed when the loading code did. So spans for decks have increased not decreased. Anyway I just approve them I do not build them (well not often) so maybe you know something I dont.

[UteMad]

Think we will leave it lay in rest... I am not a fan of 90 x 45 joists for decks anyway and only use them when forced to.. I find 140's give a much better feeling deck with way less bounce .. Although competitiors all seem to be going 90's at the moment... A new deck up the road has used 90's and gone way past 2m mark so all i can say is "good luck to them"

cheers utemad

[UteMad]

This is the TABMA deck joist span table if it helps anyone




cheers utemad