Bearers and joist sizes for deck.

[Lappa]

I've tried using the deck calculator but it seems you can put in some very thin beams and it accepts them.

I want to put a 6.5 metre X 3.5 metre deck over a paved area. it will be 270mm high to the top of the deck.

I entered the joists as 90 X 45mm and the bearers as 140 X 45mm into the calculator.

The calculator worked out that I required 4 bearers at 1085mm centers for the 6.4m length then 16 joists at 421mm centres.

The bearers will be supported at 1240mm centers.

I will be using 19mm thick decking boards.

I feel the bearers should be wider, but the calculator accepted the figures I put in.

Can someone guide me as to the correct sizes please?

Cheers

[Wrongwayfirst]

Seems about right for a rule of thumb reply, you know, all care no responsibility

I have a similar deck with 135 x 32 blackbutt boards, my dimensions area little wider than yours and it’s all fine.

I doubled up on the bearers, as I figured overkill is my friend, nothing fancy just clamped them together and went nuts with the paslode, they are bolted through at the supports so more for my piece of mind.

I assume you used block layer.com

cheers

[Lappa]

Thanks.. yes, I used that ‘Block’ program. Re you doubling up the bearers - that’s probably what I need to do going by a Qld. Govt site I came across ie. 2 x 140x45 bolted together.

https://www.qbcc.qld.gov.au/sites/de...ecks_final.pdf

Thinking of using these as the deck is going on a solid paver base

TuffBlock 300 x 300 x 90mm Instant Foundation System Deck Support

[Wrongwayfirst]

Thanks.. yes, I used that ‘Block’ program. Re you doubling up the bearers - that’s probably what I need to do going by a Qld. Govt site I came across ie. 2 x 140x45 bolted together.

https://www.qbcc.qld.gov.au/sites/de...ecks_final.pdf

Thinking of using these as the deck is going on a solid paver base

TuffBlock 300 x 300 x 90mm Instant Foundation System Deck Support

I do recall reading that Qld PDF amongst any others I could find.
I looked at the tuff block and went with pryda stirrups, I think at the time I just went with what I knew

[riverbuilder]

140 x45 will span up to 2400 easily, your span is half of that, unless you plan on having a circus come with elephants for a child’s party, should be fine.Reading this again, you’re only 270 high? Probably easier ways to frame it up.

[Lappa]

140 x45 will span up to 2400 easily, your span is half of that, unless you plan on having a circus come with elephants for a child’s party, should be fine.Reading this again, you’re only 270 high? Probably easier ways to frame it up.

thanks.

do tell about the easier ways

If I go Tuff blocks I can get away with joists only, no bearers. Going by the Qld doc I can go 2600mm with 140x45 but the Tuff blocks ( I think?) limit spans to 1500mm?

if I use the concrete Deko blocks with 140mm joists and 19mm decking, I get to my height minus 1mm. No sure on max spans with the Deko blocks though.

[riverbuilder]

The type of foundation “block” you use should have no bearing on the span whatsoever. The span between piers or posts is determined by the sectional size of the bearer and it’s recommended maximum distance between support points (span). I’m more concerned about the cost of those plastic block things, they will end up almost the same as the cost for the bearers, seems a lot.

[Lappa]

Thanks for the reply. If I use bearers instead of blocks , don’t I still have to get them off the ground? If that’s the case, what do I use remembering the height is only 270mm.

if you look at the Tuff or Deko sites they seem to say a maximum of 1500mm for spans.

If if I use their specs of 1500mm and 450mm between joists, I’m up for 45 blocks which, as you say, is expensive.

Forgetting all of the above as it appears the information I have read is incorrect or I have misunderstood what I have read;

So, to those with the knowledge out there, I want to put up a 6.4 x 3.5m deck, 270mm height, on a solid paved area - how do I go about it?

[aldav]

Attached are a couple of tables of deck joist span tables for MGP10 and MGP12 timber (I guess you're looking to use H3 treated pine?) that might help you specifying the support members for your deck. These tables are from the book 'Acceptable Standards of Domestic Construction'.

As far as the Tuff Blocks or Deko Blocks go I'd be following the manufacturers recommendation and keeping the spacing at 1500mm maximum, rather than looking under the deck in 5 years time after it's gone bouncy and finding broken plastic or crumbling concrete.

Your idea of doing away with bearers and mounting the joists directly on Deko Blocks would seem like a good one to me, although 90 + 140 + 19 is 249mm NOT 269mm. Would it be feasible to use 90 x 45 MGP12 joists with the Deko Blocks and place a 70mm thick paver/concrete block under the Deko Blocks? This would provide the finished height you want at the minimum expense.

[Lappa]

Just to clear up re span specs for Tuff Blocks - see Step 7 in the installation guide.

https://images.homedepot-static.com/...8e39dd6af7.pdf

[Lappa]

Thanks Aldav.
The Deko concrete block rests the joist 110mm above the ground. It’s 150mm high with the slot for the joist 40mm deep.

B2124337-A93E-41DC-83D6-50D7A30B3D65.jpg

I’ll look over the tables you provided

[aldav]

If you want to save more money ditch the Deko Blocks and just use concrete blocks. For a single span 90x45 MGP12 will span 2000mm - less supports - even 90x35 spans 1700mm.

I read the Deko height as 90mm, but if they're 110mm high you'd only need a 50mm paver, very doable I'd have thought.

If you want to put bearers on the ground you'd have to use H4 treated soft wood or an appropriately rated hardwood.

[Lappa]

Thanks for the help Aldav. I won’t be putting the bearers on the ground. I’ll have a chat to one of the builders when I go back to work next week. I’ve now got some idea of costings.

Now to try and get someone to quote on a concrete slab for a new shed. Concreters must be very busy at the moment going by the difficulty in getting a quote.