New deck

Hi all. I am about to build a new deck at the front of my place and cant seem to find what im looking for in the forums already so i will attemp to explain what i need to know. I want to build an extention off my front existing veranda. The new section will come out 4.5 metres and be 3.5 metres wide. Now a builder friend suggested using 190X45 (treated pine) for the whole frame. He said to build the outside frame of the deck first. But i cant remember how many lengths i will need in the middle. They will run outward on the 4.5 metre length and then i will run the 19mm merbau decking across the spans of 190X45 along the 3.5 metre length straight onto the 190X45. I will check out the stumps and bolt the 190X45 to them. Im just not sure how many legths of the 190X45 i will need in te middle section and how many stumps to put under the whole thing. Sorry about my crappy explanation. I actually know more about what im doing than comes across in my explanation ! Thanks for any advise in advance. Mako

How about a sketch or something, a picture speaks a thousand words;)

HH.

So you want your decking boards to sit directly on the bearers and omit the joists? This will mean alot more posts I believe as you bearers will have to sit much closer together..... I think the bearers will have to be 450 apart if you do it that way

Im sure Mick or someone that knows all the ins and outs will see this and comment....

This method was just suggested to me so if im advised of the best way to go about building it im all ears. I really need to work out how much it will cost me to build. I have all the merbau already and i was hoping to use treated pine round post,130mm, that i have from the vineyard i work at for the stumps (??) So i just have to buy the rest of the timber. Any idea of cost?

hi
go to this web site and you will get all the info about residential timber decks
www.hyne.com.au/downloads
jonassen

Hi Mako,
I worked it out that you need 11 joists to cover 3.5m of deck (including both ends) assuming 450 centres.
However I dont think you can do it. I think the system is do-able using joist hangers but you span is to great and your wasting too much money on oversized timber. I suggest to do it the trad method with joists on bearers.
Ive worked out (usual disclaimers) you need
1 x ledger 90 x 45 attached to the house.
2 x 230 x 42 bearers (0ne in the middle one on outside edge) supported with posts on outside & one in the centre.
11 x 185 x 42 Joists
let me know anyone if I'm wrong.
PS how do you get a sketch uo on the screen?

Spend $20 odd on a book "Decks and Pergola Construction Manual" by Allan Staines. Avail at Bunnings. I have used it as a referecne for several decks, and Council accepted the specs I selecetd from it. Severl other's on this forum have referred to it in teh past.

from it joists 4.5 long and supported at 3 points, as suggested by Bleeding thumb.(house ,middle and end) can be as little as 140 x 35 F7 seasoned (KD treated) or 125 x 50 F7 unseasoned.

Bearers would have to be 2 beams side by side as follows F7 seasoned

for the middle bearer
2/120x35 on posts 1200 apart (4 posts)
2/170x35 on posts 1800 apart (3 posts)

For outside, sizes can be smaller as it is not supporting as much.
2/90x45 on posts 1200 apart
2/140x45 on posts 1800apart
other spans listed but don't suit your deck.
There is no spec for span of 3500 or more.

Posts that you intend to use are fine, asuuming they have a stress rating of F7. How high off the ground will it be. If it isn't high and as teh posts are free, you could have more and therefore use smaller bearers and joists.

spans for merbau decking are 500 mm for 19 mm thick, 650 for 25 mm thick, although I would only go 450 to reduce the amount of springiness feeling underfoot. If you build to the min specs there is a springy feeling, the closer and bigger everything is the more solid the feel. Also it the joists have big spans of 2250 as listed above, put a cross piece midway beetween each joinst. I can't think of the name for them, but in walls they are noggings. Usus the same size as the joisat, or slightly smaller. these run at 90 degrees between the joists and stop teh joist twisting under load, which in turn adds to spring.

There are so many variables to your simple request that I would get eth book and work form there, also that way you know who to blame.