How many posts for this deck?

[Oscar1]

Hi, I’ve built a few decks mainly on concrete using Klevaklip adjustable joist supports where the height has been very limited. Now I want to extend that deck out into the backyard. The extension will be 1.75 meters by 12 meters long and again due to height restrictions I can not use bearers except for one running in the centre. The timber I’ll be using is 45x140 treated pine for everything with the joists spaced at 450mm and the deck boards are 19x90 merbau. I would like to know what your recommendation is in regards to the number of supports I would need. Attached is a rough drawing, thanks. This will be a free standing deck 

 

[JacobZ]

Hi @Oscar1,

Welcome to the Bunnings Workshop community, it is fantastic to have you with us.

Can you elaborate on what you mean when you say that due to height restrictions, you cannot use bearers except for in the middle? How much clearance do you have along the top and bottom edges of the deck? Is the ground at the centre of the deck lower than the outside edges?

Is there a reason these two members can't be bearers?

Are you aware that joists and bearers can sit at the same height if you connect the joists to the bearers using joist hangers?

If there were a way to make these two framing members act as bearers, you would just need to support each of them in line with the bearer span tables, which state that 140x45 MGP10 acting as a bearer can span 1400mm between supports. This means you would need 9 supports per bearer, totalling 18 supports between the bearers.

As per the joist span tables, 140x45 MGP10 acting as a joist can span 2600mm, so there is no need for any support between the bearers as long as they are attached to them with a structural connection using joist hangers.

The deck would end up looking like this -

I understand situations might not allow for this, but it seems like the logical solution to me based on what you've said. If there's a reason this wouldn't work, I am happy to work with you on a solution that will.

Let me know what you think.

Jacob

[Oscar1]

Thank you so much for your suggestions really appreciate it !! I was going to use joist hangers and attach them with Pryda stitching screws (I think that’s what they are called) I thought I would just put a bearer in the middle for added strength. This deck is going to be in level with the one on the concrete under the alfresco and there is not much space to play around with as the backyard from the house to the fence is on a higher level. I was thinking of putting around 12 supports just to make sure it would be strong.  Attached is a picture of the deck we are currently building which in turn will extend beyond the alfresco to the deck I have been asking for advice!!

[JacobZ]

Hi @Oscar1,

That is one fine-looking deck. I am impressed with what you've done so far and can't wait to see your progress.

These Pryda Timber Connector Screws are the screws you would use with your joist hangers.

The span between the two outside bearers is well within the allowable limit for 140x45 joists, so it isn't really necessary. You could certainly add an additional bearer down the centre if you wanted to, but this would mean you need to double the amount of joist hangers, which isn't really economical. 

If you wanted to add more supports to each bearer, then again, there is nothing stopping you, but again, it is not really necessary, as the design I've shown above fits within the recommendations of the span tables.

As long as you can install those two outside bearers with at least 9 supports each, and you attach the joists with joist hangers and connector screws, then you will have a rock-solid deck. 

Please don't hesitate to reach out if you have further questions or require clarification and please remember to share some photos as your project progresses, I'd love to see it when it is complete.

Jacob

[Oscar1]

Hi Jacob , thank you for your kind words and all the advice . I will definitely follow your recommendations and update you once we complete this section under the alfresco and start stage 2 !!!😀😀