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I'm a newbie to the site, so please excuse any stupid questions.
We've recently had a pool installed and I want to extend the existing above ground deck to give access to the pool. The existing deck is fairly large (11m x 5m), above ground on a sloping block (1m above ground one end, 4m above ground at the other). I want to add approx. 2m x 2m of decking to bridge the gap between the existing deck and the area of level land adjacent to the pool area.
I've had one estimate of $15k, and that didn't include any balustrades!
So, I've decided to take this on myself. My question is, can I extend the existing bearer? It is 210 x 75 x 3000mm, and sits on two steel posts both with "U" brackets welded to the top. I appreciate it's tricky to picture this so have uploaded a few photos.
One photo is looking from the deck to the pool, the other looking back at the existing deck. The other photo shows how the existing bearer sits on top of the steel post. The small area where the sandstone blocks are lower is where I want to extend the deck. I was thinking an additional one or two steel supports in concrete to support the new bearer, and join this to the existing bearer.
I've come up with numerous ways to join the bearers, but not sure if this would meet code. I'm just north of Brisbane if this makes a difference.
Any help would be much appreciated.
Thanks, Dave
@DangerousDave Welcome to the Workshop community.
Thanks for your question.
I'm sure our helpful members will have some great input into your project, as many of them have attempted similar.
I am a Bunnings team member. Any opinions or recommendations shared here are my own and do not necessarily represent those of Bunnings. Visit the Bunnings website for assistance from the customer service team.
Hi @DangerousDave,
Welcome to Workshop. We're really pleased to have you join us. Please be assured there are never any stupid questions around here. We have a friendly community that is more than happy to share their experience and knowledge.
Let me tag some very helpful members in @ProjectPete, @Brad and @Adam_W to see how they would go about kicking off this project.
Feel free to post anytime you need a hand with anything around the house and garden. And please let me know if you ever need assistance getting the most from the site or have any feedback about how we can ensure Workshop is even more useful to you.
Thanks,
Jason
Hey @DangerousDave & welcome!
Ya' know... as I once heard said... 'the only stupid questions are the ones that don't get asked...' so don't ever worry about that.
Okay, here's how I'd be approaching this. Rather than thinking of it as extending think more of how to connect and integrate a new, independent deck to the existing if you get my thinking.
You will need new posts one way or another so trust me, from experience, rather than coming up with complicated ways to avoid them it's easier just to add them from the start.
If you try to extend the existing bearer then from an engineering perspective you will be effectively cantilevering the end of the new bearer which needs to be avoided beyond a certain limit. A cantilever is a section that's unsupported on its end and is taking a load on the end beyond the support (I added notes to one of your pics).
The issue is that if you try to join a new bearer to the existing you'll be increasing the load on the existing cantilever and on the post both of which will have been engineered to be taking the existing load. You're also adding a load point at the join which then becomes a weak point. That make sense?
The other approach is, as I said, to create a new, independently stable deck and just join that to the existing rather than attempt to share load.
Easiest way? Create a mirror image of the existing deck with timber & post sizes and spacings & timber type etc. and then bolt the two cantilever ends together with at least 3 x M12 bolts to create a contiguous bearer web. This way any load is still the same.
Other option of-course is a new post under the bearer join point but that may be difficult to do depending on the size of the existing concrete footings.
I've added a quick sketch below to make sense of this joining just showing bearers not joists. Bear in mind that if they used a hardwood bearer you either need to use hardwood of that size or go up to larger pine. This is because hardwood has longer allowable spans & higher loading at smaller dimensions than pine.
You can buy post heads, or posts with heads, and you only need single-sided and then bolt through.
Personally whenever I add nuts & bolts in situations like this where the nut or bolt head is on timber I like to use what are often called cyclone washers as they distribute the load more which I feel you need on softwoods.
For a smaller project like this I would set-out for the posts, dig the holes, position, level, support & attach the bearers then attach the posts so they are hanging in the holes and then add concrete.
This saves the stress of trying to set every post at the right height and getting them plumb etc. You can even do this just with one bearer and use that as your guide.
Okay, hope all this rambling is of some assistance.
Fire back any questions & I'm sure others will have some thoughts too.
And please, always remember... if in doubt get advice from a tradie or engineer.
Fantastic expert advice @Adam_W. Thank you so much for sharing.
I trust that is a very big help @DangerousDave. Let us know if you have any follow-up questions about next steps.
Jason
Not a problem at all @DangerousDave hope it was of some help. And of-course we want to see some pics of the finished project 
Jumping into this convo as I’m looking to do similar (and this post is what bought me to workshop).
I get adding the second deck as a standalone and then bolting in, which is what I’m looking to do in the space in the attached image (from current deck to where the shed is).
my question is, as I’m planning to replace all the aged timber with merbau, can I extend that timber across both decks? I’m also planning for the new section to hold a 5 person spa, is there anything extra I should be doing to support that?
Welcome to the Bunnings Workshop community @PrideKnight. It's great that you've joined us and many thanks for your questions.
When you mention that you intend to replace all the aged timber with Merbau, is that just the decking or are you planning on replacing joists and bearers? As long as the new deck structure is butted up against the old and connected to it, I can't see anything wrong with running the decking boards across the two decks. An issue that might arise is any independent movement of the two structures could warp and twist decking boards that span them.
A deck that has a spa on it needs to be designed to support that weight. A general rule of thumb for a deck under 60cm tall is that you should double up on all the structure under the spa. So if you'd normally space joists at 600mm place them at 300mm, if your posts would be every 1000mm along a bearer space them at 500mm instead. If you were going to use 90 x 45mm timber for joists, use two at 180 x 90mm, etc. To calculate exact timber requirements, you'll need to look at the relevant timber span tables and building codes. Alternatively, you can employee the services of a qualified engineer to design the deck for you.
The other option is to have a concrete slab poured on that section to place the spa on. You can then build your deck structure up around it, make sure you allow access to any hatches or piping work.
Please let me know if you need further information or have questions.
Mitchell
