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Decking on a patio concrete slab

Hi All,

just got to know about posting our topic as I have commented on other topic and the admin team directed me to post a new topic.

I’m planning to build a merbaur decking on our patio concrete slab as in the photo. The slab area is 3.6 x 9 m and it is sloped with low of 150 mm and high of 300 mm to the indoor floor. I would like to have the decking same level as indoor which leaves me 150 mm spacing from concrete slab near brick wall and 300 mm spacing on the far end of the patio area.

the other side of the patio opens to our rumpus room, which is same level as concrete floor.

Can someone help me to choose the framing and connections to concrete slab? Also, I would like to hear your opinions to manage the deck level to the indoor, while providing access to the rumpus room.

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Comments

MitchellMc

Hi @Nathan88,

I've included an example of a deck layout below working with Treated Pine Outdoor Timber Framing H3 120 x 45mm for the bearers and Treated Pine Outdoor Timber Framing H3 90 x 45mm for your joists. The 120mm H3 will need to be special ordered into our stores for you.

As @Neo19 mentioned in their thread, they used Dunnings 65 x 130 x 65 x 5mm M12 Galvanised Angle Bracket and these would be suitable for fixing your bearers to the concrete slab.

I'll need a little more information on "150 mm spacing from concrete slab near brick wall and 300 mm spacing on the far end of the patio area.". Is the concrete slab sloped? You might like to consider using Builders Edge pedestal feet to adjust for the difference in height.

If you are increasing the floor height with a deck on the patio then you are going to need to create a step down into the rumpus room area. It's probably not a great idea to bring the deck right up to the sliding door and you might like to consider keeping the ground height even directly outside the sliding down then have a step.

Please let me know if you need further assistance or had any questions.

Mitchell

Nathan88

https://www.workshop.bunnings.com.au/discussion/comment/9692#Comment_9692

Dear @MitchellMc ,

Thank you for providing detailed info. Yes, the concrete slab is sloped since it was a patio area previously. The drop of indoor floor level to concrete slab is 150 mm near the brickwall and if the decking is leveled, this leaves me a drop of 300 mm at the far outside of the slab.

If I use bearer+ joist, this will rise the floor by 120+90 ( minimum) and this will be higher than the drop near the house level. Please advise.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/67156#Comment_67156

@Nathan88,

The height of the deck will consist of 120mm (bearer) and 19mm (decking board) giving 139mm total height which will allow 11mm for drainage under the bearers. The joist in your situation gets mounted to the sides of the bearers and not on top of them.

Mitchell

Nathan88

https://www.workshop.bunnings.com.au/discussion/comment/96390#Comment_96390

Hi @MitchellMc ,

Do you have an image showing how to mount joist side of the bearer. given that there are four bearer and the joist running across the bearer, I am confused how to mount them on side. Also, If i am using the angle/ Builders Edge pedestal feet , what would be the recommended spacing? Thanks

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/114804#Comment_114804

@Nathan88,

You might like to have a read through the article How to build a low-level deck by @Adam_W. Within it, you'll find details which will benefit you in your project. He also illustrates the correct mounting procedure for a single level deck.

I've also included below an example image showing spacing for supporting the bearers.

Mitchell

Nathan88

https://www.workshop.bunnings.com.au/discussion/comment/125184#Comment_125184

Thanks @MitchellMc , That make things lot more sense. I am planning to run the decking board parallel to the house (which means parallel to the bearer). Would it be possible with this design?

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/132167#Comment_132167

@Nathan88,

It's certainly possible but the bearer/joists orientation needs to be changed also. This is to reduce cost and because you need to nail into the joists.

Here's an updated plan.

Mitchell

Nathan88

https://www.workshop.bunnings.com.au/discussion/comment/136407#Comment_136407

@MitchellMc , I have a question on this design? What’s the contribution of joists here? I believe the decking boards are directly supported by bearers and bearer is supported by concrete slab.

HandyAndy

https://www.workshop.bunnings.com.au/discussion/comment/139330#Comment_139330

the bearers "bear" the weight of the deck, or transfer the weight to the footing, joists are for load spreading and fixing the decking boards.

bearers are generally beefier than joists.

joist spacing/decking board fixing is generally 450mm, some hardwoods can go upto max. 600mm spacing.

I think in your case

~7 x bearers with 4 supports each = 28 supports.

you could just fix your joists (@450mm centres) directly to the concrete, but you'd be looking at 9m x 9 joists = 81m of timber with supports every 1400mm = 60ish supports, fixed to the slab

not to mention the levelling it all.

you could possibly increase the size of the joists to 120x45, which would allow bigger spacing = less supports

using bearers will be much simpler as they run parallel to your slope, levelling is far easier. then your inline joists are fixed on the inside of the bearers with the same top height as the bearers.

hope this helps

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/141289#Comment_141289

Hi @Nathan88,

I see you have already received a helpful reply from @HandyAndy which is fantastic.

Cost of timber is also a significant factor. On the last layout, you have 25 meters of 120 x 45 as the bearers. If you were to run the bearers perpendicular at a 450mm spacing you would end up using 81 meters of 120 x45. You'll also need to join them together to reach the 9 meters length required.

If you were to just run the bearers perpendicular to the decking boards and have no joists then the overall cost might end up less. My examples are just for reference and somewhere to start your plan.

Please let me know if you need further assistance or had questions.

Mitchell

bruce93

https://www.workshop.bunnings.com.au/discussion/comment/142761#Comment_142761

Hi @Nathan88, @MitchellMc, @HandyAndy

I'm not sure if I'm too late to the party but another solution you could use for your decking over the concrete slab is a product called KlevaKlip joist Support.
They aren't a bunnings product unfortunately but are available throughout Australia and are great for doing decks on concrete slabs as they allow you to level the joists regardless of the fall on the concrete slab...

Also using these would not require the use of bearers. https://www.klevaklip.com.au/images/WordDocUploads/KK_BP_P3A4%20April%20_AJS.pdf

I've attached a photo of it in use for a deck I built for my mum back in last February and then a completed picture of the deck.

Let me know if you have any questions.

UncleAz

https://www.workshop.bunnings.com.au/discussion/comment/125184#Comment_125184

@MitchellMc Great information. I am planning my deck currently and this has been most helpful. I was wondering if there is a site that you use for the diagrams in your posts? Is this a planning tool that you have available?

Thanks.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/132214#Comment_132214

Welcome to the Bunnings Workshop community @UncleAz. It's fantastic to have you join us and many thanks for your question.

The site I use for the diagrams is https://www.blocklayer.com/deckcalculator.aspx and is not associated with Bunnings. Please be advised I use this tool as a visual aid to get people started in the right direction when constructing a deck. All relevant building codes need to be followed and you should not rely on this layout tool solely. A qualified builder or structural engineer can assist you in checking your plans before commencing a build.

We look forward to hearing more about your decking project and would encourage you to start your own discussion if you would like detailed assistance or would like to share with the community.

Mitchell

UncleAz

https://www.workshop.bunnings.com.au/discussion/comment/136440#Comment_136440

Thanks for the information. Really appreciate it. I will start a new discussion shortly.

Just_Me

https://www.workshop.bunnings.com.au/discussion/comment/9692#Comment_9692

Hi,

I'm planning to build a deck over a concrete slab alongside my house. If I use the Builder's Edge Pedestal feet to support the bearers, do I still need to attach the deck (or at least the first bearer) to the house, or can it just be freestanding on the Pedestal feet? The deck will be about 4.5m x 3.5m.

Thanks.

Jason

https://www.workshop.bunnings.com.au/discussion/comment/69417#Comment_69417

Hi @Just_Me,

Thanks for joining in the discussion. It's great to have you join the Bunnings Workshop community.

I will ask @MitchellMc to assist you when he is back on the site tomorrow. Let me also tag decking expert @Adam_W to see if he might like to share his thoughts on the pedestal feet in the meantime.

Feel free to post anytime you need a hand or have something to share. We're looking forward to seeing how your deck project comes together. Perhaps you might like to hit the Start a discussion button so you can document your progress and share it with the community.

Jason

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/69417#Comment_69417

Hi @Just_Me,

The pedestal feet are great for supporting the deck's weight but don't add much regarding structural rigidity. I'd encourage you to frame in the ends of the joists with additional timber, which will tie everything together and stop the joists from distorting. I've created the image below to illustrate. Alternatively, you could add a ledger board to the house and connect the joists to it.

Please let me know if you have more questions. We're here to help.

Mitchell

Just_Me

https://www.workshop.bunnings.com.au/discussion/comment/97732#Comment_97732

Thanks for your replies and nice picture. I like the idea of boxing it with additional timber rather than attaching it to the house. It will be a lot easier in my opinion.

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