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How to build 4.2m x 2.6m deck over concrete?

Hello everyone!

I am building a deck that measures 4.2m x 2.6m and will be 0.65m high. Since this is my first time constructing a deck, I would appreciate any feedback or recommendations on my proposed approach and materials for this project. The deck will be located in the covered section of my backyard, on an existing concrete floor.

The deck will be 4.2m x 2.7m on an existing concrete base that's stable.
Bearers will run along the length of the deck and will be 4.2m.
Joists will run along the width of the deck and will be 2.6m. Spacing between joists will be 420mm.

I have a few questions regarding the design:

a) Should I laminate the bearers and place them on top of the posts, or is it better to use a single bearer and notch the post to attach it to the bearer?

b) How many stairs should I design for, given that the height of the deck will be 0.65m? Is there any post / article I can refer to understand the best way to design stairs.

c) According to the Hyne span tables, for a continuous bearer, if the deck width is between 2.4m and 3m, a bearer built with 190x45 timber can have a maximum span of 1.5m. Since the distance between the bearers is 2m, should I use 240x45 timber instead of 190x45?

Materials:

Use 90 x 90 mm H4 timber for posts: 90 x 90mm 3.0m Post F7 H4 Treated Pine Premium KD - Bunnings Australia
Use 190 x 45 mm H3 MGP10 timber for bearers: 190 x 45mm Outdoor Framing H3 Treated Pine 4.2m - Bunnings Australia
Use 140 x 35 mm H3 MGP10 timber for joists: 140 x 35mm Outdoor Framing H3 Treated Pine 3.0m - Bunnings Australia
Use 90 x 19 mm Merbau boards for decking: SpecRite 90 x 19mm 5.7m Merbau Joined Set Length Pre-Oiled Decking - Bunnings Australia
Use Pryda 90mm M10 Bolt Down Post Anchor: Pryda 90mm M10 Bolt Down Post Anchor - Bunnings Australia
Use M10 x 100mm screws for connecting post anchor to concrete: Ramset 10 x 100mm Galvanised AnkaScrew Masonry Anchor - 10 Pack - Bunnings Australia
Use18g x45mm screw for connecting post anchor to the timber post: Bremick XTP Post Screw 18g x 45mm GALV T40 - 25 Pack - Bunnings Australia
Use M12 x 120mm Hot Dip Galvanised Cup Head Bolts and Nuts for connecting timber post to bearers: ZENITH M12 x 120mm Hot Dip Galvanised Cup Head Bolts And Nuts - 12 Pack - Bunnings Australia
Use Simpson Strong-Tie 135 x 135 x 21mm Hurricane Tie 45mm for connecting joists to bearers: Simpson Strong-Tie 135 x 135 x 21mm Hurricane Tie 45mm Joist And Rafter - 50 Pack - Bunnings Australia
Use Simpson Strong-Tie 12G x 65mm Stainless Steel screws for connecting decking boards to joists: Simpson Strong-Tie 12G x 65mm Stainless Steel 316 DHSD No Pre-Drilling Decking Screw - 50 Pack - Bunnings Australia

Thank you for your help!

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Comments

MitchellMc

Welcome to the Bunnings Workshop community @ParagC. It's wonderful to have you join us, and many thanks for your question about constructing a deck.

Your overall design looks solid, and you clearly have a good grasp of the essentials. The layout of your joists, the spacing and the materials you have chosen are all on the right track for a deck of this size. I would avoid placing the bearers on top of the posts. You could laminate bearers if you needed additional load capacity, but in a standard deck like this, a single bearer notched into the post is the usual and more straightforward method. Another option is to run a bearer on each side of the post and bolt through the post to clamp them together, although the single notched bearer is completely acceptable for what you are building.

For the stairs, the Bunnings guide on How to build a deck includes a helpful explanation of How to add a step to your deck, and it is a good place to start. Once you understand that basic method, you can apply the standard rise rules. The minimum rise is 140mm, and the maximum is 190mm. Working with a deck height of around 650mm, you can comfortably break that into three rises at about 190mm each. You may need to adjust the ground level slightly so the bottom step meets the surface neatly and remains within the allowed rise.

Your reading of the Hyne span tables is correct. With a two metre distance between bearers, the 190mm by 45mm section just misses the required span capacity, so you will need to move up to 240mm by 45mm to achieve a compliant span. Everything else in your material list looks appropriate for this size of structure. However, given this is an elevated deck, I would strongly recommend you start by contacting your local council to see if there are any special requirements or if you need building permission. It would also be a good idea to have a builder look over your plans to ensure they comply with construction codes.

Please let me know if you have any questions.

Mitchell

ParagC

https://www.workshop.bunnings.com.au/discussion/comment/60147#Comment_60147

Hi @MitchellMc

Thanks a lot for your response.

I did some more research and I am leaning towards using steel stringers for the stairs. The plan is to attach these to the posts P10, P11, and P12 (see the attached image). Here is the link to the product: Peak Products Black 3 Tread Steel Stair Stringer - Bunnings Australia. Please let me know your thoughts on this option.
Regarding my query on the span table - I probably made an error in my earlier assessment. The floor load width for B1= 0.65m; B2= 1.3m & B3=0.65m respectively. A 190x45 timber can support up to 2 meters (as in my design) when the floor width is up to 1.8m. Therefore, rather than switching to 240x45 can a 190x45 provide enough support for the deck?

Attached is an image of the area where the deck will be built. I have included a basic representation of the planned location for the posts. The goal is to have the deck boards flush with both the sliding door and the single metal gate. Please let me know if there are any other considerations I should keep in mind for my design.

Image 01.png Image 04.png

Once again really appreciate your inputs!

MitchellMc

Hi @ParagC,

Those steel stringers appear to be fine for your drop and are certainly a great option if you do not wish to create them from timber.

Your interpretation of the Hyne span tables appears to be correct, and 190 x 45mm would be fine. However, given this is an elevated structure, you'd really need to run those sorts of questions past a builder or engineer.

It looks like you have most elements covered there. I would have a think at least about what you'll be doing with the door threshold, as currently, there will need to be some type of bridging between it and the deck. Were you going to try to re-create that masonry work?

Mitchell

ParagC

https://www.workshop.bunnings.com.au/discussion/comment/60297#Comment_60297

Hi @MitchellMc

Wish you & the team at Bunnings a very happy New Year. I had time during the holidays to work on the project after consulting with the engineer on the overall design. Attached are a few photos of how the deck turned out. I did not repair the masonry work but built the deck flush with the door threshold.

For the steps, I used the wooden stringers available at Bunnings. I also oiled the subframe to extend its lifespan. Overall the deck turned out as I had expected.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/93156#Comment_93156

Lovely work @ParagC!

Well done and many thanks for sharing your results.

Mitchell

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