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How to build low-level deck?

Hi there,

I have been planning this deck project for long now in the alfresco. I have finally did my homework and draw my plan for the deck. I have attached my plans and estimate cost for all the materials I need.
My alfresco depth is 140 cm so I have to choose 90x45mm structural pines. My calculation says I’ll need all together 15 structural pines so I have added 1 extra with 400 cm gap in between.
I am going to screw the structural pines into the wall in 2 side and in the pillar. Rest I’ll add L shape brackets or timber for weight support.
I have calculated my deck boards (140x19mm) through deck calculations https://www.calculateadeck.com.au

which gives me 22 boards with 125 L/M and 575 fixing screws needed. I am choosing 5.1 m long X 4 boards for picture frame and 3.9 M long X 20 boards for rest (few extras). I’ll use 4mm spacers in between the boards and screw in every 400 cm.
I hope my calculations and method for the decking is right and want to know any improvements or different methods.

Thank you

Sambhu

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Comments

JacobZ

Hi Sambhu (@sambhusth007),

It's great to see you've put a plan together and are getting ready to get stuck in.

A few things I have noted while checking on your plans.

In the current orientation, you aren't really using bearers in a traditional sense. The timbers that you are planning to bolt to the wall at the top and the timber at the bottom edge of the deck on your plans are acting as bearers, but not in a traditional sense. This is not an issue, but because 90x45 joists need to be supported every 1400mm, as shown in the Hyne Deck Joist Span Table, you will need to support each joist every 1400mm. You might like to check out How to understand deck components and How to understand deck span tables for some guidance on this.

As you have 140mm of height to work with, 90 taken up by the framing and 19 by the decking, you will have 31mm of space from the bottom of the joist to the concrete slab. This means you would be able to use these Builders Edge 25-40mm Minifoot Pedestal Feet, which will support your deck far better than angle brackets or timber that will rot, being in direct contact with concrete.

The biggest thing I've noticed in terms of cost reduction is that you have your joists spaced at 400mm apart. The standard spacing for joists is 450mm, meaning you would only need 10 joists, including the double joists on the left and right, which is a significant reduction from the 15 you have planned for.

Another thing I've noticed is the double/triple joists on the top and bottom. As the only reason for these double joists is to support the decking boards, and the decking boards are running left to right across the joists, there is no need for these double joists. This is another reduction in materials that will reduce your costs.

Nailing our frame is the most important thing we can do to ensure you have a solid deck, with no bounce, that will last the test of time.

Overall, you've done a fantastic job so far, but there are certainly ways we can improve your plan and reduce your costs.

Let me know if you have any questions so far and please don't hesitate to ask further questions.

I can't wait for your deck to get started!

Jacob

sambhusth007

https://www.workshop.bunnings.com.au/discussion/comment/53417#Comment_53417

Hi JacobZ,

Thank you for your feedback. I have recalculated my joists to 10 and 6-9 minifoot to support weight.
I have a plan in future to use the alfresco area as a sunroom. Question: Should I minimise my deck to within alfresco area (3230 X 3280 or leave as it is to 3230 X 4700?
Also, do you have any other plan to improve and reduce the cost?

Thank you

Sambhu Shrestha

EricL

https://www.workshop.bunnings.com.au/discussion/comment/88956#Comment_88956

Hello @sambhusth007

Your decision to reduce the size of your deck will definitely affect the overall cost of the deck. Keeping the deck simple with no picture framing will also reduce its cost, not a great deal but enough to save money. My only other suggestion is to double check the measurements of the timber pieces to be used for the deck. It's important that every piece of timber offcut is to be used for the building of the decking frame.

Let me call on our experienced members @Dave-1 and @Nailbag for their recommendations.

If you need further assistances, please let us know.

Eric

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/110222#Comment_110222

Good evening @sambhusth007

Really like the thought that you have put into the plans and costings 🙂 I at first went wooooo and then started looking at the figures you have supplied and a smile crept across my face. You have stepped through a design process nicely and even stated your resonings PLUS sked for feedback 🙂 Brilliant move, you cant improve if you are the only self check!

I had the same thoughts as to spacing as @JacobZ Tho I did miss the double/triple joists on the top and bottom 😲 😀

As to the sizing of the deck, I would stay with the larger size. It makes the overall area feel larger and more encompassing, If you kit the room out later to be a sunroom having a larger nose of the deck would still make it stand out. I think the added cost would be worthwhile.

Adding subfloor low voltage lighting dots might be something you want to factor in, or running a length of conduit that you can run a cable down later on if you decide on power. Or install it directly with an outside powerpoint somewhere useful for a couple of reasons (cooking, sound, fridge) could also be an idea.

Dave

sambhusth007

https://www.workshop.bunnings.com.au/discussion/comment/122474#Comment_122474

Hi Dave-1,

Yes I have a plan to add lighting to the floor. My initial thought was to add those along the picture frame boards. But I might add to first boards after the picture frame boards. Let’s see how it goes.
Question: After how much time do I need to oil the deck?

Thank you

Sambhu

EricL

https://www.workshop.bunnings.com.au/discussion/comment/130381#Comment_130381

Hello @sambhusth007

If you are naturally seasoning the deck, you'll need to wait 8 to 12 weeks in order for the oil and tannins to leach away from the surface of the decking panels. But to skip the waiting process you can use Cabot's 2L New Timber Prep - 2L in combination with Cabot's 1L Deck Clean - 1L. These will remove the surface oil and tannins and allow you to stain the deck the following day or as soon as the deck is totally dry.

If you need further assistance, please let us know.

Eric

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