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Hi everyone. I’m hoping someone could help me on this.
I’ve been thinking to deck the whole area of my backyard (see photo). The area is around 25 m2. I have a few questions:
1. Should I still dig the grass or just put a weed mat on top?
2. The clearance from the finish level (tiled area) is around 130-150mm. I am planning to use 90x45 H3 for my joist and bearers and Merbau for my decking. I will also use Builder’s Edge Pedestal and put some pavers and blue metal underneath to play with my level as some areas are not even.
Will this be okay?
3. In terms of connecting the timber to the existing concrete, what is the best way to do it?
4. Would you recommend to connect the deck to the blockwork retaining wall as well?
5. I will space the joist at 450mm and planning to put the Builders’s Edge Pedestal at 1000mm spacing. Is this enough?
6. What size of screw should I use for my timber and when I bolt the timber to the concrete?
Welcome to the Bunnings Workshop community @Mdsyd. It's wonderful to have you join us, and many thanks for your question about constructing a deck.
You might like to start by reading through this guide: How to build a low-level deck.
You're working with some very limited height there. The portion undercover over the tiles will have 20mm beneath your joists once you account for the 19mm decking and 90mm joist height. We've seen quite a few members build decks within such limitations. My concerns lie more so with the height of your joists above the turfed area. Building a deck directly over soil can cause significant moisture issues, as pointed out by @Jewelleryrescue. You'd need to excavate the area, remove at least 100mm of soil, place down weed mat and then add drainage gravel so water can pass through the deck and easily drain away. The bottom of the joist should be coated with bitumen paint to help prevent the early onset of decay. It would be a good idea to leave the sides of the deck open and decking boards should be gapped extra wide at around 6-8mm to help with airflow.
Using pedestal feet over the tiled area and also on pavers over the soil area would be suitable.
Provided you frame in the deck and add noggins between your joists for rigidity, connecting to the tiles, concrete, or blockwork is unnecessary, as a floating deck/platform will suffice.
Your spacing is adequate with joists at 450mm and support for them at 1000mm.
For connecting your frame and noggins to your joists, I recommend Buildex 12g x 100mm 8 TPI Climacoat RapidDrive Treated Pine Screws.
Here's another helpful guide on How to build a deck.
Please let me know if you have any questions.
Mitchell
With no attachment points, you'd be creating a floating deck @Mdsyd. With a floating deck, there is no need for attachment points. To see an example, check out this guide on How to build a deck that entirely floats on top of pedestal feet. So, in answer to your question, you would not need to bolt the joists to the existing tiled/concrete undercover area and retaining wall at the back.
Could you please provide a little more information on your last question? I'm not sure if I quite follow. "Just to clarify, should I am for 5-10mm finish level below the exisiting concrete/tiled area or I should just flush it and same level?"
Mitchell
Oh, sorry, @Mdsyd. So you are not decking over the tiled area but only over the grass? If so, I'd recommend the decking be the same height as the tile. A slight difference will cause a trip hazard.
Mitchell
Yes that is correct. Tiled area will not included.
few clarifications now that is it clear than I will not include the tiled area:
1. Does the method of not bolting the deck to the tiled/concrete area still applies?
2. Do I still need to tie it to the retaining wall?
If i remove the grass the level is around 150mm clearance from the ground. Thinking dig further 30-50mm to allow for roadbase and weed mat.
let me know your thoughts.
All still applies @Mdsyd.
I'd encourage you to read through this guide on How to build a deck. Within it I show how to build a floating deck that doesn't need to be attached to anything. You can use the same methods for your project. No need to attach to the tiled/concrete area or retaining wall.
Digging down a further 50mm and adding weedmat and roadbase is essential, and I'd highly recommend you do so, or you'll have a very limited life to your deck due to the close proximity to the ground.
Mitchell
Thank you.
Lastly, There is a section on my bearers that will need to be spanned in two sections. What is the best way to join or sister bearers and joists? Would it be the same process for both?
