How to build a low-level deck for my alfresco?

[ScottR]

Hi folks. New member here and a very new to the world of DIY. I was hoping to get some advice on some of the questions I had in building a deck. I have read Adam W's article on how to build a low level deck here I posted the question below but will provide details first

Here are my details:

- 3m x 3.6m Alfresco deck on concrete with drainage in middle

- 172mm is the stepdown according to plans but I measured it was actually 190mm from the stacker door so I'm basing it on 190mm height

- For joists, I plan to use H3 treated pine 140x45mm (i need 8 of them with 450mm span each)

- For boards, I plan to use Merbau 90x19mm (I haven't counted how many I need from them)

- The boards are going from left to right.

- I plan to picture frame the deck

Question: 

1.)  Can I screw the joist to my brick wall using a galvanized hex head coach screw like this? Or maybe something longer screw because I'm using 140x45mm joists? I saw in Bunnings Youtube video here that they drilled the joist to the brick wall. I plan to do the same and use joist hangers for each and every joists connecting there. Is that advisable?

2.) On the black dots, I plan to use builders edge adjustable decking feet of 25mm. Do I need to drill the feet to the slab? As much as possible I don't want to drill anything to the slab unless it is required for my decking type.

3.) I plan to do something like this but instead of angle brackets, I will use decking feet. Is that advisable?

Thanks!

[MitchellMc]

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

1) What type of wall is it? If it's brick or concrete, you'll need to use Dynabolts. If you are connecting to the house's floor timber framework, then typically, you'd bolt the ledger board to it. That means you'll use threaded rods and have to get under the house to place washers and nuts on the inside.

2) Adjustable decking feet do not need to be bolted to the slab. They're used to construct a floating platform/deck. If the deck is connected to your house, you'll need to confirm with your local council or building authority as to whether pedestal feet are an appropriate solution.

3) The adjustable feet would be fine if this were a completely floating deck and not connected to your house. Once you connect to your house with a ledger board, then the construction is no longer a platform, and I believe it can invoke a different set of rules and construction codes.

You'll need a double joist on the left-hand side to allow enough room to install your picture frame and be able to screw off the ends of your decking boards.

Please let me know if you have further questions.

Mitchell 
 

[ScottR]

Thanks for the response @MitchellMc !  It's a brick one. Very similar to the bunnings video @ 6:51. 

Thanks for advising that decking feet do not need to be bolted to the slab. If I bolt the joist to the brick, it means that my deck is now connected to the house and involves a different set of rules? Okay.

How would I stabilize a free-floating deck if I don't plan to screw the timber joists to the bricks and without screwing the adjustable decking feet to the slab? Thinking I might have to go with @Backyardtradie 's low level deck style here which is nice but it might be too low for me as my stepdown is more than 150mm.

Any advice you can share on this? 

[EricL]

Hello @ScottR 

I suggest having a look at this discussion - Low-level composite deck over concrete and soil by @oninpena. This is an excellent example of a floating low-level deck that is held in place by a combination of angle brackets and decking feet. You're decking frame can be installed off the concrete slab by using taller and larger angle brackets.

Have a good look at its construction and if you have any questions about its assembly, please let us know.

Eric

[ScottR]

Thank you @EricL ! I had a look at this and the application looks clear. I do have some newbie questions on floating decks:

1.) What if I don't use any angle brackets? and just use a plastic builder's edge decking feet all throughout?

2.) Would you recommend something like #1 above? or it's not strongly advisable to not do any concrete slab dynabolt screwing for the deck as it would compromise stability?

3.) I'm trying to calculate the required height:

- if my required height is 190mm, I'll get 140mm from joist, 23mm for composite decking width (thinking of switching to composite), i would still have 190-163= 27mm height needed and that's where the decking feet come in.  Question: If I go with the angle bracket route, is there any measurement you recommend me getting?  Would this be sufficient? 

4.) How far apart the spacing for the angle bracket should be? From the image, maybe around 450mm from each other?

Thanks!! 

(photo from @oninpena  recommendation you mentioned that I'm trying to immitate)

[MitchellMc]

Hi @ScottR,

It's possible to use the deck feet throughout the whole deck. However, if you're in a cyclonic or severe cyclonic winds area, you should at least pin the deck down with brackets on the four corners.

It's perfectly fine to use only deck feet or use deck feet and brackets or brackets alone. Dynabolting into a concrete slab will not compromise its stability. If you need to bolt new the edge of the slab, it's best to swap out for Ankascrews that aren't as likely to crack the corner of the concrete. 

27mm is fine for the bracket. If you were to use Dunnings 65 x 130 x 65 x 5mm M12 Galvanised Angle Brackets with the shorter side bolted to the concrete, that would leave another hole approximately 100mm from the ground. This top hole will be right around the middle of your 140mm joists.

You'd be fine having the brackets every 1000-1200mm. On 90 x 45mm joists, you'd want the brackets spaced around 1000mm apart, but on 140 x 45mm joists, you can space them further as it's a larger calibre. It's the joists that must be spaced around 450mm apart from each other.

Please let me know if you have further questions.

Mitchell