Low level decking over concrete

[Fadi]

Hi everyone,

Firstly, sincere apologies for posting another low-level decking post. I was unable to find some details I was looking for. It's my first ever decking project and pretty much new to tools and products, please never mind if I don't use the correct wordings.

Here we go,

I am trying to build low-cost decking over an existing concrete slab. The height between the slab and the finish floor levels (FFL) is about 120mm. My first question is;

Is it a good idea to level the deck with FFL? Any issues/complications this will have in the future?

I am thinking of using "70 x 35mm MGP10"  as for underneath timber with Hot dip galv. angle bracket for concrete fixings with about 10mm clearance between the slab and the frame mainly for water drain and air/flow.

Is 10mm clearance good enough?

What sort of bolts shall I use for angle bracket fixing to concrete?

Also, see a detailed timber layout for comments and suggestions on spacing and etc.

Community manager's note: Check out How to build a low-level deck for expert advice.

I will be finishing it off with SpecRite 90 x 19mm 2.25m FJ Merbau.

A quick mock-up of how it will look like if everything goes smoothly;

Current situation;

Thanks in advance

[MitchellMc · Accepted solution]

Welcome to the Bunnings Workshop community @Fadi. Many thanks for your questions, I'd be happy to assist.

It's great to have you join us and we look forward to following along with your project. There is no specific issue with finishing the deck flush with existing levels. Waterproof flashing should be used when butting up against the wall of the house. You will need to use treated pine and Treated Pine Outdoor Timber Framing 90 x 45mm would be suitable if leaving a gap for water drainage. When attaching brackets, alternate the sides they are attached to. You'll be attaching the brackets to the concrete with Dyna bolts.

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

Mitchell

[Stuardo]

Hi @Fadi, we all love the idea of a deck and low-level decks are a constant question on the site. Please DON'T use the timber you suggested as it is untreated and suitable for internal use only. At a minimum over concrete you would need H3 treated timber and H4 is better. Please refer below information copied from a Queensland Government Guide for H Code (Hazzard) treated timber.

H3 - The minimum level of preservative treatment required to protect the timber from attack by decay fungi and insects, including termites. H3 preservative treatment offers protection in situations above-ground, exposed to the weather or periodic wetting. Depending on the application, preservative treatment to provide protection in H3 conditions can involve one of two levels. The lower retention level must not be used in a load-bearing application where routine inspection and maintenance cannot be readily carried out.

H4 -   The minimum level of preservative treatment required to protect the timber from attack by insects, including termites, and severe decay. H4 treatments are suitable for use in situations where the timber is in contact with the ground or is continually damp. H4 is appropriate for less critical ‘non-structural’ applications and/or where the decay hazard zone indicates a lower in-ground hazard.

As for the structural side of your deck I will defer to the professional builders on this site.  I hope your deck ends up to be a thing of beauty that you will enjoy and be proud of for a long time.

Stuart.

[Fadi]

Thanks @MitchellMc for your prompt response really appreciate that.

I will take your suggestion on board and will be going to install Treated pine timber. However, I am still wondering if I can go with the 70x35 rather 90x45 framing option as I don't want the house floor and the decking floor to be exactly flush. 

Also, you have mentioned that I will need to use waterproof flashing all around where it connects with the wall. Can you please advise what sort of product I can use here.

Many Thanks!

[Fadi]

Thanks @Stuardo for your valuable input many many thanks for that!

I will definitely be taking your suggestion on board. 

[MitchellMc]

Hi @Fadi,

You can certainly go with the 70 x 35mm treated timber, I've only recommended 90 x 45mm to ensure there is no sponginess. Thinner calibre timbers can potentially bend under load.

If the timber is to be butted hard up against the house I would recommend Protectadeck in between the two. The best-case scenario is that you just leave a small gap and not have the timber hard against the wall. Anytime timber is placed against the wall it creates a point where rot or moisture penetration can occur.

Mitchell

[rahil_xyz]

@MitchellMcHi Mitchell, how are you.

with alternating the sides the bracket is attached to, do you mean alternate each bracket on the same joist?

or have brackets on 1 joist facing the same way and the next joist facing the opposite way?

[MitchellMc]

Hi @rahil_xyz, 

I'm great, thanks for asking.

Yes, I would suggest alternating the side on which the brackets are placed on the same joist. The image below illustrates what I mean. Although not a necessity, I believe it ensures the joist stays at 90 degrees to the ground. You'll find if all brackets are on one side it can skew the joist in a certain direction especially if the ground is not perfectly flat.

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

Mitchell

[pete_brig]

Hi @Fadi 

Have U started your "deck"? I only just saw your post &have a few comments that might b helpful, if U haven't started 

Cheers Peter 

[rahil_xyz]

 

Any tips on how to fill the gap where the raised brick area is. If my joists ends at the brickwork and the merbau sits on top until where the brickwork starts. There will be a small gap left between the door sills and the merbau. My deck will be at level with the floor. And the gap hieght ( from top of brick work to floor hieght)

is 60 mm .