How to select timber sub-frame for low-profile deck?

Question

Hi team,

I am planning to add a low level deck to my back yard, approximately 60sqm.(10 x 6)

The subframe will run over concrete for the most part with the outer edges over turf which will be removed and gravel put down.

I was going to use H3 treated pine joists with adjustable feet supports from Bunnings, but I am restricted by my door sill height of 90mm.

My decking boards are 22mm. I was planning to use 70x30 H3 treated pine but with feet this would be too high.

Could you suggest anything different or offer some advice.

I am running boards left to right as per photos and it is approx 6m to sandstone wall and 10m to fence on right hand side.

Any advice is greatly appreciated

Dave-1 · Answer

Good evening @ianR

There are a lot of low level deck questions and projects in here :) Have a peruse through them and pick and choose bits that match up with your height requirements. The main things to keep in mind are

* drainage (if the boards are going to run perpendicular to the sandstone that means the joists will run away from the hose so drainage is going the right way)
* breathing, the space under the boards needs to be able to breath, with the section over the ground even if you dig it out and replace it with gravel (not sure why the gravel is needed as it will be covered with the deck) or leave it with a weed mat the water still needs to be taken away otherwise you will end up with issues.
* Being so close to the ground overall will add drying out issues.

There are people that have used spacers to keep the joists off the concrete, right angle brackets have also been used to support the joists and that seems to work well. If you do drill into your slap remember that one day you may want to remove the deck/right angle brackets so drill the holes deeper than the actual bolt so you can undo the bolt and it can stay bellow the concrete.

I think your project is doable, tho you may have to think outside the square for parts of it :)

Dave

Nailbag · Answer

Hi @ianR

I would follow the links @EricL has provided as a starter and then research the countless other listings of this exact same project within the community. Your main objective is to build a frame that has a finish height 20mm below the bottom of your door sill so your walking out onto a flush to internal floor. So, 100mm will be the top of your sub-floor frame. And personally I would set it out so the boards run parallel to the house not end to end for aesthetics.

Nailbag

EricL · Answer

Hello @ianR

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your low-level deck project.

Would you be willing to consider having the decking panel surface be at the same level as your aluminium door framing? This is of course on the condition that there is enough space for this idea to work. Another option that comes to mind would be to do a shallow bevel cut under the frame so that it does not touch the ground.

I would suggest going for a 70x45 but if my first proposal works then a 90x45 would even be better. I suggest using angle brackets for the length of the joist, again on the condition that it is not too high. By the time you get to end I recommend using

https://www.bunnings.com.au/builders-edge-70-170mm-bigfoot-xl-pedestal-feet_p2450075

. I recommend having a look at this discussion - Low-level composite deck over concrete and soil by @oninpena. This is an excellent example of a single layer deck frame that has a sloping concrete base with partial overlay over a soil surface. In theory it is very similar to your installation conditions.

I propose having a look at these guides - How to build a low-level deck by @Adam_W and How to build a deck by @MitchellMc. These guides will help you when planning your decking frame. My best advice would be to get some 90x45 and 70x45 offcuts if possible and a sample panel of your 22mm decking panel. I'm a firm believer of "seeing if it fits" philosophy. If the materials you have in your hand fits into your available space, and does not appear to be a tripping hazard then you can build it as you see it.

I also suggest having a look at the Bunnings deck building guide:

* How to plan out your deck
* How to set out a deck
* How to install stumps
* How to install bearers
* How to install joists
* How to lay decking
* How to add a step to your deck.

Let me call on our experienced members @Dave-1, @Nailbag, @myprojectresto, @Graeme50, @LD44, @Samsdeck and @DIY4Knuckleheds for their recommendations.

If you have any other questions we can help with, please let us know.

Eric