How to construct low-level deck over concrete?

[muzza1]

Hi, It's been really useful reading posts about low level decks here, but every one is a bit different so I'd appreciate some guidance with my project.

Intending to make a wooden deck for the front porch area of our older style cottage in Christchurch NZ. Thinking the deck can come up to the bottom of the front door sill, which is 120mm from the concrete/ground at the smallest clearance point. The concrete falls away from the house at around 2°, so with a level deck it would be 230mm from the ground at the entrance, and so needs a step.

I've read about using 90x45 framing timber as joists, haven't selected boards yet but maybe they will be 21mm thick, leaving only a small air gap maybe around 10mm. Then with a step up to 230mm at say 115mm, there's not much height to work with. So my first question is can I use 75x45 joists? What would the spacing be?

Suggestions on boards to use are welcome, often Kwila is the go-to around here...

Fixing the joists to the concrete ( which is a bit uneven), could be L brackets or maybe pedestal feet, with dynabolts.

I've drawn up a model of the deck to help convey what I'm thinking, and some photos as well. Would be great to get your ideas!

Many thanks

Muzza

[Dave-1]

Morning @muzza1 

@MitchellMc has pretty much said the same way i would work with the side skirts

Cant wait to see some pics!

Dave

[muzza1]

Thanks again all. Really is a great to be able to access all the advice, much appreciated!

With the skirt overlapping and fastening into the patio face, I'm wondering about gaps. It's been a key consideration from the start to have a good gap under the framing, is it OK then to pretty much close the gap where the skirt meets the patio? 

[Dave-1]

Good Evening @muzza1 

Im not sure what you mean. If you have a look through my outside bench project Outside bench you will see how I created a skirt backing and then installed a skirt. For you it will be the reverse. So from the top joist you will have the drop down posts so you will be able to screw the skirt to them.

Id leave a little bit of an airgap, say 30mm just to allow moisture no avenue to build up against the timber.

Dave

[MitchellMc]

Hi @muzza1,

Closing the gap will reduce airflow under your deck. Lack of airflow leads to the early onset of decay. It's really a trade-off between aesthetics and the lifespan of the deck. It would be best to leave the side open, but it's up to you to decide whether that's an acceptable look.

Mitchell