Modifying an existing concrete slab

[Twheeler1986]

We have an existing concrete slab out the back of our townhouse designed as our second car space. I am looking at the possibility of putting a timber deck over the top which would still enable the parking of a car, but also provide an outdoor entertainment area. Is this possible?

The joists would be effectively right on the slab, bar from spacing between the joists and the slab to accommodate drainage and the joists would be closer together (300 to 400mm centres) compared to the normal 500 to 600. I would probably also double each joist.

[Jason]

Welcome to the Bunnings Workshop community @Twheeler1986. It's great to have you join in the discussion. 

You might like to start with this helpful resource by experienced member @Adam_W: How to build a low-level deck. It includes some of the important considerations when building a deck, such as ventilation, drainage and rotting. 

I wonder whether you might like to consider a paving paint instead. Let me tag some experienced Workshop members in @Brad, @tom_builds and @Seaton for their thoughts. Our resident Bunnings D.I.Y. expert @EricL will also be happy to assist when he is back on the site on the weekend.

Jason

[tom_builds]

Hi @Twheeler1986,

Welcome to the community! And thanks for the tag @Jason. 

I wouldsuggest that speaking to an engineer would be your best bet if you want to design a deck that can withstand the forces of a car being parked on top of it, as it won't just be theadditional weight but also the inertia and friction of accelerating and braking on top of the deck.

Could you potentially consider fixing decking boards directly to the slab? This would work best if the slab were undercover and not exposed to moisture, hoever with no clearance from the slab the life expectancy would still be reduced. It would, however, remove the risk of your deck failing with the car on top of it.

Best of luck with your project.

[Brad]

My 2 cents worth...

Put bearers where the wheels will run and allow for a margin of error, Not My Wife can make her car go places it doesn't belong while parking including over the concrete barriers. The scars on the shop car park fence show she is not the worst offender.

I have used steel where moisture was a problem and as much as I don't like the extra work it creates it will last longer.

[EricL]

Hello @Twheeler1986

It's great that you've received fantastic advice from @Jason, @tom_builds, and @Brad. I totally agree with the recommendation of consulting an engineer. The extra elements of weight, friction, and loading are things that you will have to consider while designing your deck. Standard decking practices and materials may not be enough to hold the weight of your car. I suggest getting the specifications of your car and making a rough sketch of your plan before consulting the engineer. This sounds like a very interesting project, please keep us updated, I'm sure our members are keen to know what the build requirements are.

If we can assist you further, please let us know.

Eric