Timber Deck on concrete slab

[Tubby2]

I've just moved into my new house and it has one of those 'alfresco' areas out the back that I want to put a deck on. From what I can tell the slab does not have any fall. I want the finished height of the deck to be about 150-180mm above the height of the slab. I envisage putting joist straight onto the slab but that raises the question of drainage.

Would it be ok to put the joists onto the slab or would I need to lift the joists off the slab 10mm? If so how would/should I raise the them.
The direction of the deck I want is extending out from the house so the joists would have to parrallel with the back of the house further impeding drainage.

Anyone got any ideas as to what I should be doing?

Cheers

[ozwinner]

What about you set your joists to the required hight leaving a 10mm gap between the concrete with cement sheet stuck down with globs of silicon?
Set the globs every 300mm or so, it would have a bit of spring but not much.

Just one of my crazy thoughts.

Al

[Tubby2]

I was thinking along those lines, My initial thoughts were to dyna bolt the joists down to the slab but put a couple of washers thru the bolt between the joist and the slab. Its just a lot of drilling into concrete and a lot of dyna bolts. I like the idea of just silicon (no driling).

[SilentButDeadly]

Pryda half stirrup posts in the 65mm leg length......bolted to concrete slab.

100x50 galvanised Rectangular Hollow Section for your joists (bolted or screwed to Prydas
http://www.onesteel.com/products.asp?action=showProduct&productID=205&categoryName=Pipe%20&%20Tube just make sure your wall thickness is good enough.....Note: Chinese steel is cheaper than OneSteel..and you could probably get away with 75x50 if you need to

Screw decking to RHS.

[Tubby2]

Ahhh! Steel joists. Didn't even think of that.

Thanks SBD.

[Bleedin Thumb]

I would just chock up your joists with blocks of treated pine and use Maxbond ..but that is probably more a reflection on my building techniques rather than what is the correct way of doing it.

SBD's suggestion sounds quite structural... if your after that sort of thing

[UteMad]

If you can go 180mm up Get H4 treated 90 x 70 bolt it to the slab so 70 mm is the thickness... Use this as the bearer and put 90 x 45 on as joists and deck as per normal....
This gives you 180mm ....

Before worrying about drainage you first must see which way the water runs off....

If it runs through the bearer either pack it up with plastic packers or mak wedges or cut grooves through to let wat run through

Cheers Utemad

[Tubby2]

If you can go 180mm ................................
.

Before worrying about drainage you first must see which way the water runs off....

Nah cant go that high. I would then be stepping up to get out the back door.


The whole house slab was poured in one go including the out the back and as I've noticed lately with all the rain is does not fall anywhere. Its dead flat.

[UteMad]

Nah cant go that high. I would then be stepping up to get out the back door.


The whole house slab was poured in one go including the out the back and as I've noticed lately with all the rain is does not fall anywhere. Its dead flat.

No worries it was just that original post said you had up 180mm ....

Why not screed in some fall with a cement bed to get the water off then tile or pave it??

If not get your runnoff sorted then lay treated battens in the direction so as not to block runoff and deck it.... 40mm for bed 45mm for batten 20mm for deck gets it to 105mm which is way under what you originally stated..

If you want the cheapest option core hole the slab where the water pools but this could cause water to erode under the slab so better to go with the screed bed alternative.... Make sure you get who ever beds it to mix up a bondcrete cement and water mix to stick the bed to the existing concrete


cheers utemad