Deck over a slab!

[Jack1064]

I have some questions for you guys,
Heres the situation, Im getting ready to put sod down in my backyard, and already have flower beds and all that good stuff, but all I have is a 12x13 slab of concrete that is pretty bad looking. I also added some pavers to make the slab a little bigger and give me some room for my grill, the pavers are in there with a sand/topping mix that gets pretty hard and these will not be easy to remove if thats what I want to do, they are bordered by 4x4's, the extra paver patio makes the total slab about 12 x 19. And these pavers are not perfectly level. So my idea was to put a small low deck directly over the concrete slab, I think this would just add a lot to the yard. So heres what I was thinking about doing. First I would put down several 2x4's running perpendicular to the house, I was thinking using a Powder Actuated nailer, Then I would put (5/4 x 6 x not sure yet) over the 2x4's. I think this would work fine and probably be able to get done in no time at all, but I dont want to only do this over the original slab, I want to make it big enough to actually use, but I am not sure what to do about the pavers and how I should go over these, I dont want to spend a ton of money on this project, but I want it to look good and do it right. Any suggestions on what you guys think I should do. Thanks a ton! Oh by the way I live in South Carolina, so the winters arent bad, and the deck to the door is 2 1/2 inches

[crokett]

I've built two decks over patios.

How big is the drop between your back door and the existing patio?

To support the sleepers out over the paver area I would not rest them on pavers. I would add a beam and either pour fittings or use precast concrete anchors. with 6' of span between the end of the concrete and the end of your pavers you will need a second beam to support 2x4s, especially if you lay them on the faces. 2x6s on edge can span that easily but I don't know how tall you want to make this.

Before you lay your sleepers on the concrete, rout or cut dados across the faces and lay them dado side down. Depending on how the concrete is pitched, this will let water drain.

[Jack1064]

The drop is only 2 1/2 inches, Im not sure if I really understand what you are talking about doing over the pavers, I was just planning on putting down 2 x 4s and the attaching the 5/4 x 6's to them in order to make the deck but just not sure what to do over the pavers, this will mean my deck is really only about 2 inches high.
Thanks

[pelligrini]

With only 3' of pavers you could probably get by with running the 2x4 flat out across them at 24" oc. Even if you put the 2x4s flat the deck will still be 1/4" proud of the inside. Hopefully, there aren't any doors that swing out over it. I'm also taking it for granted that the deck slopes away perpindicular from the house. If not, you might need to rethink the 2x4 sleepers over the pavers.

[crokett]

In your OP you said you didn't know what to do over the pavers. I thought that meant you want to extend the deck over the pavers but aren't sure how to do it.

I am saying that 2x4s laid on the flat can't span the 6' you have from the end of the concrete to the end of the pavers without some support. Or they can, but not for very long. I would not rest the 2x4s on the pavers. You said the pavers are not level already and even if you shim them they probably won't stay level. I would either dig and pour footings at the corners and run a support for the 2x4s to rest on, or you can get something like this:

http://deckplans.com/support/sizeshape.html. These work, I have used them.

You would have to dig holes and put these in the ground to get down to the level you need.

A 2x8 will span corner to corner ok, or a 2x6 with support in the middle will span.

As far as the slope pelligrini mentions, if the patio isn't graded away from the house already, you can cut shims to put under the sleepers to grade the deck away from the house. Also space it off the house 1/2" or so to allow water to drain and don't attach it to the side of the house.

[Jack1064]

Crockett,
I think I understand what you are talking about now, but to make sure I am gonna go home today and take some pics and then post those and get some more advice from you guys,
Hope that this is ok, Thanks
Mike

[pelligrini]

Photos always help.

One bad thing about laying all the wood down on the pavers and concrete is that it will rot quicker. Especially once there is time for dirt and debris to accumulate.

[just started]

Check the building code in your area before you do anything. Most places regulate decks now and if you don't follow the regs they will make you tear it up and do it over.

[docrowan]

I've not built a deck before, but it seems to me that you're running a high risk of having water pool up underneath the deck, leading to problems with rot even for pressure treated material. Also you could create a breeding ground for mosquitos. Right now the water is likely running off, but it has no restrictions anywhere. Lay down a series of 2x4's and attach them firmly to the concrete, then have shade preventing the sun from evaporating it, and it's a possibility.

Crockett, the deck's you've built over concrete: did you lay the 2X4's face down on the concrete, or did you build a "standard" frame for the deck with the 2X4's laid on edge?

Edit: I just saw Crockett's suggestion to rout dado's across the 2X4's and lay them face down. Where's my sign!

[crokett]

Chris,

One I built was post and beam. The other was 2x4s on edge - we had the height to do it that way and we could use longer screws for the decking boards.

An alternative to routing the dados is ripping some treated 2x4s into 1/2" thick strips and putting these across the sleepers to raise the framing off the patio. I've seen it done that way but don't know what the OP's clearances are.

[pelligrini]

As long as the sleepers/joints are running with the slope there shouldn't be any pooling.

We have been doing a bunch of roof decks on flat roofs similarly. We have been laying down tapered 2x12 and smaller joists directly on some modified bitumen roofs. We do put an extra strip of roofing material under the joist though. The joist is tapered to match the roof slope, usually a 1/4" or 3/8" per foot. We also try to locate the 24" OC joists directly above the roof trusses. We've tried some other solutions, but this way we don't have to deal with any point loads.