Decking Over Concrete

cden

have a couple questions. 1st looking at building a deck aprox. 40x16. i only have a maximum of 6 inches of ground clearence. thoughts on pouring a concrete slab and then gluing and fastening 2x4s flat over concrete, then my decking. 2nd i've heard that a composite decking needs around 12 inches of air space underneath it. any ideas would be great.

Greg Di

You are in for trouble. Sounds like a patio would be more appropriate unless the client doesn't plan on using it too long.

Many synthetics will work with zero venting, but the lack of airflow and drying will just destroy the framing over time. No place for the moisture to go really.

One option you might explore is Bison Deck supports. I have used them for low decks (not 6" low, about a foot) and they work great, but surface prep is critical.

http://picasaweb.google.com/FineHome...nts/BisonDeck#

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Stone Mountain

I've had occaision to rip up floating decks 40 years old that were built on top of old rail ties buried in the ground.
Nothing wrong imo to building a low level deck with only inches to spare.

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Meetre

over excavate the site, digg a foot of ground out, add some dranage, maybe some plastic ground cover, and build over the hole to get clearance and air-flow. or do a patio.

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John Hyatt

John agrees with the Stone. I have done many installs like that. Tapcon 1 1/2'' pt blocks to the slab frame off of them. No problem for me or my Wallets. J.

deckman22

Someone that's a deckbuilder should know the answers to these questions, 1 post says he's a HO looking for advise.

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cden

ok a-hole you still didnt answer the question. seems like everybody else had good and different advise. Could be a little more like greg di. At least he's a professional with good advice.

cden

MALCO.New.York

When I was a wee-lad, my Father built a 5' Tall, 120' Long, Rail Road Tie wall and another that was 10' Tall by 20' Long. Both were back-filled with dirt with NO DRAINAGE. The walls have no more real Integrity today, but they are still standing. My point is that they last!

REAL RAILROAD TIES. Not the Crapola from a yard. Get them from the local RR Company. Hell. Ours still had the Cleats and Spikes attached to them.

There is a Distinct smell of Creosote in the Summer. Less than pleasant!

http://www.railroadcrosstie.com/?gcl...FQpzHgodSH9Tmw

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Bodger

Ouch!
I think Deckman is curious as to whether you're a contractor seeking advice or an HO looking for same.

An intro would help clear that up, and if you're the latter, there is a DIY site that you can be referred to that's affiliated with CT if I'm not mistaken.
Best of luck.

MALCO.New.York

No one told you to dig a-hole. You were instructed, by a few different guys, on alternative methods.

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cden

I have been a carpenter for 10 years. lead man for five of them. I have mainly done new residential homes in average of 2000 to 4000 square feet. I have recently moved to a new city (small one), and know very few people. So i work for a contractor building new homes. in case you havent noticed economy is a little slow, so i do deck work on the side. I joined this forum to expand my knowledge. unlike other people, I do not claim to know everything. ISNT THIS WHAT THE FORUM IS FOR!!!
Glad to meet everyone
thanks
cden

cleveman

cden,

I've built a deck on top of a patio which the ho got tired of. The existing patio should be sloped away from the house for drainage.

So if they want wood, you can excavate out like others suggested.

You could build it on top of a patio if you wanted to pour a patio first. In this case, you'll still want to excavate out to give yourself 4" base, then the concrete, so you'll want to excavate out about 8" deep.

Then just use 2x4's for floor joists resting directly on the concrete.

Of course use PT wood for the 2x4's and decking. I don't know about airflow for the synthetic decking, but the PT has held up in my climate for 15 years on a western facing deck.

cden

thanks cleveman

I was planning on pouring a slab just keep the deck at a low profile as the customer wanted. But was worried about air circulation and mold with different decking materials.

cden

Greg Di

You are going to have to dig one way or another. With the Bison supports you totally eliminate the need for a slab. They are designed to float on compacted gravel. They are inexpensive compared to pouring a slab. The project I showed maybe cost $400 in Bisons to do. And, we did everything in one day.

Drainage is a major concern with any of this, so make sure you plan accordingly.

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BuiltByMAC

poured concrete beams would be another option. If it's 40' along the house, then pour (3) 40' beams (with breaks for drainage falling between joist locations) - 1 at 18", 1 at 8', and one at 14'6" from the house.
Plan joist layout and stick j-bolts in beams to fall in joist bays.
run 2x6x16' joists on beams
blocking on the flat between joists for j-bolt locations, all other blocking run vertical.
1" decking puts you at 6 1/2" - can you fudge that last 1/2"?

Much less concrete than a slab...

Mac

neolitic

If I was going that route,
I'd think about one more beam
and 2X4 joist.
Keeps the spec'ed height and
allows ground clearance (ground
contact TYP is hard to find here
except in 4X).
Don't know how much concrete
it would save if he has frost depth
to deal with.
I think he's around Carbondale(?),
and I'd guess something like 30"
frost line?

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neolitic

Oh, BTW, OP?
Demand your rights from the
government.....
not us.
You don't really have a right
to the answer you want on here.
Respect will go along way though.

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cden

greg di,

thanks for info. I have already contacted the bison jack dealer close to me.

Just finished my bid including the bison jacks.

thanks to everyone for the info
cden

cden

is my location not on my profile?

southern il. if it helps any
cden

neolitic

It is.
Just guessing that Carterville
is down state.....
near Carbondale?

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