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Laying 2x4s flat on a concrete slab

Posted by nuckphoto (My Page) on
Thu, May 6, 10 at 14:06

We are planning to build a deck out back but the patio slab is only 3-4 inches below the patio door threshold. Can treated 2x4s be laid flat on concrete to support the decking? There will also be posts for the deck cover. The slab drains away from the house and the deck won't be attached to the house. But we are hoping to extend the deck beyond the slab.

Will this work or any other ideas?

Thank you.


Follow-Up Postings:

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RE: Laying 2x4s flat on a concrete slab

That is exactly what I am doing and it appears this is OK with the County residential engineer. I met with him, showed him the plans and he did not have an issue with this. I have a freestanding deck designed (joists are same level as 2X4s on existing patio (16 inches oc), patio is 15 inches above grade and the back door is about 5 inches above the patio). I plan to run 5/4 deck boards from the deck accross the patio and attached to pressure treated 2X4s. I have the final meeting with the engineer tomorrow to get my permit if all is well.

--Nate


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RE: Laying 2x4s flat on a concrete slab

Make sure you use PT wood that's treated for ground contact.


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RE: Laying 2x4s flat on a concrete slab

Not quite following you, natewall.

I will be using PT 2x4s, weedyacres.

Thanks all.


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RE: Laying 2x4s flat on a concrete slab

There's regular PT (.20 pcf) and there's PT that's treated for ground contact (.40 pcf). Get the latter.


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RE: Laying 2x4s flat on a concrete slab

Your actually much better off getting some CCA beams and ripping them down to size for runners.
IMO, this is a lot better than ACQ40 for your application.

See ya,
Kelly


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RE: Laying 2x4s flat on a concrete slab

Thanks for the reply, Kelly, but due to the arsenic in CCA treated wood, we don't want use it. I think the ACQ will suffice.

On another note, water does drain away from the house on the slab but puddles on one of the far corners. I was thinking about digging a small ditch with gravel in the bottom and a drainage leach pipe along the far edge to aliviate that problem.

That sound OK?


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RE: Laying 2x4s flat on a concrete slab

Nuck,where are you? Over here the only pt lumber sold is MCQ, Acq has not been around for a couple years.

The ditch will probley work. I usually tapcon the stringers to the slab.

As a side note CCA lumber will offer no danger at all to anyone and never has. In the 90 years or so its been in service there is no record damage to Anyone or Thing. CCA .40 .60 is still being made for areas around water and Com use the idea being fish can handle arsenic just fine but copper will kill them dead on contact. J.


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RE: Laying 2x4s flat on a concrete slab

quote" I was thinking about digging a small ditch with gravel in the bottom and a drainage leach pipe along the far edge to aliviate that problem. "quote

This is fine, I suggest putting some weed barrier fabric folded in half for 2 layers underneath your rocks. You'll be grateful you did. I use perforated 4" ADS with fabric in mine to the lowest spot and then connect to a solid pipe ran to a lower elevation somewhere it can send the water, or place a catch basin at the lowest spot and then run the solid pipe. Your rock swale will flow water to the basin. I like the first way better because if the grate for the basin becomes clogged with debris the water will still build up in that area.

I agree with Johnmandoo on the CCA. I've used it to build bulkhead at the lake for a long long long time. Nothing does better with water contact, It doesn't leach the arsenic as many believe, it's left behind in sawdust or ashes after burning, that's why you don't burn this material.

I'm not saying the 40 is bad, just that this is better for a long life span.

See ya,
Kelly


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RE: Laying 2x4s flat on a concrete slab

Thanks, all. I'll take all your info into consideration. But the problem at the moment is finding 2x4s treated for ground contact. All I can seem to find are 4x4s.

"I suggest putting some weed barrier fabric folded in half for 2 layers underneath your rocks."

So, that's weed barrier under the gravel? Weeds will grow down there with no light?


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RE: Laying 2x4s flat on a concrete slab

Use the best treated lumber you can find then retreat with Jasco Termin-8. My outfit has been doing this from the begining of mcq lumber.

I have found laying down any plastic/fabric under a decking project works in reverse,holds water and gives a place for bugs to hide. J.


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RE: Laying 2x4s flat on a concrete slab

nuck: To find ground-contact PT, you may have to special order anything that's not a 4x4 or 6x6. I used 2x6's to anchor my stairs on concrete, and Menard's had to special order them for me.


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RE: Laying 2x4s flat on a concrete slab

Thanks everyone. I'll probably have to special order the PT 2x4s and the Termin-8 since I can't find it locally at all. I tried when I was replacing the mailbox post.


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