building a low (on the ground) deck

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Old 04-15-06, 12:13 PM
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building a low (on the ground) deck

I would like to build a deck and have it be right on the ground. It needs to be low because there is very little clearance going from my door to the yard, so I don't have space for big beams and joists.

One idea that I have is to cover the area (about 10'x10') with gravel and build a 2x4 treated wood frame on the gravel. And then use redwood planks on top. That's about all of the room I have in terms of thickness, (3.5" + 1.5" = 5") 5" thick.

I've also heard of plastic wood that is structural, so I would like to find out more about that.

Any suggestions appreciated!
 
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Old 04-15-06, 02:53 PM
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Yes, there is structural plastic lumber, and that would be the best thing for you to use. Google 'structural plastic lumber'.

PT (ACQ) would only last a few years, due to a combination of ground contact and the lack of ventilation. Plastic lumber would not be bothered by either. It's expensive, but you are only buying it once, not every 5 or 6 years. Use a decking that will span 24" O.C. to reduce the amount of plastic lumber you need. (Geo Deck comes to mind.)
 
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Old 04-15-06, 03:40 PM
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"PT (ACQ) would only last a few years,..."

Lefty - Is that unique to ACQ treated lumber? I have some pressure treated on the ground that is at least 20 years old and still looks like the day I put it down. I think it is CCA (the bad stuff).
 
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Old 04-15-06, 03:49 PM
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Wayne,

If your PT is 20 years old, it is indeed CCA.

ACQ can be used for ground contact as long as there is ventilation for it. The way arlo is proposing building this deck, he won't have any ventilation, and the combination of ground contact and no venilation is what will kill ANY wood in a matter of a few years.
 
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Old 04-15-06, 04:11 PM
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MIke: aren't they making some framing members out of the "plastic" geo stuff? If so, wouldn't this help in the moisture, unventilated areas.
 
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Old 04-15-06, 05:33 PM
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Larry,

Geo is a composite decking -- it CANNOT be used for anything structural. Plastic lumber is available in structural grades. Being plastic, it's impervious to water, earth contact, termites, etc. It's expensive, but arlo would only be buying it once. With a composite decking on it, he would have a deck that would last 20, 30, 40 years -- maybe more. And the framing would be pretty much eternal. His grandkids could use it if they ever had to replace the decking itself.
 
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Old 04-15-06, 05:38 PM
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Arlo,

I just reread your initial post. Are you serious about using redwood for the decking? Have you checked the price of con heart select recently? If you can afford that, knowing that it won't last more than 15 to 20 years (probably not much more than 10 with the deck that close to the ground and no ventilation), then the cost of structural plastic lumber shouldn't be an issue.
 
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Old 04-16-06, 09:35 PM
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some more questions/ideas

Thanks for the suggestions. Yes, con heart is expensive, but we have budgeted for the yard. I already built a regular redwood deck about 4' off the ground and we like it. This will compliment it.

I'm thinking that I could skim off a couple of inches of dirt then cover it with weed plastic and 2" of gravel.

I'm not sure how to handle the next part. I was thinking either the plastic or the treated wood, but then laying them in the gravel as "sleepers", meaning on their side rather than on edge. Maybe putting them every foot.

I was also thinking that depending on how much it costs, I could use plastic decking, again, as a sleepers, instead of treated wood or structural plastic. Seems like if I do the sleeper method, space closely, there isn't a need for anything "structural".

My main concern with this method is that the sleepers won't contact the gravel evenly and there might be some bounce, which I don't want. Maybe once the frame is built I could adjust the gravel as necessary.
 
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Old 04-17-06, 04:17 AM
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Regardless of how you actually construct the deck, if you don't start with concrete footings, it's going to have 'bounce', and eventually plenty of it.

Redwood 2X6 will span 24", so lay your joists at 24" O. C. Select your joist size. ACQ 4X4's (your joists) need support (a footing) every 3-1/2' to 4'. ACQ 4X6's can span 5-1/2' to 6', so you would need fewer footings. The larger the 4X, the fewer the footings. Once you have that selected, dig the footings deep enough so that you can trench for the joists, set a pier block, and post up to the joist. Keep drainage in mind. Those trenches are going to fill with water in the winter, so you want them to follow the natural slope of the surrounding grade and give them a drainage system. The LAST thing you want is standing water under the deck. Not only will that shorten the life of the deck, it'll become a breeding ground for mosquitos as well.

Low level and at grade decks are a lot of extra work because of the extra dirt that has to be moved and the drainage system that has to become part of the project. That's why they cost so much more.
 
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Old 04-20-06, 08:52 AM
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what about using a pad

Lefty - If height is a problem, what about pouring a concrete pad about 2" thick that is sloped at whatever you want the deck sloped to. Then Arlo could put PT sleepers directly on the concrete.

Maybe a bit more expensive, but would it solve the problem?
 
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Old 04-22-06, 04:14 PM
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Yes, a concrete slab and placing sleepers on it would work. But make the slab 3-1/2" thick, not 2". Slope it like a patio (about an inch in 8'), set standoff post bases to keep the wood off of the concrete, and level the deck with little bitty posts as needed. The 4X4 joist can sit directly in the post base at the high side of the slab, then add a bit of 4X4 in the post base to compensate for the fall of the slab.
 
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Old 04-25-06, 09:16 PM
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sleepers or "standoff post bases"

Lefty, are you saying that you thought the sleeper idea on a 3.5" thick pad was ok, but you prefer the standoff post bases? That's the way I understood you, but just wanted to check.

Also, regarding the thickness, what would be the problem with the thinner pad? Do you think it would tend to crack too easily?

Thx again!
 

Last edited by arlo; 04-29-06 at 10:30 AM.
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Old 05-07-06, 03:43 PM
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I am in a similar situation regarding thinking of building a low deck. Actually what I wanted to do was place the treated wood directly on the ground and then build the deck on top. But this deck will be covered. Is this doable? What if I placed the deck boards on a railroad beam foundation? Thanks in advance for any help.
 
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