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Low level deck beams below ground level

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Apr 14, 2013, 12:42 AM
ScottieSLG
Low level deck beams below ground level
We are building a deck on a sloped yard, and we would like about 5 feet inches of the deck to be slightly below ground. The question I have is concerns about the wood rotting. Should I dig it out and use gravel inbetween the girders and joists? Would this provide sufficent drainage? Are there any other considerations?

This message has been edited. Last edited by: ScottieSLG,
Apr 14, 2013, 08:44 AM
joecaption
Got a picture of the area to see why you would need to do it this way?
Does not sound like a great plan.
No 2X's are rated for below ground use.
If there's no air flow under the deck the bottom sides will stay wet and the top will dryout which will cause the wood to cup and rot.


joecaption
Apr 14, 2013, 01:03 PM
ScottieSLG
I can't seem to get a pic uploaded from my phone...

If I were to dig out, say, 4' and put some cinder retaining blocks and leave the underside of the deck open for sufficient air flow, would that work? That would leave approx 2' under the deck for air flow.
Apr 14, 2013, 01:05 PM
ScottieSLG
Oh geez... I just re-read my initial post. I meant 5 INCHES, not 5 feet.
Apr 14, 2013, 01:34 PM
Jaybee
Digging out will work. That will keep all the main framing up off the ground. Pressure treated lumber comes in ground contact and above ground usages - unless you special order, only the larger dimension material like 4x4's and 6x6's are rated for ground contact.


Jaybee
Apr 14, 2013, 01:42 PM
ScottieSLG
Is contact with soil any different than contact with gravel? Seems like gravel would still allow for air flow and stay relatively dry?

We would like to be able to put pavers in going right up to the edge of the deck, so I'm hoping that for a short 3-4' width span we could put gravel down that the pavers could be placed on and still keep rot out.

Also, what is the absolute minimum distance from the ground that I should raise my girders to allow for proper air flow?

This message has been edited. Last edited by: ScottieSLG,
Apr 14, 2013, 08:15 PM
Jaybee
Gravel is just about as bad as dirt. You need some separation otherwise moisture will be held in place against the wood - even if it's gravel. Same with pavers, if the pavers are in contact with the PT frame, water will be trapped at the contact point every time it rains. As it is in constant shade under the deck, it will take a long time to dry out. The more distance from the gravel the better - shoot for 4" minimum as stuff could build up over time. If you are up off the ground by 4" or more, then you'll have more than enough air flow. With the air flow requirement, all you are trying to do is to keep from making a mold-breading trap.


Jaybee
Apr 14, 2013, 09:40 PM
ScottieSLG
Thank you, Jaybee. You've been most helpful!!