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tpierrepont 06-19-2008 10:33 AM

Problems with foundation for deck...HELP!
We are in the midst of preparing a site for a new deck off the front of our house but have run into a major problem! We removed a few inches of topsoil to help level things out, covered the soil with landscape fabric and then topped that with about 2 inches of gravel. Last night after a bit of rain we walked out onto the prepared site and most of it felt like we were walking on jello!!! What happened and what can we do to fix the problem??

Termite 06-19-2008 11:15 AM

Removing the topsoil could have exposed a layer of fatty clay, which will retain water much better than the topsoil might have. The addition of landscape fabric makes things less breathable, and will not aid in evaporation of water (it won't prevent it, but just like mulch, it'll slow it down).

In removing the topsoil, did you maintain positive slope away from the house? You mentioned leveling it out, which is not good. Your grade should slope no less than 6" in the first 10' from the house. If the water can't drain, and it can't percolate into the soil, you've got Jello.

I'm assuming that this sitework was done for the area underneath the deck? What you're describing would not be adequate for the footing itself! You need to dig piers.

tpierrepont 06-19-2008 11:56 AM

Yes, this was the area we prepared for underneath the deck. It will be a low deck so we had planned on using dec-blocks...I suppose we let it dry and start again and make sure there is adequate drainage?? Should we remove more topsoil or will it make it worse?

TexasEd 06-19-2008 12:31 PM

It sounds like you took off soil at the top by the house and basically flattened out the ground so there isn't a slope anymore in an effort to level everything to use deck blocks.

When it rained the water did not run away from the house because there was no slope so it just soaked in there.

You need to make sure you have at least 6" of slope away from the house in the first 10 feet. This is true for the area under the deck as well as your lawn.

Put the slope back and then level only the spots for the deck blocks, not the whole area under the deck. Make sure the soil you put back is compacted so that you still have the proper slope after settling.

Termite 06-19-2008 01:07 PM

Deck blocks are a poor idea and really don't have much use in quality deck construction, assuming they're only bearing on the ground. The blocks are at the mercy of the earth (frost heaving, settlement, washout, excessive moisture, etc).

Not sure where you're located, but the majority of jurisdictions require an actual footing (below grade) for a deck. Whether it is required in your area or not, it is the best practice.

Ron6519 06-21-2008 04:39 PM

How the deck is supported is also based on your location. People in Florida can do it differently then people in North Dakota.

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