You need ventilation under a deck to avoid moisture-caused problems (insects, mildew). If there's 8" clear under the joists, that should be ok. If you want the surface of the deck to be 8" up, then you'll have virtually no real clearance/ventilation, so I wouldn't go that way.

How steep is the slope? If it's steep, then the outside of the deck would be much higher off the ground, and that would give you enough ventilation. If the deepest it gets is 8" then I'd level it out and pour a patio.

8" is lower than I would go. The area is about 15 inches on one side to 40 inches on the other. This spans about 18 feet.
My consideration is a step down deck rather than one going evenly across, and stairs. I have a faucet that I would prefer not to move or raise.

Thank you for the information. (a crude drawing included)

15-40" off the ground is fine.

Thanks!

Keep it high. Build some storage bins underneath to stash junk.

Thank you OldFixer, but I prefer to be rid of "junk" :)

We had two decks in our back yard connected with boards like a bridge and it was built around existing trees. It was as low as we could go. One place I could put bricks to keep opossums out other place is was touching the ground.

Beware of treated wood. The previous treated board had arsenic in it and it was dangerous to children. They stopped using it, don't know what it is treated with now. I would use red wood if possible, ours was redwood.

This post was edited by EmmaR on Sat, Jul 12, 14 at 16:06

Very nice EmmaR! I like the lush feeling and pond.

I have a treated wood deck that is 20 yrs old; I don't know if I could afford to replace it with the additional deck. Something to definitely check into!

Thank you............

You need to be careful of the deck if treated wood was used. They don't make it anymore. Kids are more vulnerable than adults plus they sit on it and crawl around on it. Yours may have arsenic in it. The instruction when handling it was to wear gloves when touching it. They can't use arsenic anymore.

"You need to be careful of the deck if treated wood was used. They don't make it anymore. "

????
http://www.familyhandyman.com/decks/comparing-deck-wood-cedar-pressure-treated-wood-composite-decking/view-all

Here is a link that might be useful: decking

Pressure treated wood is most definitely still available. They have stopped producing CCA pressure treated and moved on to another chemical that the name escapes me of at the moment. This new material is allegedly safe (but CCA was considered safe at one time as well).

I would put a heavy black poly on the ground and cover that with pea gravel or other small stone. In all likelihood you will not be going under there, but a little careful ground prep is nice. In a pinch, you can look and see what is going on under the deck.

Thank you millworkman and Jackfre.