Footing for deck on slope with one side near grade

The big drawback is that your footings aren't done right or don't hold up well and you have a deck that slants a little compared to the house. You could end up with a little dip or a lip when you walk out the door. This may take one year or 30 years or 100 years. If you don't have a ledger it will happen. If you are building on very solid ground maybe your concerns aren't as bad but eventually these two things will look like they don't belong together.

Builders like doing it this way because as long as the footings are good the deck should generally stay where it is compared to the house for a few years. Also what do you do if your deck is slanted 5 degrees or is pulled out from your house an inch or two. I really doubt there is a monetary remedy for slight frustration. And the flip side for builders is attaching. Messing up your structure or allowing water into your structure is not only very quantifiable but could also come back to hunt them soon after a build. So $$$ will dictate that a builder wouldn't attach to your house if it were their choice - especially if they are subcontracting it out.

Flashing a house for the ledger isn't rocket science. There should actually be flashing under and over the ledger. I have helped put up 5-6 decks, always used a ledger and never heard anyone have water issues. And these were just all put together neighborhood style - no pros. I can't imagine not using a ledge unless the deck was only a foot or two off the ground.

For your situation I could see going either way. The fact that you are going through concrete is actually good for waterproofing - concrete doesn't rot if you have an issue. But I do understand that you want it to be easy and without a window or door it would have to really go off course to look wrong.

1. It is a little small, but yes you can support a 6x6 post on a 10" diameter concrete pedestal. However, any steel hardware you embed in the concrete to attach to the post needs to have proper clearance from the edge of the concrete. Code requires 2" clearance. Something like a Simpson PBS66 would work. Make sure you consolidate the concrete well, so you don't get voids around the top of your pedestal. Also, slope the top of the concrete slightly away from the base of the post.

2. Not sure what the "BigFoot System" is, but to determine your footing capacity determine the area at the bottom of the footing (in square feet) and multiple that by your allowable bearing pressure. You stated you are using 2000psf allowable bearing, which seems reasonable for a footing bearing 48" below grade on sandy soil. If your footing is 25" by 25" your allowable bearing capacity would be 8,680 pounds. You then calculate your post load, which must be less than your capacity. To calculate your post load, first determine the tributary area to the post. This is simply 1/2 the joist length on each side of the post times 1/2 the beam length on each side of the post. Since at your maximum loaded post the joists and the beam span the same amount on each side of the post, the maximum tributary area is 7' times 4.6', or 32.2 sq. ft. The uniform load on your deck is the dead load plus the live load, or the dead load plus the snow load. The dead load is the weight of the lumber, and 10psf is a conservative value. The code required live load for a residential deck is 40 psf. I don't know where your live or what your snow load is, but you could call your local building department to find out. Considering dead plus live load, your maximum post load is (10psf + 40psf) x 32.2 sq. ft. = 1,610 pounds.

My suggestion would be to only have five footings in each row. They would be spaced 5'-9" apart. Not sure what kind of wood you are using, but your double 2x8's should be strong enough.

The code also requires special attention for the attachment of guardrails to the deck and for the attachment of the deck to the house. Check out Simpson's DTT2Z and DPTZ.

This is actually a fairly complicated problem, so consider having somebody review your final plan.