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bubbler 08-16-2011 08:20 AM

foundation walls to support a deck
I could have sworn I posted on this topic here a while back, but I don't see it listed in my threads, so I'll ask again.

I have an 8x14 deck on the back of my house. Under the deck is a walk out area from the basement. I think at one point there may have been retaining walls defining the size of the walk out, but they are long since gone, and so now it's just some small mounds of dirt forming little hills. The result is that the ground from the peaks of these hills just sort of slopes into the walk out area. The walk out was also paved with concrete which was then covered by an inch or so of dirt as it washed down there during rains. The unfortunate result is that the walk out would flood during heavy/prolonged rain, the water would rise above the threshold of the basement door and enter the basement (which is unfinished and does have a sump pump, but it still sucks).

My temporary solution has been to break up the concrete and dig out the area another 2-3"... now the rain water soaks into the ground more easily, and there is a larger volume to fill before the water would hit the threshold of the door.

Here's a picture of the area--

As you can see from the left side of the pic above the front yard is considerably higher then the back, I'd say at least 6'. The right side of the pic shows the driveway which is also higher.

Here's a sketch of the current deck:

In the pic above the steps are on the left and the red dots represent the existing support posts.

I'm getting ready to replace the deck and I'm considering my options.

What I'd like to do is expand the deck from 8x14 to 14x15 and to also make the walk area very well defined, with 2-3' tall walls, so that I can use it for storing some things like lawn furniture, snow blower, etc. I'd also like to incorporate some steps into one of the walls to make it easier to get in out.

Here's a sketch--

the dashed line is just for reference, it doesn't represent anything other then the approx. location and size of the old deck compared to the new one. The red posts are also placed approx. where I feel they will need to be for the new deck, I am not re-using anything from the old deck.

btw, the width of the steps in my sketch are not to scale, they'd be 7-8' wide if they were :) I'm looking for normal width steps, like 30-36" or so.

So what I'm thinking is that I could have a foundation/masonry contractor come in to dig footings and pour a my 14x15 foundation (but only 3 walls since I already have the house wall). One wall would incorporate some concrete steps as shown--the steps will lead down into the walk out area. The walls would be about 3' tall (whatever is necessary to clear the highest point of nearby ground, while also being up to code for accessing the steps down to the walk out area)

In my shot above I also show where support posts for the new deck could sit on the foundation wall. I put one in the "center", if needed that would just be a typical 7-8' post set onto a sonotube footing that ends about ground level. I have a professional carpenter I've used for other projects, we talked about building this deck, but I haven't shared these plans yet. He may have some ideas for how that center support post could be eliminated (I am assuming because I have a 14' span I'd need split the joists and put another beam in the center). For the house side, I figure I can either attach to a ledger (as the current deck is) or have some posts put in so that the deck is floating (I may need a 3rd post in the center at the house as well in the case)

The walk out will be dug down about 8-10" below the threshold of the the current basement door and about 3-4" of gravel added as a "finish" surface. The idea here being that now I have a well draining area that hopefully won't flood. As a back up I'm considering digging a sump hole in one of the far corners (maybe corner where the steps lead up to the deck), so that in the even of an extremely high water table event (happens in our area), or super heavy rain, I can have some means of "bailing out" the area if necessary.

What I'm hoping I can get some help from you folks with is--

1) Does this seem like a reasonable plan, or is this ridiculous overkill and I should explore other options?

2) Can anyone give me a ballpark for what I might pay to have the 14x15 foundation put in by a contractor? I'm in MA, so our freeze depth is 4', so I'd need 4' deep footer, plus the walls would be 3' or so themselves.

3) Is there an easier way to do this that I'm missing? I thought about just building a retaining wall myself from the stack-able blocks, but they all seem to have a max height of 2-3', so I'd be at or beyond the max heights. I also am not sure how I could incorporate the supports for the deck that way--I'd need to have sonotube footings either inside or outside the retaining wall perimeter... I suppose it could work, I'm just not sure if at the end of the day it will be any better/easier/cheaper then having someone put in cement walls (or a CMU wall).

bubbler 04-12-2012 03:27 PM


Dug out the area behind the house to form a ~22' long walk around space that extends about 10' out from the house. The retaining wall on the "left" side is about 3' high and the one on the "right" side is about 4' high. The one at the back is only about 1' at it's lowest and 2' at it's highest.

There are (3) 12" footings holding up the deck, and there are an additional (2) 12" footings holding up the 4'x5' platform that two sets of steps lead off.

The (3) deck footings are located inside the "walk out" area formed by the retaining walls. The (2) platform footings are on the other side of the retaining wall.

It was done with permits and inspections, so the town--which uses the 2009 IRC Deck Building Guide as their code--was happy with the setup.

It's cedar decking w/ PT for everything else.

I still need to grade around the retaining walls, and I probably will add a 4x6 landscape timber on the "long" side of the stairs as I intend to fill the area under there with additional crushed stone (the walk out area is 3-4" of crushed stone).

The overall size of the deck is now 14'L x 12'D deep, not including the platform for the stair landing. The original deck was 14'L x 8'D.

This is an unbelievable massive improvement over what I had, which was basically falling down and unsafe to be on (had to have company be out on the lawn and exit from front door because I was too worried about having *anyone* on that old deck)

I'd like to say that I did it myself, but I ended up hiring a contractor... my life/work schedules, not to mention my back, made hiring seem like a much smarter idea. I shopped around, this guy I ultimately went with was willing to to do 50% more work for 50% less money then everyone else, he was not what I would call a savvy business man (which the other guys seemed to be), but I could tell from his portfolio of other work that he knew what he was doing (he had a photo album of the dozens of other decks he's built).

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