building a deck on a retaining wall, and other advice

bubblahMay 28, 2011

I've got house on a sloped lot, it slopes down from the front yard toward the back.

The basement has a full-size door that walks out into an area underneath the back deck.

The walk out area under the deck is lower then the immediate surrounding area, ideally the sides should be built up a bit to keep water flowing away from the walk out, but the place hasn't been cared for in years, so currently they slope quite a bit into the walk out under the deck, as a result during heavy rainfall that area can get very saturated, particularly if the water table is high. The dirt level is only about an inch or two below the door sill, so that can lead to water flowing into the basement under the door! :( The water does get into the ground, so I'm sure it's just a matter of expanding the area and keeping the whole level lower then the door sill.

The deck itself is positively trashed and ready to fall down... I wouldn't be surprised if it's the original from 1950 when the house was built, it's /that/ bad.

Long story short, what I'd like to do is replace the deck with one that is about 50% larger, ideally I'd like to build 3 retaining walls so that I expand the walk out area under the deck and have the deck posts supported on the wall, like a foundation. On one side, probably either left or right, I'd have steps built into the retaining wall to lead from the yard to the walk out.

I'd like to lower the level of the "finished surface" in the walk out area by a couple of inches, so that it's about 3-4" below the current door sill plate. I'm thinking the "finished surface" would either be compacted gravel (2-3") or a highly permeable paver. That would give me about 5-7" from the bottom of the sill to dirt, so hopefully that will help resolve the water issue.

My questions are--

- Any thoughts on this plan, things I should look out for, or that I might be overlooking?

- Can a retaining wall be build such that is acts a support for the deck?

- Around here the footings for the deck must be 4' below grade, so that does mean that my footings need to be 4' below the level of the finished surface in the walk out?

- Would I just be better off having block wall (CMU) foundation walls built and then putting up some sort of a stone veneer and cap to make the visible parts more attractive?

I'm planning to have the excavation and wall down professionally, right now I'm trying to research what is best, what to watch out for, etc... I'll be working with a professional carpenter (friend) that I'm hiring to build the deck on top--I think that will be a "no brainer" once we have the retaining wall in place, I'm not looking for anything too fancy, just a typically rectangular deck. Of course I'd work my friend to plans together ahead of time to coordinate the location of supports for posts...

Forgive what an eyesore I have back there :), I'm hoping expanding the walk out will give me a better place to store the trash barrel, and I'm going to be building a shed to store the rest... I've also since repaired the bare spots on the lawn... as a I said, this place hasn't been cared for in years...

The sump pump discharge is another thing I need to figure what I can do with... the back of my lot is the low level for the neighborhood, so there's no way to bury the pipe and lead it elsewhere. My town has a storm sewer system, for an expensive fee I may be able to plumb it (and my gutters) into that.


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That deck's got a boatload of code violations (from today's code, at least) and should be reconstructed. I'm with you there.

If it were me, I'd put 2 retaining walls even with both sides of the house and extending away from it, to "box in" the basement level area and eliminate any directing of water towards the basement door. Grade the slope slightly away from the house.

Then you've got a nice big flat space to work with. Dig holes and pour footings for the deck posts (yes, 4' footings mean 4' below ground level--it has to do with frost lines), and build from there. I don't see any big savings by trying to incorporate post supports into the retaining walls.

I'd probably expand the deck to at least 2x of what it is now. It doesn't add that much cost to it once you've got things started, especially if you're DIY-ing it.

And I'd move the stairs to the side furthest from the house so they don't block the basement window.

    Bookmark   May 31, 2011 at 10:42PM
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Hi Weedy,

Thanks for the reply--

We currently don't even walk on the deck, the beams meeting at the outside-left corner have completely rotted away and not supported by the posts... I swear it's inertia and friction holding the thing up this point...

I like your idea of having just two retaining walls and leveling out the area, the trouble is that the lowest spot in my yard is not quite as low as I'd like the area under the deck to be, meaning in order to water away from the house I'd have to either build a retaining wall there or build up a small mound to provide grade. This is why I was thinking of building retaining walls on 3 sides to box in the whole area under the deck while incorporating a set of steps into one of the walls (probably right side) to keep access.

For the footings, I figured I needed to 4' lower then the lowest point around me, just wanted to hear another opinion... this a lot of digging!!

Regarding posts and retaining walls... my idea was that the footprint of the deck is exactly the same as the retaining wall--so are you suggesting making the deck larger then the footprint of the retaining wall, meaning the posts are set "outside" of the retaining wall? or smaller? I wasn't really expecting to gain much by incorporating posts into the retaining wall, just trying to maximize my space under the deck for storage.

Currently the deck is about even w/ the window on the right side, and off by only a couple of feet on the other, so expanding the deck parallel w/ the house could only grow by 2-3' before it starts to overhang the windows (I think it's 8' now, so it could grow to maybe 10')... I could certainly grow the deck perpendicular to the house, that might be the best option, that would also allow me have more of the deck in the sun which would be nice.

I'm doing a a "hybrid DIY" on the build, I'll be hiring a family friend who is a professional carpenter, so I do have hourly costs associated with the build, but all the same I'd still rather spend more now to get a better build :)

Ideally I'll be getting "serious" around July 1st, applying for the permits, taking down the old deck, etc...

    Bookmark   June 1, 2011 at 4:49PM
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"I'd like the area under the deck to be, meaning in order to water away from the house I'd have to either build a retaining wall there or build up a small mound to provide grade."

I was just thinking... one option here could be a very short retaining wall on the "long" side of the deck, maybe only about 12-15" high with a step inside as well... so from the yard you'd walk up a gentle slope to that wall, then there would be just one step down into the lower area.

That would allow just the two retaining walls, and depending on whether I needed posts on the short sides I might not need to worry about incorporating them into a retaining wall at all.

    Bookmark   June 1, 2011 at 5:02PM
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Here's what I envisioned.

If you can't grade the slope away from the house forever, at some point it starts sloping back up (or has a step or retaining wall), but not until it's far enough away from the house that it won't get into the basement. That's not a problem. Just slope down until you're past the deck/patio area.

BTW, we helped a friend redo their deck of similar construction and vintage. It was about 10x10, a bit wobbly, and when we removed the single tapcon screw holding it to the brick, it collapsed.

We got from before to after (photos below) in a day. (We had to come back the next weekend for a couple hours to finish up the stair handrails). If you're organized and have a good advisor, you should be able to knock it out quickly. Obviously you've got to do some grading and wall-building first, but the deck construction can go pretty quickly.

    Bookmark   June 2, 2011 at 5:08PM
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I'd never even considered the retaining walls out at the corners of the house, that certainly gives me something to think about!

Looks like a nice deck you put up!

My adviser is a veteran carpenter, I've personally seen work he's done for those who recommended him, they all say the same thing "It's built to last forever", so I'm lucky, but also worried because I only have one shot to get it right on the design :^D

    Bookmark   June 3, 2011 at 5:11PM
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I think it's just asking for future problems if you add a wall and keep the space around the door lower than the surrounding area. I suppose you could put in a drain and pipe it (and the sump pump output to the back of the yard to a dry pond or something.

If the door isn't needed for emergency egress you could just eliminate it. Or replace it with a bulkhead door.

But I like weedy's retaining wall idea better. Maybe you could get by with just the wall on the right side? And you might consider extending the deck a little and putting the stairs down to the top of the right wall - you'd need a shorter set of steps that way.

Just a couple more ideas.

    Bookmark   June 5, 2011 at 9:11AM
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