One somewhat worrisome thing was the downspout at the rear of the house,
that brings all the shed-dormer roof runoff out to one of the drainage
pits. The lowest junction is right by part of the foundation wall, and if
that particular bend were to become disconnected then all that water would
dump on the ground right by the wall and probably find its way into the
basement fairly easily.
It's the same lower bend that received the "silencer" under the two-story drop, and is held together by several zip-screws *and* meta-supported by suitable blocks underneath the horizontal run. It had already been observed to leak a little and I wanted something besides a little sketchy grade adjustment in dirt to make sure any water landing in that area would be positively directed away. Waterproofing the wall itself is NOT an option because of the impermeable foam insulation on the inside, thus the only way soil moisture rising from capillary action can dry is outward. Sealing the wall, even over a limited stretch, would likely spell slow doom for the ungasketed sill area on top of it and besides, such treatment would have to also continue substantially below grade since freely infiltrating water would be right next to it all the way down. The right answer was to make sure the water went elsewhere.
The solution would also have to integrate with, or at least not interfere with, the splash dissipation system under the gutterless cheekwall-roof ends -- simply an area of half-inch angular stone laid directly on the ground, which was already starting to get overgrown with stuff poking through it and thus needed a bit of rework. So it was time to re-engineer this entire area and accomodate the two relevant drainage systems going through it in a more robust fashion.
A secondary protection system could conceivably be all above ground, and thus commeasurately ugly. My long downspout extensions and their reclaimed-flue-pipe anchoring system were already somewhat "industrial" looking, and even though the soil right next to the house generally stays too dry to support plant life I wanted to at least give some form of ground cover a fighting chance to grow in and build some token amount of green stuff toward the wall.
[Images are linked to larger versions.]
|The plan was to carve out a slanted area under the elbow on which an impermeable layer would sit, extending from the foundation wall downward and outward, starting only an inch or two under final-grade dirt. Excavation was slow, because 1> I was finding a lot of rocks and obsessively saving certain sizes thereof aside, and 2> I kept running into some fairly tough roots. I couldn't simply pull some of those up without having my hole suddenly wind up fifteen feet long in some random direction across the yard, so the answer was to just chop 'em back. If these had come from the nearest pine, they had run impressively far to get over here.|
|Exposing a little more of the wall showed that it actually *has* some semblance of damp-proofing on it, albeit 1956-vintage and in fairly sketchy shape by now. About what I expected when making guesses as to its condition in part 01 of the main retrofit writeup. No worries, really; the basement is pretty dry especially after all the air-sealing on the interior insulation job, and the minor humidity it gets probably comes up through the slab.|
|The drain-plane would be this old bit of aluminum flashing, which had last served to help protect the head of the basement-bulkhead [visible in the main writeup at the end of part 06]. It had since been lying on the ground under a small pile of junk wood for about two years, but was still entirely serviceable with only a couple of small screw holes to patch up. I ran doubled layers of aluminum tape along the top to serve as a somewhat more flexible leading edge, that would self-align closely against the cinderblock once dirt went in on top of it.|
The idea here certainly isn't new -- there are some nicely detailed
precedents in articles over at
Green Building Advisor [where it's an "underground roof" instead], and
all presumably stemming from Bill Rose's
original article[PDF, 1.2 Mb]
While the primary intent is water management, some new energy-efficient construction might use a layer of 2" or so foam insulation set at a similar angle but run out six or eight feet from the foundation all the way around the perimeter, forming an insulated underground "umbrella" to both deflect drainage water and also insulate a much larger volume of earth around the building envelope against seasonal temperature changes and frost penetration. As tempting as such a project might be for this place, it's far more digging than I'm up for at the moment and of dubious value while the block wall itself is still open to the cold air.
I also didn't bother connecting the upper edge to the wall, figuring that packed earth right along there would be enough of a retainer.
At the bottom would be a bit of space to interface to that lovely
sandy permeable subsoil, which a layer of 1-inch or so stone would
help hold open to allow better water flow. I also stabbed a bunch
of channels into the outer corner of the hole with the end of the crowbar,
just to loosen that soil up a little. I wasn't building a major
drywell here, just somewhere for stray infiltration to go.
Almost all the stone used was what I'd just recovered out of the digging and a little extra from an existing cache across the yard, so I didn't have to go buy any rocks for this at all. Separating out the stone was a little fiddly and OCD, but worthwhile for such a small volume.
Filter cloth went down over all that, and as I started working backfill
up on top of it I also continued building a thin layer of stone on top
of the flashing. This would create a narrow but very permeable slot
right on top of the aluminum, making sure any water reaching that level
would immediately run *outward*.
I ended the stone layer about three inches from the foundation wall and the filter-cloth came down over it all to meet the aluminum, thus closing off the head of the slot away from the wall itself. The idea was that solid-tamped earth would be against the top edge of the aluminum and the wall itself to help seal everything, but incoming water from a compromised downspout would readily find the top of the drainage slot and head away.
It was a comforting theory, anyway.
The rest of the backfilling was pretty straightforward and doesn't really
need more detail; but I didn't bring everything back up to grade just
yet. I wanted to rework the splash catcher in a more elegant fashion,
and left enough of a pit to sink another thin bed of rocks and then a gentle
"vee" of bricks right in the same area under the cheekwall roof end.
The splash-dissipation stone would sit on top of that instead of the dirt,
somewhat better contained against being scattered away and protected
against weeds growing up through the middle of it. Small gaps
between the bricks would let the caught water escape down into the soil.
We couldn't possibly imagine where the idea of bricks held slightly apart as a drainage component came from, now could we...
|The finished area, now embodying three distinct drainage systems in one picture although one is now hidden under the surface. When beginning all this I had recovered and cleaned most of the half-inch stone from the original splash bed, and restoring that into the new brick-supported structure used somewhat less so I had a healthy amount left over. Overall this would likely be a much lower-maintenance system than what was down here before.|
|A few months later I finally got around to reworking the splash pad under the other cheekwall, which was similarly beginning to disappear under random plant growth. Work began with collecting and cleaning off the existing stone, this time made easier with a temporary sieve from 1/4" mesh hardware cloth. The relevant catch area was re-eyeballed relative to the roofline and carved into the ground with fairly sharp edges, trying to disturb as little of the surrounding soil as possible.|
|Since this side wasn't backed up by the underground flashing I wanted to engineer it a little more as a real drainage structure, to guide water away from the wall as much as possible. Again, many of the rocks shoveled out with the fill were re-used to start building a deeper channel on the side away from the house, and I wanted to try and use up various other little collections of stone still kicking around to make it all as permeable as possible toward that side. I started with a thin layer of loose sand recovered from winter road treatment [the grey stuff], to help buffer the lowest stone against the subsoil. Again, standard approach of larger rocks down below, decreasing in size as things worked upward.|
|That's harder to do when limited supplies are on hand, unless one is intimately familiar with estimating compacted volumes of stone. I had a modest pile of the 3/4" angular stone left over from the pavers job for the mid-layer, but after laying all of that in I realized that the level was still too low. I pulled most of it back out and added more larger rock underneath, and bermed in more of the upstream-side volume with less permeable fill dirt to encourage water to head for the low side of the trench.|
Eventually I had a reasonable bedding layer, using part of the recovered
1/2" stone to make leveling easier, and started laying the bricks in.
They got thumped down pretty firmly, to make sure all the stuff underneath
got reasonably compacted now so it wouldn't settle too much more later.
The green arrow points to one critical feature: small stones wedged into the triangle between the bricks, to keep the inner ends just slightly apart and ensure drainage along the centerline of the layout.
|The remainder of the 1/2" stone conveniently re-filled the pad -- done! Quite a bit of fill dirt was left over, which simply went onto the mound toward the back of the yard. An ongoing low-level project would be to screen more grades of stone out of it, but for now I figured I was finished messing with drainage bed construction for a while.|