Exterior wall on concrete pad - waterproofing under wall? (Illustration included)

JustADoc

One exterior wall of our home separates our den from an exterior patio - the den and the patio share the same continuous concrete slab. We are currently rebuilding this exterior wall. Illustration below:



What goes between the bottom plate and the concrete pad in terms of waterproofing? How do we keep any water from passing under the exterior sheathing layers, under the bottom plate, and into our home? Remember, they share the same concrete pad, so there's nothing stopping it should it end up on the patio.

I'm sure this is elementary but I've never built a wall separating the interior and exterior in which the elevations are the same on each side.

Thanks ahead of time!

AndyGump

I think you have a serious mess there.
Do you know if there is even a footing under the "exterior" wall?

Perhaps the wall of the "porch" was intended to be the exterior wall?

What is your average grade height?

Andy.

Joe Carola

How can that be? Was the den an addition and just built on top of the patio?

Is there a footing underneath that patio to support the wall and roof?

If there is a footing supporting the wall, you should cut the bottom of the studs across the length of the den and add a row of 8" block because nothing will be full proof to stop water from getting underneath the wall. You're supposed to have 6-8" above grade and slab to the framing. Whether it's a slab, grass or dirt, your slab is now grade height.

That's because no one is supposed to to that. Did you buy the house this way?

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Joe Carola

JustADoc

Andy, thanks for your quick reply.

The wall opposite the one in question was originally the exterior wall of this home (circa 1970ish) and the entire concrete slab was an exterior patio. If you look in the leftmost side of the photo below you'll see an exterior corner - the wall at that corner was the exterior. Everything to the right was an addition. At some point, the previous owner made the decision to convert that portion of the concrete slab into a den that you step down into. The rest of the home has traditional footers and floor joists on an earthen foundation and thus sits off the level of this pad. However, this den shares the same height.

We do not see any obvious signs that they poured footers for the wall. However, the wall bears very little load. It's parallel with the ceiling joists/trusses and has nothing above it but the roof. Said roof extends to both sides and is supported in each corner. Essentially, this wall splits the span in half. See below, wall highlighted in red. It has been this way for roughly 40 years and there's no signs structurally of any damage. The structural engineer signed off on the second story balcony (which also needs to be replaced) so we assume it was structurally sound enough for that. Of course, the balcony too needs to be replaced.

In terms of this wall, we're just undoing the effects of water damage over the years due to poor drainage (which is in the process of being corrected concurrently). The bottom plate was not PT lumber and thus needs to be replaced. The bottom foot or so of wall sheathing is also damaged. In replacing the wall sheathing (hematote or something like it) with CDX we want to try to make it as water tight as possible. The only house wrap on this wall is a very light tar paper.





From the front of our home to the drainage ditch along the front of our property we have about an 8 inch drop to the bottom of the ditch. That's across about 40'. That's one source of our troubles in doing anything - we have no grade to work with. We also cannot built up the foundation around the home because as you can tell in the photo above there's nothing to work with - we would have to pile dirt up against our home.

We just make do and will be utilizing sump pumps where we can to overcome grade obstacles.

The current battle, however, is this wall... just not sure if we silicone under the baseplate or what in order to make it as watertight as possible from the outside elements. That doesn't seem like enough.

This photo is with the carpet pulled up and before a new door was installed. We're not removing this old tile - it's in decent shape and contains asbestos so we're just going to tile over it. As you can see the elevation between the exterior and interior is the same.

JustADoc

My parents bought the home in the mid 1980s and had the second story added later on. One issue all along was that the home should have been built about three blocks higher to allow for more grade. The other was that half-effort construction caused a lot of problems. That's what we're in the process of trying to undo.

For the first fifteen years or so they never had any issues with water getting into this room. Occasionally a little water would get under the door to this den in a very strong storm, but it was rare. Erosion and new construction on the hill behind us changed that. That, compounded with terrible yard drainage, has flooded her five times this year with about an inch of water under the door. The source of the water, however, was water backing up a PVC drain on the patio and that entire PVC drainage system has been replaced and a backflow installed. I don't consider it a permanent fix and will be putting a channel drain in soon with a sump pump basin as a collection point to pump it above grade.

Literally all of the homes in the neighborhood are this way. Everyone, over the years, has dealt with this same issue. I suppose it's her turn.

In terms of framing, the wall is built like an exterior wall should be, it's just old materials that need updating. It would probably be possible to lay a course or two (or more) of block as a base (edit: for the walls) for this entire room if need be. Would that be the easiest solution in the long-run?

JustADoc

One other note as this has been suggested once before. As I said, you step down into this room, and there is also a 1 foot difference in ceiling height. from the rest of the home to this room. Of course, this means that we cannot possibly build a floor joist system in this room and raise the ceiling height without raising the roof. That would, ultimately, be the true fix all of the problems I'm sure.

kwikfishron

Other than reworking the concrete and raising the bottom of the wall you could add stainless steel flashing along the base seated into a bed of polyurethane caulk. That along with the channel drain that should solve the water problem.

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JustADoc

Had a guy who is a contractor with a long background in masonry over today for an estimate. He made some good suggestions and I wanted to get an opinion on his plan from you guys.

He suggests we basically rebuild the walls of this room by placing a course of blocks two runs high around the entire outward facing perimeter. This course of block would become the foundation for the walls. This would basically raise the wood a minimum of 16" off the ground and it would never be directly exposed to standing water. He wants to seal this entire run in UGL DryLok coating to help with waterproofing. The blocks would be filled with cement and screeded to give a level surface on top of the block run. The stud walls would be rebuilt on top of the block just as they are current built on top of the pad. The wall isn't load bearing but he said he would still brace it with 4x4 posts as he works to hold any weight it might support.

Additionally, since there will eventually either be a picture window or two side-by-sides in this room and it will never be a room anyone sleeps in, he suggests we lose the door. It's not possible to raise the door 16" from the pad without having to have a trip hazard and it will always be a point of water infiltration. We're OK with this and had discussed it as a possibility before he recommended it.

On the inside, we would just rebuild the walls and replace the insulation and drywall. Working with the 16" of block at the bottom will make it a pain to do drywall and molding but we'll manage. On the outside, we can replace the sheething, add Tyvek (which isn't there currently), and either cover the wall in brick, stone veneer, siding, or a combination thereof.

So, the essence of his recommendations was that we cannot do anything to change the fact that the inside and outside share the same concrete pad and thus the same elevation. However, if we axe the door, and give the exterior walls a 16" tall block foundation for the walls with DryLok it will likely waterproof the room entirely.

Logically, it makes sense. The question for you guys is whether or not logic is right?

JustADoc

Thanks a million for your illustration, Ron! I didn't even notice your changes to the photo at first. That's nearly exactly what I initially wanted to do and we still haven't scratched that idea.

Give me your opinion on the block idea just posted that we received today. I value your input greatly.

kwikfishron

We’ll let the concrete guys weigh in on the proper methods for your proposed foundation.

I will say though I don’t understand the point of the second row of block.

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JustADoc

Simply height, I gathered, to place the base plate and studs 16" above the patio surface (aka water) vs 8". I asked the same question. He didn't want to place wall sheathing over the block because of the potential for it to just rot again 10 years down the road. I don't see any reason to either. So, the first sign of wood would be 16" off the surface.

Whatever finish surface we decided on - brick or stone veneer - would be adhered directly to the block runs on the exterior.

AGWhitehouse

I 100% agree with this approach. Can't remember where you are (geographically) but in Connecticut code requires a min. 8" seperation between exterior grade and any wood for termite and moisture protection. You found out what moisture can do over time...

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JustADoc

It's the most logical plan we've been presented with yet. We're going to go with it pending code approval.

No doubt about that. I removed a section of the baseplate with a gloved hand and sucked it up with a shop vac if that tells you anything!