Backfilling basement of demo'd brick "rowhome"; Foundation Drain

[Ben29]

I am working with a an old commercial building (circa 1900) with exterior brick bearing walls. The adjacent building was recently demolished. The buildings were abutting each other, but they did not have a shared party wall. It appears that each building had a minimum 3-wythe thick (~13" thick) brick bearing wall, and those walls abutted.

Each building has a basement. The plan is to repair and parge the remaining brick wall and backfill the demolished building's basement.

The city has a specification for repairing brick rowhomes in a similar condition. I noticed that the specs do not require a foundation drain. I want a foundation drain, but I don't know where to tie it in to.

The city specs say to tie the new CMU block wall into the remaining brick wall with heli-ties above and below the 1st floor. I'm not sure if this is the right move.

 

[Ben29]

 

[JAE]

Here's a few of my comments on this:

1. The ties to the existing brick provide for what? I don't see a need as the backfill soil will always be pushing the new block wall into the existing wall.
I suppose there's a need for some type of positive connection but that would be it's only purpose.

2. The 45 degree sloped concrete wash will NOT provide a water tight condition. That concrete will crack and also probably shrink or move away from the existing brick wall causing all sorts of avenues for water to get down between your block wall and brick - further exposing the brick to moisture infiltration. I would think that a true waterproofing flashing of some sort would be preferred here - using a reglet or some type of band attachment along the brick. Then flash over your block wall with a drip.

3. I would think that the base of your block wall (the new footing) would want to be aligned such that the horizontal thrust of the wall would be directly taken into the interior basement floor slab. Having it above the floor would risk shearing the brick sideways if your footing was above the slab.

4. You could consider moving the vertical rebar from the center of the block to the inside a bit to provide more strength but that may not be necessary depending on the earth load and wall height.

5. Can you actually build a new block wall as shown there with respect to the property line? Usually the property line is located at the outside face of your existing brick wall. Wouldn't this block wall be on your neighbor's property?

 

[RPGs]

Nothing like some good ol' Bawlmer rowhome fun.

What are your concerns with the helical ties? I agree with JAE it is likely just a nominal positive connection.

To me, it makes sense that the city doesn't specify a foundation drain on their typical rowhome demo details--I can imagine how badly requiring foundation drains there would hang up their permit department and trigger liability issues for getting them drained properly, considering the insane variety and condition of the rowhomes and properties.

Well if you can't daylight the foundation drain somewhere reasonable then you'll have to get it to a sump inside your basement and pump it out somewhere (likely back on the same property). If power goes out, you've given the water a nice way to flood the basement and negate that nice new waterproofing membrane along the foundation wall. Excluding some severe groundwater flow, I would probably think you're better off focusing on good surficial stormwater management where you can control it.

 

[Ben29]

JAE,
Thank you for the thoughtful, thorough response. Regarding your point #5: Technically, "my building" is the one they demolished, so we are all good regarding the property line.

FWIW - the city is working off of a "new weather wall specification" and this is the first time they are trying to implement it. The old wall specification did not specify a positive anchorage (ala heli-anchors) to the remaining brick wall.