Exterior Concrete Slab Pour over Living Space below

[tbz]

So a little out of my comfort zone here, working on research for an exterior concrete slab deck off the side of the home over living space below and can't seem to find any information on any forums or even books on how the details should be done.

The home has a brick ledge on 2 sides, one side 8ft the other side 16ft, the other sides will be block walls. The thought is to run Steel pans from the brick ledge over the front wall.

This is an 8ft run, the concern is the flashing of the masonry to seal at the masonry face at the brick ledge and over the top of the lower walls.

Just looking for a pointer to another location or source book for these types of details.

Thanks

 

[Paul Sweet]

The couple times I did a slab over a finished space I detailed the top of slab several inches below the finished floor above, rigid insulation on top of the slab (this might not be practical with the insane R values in the new energy codes), an EPDM membrane, 2" of gravel to allow water that penetrated the finish porch floor to get to the drains, a mortar bed, then the tile or stone porch flooring. The membrane should be turned up several inches above the porch floor and extended all the way to the outside of the masonry.

 

[Wstubbs]

https://www.jlconline.com/how-to/foundations/concrete-slab-over-living-space_o

 

[tbz]

Thank you both, but everything I am finding is for interior CC floors over living space, this detail might help explain.

The room will be un-heated, more of a root cellar than living space. But insulating under the concrete deck would not be an issue for it will be unfinished space.

The sketch in detail #1 is a plan view, this is a cut view, hope it helps explain the questions on the details for water proofing/sealing.

 

[walker.t]

The sketch in detail #1 is a plan view, this is a cut view, hope it helps explain the questions on the details for water proofing/sealing.

Please confirm my understanding of what you’re trying to do:



1. Concrete walls on two side, there is a haunch cast in both walls to serve as a brick ledge.
2. Brick not shown on your detail, presumably this would bear on the concrete slab forming the roof of the basement “root cellar.”
3. Floor framing to bear on plate shown on the concrete wall.
4. Concrete deck sloped to drain, I didn’t show the metal decking below the slab.
5. Two block walls at perimeter, these are retaining grade.

Please clarify these items:
1. Your original post says that the two outside walls are block, your detail shows one of these walls and shows it as concrete, which is it?
2. What are the blue areas in the two walls cut in your section?
3. You show a sloped surface on the slab, is your intention to have a flat surface of some kind installed over that?
5. Assuming the opening you show on your plan is a door, what’s the vertical distance from the door threshold to the top of grade?
6. If this is new construction, why are you using block instead of using concrete for all the sub-grade walls?

 

[tbz]

Please confirm my understanding of what you’re trying to do:

1. Concrete walls on two side, there is a haunch cast in both walls to serve as a brick ledge.

The brick ledge is just there to hold the slab, no brick face, vertical siding

2. Brick not shown on your detail, presumably this would bear on the concrete slab forming the roof of the basement “root cellar.”

Again no brick

3. Floor framing to bear on plate shown on the concrete wall.

Superior Walls - Noted block out of habit, my bad.

4. Concrete deck sloped to drain, I didn’t show the metal decking below the slab.

Yep the intent

5. Two block walls at perimeter, these are retaining grade.

They will be inground

Please clarify these items:
1. Your original post says that the two outside walls are block, your detail shows one of these walls and shows it as concrete, which is it?

Superior Pre-Fab Walls (Concrete)

2. What are the blue areas in the two walls cut in your section?

Insulation in the pre-fab walls (Manufacture details)

3. You show a sloped surface on the slab, is your intention to have a flat surface of some kind installed over that?

There will be (3) 4" steel columns bearing on the front wall (16ft direction) going up to the roof line to hold the beam.
The columns will have 2 "C" channels, 1 front and 1 back of the column with a ledger board on top, thus a wood deck flush with the main floor level will sit above this concrete slab.

5. Assuming the opening you show on your plan is a door, what’s the vertical distance from the door threshold to the top of grade?

Front walls are 8'-8" and the main house walls are 10ft, the door below has plenty of head room.

6. If this is new construction, why are you using block instead of using concrete for all the sub-grade walls?

Pre-fab concrete walls again my bad, built with block for decades, old term habit.

 

[walker.t]

The brick ledge is just there to hold the slab, no brick face, vertical siding…

Thank you for all the additional information.

the concern is the flashing of the masonry to seal at the masonry face at the brick ledge and over the top of the lower walls.

So when you are saying “masonry” you meant to say concrete, right?

Superior Pre-Fab Walls (Concrete)

Their product looks interesting. I don’t believe their claim that the 1.75” thick 5000 psi concrete shell does not require additional dampproofing, but I’d assume they have some sort of testing to back that up. You should ask them if they can fabricate panels that you can use as roof panels.

thus a wood deck flush with the main floor level will sit above this concrete slab

OK, good to know.

I’ll try to get specific suggestions to you tomorrow.

 

[tbz]

So when you are saying “masonry” you meant to say concrete, right?

Yes, the walls are pre-fab concrete ( https://www.superiorwalls.com/superior-walls-customers/builders/)

Their product looks interesting. I don’t believe their claim that the 1.75” thick 5000 psi concrete shell does not require additional dampproofing, but I’d assume they have some sort of testing to back that up. You should ask them if they can fabricate panels that you can use as roof panels.

Started using there walls back in 2019, and over twenty years later I can a test, they have out preformed the concrete walls for dampness feel in a location where I had them side by side to compare.

As to the roof panel, it was the first thing I did by calling tech support before starting my own research. They don't do anything but the wall systems.

 

[jar546]

Started using there walls back in 2019, and over twenty years later I can a test, they have out preformed the concrete walls for dampness feel in a location where I had them side by side to compare.

For the record, I have seen at least half of a dozen Superior Walls failures at various levels over the years I was in Pennsylvania. In almost every case, it was an installation problem. The issue with Superior Walls is that they are finicky and leave no room for installation error. Something as simple as the contractor not installing the sill plates properly can cause a failure based on unbalanced backfill. In another instance, the contractor changed the location of the basement stairs, and there was a failure at that point because the stairs were moved from the center of the house to an exterior wall. Other times, the failure was inward movement between panels a few inches without explanation.

My recommendation is that if someone is going to spec out Superior Walls, they need to be extremely specific about soil type, unbalanced backfill, location of the basement stairs, etc. and do site visits to make sure that the "authorized SW installer" is actually following the installation instructions to the T. Remember, superior walls are not placed on footings, they are placed on gravel. They certainly have their place, but design and installation has zero room for error.

 

[tbz]

Jar,

I sat through a round table discussion on common installation failures by a local builder's group on the walls way back in 2004.

It was an eye opener, and stair flights along side walls is an issue that needs to be tightly monitored for unbalanced fill. There are a few ways to do it, but it's requires the information be provided during the design, not changed afterwords as noted.

Sill plates are very important for their attachment as you also noted, and the floor joist attachment to those sill plates is also very important.

Also, the pea gravel bed, drainage piping and the virgin soil base are huge things that need attention also.

There is one major drawback that I hate the most, and that is having to pour the basement floor before being able to backfill once the FirstFloor deck is installed.

With this project, the basement is getting plumbing in the floor and then radiant heat. Thus, the framing and roof will be completed prior to the basement being poured and backfilling the excavation.

The framers will have to work with the ditch open on all sides.

 

[walker.t]

Yes, the walls are pre-fab concrete

Thank you for this and your other comments in response to my #7 post.

As for specific suggestions. I looked at a plan set I have on file for a residence that has a small area of concrete roof under an open exterior stair, it has living space below it. They specified a fluid-applied membrane, unfortunately they didn’t provide any details as to how they turned that up the adjacent walls, I have never specified fluid-applied membrane to know if you can just paint it up the wall and leave the edge unprotected.

Though you might not find specific details showing the exact configuration of this condition, I think general details of flat roof construction at parapets and a drip edge above a gutter would apply.

Roof slab/upper wall. Assuming we’re using EPDM, membrane is turned up the wall and terminated with a termination bar. If this is close to the bottom of your exterior sheathing, I would cover the top edge of the EPDM with flashing that is shingled under the building paper. If the termination bar is too far below the bottom of the sheathing, I’d install counterflashing over the top of the membrane and leave a gap between the top of the counterflashing and the flashing at the bottom of the wall sheathing.

Lower slab edge. I would not let grade cover the edge between the wall panel and the roof slab. Membrane is turned down the edge of the slab and finished with a termination bar, I would attach the termination bar below the roof slab/wall juncture. I would then want to find some way to cover the big space below your deck and the top of the roof slab. Here’s a sketch of an idea for a soffit, the bottom trim (shown in green) has a gap behind it so water drains off the membrane. The problem is the vertical measurement, from the bottom of the trim to the top of the deck as modeled is almost 30”, you probably don’t this so far out of grade.