A brick wall that was not accounted for...

[JFG_mtl]

Hi,
I have clients that gotten screwed by the incompetence of their contractor and by the city.
To summarize it, they got the permit to build a small extension (6 feet by 6 feet). They built the structure supported by piles and the existing foundation.

A city inspector came on the site and he realized that one of the walls was to close the property limit and that it needed to be protected from fire with a brick wall.
We did try very hard to get other fire protection solutions, but there is no way around it…. It needs to be brick.
The problem is that the wood structure has been built and the brick was not planned. I posted two pictures (from behind the structure and from the outside).
All the wood structure is above the pile. The wall you can see under the main structure was only meant to close the space under the structure so it has no structural value (or foundation).
The brick wall will be 6 feet long and 12 feet high.
The project is in Montreal so we need foundations that are protected from freezing.
I have three solutions that I think could be viable to support the brick wall. But I have concerns for all of them. I’d like your opinions.

Solution 1: Building an insulated slab on grade:
I’d dig 18 inches, place 4 inches of high density isolation, 12’’ of compacted 0’’-3/4’’ and pour a 20’’ width slab.

My main concern for this solution is that I would need to dig a large surface to be able to extend the insulation 4’ in all direction.
After this, the brick wall will be supported on the slab, but it will be linked to the wood structure (the usual brick supports). Should I fear a different settlement of the piles and the slab on grade?
Finally, I am a bit uncomfortable with a slab supporting a brick wall. I have never seen it and I fear what I have never seen work.

Solution 2: Using the existing pile
I’d support the wood structure to be able to cut the pile and install a new steel beam between the existing foundation and the top of the pile.
My main concern is the eccentricity of the load. The centre of the brick wall is located at 10’’ from the centre of the pile. The torsion would require a big member or something I would build with an HSS and a plate under maybe?
The other concern is the capacity of the pile. I haven’t checked it yet, but I have great doubts it will be enough to support the load of the brick wall.
It seems like a bad idea overall

Solution 3: A new pile with a new I beam.
I would install a new pile (right under the centre of the future wall and install a steel beam between the pile and the existing foundation.
I think this is going to be the most economical solution. But like the first 2 solutions, should I be worried about a differential settlement between the pile supporting the existing structure, the new pile and the existing foundation?

Obviously, I am very open to comments and suggestions for better solution or improvements.

Thank you very much.

 

[chicopee]

Instead of a brick wall have you explored with the city inspector the installation of a deluge system for fire protection?

 

[phamENG]

JFG - this does sound odd. What type of building is it? 6x6 is very small, so I'm going to guess residential. I'm in the southern US so I'm not familiar with codes in Montreal, but the International Residential Code as adopted around here only requires a 1 hour fire separation for exterior walls within 5ft of a property line. That rating is usually easy to accomplish with 5/8" type x gwb on each side of the wall.

To your questions, though:

1) I don't understand what you mean. Sounds more like a continuous spread footing than a slab on grade. This could work, but you will have a lot of movement between the structure and the brick. Just get it below the frost line and you'll be fine. How tall is the wall? If it's a single story, you'll probably be ok - just make sure you detail the joints carefully and work with the architect to provide for movement at finish interfaces (oversized frieze board that's not connected to the brick, for instance). You have a deep foundation so I'm guessing there's a geotech. Ask them about estimated settlements and see if the detailing is feasible.

2) Probably a good idea if you can make it work. You don't have to drive new piles, and you get your fire separation. More complicated engineering, though.

3) Easiest engineering solution, but what kind of piles are they? If they're driven piles, you'll have a hard time with installation. If you're close enough to the property line to trigger extra fire separation requirements, you're probably too close to get a rig in to drive piles. Even if the rig fits, that's a lot of vibration going into your new structure and potentially into adjacent structures. You'll also be pretty tight into your building if it's to be centered under a veneer. If you mix pile types, then there's some possibility of differential movement. Less likely if you keep the foundation elements the same.