Foundation Insulation Installation

My 1600sqft house is all on slab. 

It's also hydronic radiant heat. 

It absolutely BLEEDS heat through the external foundation walls, which, for half of the house, is about 4'-6' of exposed masonry with really rough stucco over it. 

I know I need to insulate these walls, but I really don't want to have to chisel the existing stucco off them. I also don't want to install 2" foam panels only to the air just go right under them and make them pointless. 

How to install foam panels over existing stucco masonry?

Check out this company. They have a pretty nice system that uses construction adhesive on molded in rails.  I suppose it will depend on how rough your surface is.

https://www.insofast.com/insulation-panels-for-exterior-residential-walls.html?#

I hate to break it to you, but you'll need to dig down 24" minimum and adhere rigid insulation board to the foundation from the frost line up to the top of the foundation wall.  Depending on the condition of the parging, you probably don't have to remove the mortar, or maybe you can parge another coat over it to even it out.  Then you'll need to put FRP foundation panels or something similar over it to protect the insulation board.

[edit]  Just saw your pic.  The surface texture is rough but the planar surface itself is nice and even.  I don't think you'll have to coat that wall.

Do I need still need to go down 24" when its only the top 12" that are the major heat loss? 
 

When I took thermal images of these walls last winter, it was only the top 12-24 inches that were warm. At soil level, they were the same temp as ground - at least on my largest faces. 
 

Other areas of the house are largely covered with soil and cindere, which actually has some insulation properties.

pheller said:

Do I need still need to go down 24" when its only the top 12" that are the major heat loss? 
 

When I took thermal images of these walls last winter, it was only the top 12-24 inches that were warm. At soil level, they were the same temp as ground - at least on my largest faces. 
 

Other areas of the house are largely covered with soil and cindere, which actually has some insulation properties.

If you've seen thermal imaging, you can probably get away with the top 24" of the wall.  Normally you would be required to do 24" back from the edge of the slab (horizontally) or 24" down at the slab edge (vertically) in a new installation.  Even if the finished grade is only a few inches below interior floor level.  Since this is an existing house, you probably don't need to do that where there isn't much exposed foundation, but you will still be losing some heat there.

At this point, anything is better than nothing. 

My main goal will be getting as much insulation on that wall, looking as good as possible, as cheaply as possible. 

So, I don't need to remove the existing stucco? Just use some sort of expanding foam in between the panel and the wall?

I would use rigid insulation board like blue or pink styrofoam, covered with a weathering / finish surface.  Ideally you want 2" but 1-1/2" would help. 

Looks like you can get it with a prefinished face for exposed surfaces.  Adhered or mechanically fastened to the wall surface.

Yea I've actually been eyeing Stryo FP Ultra panels for this project. Trying to ask them about installation methods has been a challenge, but they did send some nice literature. None of it covered my unique case of a pre-finished rough-texture wall. 

With my level of roughness in that stucco, its not necessary to go whole-hog on trying to limit the air gap? I assume if I used a combination of adhesive and tap-its that I'd probably limit air movement considerably. 

Correct.  As long as you run a healthy, continuous bead of adhesive and / or sealant around the perimeter of the board, you should be good.

Rad. Thanks man!