Retrofit external insulation for a brick foundation – ground/below-grade interface
I’m exploring adding rigid insulation to the exterior of our brick foundation. We’ve done a substantial amount of retrofit insulation/air sealing retrofit on the rest of our house and the foundation stands out as a serious remaining weak point.
To give a sense of the size, our footprint is roughly 20’ x 30’. The exposed portion of the foundation wall is 4’ on three sides and 6.5’ on one of the 20’ sides, where the basement walks out into an excavated below grade area in our back yard.
In most cases the foundation wall descends directly into the local soil. In others, it seems that a course of cinder blocks has been added against the brick. These blocks are set just above grade and covered with a thin layer of concrete. On the 6.5’ portion of the foundation along the yard the foundation meets up with a concrete sidewalk surface.
What are my options for dealing with these ground interface areas?
On the extreme side, I’ve seen this video from our friends in Minnesota, which demonstrates minimal exterior trenching that allows rigid foam to be installed all the way to the bottom of the foundation wall.
This looks fairly invasive/expensive, and I’ve no idea if the required excavation equipment and associated liquid spray foam is even available in our area.
On the flip side, I worry that simply ending the insulation layer at or just above the local ground level will leave a significant uninsulated or low-insulated area at and just below grade.
I haven’t attempted to get any of this work quoted yet. If there’s reason to think a trench/excavation-free project would still provide some significant improvement, I’m open to doing it myself.
I’d be grateful for any guidance or inspiration here.
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