Adding slab edge insulation on an existing structure

Jack

I was asked by a friend (a GC) to visit a home he has been working on. About 2400 sq ft, 14 yrs old. Radiant slab. Had some sort of LP boiler running it, which is now gone, replaced by a 15 kw electric boiler. She belongs to a neighborhood co-op and gets LP at a reasonable rate. She has a VC Defiant wood stove that she likes, but is concerned about lugging wood as she ages. Smart call, I'd say. Solar company said that with the 15 or so PV panels they sold her that she would be in high cotton on the PG&E bill. $700/mo of cotton with occasional use. I asked the owner if she liked the radiant and she replied that she loved it, but due to cost, must abandon the slab. This is a well built place, single story, Loewen windows, etc. The 50kbtu is fine as it heated the place this past winter. She is just NE of Sacramento at 3000' elevation in the foothills of the Sierra. Lovely winters, after the NE;) I much prefer CA winters to summers. After some wrangling the solar company is removing the whole system and putting it back to what was there previously. She will be out the $4500 she paid a local plumber to install the elec boiler, but will get the $20+ k she has in the solar...so she said.

At 2400 sq ft on single story there is a substantial amount of perimeter insulation to be added. So, in your experience, is it worth doing? Insulation type? Installation detail? Flashing? It seems a shame to abandon the slab. The GC is excellent and would do a good job on this. I will observe from a distance;) Any suggestions would be gratefully received!

Gordy

So I'm going to stab there is no insulation under the slab? This is a slab correct?

Perimeter insulation would do nothing but help. It's tough hand work. How much it would save is a question mark. That's quite a few LF 200 for 2400 SF. Does not sound like much until you start digging. There are mini back hoes that can dig right along a wall. They have a pivotal boom. At the base. Depends on what is all around the house.

It's a tough choice for the owner. You could mock it up on a heat loss program to at least compare losses with, and with out.

SWEI

We have used a couple of different details with success. The specifics depend on slab edge alignment with finished wall, whether there is siding or stucco, etc. Termite potential there will dictate some additional care if there's wood framing on top of the slab.