Insulating a slab in zone 5b

Old 07-07-18, 04:24 PM
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Insulating a slab in zone 5b

I've been reading articles about insulating my on grade slab. How deep should I go to insulate? Also doesn't digging deep than the slab around the perimter compromise the slab? A little input from Northerners would be appreciated. Building will eventually be heated.

My understanding is in my AO I'm supposed to have 24" verticle and 24" horizontal. Slab pretty much sets on top of the ground. there is about 10" of slab above ground but still meamens 14" of digging around the primeter. Seems to me going 14" deep around slab would compromise the structural integrety of the compacted earth on the edges of the slab. Building will be heated someday so code says I have to insulate.

Any input on this? Thanks in advance
Old 07-07-18, 06:09 PM
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Hope I'm missing something.
Insulating around the outside of the slab will do you no good.
It should have been insulated under the slab before it was poured.
What I did in my own slab house was use 6 mil plastic, 3/4" blue foam, 3/4" Advantech, Tap Coned in place into predrilled clearance holes. (Predrilled so the panels do not lift up as the screw goes in.)
It's been that way for over 8 years and is still rock solid and the floors warmer.
Old 07-07-18, 08:18 PM
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According to everything I've read insulation the perimeter of the slab is a very good idea. NYS its building code. I'm not saying it shouldn't be under the slab but

from the link

Slab perimeter (edge) insulation must be installed where the slab is part
of the conditioned space of the house. This includes a slab-on-grade house
or addition, the walkout portion of a heated basement, or a breezeway that
shares a slab with the garage.
Slab perimeters must be insulated where the top edge of the slab is above
grade, or less than one foot below grade (see Figure 6.6). The R-value to
use depends on the results of your compliance analysis. If the slab edge
insulation is on the exterior, the insulation must be protected with a rigid,
opaque and weather-resistant barrier that extends at least 6" below grade
(ECCCNYS 102.4.1).
Slab perimeter insulation must run all the way to the top of the slab. It
may go down, or down and across, for a total of 24" (climates less than
6000 HDD) or a total of 48" (climates more than 6000 HDD). If you are
using the ECCCNYS Chapter 6 tables, 48" slab insulation is required in
climates over 5,500 HDD according to table 602.1. See Figures 6.7-6.8
for examples.
Note: “Heating Degree Days” (HDD) are a measure of how severe the
heating season is. With the exception of the southeast corner of the state
(Orange, Putnam, Rockland and Westchester Counties, New York City
and Long Island), all of New York has a climate of greater than 6000 HDD.

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