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Radiant Floor Heating/Basement slab perimeter insulation


They are a day away from pouring my basement floor.  It is a 2280 sq ft ranch style home with a one room loft.  The home has 7 corners.  It has a full basement that sits 8 ft below grade.  I live in Southern Ontario, Canada, on a heavy clay soil.  Do I need perimeter insulation?  Everyone is tells me no because the slab floor will set 4 ft down from the frost line.  They are using a R12 insulation under the slab that won't even come to edge of the footings, I think they said it would start 12" in.  I asked about the line spacing and was told they will 12" on centre, I think he said it was a 1/2" line.  The home is 45'w x 68'l.  I'm just a girl in man's world asking questions.  Can you please help?

Dear Lesley,

The hand that rocks the cradle...

Concrete guys like their slabs to "rest" on the foundation, but by definition they "float" on a properly compacted substrate and could never be held up at the edges. The edge insulation is not my main concern but the slab insulation, usually 25 psi, should run to the outside wall and over the heat sucking foundation. I usually use Thermax at the outside wall and up to the sill plate which should be foamed after all perforations are made.  

If the exterior wall is insulated, the "edge" or end, of the slab insulation below grade is a small thing.

Tell them the deal is off and you want the insulation to run over the exposed edge of the foundation in full sheets where possible i.e. no fitting in scraps of 1 footers all around.

As you can see from the attached DOE document there is more than one accepted way to insulate a basement, but when you elevate the floor temperature extra insulation makes sense.

Show your builder Fig. 3 at this link.

A smart guy will appreciate the guidance.  

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Morgan M. Audetat


Radiant panel heating design, including floors and ceilings, European wall panels and snow melting for residential and light commercial buildings..............................................................-Master of Steam and Hot Water,City of Minneapolis....................................................--- Master Plumber, State of Minnesota...........


30 years..... Charter Board Member - Radiant Panel Association, former manufacturer of condensing boilers, former national distributor of radiant floor products, son and apprentice of mechanical & plumbing contractor. Current mechanical/plumbing contractor specializing in hydronic based, integrated HVAC systems. Radiant floor heating/cooling. Snow Melting. Condensing Boilers. Indirect water heaters. System design, consulting and technical training world-wide. Licensed contractor, designer, installer and consultant.

B.S. University WI 1981 CONTINUING EDUCATION: Viessmann Condensing boiler and Solar water heating certification 2010, N.D.S.U. Lead Worker RRP certification 2010, Knight condensing boiler certification 2009, Wrightsoft Manual J CAD certification 2009, RPA Designer & Installer Certification 2008, Nate Hydronic/Forced Air Certification 2008, Uponor/Wirsbo advanced design school certification 2007, Buderus Wall-hung certification 2007, Power Limited License (low voltage controls) 40 CE credits 2005, Basic Hydronic Certification IPEX & Northern Alberta Institute of Technology 1998, Charter Board Member - Radiant Panel Association 1994, Residential Off-Electric to Hydronic Conversion Heating School Canadian Hydronics Council 1994, B&G Little Red School House 1993, Rood Utilities (now Auburn Technical Institute) Oil Burner School 1993 ,Tekmar Controls residential and commercial 1993, Division Manager and Advanced Hydronic Seminar Instructor for the first Exclusively Hydronic Radiant Floor Distributor in the USA 1990, Hydronic Radiant Heating Association Workshop participant with Richard c. Bourne, PE spring 1988, Master Plumbing, Hydronic, Solar Course Red Rocks Community College 1987.

Awards and Honors
2009 System Showcase Award - Radiant Panel Association

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