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Table of Contents
For more information on insulating
heated slabs visit the
CMHC links on the radiant systems pages.
statement on bubble foil insulation can be read in it's entirety
22 Radiant Heating Myths
Bad Science, By
John Siegenthaler, P.E.
Uninsulated vs Insulated
Ref.: Dr. Straube
Ref.: Foundation heat loss from heated concrete slab-on-grade floors by Pirawas Chuangchid, Ph.D., Moncef Krarti, Ph.D., P.E, Joint Center for Energy Management (JCEM), CEAE Department, University of Colorado at Boulder, Boulder, CO 80309-0428, (CB 428) USA
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Building Systems, Part II
With all the magical claims consumers get sucked into, there has been one product that has
stood the test of time, holds all other newcomers to a
high benchmark, delivers as promised and it's extruded polystyrene insulation. Its
high compressive strength makes it ideal for heated driveways and
its moisture resistance closed-cell
structure delivers stable
long-term R-value in building assemblies.
To avoid the snake oil foil trap please feel free to use this excerpt from our written specifications on under slab insulation.
Thermal Specification: All under slab insulation shall have been evaluated to CAN/ULC-S701-03 by the National Research Council's Institute for Research in
Construction (IRC) through the Canadian Construction Materials Centre (CCMC) and must bear the manufacturer's name or trademark and CCMC evaluation listing number.
of Acceptance: Type 2, 3 or 4 as per CAN/ULC-S701-03, Material Properties.
R value to meet current edition of the
Model National Energy Code, National Building Code and authority having jurisdiction.
Where appropriate, insulation R Value shall be adjusted upwards for slabs bearing on grades with higher thermal
conductivities and at walk out perimeters.
Click Image for Larger View
Structural Specification: (insert your business name) does not purport to have structural expertise in specifying what Type (2, 3, or 4) is suitable for the application, therefore the onus is on the general contractors to specify the Type based on a professional (Civil/Structural)
engineers written evaluation of application in consideration of live and dead loads, soil properties and compaction, water table location and methods of construction.
Key Concepts in Insulating Heated Surfaces
Graphic Copyright Dow Chemical
objective of any radiant based HVAC system is to direct the energy into
the space to the benefit of the occupant. Downward
loss, or heat transferred to the earth is energy not
contributing to the purpose. Heat loss to grade is
a function of the temperature of the heated slab, soil type
and moisture content. The higher the moisture content and
soil conductivity the
greater the downward heat loss and thus the greater the
amount of dollars to heat dirt, rock and sand instead of you
- the occupant.
Insulated Heated Concrete Slab
Graphic Copyright NRDC
properly assembled concrete slab will outlast most other
assemblies in a home. To achieve this longevity and
reliability it must have high compressive strength and
Graphic Copyright NRDC
to operate a snow melt system compared to the cost of hand
shoveling but it may be less than the cost of injuries,
hazards and security risk associated with accumulated snow
and ice. The only way to ensure every dollar spent to melt
snow goes into the slab instead of the earth is to insulate
with high strength extruded polystyrene insulation designed
for vehicle traffic.
We recommend you download these documents below
Dow's website by clicking on the illustration.
Radiant Floors for
Excerpt, “There is a growing demand in both the United States
and Canada for the installation of radiant heating. There are
several ways to heat a floor, including circulating water
through cross-linked polyethylene tubing…"
Excerpt, "Radiant floor heating has been used in aesthetic
and energy-efficient building designs since the Romans
channeled hot air under the floors of their villas centuries
ago. Today, advances in materials and technology are
increasing the appeal of radiant floors, offering the
promise of cost-efficient comfort for commercial and
Sealant and Adhesives
envelope solutions...improve the
comfort and energy efficiency of
The Right Way.
Illustration. Click the image to see a larger version.
A note on moisture and
The three biggest enemies in downward heat loss is subsoil
temperature, soil type and moisture content.
For example moist clay will transfer 7.4 times as much heat as
Imagine your heated slab operating at a 90 deg F core
temperature over a 55 deg F clay having over 20% moisture
content - draining over 44 Btu/hr/sf out of the slab into
the aquifer - that's 44 Btu/hr/sf that should be going onto the
How much is 44 Btu/hr/sf? Well that's more than three times the
amount of heat it takes to keep a R2000 home warm.
To view a comparison for soil types and moisture content -
To combat downward heat loss one must insulate below the slab.
In Canada and in other parts of the world, insulating under slab
is required by the building codes.
Building Systems - Part I, Product Claims