Bond break

Are we done with the insulation yet? Oh no! The devil is in the details, as I found out during my research on how to put the basement floor back together.

An insulation installation can easily become ineffective, unless the contractor or owner has some understanding of how to minimize heat loss. If heat loss, such as thermal bridging, is not managed properly it can get costly, because of the dollar amount spent on insulation and limited energy savings.

See also: Thermal control in buildings (

We plan on radiant heat in the new basement floor. The horizontal interface between the floor and underlying soil is rather large, and so is the heat loss potential.

The rigid foam board insulation that I began to install is one big thermal break, minimizing the heat loss into Mother Earth. Every unit of heat I don’t lose downwards will be available to heat the basement living space instead.

I also have to worry about thermal bridging along vertical interfaces, along the edge of the new concrete slab. This is a detail often overlooked or neglected.

To prevent thermal bridging from the concrete floor through the foundation wall down into the soil, I have to install a small vertical piece of insulation along the edge, also called bond break (see also sketch below).

The bond break is simply another piece of 2 inch thick XPS insulation placed vertically along the foundation wall. I cut and placed it so that the top of the bond break is at the finished basement floor elevation. As such, they serve as an elevation guide, which will make the pouring of the concrete floor much easier.

But first and foremost, the bond break directs heat into the living space where we want it.

What else would contribute to heat loss? Well, I have the footings of the existing steel columns and new spread footings.

Both are in direct contact with the thermal mass of the soil below and as such should receive a bond break at the interface to the concrete floor.

About Marcus de la fleur

Marcus is a Registered Landscape Architect with a horticultural degree from the School of Horticulture at the Royal Botanic Gardens, Kew, and a Masters in Landscape Architecture from the University of Sheffield, UK. He developed a landscape based sustainable pilot project at 168 Elm Ave. in 2002, and has expanded his skill set to building science. Starting in 2009, Marcus applied the newly acquired expertise to the deep energy retrofit of his 100+ year old home in Chicago.

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