How to put it back together

I listed the various reasons why we wanted to start fresh with a new basement slab. I also mentioned a number of items and functions we hope to integrate into the new floor. It is time to figure out how we will put it all back together.



After some back and forth, we decided that a hydronic radiant floor heating system is the way to go in the basement. It makes sense and becomes somewhat cost effective, considering that we’ll start with a new floor slab. The system will meet the heating loads for the basement and add comfort.

Building codes, energy codes and Chicago Green Homes requirements aside, insulating a floor slab with a hydronic radiant system becomes imperative (see also Basement floor post). I already have half the insulation I need for under the slab. But that is only half the story, as I learned through my research.

I will have to create a bond break with the same XPS insulation around the entire floor slab perimeter (see detail above). It provides a thermal break to the foundation wall and prevents heat from bleeding out of the floor slab.

We will have to carefully seal the bond break at the top for moisture and radon gas control. If there is any radon, it should remain under the slab, where we will provide a controlled escape route. A system of perforated drainage pipes in the aggregate base is connected to a vent stack, helping to collect and remove any radon.

See also:EPA’s A Citizen’s Guide to Radon

Moisture control is built in at several levels. I already mentioned the seal over the bond break (see detail above). In addition, a polyethylene vapor barrier between the concrete slab and insulation prevents water vapor diffusion from the subgrade into the floor.

The aggregate base supporting the floor slab is ½ inch stone that also acts as a capillary break. The stone base prevents any water from wicking up from the subgrade towards the floor.

While at it, we also would like to include a perimeter drain along the entire interior of the foundation wall.  The purpose of this drain is to keep the footing reasonably dry. The dryer the foundation wall the less moisture will wick up and diffuse into the open basement, where it may cause condensation problems.

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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