Porch floor aggregate base

I feel I’m getting seasoned – like a routine is setting in. It is a nice feeling, supported by the confidence that you know what you are doing.

The underground plumbing for the back porch is done. I now can focus on the concrete floor installation. And I’m dealing with literally the same principles, design and process as for the basement floor.


The basement section of the back porch will be enclosed. And we would like to heat the enclosed portion during the cold season as needed. That means we will have insulation under the floor slab, bond breaks around the edges, and PEX tubing in the concrete for the radiant floor slab.

But first things first: I have to install a proper aggregate base on which I can install the next layer, the XPS insulation.

We used a 100% recycled ¾ inch stone (ASTM C33 #57, or IL DOT CA7). The beauty of this material is that it is “open graded.” In other words, it has no fines and a lot of pore space. As such it is an effective capillary barrier and prevents soil moisture from rising up towards the concrete slab – which in turn helps with the issue of moisture management.


Shoveling the gravel into the hole was the easy part. But I also had to screen the gravel so that I end up with a consistent surface on which I can lay the insulation. The screening was complicated by the two floor drains, because I had to make sure that all the various floor sections slope into the right direction.

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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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