You?ve reached a big fan of porous concrete. Beyond the green benefits of permeability, reduced heat island effect, reduced stormwater infrastructure, more efficient land usage, and the ability to feed tree root structures without large tree wells, it looks like a Rice Krispy? treat ? and I?m a big fan of food.
You?re right to ask about pre-made squares for a small residential area. Poured-in-place for small spaces is an expensive proposition because of the various steps involved. Decent-sized residential jobs might run $6-8 per square foot, whereas larger commercial jobs might run about $2-3 per square foot, depending upon the engineering involved.
I have not seen pre-made squares, except as samples. That doesn?t mean they aren?t out there. Keep in mind that, depending upon your average storm and your soil type, you will need some kind of aggregate sub-base to serve as a buffer while the soil absorbs the water. Also, if you plan to put vehicles on this, you should really have it engineered by a professional. Colorado also has interesting laws preventing the retention of rainwater. Chances are that your project won?t be affected, but you might check with your local building department to make sure.
Depending upon your application, you might consider permeable pavers or a grid system filled with grass or aggregate. There are several systems on the market or you can make your own with traditional fence ?window? blocks from a local brickyard.
Permeable pavers usually come in the form of traditional brick pavers with nubs or some kind of interlocking shape to create channels between the pavers. Those channels are filled with sand or small aggregate and allow the water to flow between the pavers and into the sub-surface. It is an imperfect but workable solution to permeability. However, there are now some brick pavers out there that are truly permeable in themselves. Water will flow through the primary material, though they look like and lay together like common brick pavers. One I have seen demonstrated is EkoPaver from the Level 5 Group. Level 5 Group is an R&D group and, when I saw the product last September, it was not yet available widely on the market.
With either porous concrete or permeable pavers, check with your local supplier or installer as to any freeze-thaw issues in Denver?s climate. The pores in the concrete or pores and channels in the pavers, as well as the aggregate sub-base, are perfect places for water to work into, freeze, expand, and break or heave the pavers. Local expertise is best and they may have a specific system that works well in your climate. This is not to say you will have a problem. An installation of porous concrete in Flagstaff, Ariz., which has a climate similar to Denver?s, has held up well to winter freezing.
As far as who carries them, check with your local brick supply company. Also, we of course recommend checking in with your local green building supply store. Try Planetary Solutions in Boulder or Laurie Dickson at Eco Home Center in Durango or Building For Health EcoCenter in Carbondale and Steamboat Springs. They may or may not carry them, but they will know who does.