[Orchard Ex]

I would like to offer some permeable paving options next year for residential driveways and parking areas. What differences are there in base prep from a standard paver base? In another thread an infiltration bed was mentioned but one of my distributors specs a standard compacted base/sand/paver type install then backfill with topsoil or gravel depending on the paver type.
Does it depend on what type of rain event it's being designed for?
e.g. would a "standard" install using eco type pavers be able to hold a 1" rain event?
Thanks,
Korey

[ecoscapes]

I am interested in offering this too, but I don't quite see how you can get get clear 3/8 minus to make a nice flat bed for the pavers. The understanding I have about permeable pavers systems is that it should always be engineered just like taller SRWs. I wondering anyone on here is doing permeable pavers and could share thier experience and expertise?

[mark allen]

I did a job a while back, and DO NOT have any sand in the base, it needs to drain, using a clear stone that is angular and compacts and then top it off with smaller 'chips' that are free of sand, the idea is to let the water drain thru.... not drain part way. talk to your brick rep or check out Unilock or Paveloc website ( others too). if it is for driving on, a deeper base will obviously be required.

[Stonehenge]

We did a paver driveway using Unilock's Turfstone. An interesting project, for certain. We prepped it like we would prep any other driveway, 12+ inches of 3/4- crushed stone, but unlike most of our paver installs we did install an inch of sand as a bedding course, but more importantly as a growing medium. Within each of the cells we swept a mix of grass seed, topsoil, sand and super-absorbant (brand names includes Soil Moist and TerraSorb).

It worked pretty well, but I think the drive could have performed better with more organic material in the bedding layer. Also, because the sizes of honeycomb holes was rouhgly 2"x2", the concrete on every side was a pretty serious heat sink. I wouldn't suggest this type of install in a situation where there's going to be lots of sunshine and heat all day. The turf will just cook.

For non-turf applications, install as you normally would, and over the top I believe it is recommended to use some sort of clear stone filler. Sand won't stay in place (and poly sand would defeat the purpose), so clear stone provide the best opportunity for water to drain through. Though if you'd like to use the 1" bedding course of sand, I don't see why that would impede water flow through the base. I believe ICPI specs sand in part for it's draining properties.

My $.02, anyway.

[ecoscapes]

Mark
From what I understand you are correct. I just don't understand how you can get the clear 3/8"minus nice and flat like you do sand with other installs? I would think that sand would be permeable but I think the problem is that it will wash out with alot of permeable paver patterns. If anyone specializes in permeable pavers and knows a little more I would appreciate the input!

[agla]

There are two different reasons people use these products. One is for permeability the other is to get relief from lot coverage regulations. In fact, many of the people who have spec'd permeable pavers for drainage reasons only have done so to get relief from other regulatory bodies, such as a conservation commission. Often times, there is no specific goal for how much runoff is reduced is the point that I'm making.

I and others who I worked with (civil engineers) spent a great deal of time last August trying to find the information we needed to calculate infiltration. All we found from any of the manufactureres were qualitative assessments and no quantitative assessments that we could then apply to our own conditions and soils.

We were pretty well left with hiring in a geotechnical engineer to make specific calculations, or to stay with the generalization that more infiltration was better than less infiltration. Due to the size and scope of the project (part of a residential driveway ~800 SF), we chose the latter. I would expect that the same will hold true for most projects that are going to be left for a contractor to design.

How much runoff that gets absorbed is also determined by storm intensity, slope, and perc rate of the soil underlying your base preparation as well.

The bottom line is that if using permeable pavers is done to feel good about reducing runoff in a qualitative way or to reduce lot coverage, do the best you can at balancing your quality of construction with increased porosity. If it is done with specific runoff values as a goal, they should not be turning to landscape contractors to design what the manufacturer can not even outline in their technical bulletins, or what local civil engineers can not calculate. The contractor should have a set of plans and spec's to follow in the latter case.

[PSUscaper]

After reading all the articles on the subject, it doesn't seem like anyone has really come out and said 'permeable pavement is GREAT!'. In fact, it seem rather disappointing to me.

As AGLA mentions, a lot of factors involved. From what I've read, they aren't very good of run-off when it comes to heavy storms. As rainfall rates increase, run-off increases, which to me, is the time you want the run-off collected the most.

Also, there seems to be HUGE issues with how long the surface stays permeable. How long does it take dirt, oil, tar, garbage, etc. to build up and block the pores???? From my own experience with how long junk builds up in pavers, I would say not long.....which brings me to the point of maintenance. How much work is going to be needed to clean the stone in the holes? Every couple of years you have to power wash/remove the the dirty stone??? I have seen no real information on this, and I think there is a reason for it.

The last factor is simple, and that is overall appearance. I've seen a lot diff't systems, but in the end, I think they all look pretty ugly and most of all, are MESSY. It seems like the 3/8" stone or whatever is used tends to migrate all over the surface of the pavement. That may be a hard sell.

I love the idea, and think there are applications, but somehow think this is more of a environmental 'feel good' thing more than anything else.

[ecoscapes]

I somewhat agree with you PSU, but anything new always has its glitches. I know that willow creek pavers seem to have a nice perm. paver. I guess as far as cleaning -- most commercial parking lots are already swept -- I don't think it would cost to much more to change that up. I believe the real use of them is for commercial sites to get around making ugly retention ponds and take up all that land on thier lot. Instead thier infiltrate thier stormwater thru thier pavement. I think the turf stone is ugly and doesn't do it for me.
I guess my concern would be that if you had a clay layer down a two feet in your sub soil -- you would have to remove that as well cause the water would never infiltrate that area and would cause heaving in the winter. I don't know that this would be the case but that would be my guess. I would believe you would need soil cores from the site not just soil test before engineering. Does anyone know this?

[mark allen]

eco, to answer about the sand as a base, I would think that it would all wash down into the clear stone, as I recall we used a layer of fabric over the stone to prevent that, as far as leveling and smoothing out the chips, Yes it does take a bit longer but can be done, I wish I knew how to use my digital camera, I would take a picture of it.....

Stonehenge, I did a driveway out of the Unilock turfstone and the homeowners had us stain the tops to match the color of the window trim on the house. On another project, jsut a parking space for a boat on the side of the house, we painted it green to match the lawn, Yes there are slight wear marks on the paint now, but this was 4 years ago and it all looks like lawn...

I agree with agla on hiring a landscape contractor for that. And an engineer for drawing the plans.

[Adam Buckpitt]

I have been researching permeable pavers all year in 06 and it is hard to get clear info. I googled Dr. Bill James who has done much research on permeable pavements. He has very good articles about maintenance etc. Also Pete Belagio (Paver Pete) has info on permeable pavers. ICPI also has a book called Permeable Interlocking Concrete Pavements wich touches on design construction and maintenance. Pavetech also offers a course in permeable paver installation as well as materials. Pavetech.com. It is an interesting subject to say the least and is worth investing some time. I will keep tabs for any other suggestions.

[AZTLANLC]

Using 1/4" or 3/8" gravel is much easier to spread than sand, in fact since i tried it the first time I now use that for all my installs 3/4", the beauty is that you can actually walk on it with minimal disturbance and after compaction non will be notice.

Back to the use of permeable parvers you also have to take into drainage, so install perforated pipes on the base and daylight to proper place.

[Adam Buckpitt]

You should only install perforated pipes if your soil won't absorb the amount of water the base will hold in 72 hours. It is important to look at your soil very carefully for permeable pavers.

[mark allen]

Adam, Please continue......
thanks

[Adam Buckpitt]

I have been researching permeable pavers most of 06 and found that it is very specific in application. Putting perforated pipes in the bottom of your base and daylighting it doesn't reduce stormwater runnoff. It should be done when the soil is heavy clay or silt etc. One of the advantages of permeable pavers is that if space is tight for parking or something the base of the permeable pavers can act as an underground retention pond allowing you to use more of your land for parking and road. Permeable paver base works best when the soil under it can absorb the water from the paving surface as well as any area around it that will drain into it in 72 hoursl. If frost is a consideration 48 hours might be more appropriate. Maintenance is key for these pavements as well. Hope this helps!

[Bunky]

I do not know if this helps but I work for a Concrete Manufacturing Company in Wisconsin and we have facilities throughout WI and Illinois. I have designed a new permeable paver that we will be introducing in 2007. I have done a lot of research and attended the Permeable Paver course at Pave Tech. The class was taught by Advanced Pavement Technology. The system is designed to have more effient storm water management and improve the quality of storm water run-off. Clear stone (no fines) are to be utilized throughout the entire installation. Depending on the application, you will need to use larger stones on the base and work your way up to smaller stones. The bedding course is to be 3/8" clear stone. Fabric is not suggested because it could retain fines and act like a coffee filter, but geogrid would work fine for the larger jobs. Most applications will start with 3" size stones and downsize every 3"-4" until you get to the bedding stone of 3/8" . I have been told that the 3/8" stones are easier to set up for the pavers than one would think.
Having a Permeable Parking lot of driveway "cleans" the run-off water before it gets to the rivers, streams, lakes, etc.. In some situations it may elliminate having to have a retention pond, or require a smaller pond on site. Land is very expensive so the savings could be huge. This system does not require a large pitch. 1% pitch (+/-) is suggested for most applications.
The Turfstone Pavers that was mentioned earlier are mainly designed for erosion control, however they do act as a permeable paver. The issue with this system is that they are a risk managers nightmare. They do not work well with high heals, and with the use of canes and walkers. Another positive with this system is that the area will stay drier and warmer in the winter because of all the air pockets throughout the system.
The downside is that the 3/16" six stones that get swept between the joints can get a little messy. They can come out and get scattered around from time to time. The voids will eventually get "plugged" and will need to be power washed out or sucked up with a sweeping machine. This is suggested to be done every 5-7 years.
There are advantages and disadvantages, but the end results can be huge savings for the owners and the LEEDS program suggests this application to be done on more and more jobs.
Sorry this was so long. Hope it helped.