[PaverDrew]

Due to our proximity to the Chesapeake Bay and it's tributaries, pavements reducing run off are becoming more and more prevalent. My problem lies with the specifications used by most engineers and architects.
Most applications are spec'd using a typical crushed aggregate base instead of a base utilizing various sized clean gravels. Instead of providing a system that allows water to perk vertically and naturally filter itself before discharge into the water table, the spec'd systems allow water to move below the paver but along the compacted base, often resulting in base saturation and movement. This, in my opinion, provides a false sense of environmental responsibility to both the designers and property owners. It seems that either they have done this to keep install costs down, or municipal requirements are sub-par.
It has occurred to me that designers and municipalities are just unaware of the differences between a typical install and a true permeable system, which leads me to ask... as installers, how can we change the views of these individuals and correct this problem? I would assume that this is where ICPI can assist, though from reading previous posts they don't have the support of many members here. Manufacturers should help shoulder the burden, but I have'nt gotten great response as yet.
What are your two cents?

[Bunky]

As a manufacture of this product, I can not agree more. We have just designed a Permeable Paver and am currently working on a design/installation manual. We suggest that the base material utilized be the clean/clear stone and the soils be left alone and NOT compacted because this will close the pores and not allow for water to "perk" as fast as possible. Here in Wisconsin we have a lot of clay. I have been looking for an outside company to test our product, but there does not seem to be one out there anywhere. It appears that what the ICPI suggests is what is specified on jobs. I have completed our own tests on these pavers and have great results. These are somewhat new for our area and everyone seems to gravitate to the internet when creating the specs. I like the concept, but am worried because there really can not be a generic installation for these since every job has different types of soils. I would like to see these treated like SRW's. Engineer/design plans for each jobsite due to the diffent types of soils. They require "perk" tests for each septic tank installed at a new home, why not the same for Permeable Pavers????

[agla]

Just how much runoff enters through the surface of these pavements in a rain event? Is it possible that the bulk of it will not enter the voids in the surface to begin with? If the base is efficient enough to keep up with that amount, it makes no sense to make the base more capable than the surface to absorb it.

I think that a lot of people have the expectation that these will handle all of the runoff. They won't.

If in fact the surface can take in more water than the base spec's can absorb, it seems like there are two things working against each other from a construction point of view. One is the stability afforded by a well compacted base and the other is porosity. I guess that a third one would be smoothness of the surface to set the pavers on.

No one wants to have settling and no one wants to beat themselves to death trying to lay a smooth surface on a bed of large loose gravel. You can't put a layer of sand over the open pores or it migrates it would seem unless there is a barrier which would further impaire water movement. The last thing anyone from design to installation wants is a failed surface.

It would seem that anyone with a financial risk in the process is going to err on the side of stability over porosity. It is much easier to get sued for a pavement falling apart than whether the pavement absorption rate is meeting the goals.

Another thing is that these systems usually work in conjunction with other drainage systems such as retention swales and ponds or rain gardens. They are not going to do it all, but are a functioning part of the total package.

I'm all for having these work as efficiently as possible, but part of the efficiency is performance as a pavement. Another part of efficiency is ease of installation.

I'm always asking one of the larger paver reps in our area about drainage calculations for these. He says, we have all kinds of stuff, but everytime it is qualitative when he comes in and lays it out. He'll say it all depends on your soil under it and what you use for a base. Well, no $6!^, how about some standards results for some examples of base preps and we can figure out what our soil will do underneath it. And we are back to square one.

We perk test for drainage all of the time. It seems that the biggest mystery is how fast the water gets through that top surface. There needs to "c" values calculated for these, so regular drainage calculations can be made. It can't be that hard.

Honestly, I think it is that the "c" value is pretty high and they would rather have a lot of people buying the product and feeling good about it than knowing the truth.

[Paul]

We have to remember also the conditions in which the pavers are laid in relation to grades. I have seen these pavers laid on a 3% slope pitched one way! Tell me how much water are you going to carry before it runs out the bottom of the grade?

Every installation design I have seen has the proper base and surface course, of course all that I have seen are in the public sector so they have proper engineering, and sub drainage under them. The sub drainage may be restricted to delay the outflow so the storm system can handel the flow.

[grlandscaping]

Permeable paving will handle the amout of runoff you design for it. Just as all of us in the hardscaping industry, we always tell our customers that each job is different and special considerations need to be taken, so it isn't as easy and handing over some specs and calling it good. One thing for permeable paving that is a constant is the fact that you will be using 2 or more sizes of aggregate for the system. The bedding layer is usually 3/8 to 1/4". This isn't that hard to set pavers on, so your concern with with getting pavers level on large aggregate isn't as tough as you think.

Compaction is key with permeable pavers, just as it is with normal pavers. Just because that you don't have fines included into the base doesn't mean you don't obtain 95% proctor, you absoulutly do. Most systems will have 3 different sizes of aggregate, and the main purpose of this is to create a choking layer so that smaller aggregates in the bedding layer don't migrate down into the sub-base (which usually is 2 to 3" sized aggregate). This subbase when fully compacted will typically have 40% void space for storage of stormwater. Each permeable paver will have an infiltration rate for their system, so when you are looking for that info, just look to the manufacter.

Installation of permeable pavers realitivly the same as any other paver application, it comes down to a thicker base installation. There is a little more care taken in making sure you don't let fines into the system and not compacting the soil base, but nothing that can't be taken care of.

Paul, your question on slope is easy, it is designed to be on a slope. I'm working with a driveway currently that has a 5% slope and we will be using permeable pavers. Special considerations need to be taken so that when the water hits the bottom of the slope the excess water has an exit, which in this case we are using corrogated pipe to discharge the water out towards a rain garden. It would be nice if we could have simple solutions to everything, but we can't. Just takes a little more thought and considerations to make special circumstances work.

Andy

[nwhardscapes]

We have been installing Abbotsford Concrete Products Aquapave system with good results. The paved surface performs just as traditional pavers with virtually no surface runoff. Many factors contribute to the overall permeability of a picp system, mostly whether or not the contractor follows the proper installation guidelines i.e. not compacting the sub-base, adequate base of varying sizes with no fines, use of filter fabrics, and an approved joint stabilizer. Abbotsford attempts to solve this problem by only selling the system to certified installers who have completed their course. While they are a west coast company, I noticed in the latest Interlocking Concrete Pavement magazine that they have east coast manufacturers licensed to manufacture and sell the system. Check it out online at Abbotsford Concrete Products - pavingstones.com