Parkway rain garden excavation

I had to excavate our parkway rain garden to a ponding depth of six inches. It was a very simple task, except for the treasure hunting aspect of our urban soils.

I didn’t want to start with the excavation until I had a barrier around the rain garden. Although the drop into the bottom of the rain garden wouldn’t be more than nine inches, I still was worried someone could fall into it. Now that I had a fence surrounding the parkway rain garden, with the exception of the fence panels, I was ready to start digging.

My goal was to plant my rain garden plants into a medium that resembles top soil. That was not an unrealistic goal, considering that the top layer in the parkway was a fairly good quality topsoil. But what was lurking underneath made things a lot more interesting. In a way, it was a little bit like archeological discovery that told a story corroborated by the surrounding landscape.

The parkway rain garden will stretch across two city lots. To the east is a vacant lot. It once had a building on it, but that was torn down. I am not quite sure when but it must have been sometime after the 60s. To the west is the lot on which sits our house, which was built in 1902. It think it is fair to assume to most buildings on our block were built around that time, including the house that once stood proudly on the vacant lot.

In my preparations for excavating I noticed that the parkway at the vacant lot had topsoil layer of about four inches, followed by a good six to eight inches of soil mixed with rubble. Below that was a decent layer of dark colored subsoil.

The parkway section in front of our house did not have the rubble layer. The topsoil slowly transitioned into an equally dark colored subsoil. It comes close to an uncontaminated or clean soil profile.

That may speak to the construction methods around 1900. I could assume that the crews cleaned up the site once they were done with the building, but I seriously doubt that. I think it is more likely that back in the day, builders didn’t use the equipment we have available today, and thus didn’t recklessly ruin the soils the way we do today.

The rubble layer at the vacant lot, on the other hand, most likely dates back to the tear down of the building.

Overall and given our urban environment we are blessed with decent soils, which we could maintain as long as I could find a way to address the rubble layer.

My method was as follows: I started by excavating and saving the topsoil, which is now in a stock pile in the vacant lot. Next I excavated the rubble layer and hauled it off site. Once I started excavating to the west, I relocated part of that topsoil to the east, until I had met my ponding depth of six inches.

A Tom Sawyer moment

When I started excavating, it was still summer break and the kids on the block were stifled by boredom, including four brothers who live two houses down. First they found some distraction by watching me dig. That lasted about ten minutes. Then they riddled me with questions. That lasted a little longer. Then they argued among each other who would do the best job digging. And finally they were begging me to help.

I got my spare shovel and let them have a try. To my surprise, the youngest and smallest of the four was not only the most skillful, but also the most relentless. He almost kept up with me. And once the last of his brothers had his turn, he wanted right back into the game – and I was grateful for the help!

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Parkway rain garden planning

Did I mention that I would like to convert our parkway into a rain garden? In case you haven’t read the previous posts, let me mention it again.

A rain garden is a shallow excavated and vegetated area that allows stormwater runoff to infiltrate into the ground. That begs the question: where will the stormwater for my parkway rain garden come from?

The contributing area

The adjacent concrete sidewalk will contribute some runoff, but not much, because the sidewalk surface area is actually smaller than the parkway rain garden.

The stormwater that I would really like to manage in the rain garden comes from the street and gutter. Surface drainage on our street is poor and we always end up with standing water in the gutter – sometimes for a couple of days, and sometimes for a couple of weeks. I would like to drain and infiltrate the street runoff into the parkway.

With that goal established, I could look at the appropriate rain garden depth and storage capacity. The elevation of our curb averaged around three inches above the gutter. The top of the curb roughly equaled the grade elevation in the parkway.

To manage the street runoff from the half of the street bordering the parkway (924 square feet), I should plan for a six inch ponding depth across the 470 square feet of rain garden. At a tested infiltration rate of two inches per hour, the parkway rain garden should be able to handle the 100 year design storm for the 924 square feet of contributing area.

The issue of conveyance

The next big question was, how do I get the runoff into the rain garden? I have a street curb that is in the way.

Typically one would rely on curb cuts to allow the water to flow from the street and gutter into the rain garden. But this is not my curb and I don’t want to get into trouble with the City. Whatever I do has to be easily reversible in case they end up not liking what I am doing.

I think I’ll start by drilling a number of one inch holes through the curb at the gutter low spots. Those holes can be easily filled and patched if needed. But because the holes only allow a limited amount of volume to flow through at any time, I may not be able to get all the runoff from intense downpours into the rain garden. So even though the rain garden could manage a 100 year design storm, the limited conveyance capacity may reduce that effectiveness.

I also will have the issue of maintenance. There is always a lot of debris in the gutter, which could clog the one inch holes. I will probably have to check on those holes a couple of times a month to keep them clear.

And I have two paths crossing the parkway, which leaves me with three rain garden cells. To connect these cells hydraulically, I incorporated PVC pipes under the path. This way runoff can easily flow from one rain garden cell into the other.

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Parkway path

I get a kick out of reusing and repurposing salvaged materials, whether it is in the house, the yard, or in this case, our parkway landscape.

We have two gates to our property: the main gate leading up to the front door and the side gate leading into the side yard. It made sense to provide a path crossing through the parkway landscape at each gate.

We already had a path crossing at the main gate, although it needed some additional work. More about that later. But there was no formal path crossing at the side gate. While laying out and installing the parkway knee fence, I made sure to provide a gap for a path to connect to the street.

A material question

No, I will not use poured concrete. Boring! It can be the default pavement choice around the country all day long. That doesn’t mean I have to like it or bow to it. And on top of that, it’s not even that practical. It tends to crack over time. And repairing it always looks like – well – it has been repaired.

 

I had some beautiful salvaged graystone and clay pavers in my yard that were perfect to craft a path crossing through the parkway. I knew I could repurpose the graystone into a curb flanking the path left and right. The clay pavers are modular, which makes for a much higher quality pavement if installed correctly. It doesn’t crack, because it has cracks already built into it – the joints between each paver. And it is easy to repair, because – well – it’s modular.

Building it up from the base

I put a decent eight inch base down using recycled aggregate and made sure to compact it thoroughly. Integrated into the base were two two-inch PVC pipes. They will hydraulically connect the parkway rain garden to the east and west of the path.

I also had the city water vault and shut-off valve in the path of the parkway path. (Probably not perfect, perhaps even painful, to pitch this many p’s in one phrase. But once I plunge into a pattern of packing p’s I am past picky.)

I had to align the pavement elevation with the valve and vault. The elevation of the valve was set and I couldn’t change it. But I could adjust the elevation of the vault base and I did, so that it matched the path slope determined by the valve.

With the pavement elevations set, I put a concrete base down and set the curb using my salvaged graystone. Most paver installations need a structural constraint around the edges, or otherwise the pavers start migrating over time. That is particularly true if they are adjacent to a downward slope like my planned rain garden – even if it’s only a four or six inch drop. So the curb on a concrete base was a must.

After the concrete had cured for a day, I could bring the gravel base up to the right elevation and start to screed the sand bed (setting layer) for the pavers. Then I set the clay pavers right into the sand bed. There was some fitting involved along the edges and around the vault. To fill the smaller gaps I switched from clay pavers to graystone scraps.

To finish the job, I needed to fill in the paver joints with sand, make sure the pavers sat firmly in the sand bed, and assure the paver surface was even. The sand can be broomed and washed into the joints. To set the pavers firmly I used a two by four and a hammer and whacked the pavers into the sand bed. That process also allowed me to get to an even surface.

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Fence rails

I had a fence to build! The details, materials, and design were fleshed out. I was itching to to convert the theory into an actual, built product.

The fence posts were in place, which allowed us to install the bottom and top rails. Because the bottom rail will sit right at the pavement edge, we had to excavate a little more along the sidewalk. The curb side edge was already excavated from our paver edge installation.

We cut the top and bottom two by four rails to length and attached them with structural connectors to the posts. At the same time, we pre-drilled the two by two rails that will hold the rebar and attached them to the back of the two by four rails.

I chose to only install the fence rails around the perimeter, because I still have to excavate for the rain garden. That will be easier to do if I can move up and down the parkway and in and out at the path crossings.

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How was that possible?

A couple of years back, after all major air sealing, we had a blower door test result of 2.1 ACH @ 50 pascal. This February the results dropped to 0.62 ACH @ 50 pascal in a follow up test! How was that possible?

From what I have read and heard, once the major air sealing is completed, it becomes increasingly difficult to tease out additional improvements in the blower door test results. And a drop from 2.1 to 0.62 ACH @ 50 pascal is – well – a massive improvement.

Let’s start by looking at what I mean by…

Major air sealing

In one sentence: We took good care of the building envelope.

On the 1st floor we had an application of closed cell foam followed by a layer of open cell foam. The 2nd floor just got one layer of closed cell foam. The closed cell foam on both floors was acting as our air barrier across the masonry wall plane.

The closed cell foam only provides a functioning air barrier if it is diligently installed. On a sloppy spray job, you may have to contend with leaks in your air barrier. I point to some examples here: on the open cell job on our 1st floor.

We air sealed the top of the attic with drywall, which was taped and mudded. The gaps around the attic edges were sealed with another bead of foam.

All penetrations through the building envelope were diligently sealed, typically with foam. Examples are:

  • The ERV fresh air intake and exhaust
  • The range hood exhaust
  • Any electrical conduits leading to the exterior
  • Any low voltage conduits leading to the exterior
  • The supply and return lines to our minisplits
  • Etc.

You can seal around electrical conduits, but that still leaves with a big hole – the conduit itself. To plug the conduit, we diligently used duct putty.

I made sure we had decent weather stripping on our exterior doors. And then there were the windows. We had good quality replacement windows on the 1st floor, while the 2nd floor still had the old double hung vinyl windows. However, I made sure the perimeter of each window was properly sealed.

This was our baseline that gave us the blower door test result of 2.1 ACH @ 50 pascal. Now let’s take a look at what may have caused the drop to 0.62 ACH @ 50 pascal.

The 1st floor

I took a mental walk through all improvements on the 1st floor, major or minor, since we completed the major air sealing.

There was some additional air sealing on the kitchen back door. This is a fancy way of saying, “I installed some additional weather stripping.” The back door was pretty air tight to begin with, though, so I am not sure that this effort contributed that much.

There was the transom window over the kitchen back door. It had a temporary window that most likely was not properly air sealed. I didn’t replace it with a properly sized window until I ordered the replacement windows for the 2nd floor last fall. This should have contributed to the reduction in air leakage.

 

I suspect that the biggest impact lies with the air sealing work I did on the 1st floor casement windows. Regular readers may recall my air leakage problems in the corners of the casements. The manufacturer was not able to resolve the issue, but was gracious enough to refund me the money for the leaky windows.

As described in a past post, the problem came down to 1/16 inch and I was determined to plug that gap. I invested a little research time online and found a single coated, low density, PVC foam tape, 1/16 inch thick. I installed it on the operable part of the casement, right across from the gaskets on the casement frame. The foam tape pushed against the gaskets, closed the gaps, and eliminated the air leaks. I could tell it did, because the cold drafts on windy winter days disappeared.

 

 

2nd floor

Like on the 1st floor, I did some additional air sealing around the 2nd floor back door. The most significant improvement may have come from my work on the door threshold, which was not properly sealed.

But the biggest reduction in air leaks must have come from the 2nd floor replacement windows, which I installed last fall. I thought I had done a good job air sealing the old double hung windows after we finished with the spray foam installation, but the blower door test numbers tell me otherwise.

Conclusion

I clearly underestimated the amount of air leakage from the 1st floor casement windows and the effect of good quality replacement windows on the 2nd floor. Or, I overestimated the effect of my air sealing efforts on those old double hung windows.

The more I think about it, the more I am convinced that the windows were the major contributors to the drop from 2.1 to 0.62 ACH @ 50 pascal.

So, maybe it is not that difficult to improve your blower door results after all major air sealing after all! Or maybe I have a unique definition of what “major air sealing” means.

And here is another thought: I made it my job throughout our deep energy retrofit to stay on top of all air sealing efforts and moisture management issues. That was my responsibility. There was no hole in the building envelope I didn’t know about or I didn’t make sure was sealed properly.

Most other remodels, gut-rehabs, energy retrofits, or even new construction that follow conventional methods probably won’t have that one person who is in charge of tracking the air sealing. There are a number of contractors and tradespeople coming and going, all doing their own thing, but no one person has a real incentive to pay attention to details – sometimes not even the details of their own work. Air sealing is probably not on their mind, or may not even be a concept to some.

Usually there is the general contractor, who, one could assume, would be in charge of managing all contractors and tradespeople and making sure air sealing is tracked and accounted for. But the success stories seem to be more an exception than the rule.

Building green has an uphill battle ahead with a lack of skilled labor, with contractors that often don’t think an inch beyond their own trade, and with no one on the job site who is responsible for tracking air sealing from the planning stages to the final execution.

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