Wawa wall, proposed solution, 2/22/2019

At last night’s (2/21/2019) BAR meeting, we learned that there’s no wall separating the proposed Wawa from the adjacent neighborhood because, in 1974, the Town judged that a wall was not needed for that property.  And, apparently, despite the change in use (from a quiet little office building to a potentially 24/7/365 convenience store), … because they didn’t need one in 1974, the Town thinks they don’t need one now.  Or they can’t legally require one now.  Or something along those lines.

For their part, Wawa said that putting in the wall that would be required under Vienna commercial zoning regulations (masonry wall, 6′ tall, along the entire property line) would result in killing some mature trees.  So they didn’t want to be seen a stepping in and immediately cutting down mature trees.  Instead, Wawa offered to put in additional low (3′ to 4′) evergreen shrubbery along that lot line.

Fair enough.  But shrubbery doesn’t stop noise.  What to do?

Let me offer a suggestion:  Wawa should consider voluntarily putting in a 6′ concrete panel fence at the back of their property.

Detail follows.


Suppose, for the time being, that somebody in the Town — either the Planning Commission, or the Department of Planning and Zoning, could rule that a wall is required, per our existing commercial zoning regulations.  If that were the case, then Wawa would have no choice but to build the wall that Vienna commercial zoning law requires — 6′ tall, masonry construction (brick, block, or stone, laid up with mortar), right on the lot line, for the entire length of the lot line.

So, just assume for a second that there is some risk they’d have to build that.

Now suppose that, instead, Wawa simply decides to build a wall, on its own.  In that case, it doesn’t have to build according to the rigid standard set forth in the law.  It’s not building it as required by law.  Wawa could build whatever it wants, subject to approval by the Town based on the general looks of it and the soundness of the construction.

My contention is, Wawa could get more sound reduction, for less cost, and less destruction of mature trees, if it put up a different kind of wall:  A concrete panel fence.  I’m not going to show images due to copyright concerns, but just Google for images of “concrete panel fence” and you’ll see examples.

Here’s what I think I know, based on some hasty internet research. I’m just going to state these without citation as to source.

First, even a garden-variety concrete panel fence attains the same noise reduction as a brick wall (typically stated as 5 to 10 decibels for traffic noise, or “up to a 50% reduction in noise”, or “up to two-fold reduction in noise”).

Second, panels specifically engineered for noise reduction achieve substantially better sound reduction than a brick wall, a claimed 20 decibel reduction (or four-fold reduction) in noise.  Here’s an example, and another example, where they claim (up to) 20 decibel (or four-fold) noise reduction from an engineered concrete-panel fence.  (You can see the “decibel scale” on this page to see that a 20 db reduction is substantial, more than the scale I needed to illustrate levels of street noise on Maple.)

Third, a concrete panel fence is half the cost of a traditional masonry wall.  I just have to take the word of a few websites on that, but it makes sense.  It certainly involves less labor.  Doesn’t require a continuous foundation.  And certainly for industrial-scale projects, the market suggests they are cheaper.  If you look at the sound walls on arterial highways in Northern Virginia, almost none of them are masonry construction (block, brick, or stone, mortared together).  All the new ones are (gigantic) concrete panel fences.  That ought to tell you about the cost-effectiveness of traditional masonry construction for this purpose.

Fourth, these fences do not require a continuous foundation, only separate holes to pour foundations for the posts.  So not only are they cheaper, they are more flexible and may generate less damage to surrounding vegetation.  The point being, you can easily “step them around” an existing large tree if required (just add a little “U” to the fence — two new posts, three short panels.)   And a single hole for each post would be far less damaging than the continuous foundation required for a masonry wall.

Fifth, because this is at Wawa’s discretion, they could integrate this into the overall design, instead of having it tacked onto the property line.  Here, I’m thinking they might (e.g.) put a turn in the fence to connect it to the existing proposed trash room at the back of the property.  That achieves the acoustic barrier without wastefully running a length of fence behind the trash room (which then serves as a sound barrier for that portion of the fence/wall).

Sixth, if done voluntarily, Wawa would get kudos for being a good neighbor.   Separately, it would gain noise abatement expertise.  To the extent that Wawa is moving into these neighborhood-adjacent suburban markets, the information it gains from researching and constructing this wall might benefit them down the road.

Seventh, the property owner or the tenant (Wawa) would likely have to agree to maintain the wall in perpetuity. Or for the duration of their tenancy.  This is the only way to generate the right economic incentive to choose a durable construction method.  For example, there are other quite effective sound-barrier walls, but they all involve “soft” materials (plastics and such) that are unlikely to be durable on a decades-long time scale.  You probably don’t want builders choosing those options.

Eighth, if there is some credible threat that the Town might mandate a wall, per commercial building regulations, pre-empting that mandate with a concrete panel wall might make good business sense in a straight dollars-and-cents calculation.  If they are proactive, Wawa gets to put in a cheaper, better performing alternative, possibly engineered to fit into the site at minimum cost.  If they are forced to build a wall, as I read it, it has to be a 6′ masonry wall, in a straight line, along the entire lot line.  Fully realizing this is small potatoes in the context of this rebuild, avoiding risk is always a good thing.

The upshot of this is that the Town of Vienna requirement for a masonry wall, along the lot line, certainly made sense when it was written half a century ago. Because, at that time, if you wanted to block sound, that was the option.  Even now, it’s certainly a safe choice, and in most cases, a reasonable choice.  You know what you’re getting and you know they have to do it right (else it will soon fall over).

But in this case, we should not fall into the either-or trap.  Either the legally mandated wall, or nothing to block the sound.  Plausibly, a voluntarily-proffered  concrete panel fence, engineered to be an acoustic barrier, might be a more efficient solution.  Lower cost, greater sound reduction, and less damaging to mature trees on the site.  And if it works well, when this issue arises again in Wawa’s expansion to similar sites elsewhere, they’ll have a solution in their back pocket.