Green Builder Offers Solutions to Proposed Impervious Surface Code Change

Residents and developers are invited to weigh in today and tomorrow on a proposed Dallas development code change that would limit impervious coverage for residential and nonresidential development.

Impervious coverage, according to the City of Dallas, is any surface that prevents or substantially impedes the natural infiltration of stormwater into the ground, and includes, but is not limited to hardscape surfaces such as asphalt, concrete, wood, crushed granite, pavers, synthetic turf, compacted soil or rock, and similar surfaces. Linear borders such as landscape barriers, retaining walls, and fences are excluded in these calculations.

The Zoning Ordinance Advisory Committee discussed the matter in August 2023, and the City Plan Commission requested workshops to hear from the public. 

Virtual listening sessions are planned from 6 to 7 p.m. Monday, April 22, and from noon to 1 p.m. Tuesday, April 23. 

Learn more about the proposed code amendment here. ZOAC is expected to hear a staff recommendation in May, and the matter will go before the CPC in August. Ultimately the Dallas City Council will determine whether to change the code.   

Developer Response to Impervious Coverage Code Change Proposal

Sustainable building pioneer Alan Hoffmann of Hoffmann Homes has some simple solutions to the concrete heat sinks and stormwater runoff challenges: developer incentives, rainwater capture, rain gardens, permeable paving systems, and rocks. 

“I have some skin in the game,” said Hoffmann, who builds insulated concrete form homes. “Pavers can be an option but they still create a lot of stormwater runoff. You can do a rock treatment where you’ve got cement borders, but the problem with rock is they can run up. Cars tend to mess them up. Rock is not a permanent solution.” 

Hoffman uses Truegrid permeable paving systems made from recycled plastic circles molded together and interlocked. 

“It allows the moisture to get into the soil but it doesn’t allow the rock to create ruts and it keeps everything level,” he said. “In order to get more density — and that’s what everybody wants — that means the houses get closer to each other and lot sizes get smaller, but where does the water go?”

Hoffman later clarified that developers want density and the city needs it, but it should be implemented in a smart manner. 

“We’ve already got in our development code the ability to do density that’s not tremendously invasive,” he said. “When I’m buying a piece of dirt, if it’s got a multifamily zoning and a single-family R-75 on it, I’m not going to rezone it, I’m just going to replat it. That saves me from the zoning meeting with everybody showing up with pitchforks and torches. I’m just going to do a shared access, because, by right, you can do that … It’s Dallas’ ace in the hole in terms of competing with the suburban markets.” 

Limiting Impervious Coverage

Impervious surfaces impact stormwater runoff, flooding, and the “heat island effect,” according to city documents. 

“Limiting impervious coverage can improve health equity, as many disadvantaged areas and low-income communities are more prone to destructive flooding and the dangerously high temperatures allowed by less shade coverage,” Senior Planner Lori Levy said.  

According to the August 2023 presentation, a code update is needed to align development practices with the Comprehensive Housing Policy, Racial Equity Plan, and Comprehensive Environmental & Climate Action Plan. Additionally, the update should reduce the environmental impacts of flooding and the heat island effect exacerbated by stormwater runoff from lack of soil infiltration through impervious surfaces. It’s also necessary, city officials say, to ensure compatibility within existing neighborhoods. 

Developer Incentives 

Hoffmann serves as a technical adviser on the city’s Environmental Commission and was on the Facilities panel of the Community Bond Task Force. 

Dallas streets are designed for a 25-year flood but the city has recently experienced 100-year floods, he said. So can the city retroactively address bad design? 

“No,” Hoffmann said. “I mean, you can, but, we’re digging that giant drain for East Dallas. You can mitigate stormwater runoff through rainwater capture. Instead of creating these permeable solutions, why don’t we incentivize rainwater capture? That slows down the water. Rain gardens are another option.” 

Rain gardens are four-foot-deep, 10-foot-wide trenches with a French drain connected to the curb. 

“It’s like an underground storage tank,” Hoffmann said. “It’s a permeable, below-grade detention tank. It’s a way to slow water down. The permeable surfaces are needed if you’re wanting your trees and your ground cover to grow.”

The way to reduce runoff on a 20 x 20 double-car driveway is to make it a permeable surface with rock and a Truegrid system, Hoffmann added.

“That water will soak into the ground rather than running off and going into the stormwater system, creating flooding downstream,” he said. 

Hoffmann said he plans to attend one of the listening sessions and will emphasize the need for incentives. 

“I think the reality is, you’ve got to let the marketplace catch up with the need,” he said.