May 4, 2023 at 2:57 p.m.
Chisago City Council looks at green roof roof plan
For the second month in a row, the Chisago City Council encountered a somewhat unusual request. In March, the council approved plans for a car condo near Lake Martha. (A car condo is not a residence but specifically is designed to house collectible vehicles.) At its April 25 meeting the council was asked to approve a variance for a house with a vegetative green roof.
After hearing no public comments at an April 17 public hearing, the city planning commission had approved the variance requested by Greg and Tanya Paine for their home at 11325 Interlachen Rd. Planning commissioners said that some elements of the variance, which included reduced rear yard setback, greater than maximum height, lower pitch roof than allowed, and greater than maximum impervious surface area, actually made the Paine’s residence more similar to its nearby neighbors. The neighborhood in question is located on the shore of Chisago Lake. The subject home is a rebuild of an existing home located on a nonconforming lakeshore lot in the Surfland neighborhood. When approving the variance, the planning commission stated that adjacent houses also have less-than-required rear yard setbacks and greater than maximum impervious surface area.
The “environmentally friendly” green roof that the Paine's propose is intended to absorb and slow water runoff, and help alleviate impervious surface concerns; however, state shoreland rules, which haven’t been updated since 1989, don’t address green roofs. The property owners explained that the green roof requires a low, 2 percent slope,. It is covered by a synthetic rubber membrane. Applicant Greg Paine told the council that the “green” element of the roof is composed of specially engineered soil designed to retain moisture. Vegetation is used to help the soil on the roof withstand rain and high winds.
Information provided to the city stated, “the most common vegetative green roof cover is three-to-four inches of lightweight growth media planted with succulents, herbs, and sedum, a low-growing ground cover with water-storing leaves.” When the roof becomes saturated, drains placed a regular intervals will channel excess run-off to rain gardens around the house where the water is slowly absorbed.
The green roof is said to minimize run-off into lakes and community sewers, filter out pollutants in rain water, and insulate the house from heat and cold. Paine, adding that he is not an architect or engineer, said they are using an experienced structural engineer who has designed more than 150 green roof projects in the Twin Cities area. He also stated that the green roof is more expensive than a conventional roof and is not a “cost-saving” measure.
Although it received no comments from the public, the city did receive written comments from Department of Natural Resources Shoreland Program Manager Dan Petrik. Petrik’s letter pointed out current shoreland rules do not address green roofs, which means there are no standards to measure the value of green roofs when it comes to meeting impervious surface requirements.
Petrik raised a number of questions: “What rainfall event will the green roof be able to manage before shedding water to the ground? How does that compare to soil conditions in the area? How well will green roofs hold up in Minnesota?”
He went on, “It might be difficult to sustain vegetation (on the roof) during both drought and wet conditions and through hot and cold. Will the roof be irrigated during periods of drought? If a green roof doesn’t end up working out for the current or future homeowners, and they remove it, how is their excess impervious surface (then) handled?”
Petrik concluded, “While the idea of a green roof may be an attractive idea and possibly a good stormwater practice, given the above concerns and the general limited resources and interest of the average homeowner, green roofs don’t seem to offer much in terms of shoreland protection.”
City planning commissioners, however, agreed that the Paine’s plan appeared to be environmentally friendly, and approved the requested variance as did the city council. Councilmember Craig Meyer commented, “This seems like what they used to do with earth homes but they’ve gone to the next step.”
In other building and zoning business, the council:
- approved a variance for a building expansion at Kendall Howard, 10152 Liberty Lane, that will encroach into the setback from public right of way. Building Owner Randy Herreid said that the company would rather expand their facility in Chisago City than use storage space in Blaine. Kendall Howard manufactures shelves, cabinets, technical furniture and accessories.
Acknowledging a benefit to the community and confirming the setback will not impede snowplowing, the planning commission approved the variance request following an April 17 public hearing. The planning commission and city council also approved Herreid’s request for a license to construct a parking lot that will use a portion of the right of way along Karmel Avenue. The current right of way on Karmel is more than needed for a city street staff explained. (Right of way was wider when Karmel was a county road, before the area was annexed into the city. ) In approving the parking lot license, the city retained its right to use the right of way for future potential road construction and drainage.