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Green-roof bids for Target Center are ‘on target’

I’m writing in response to Jay Weiner’s “Target Center costs go through the green roof” post (Monday, Oct. 27).

The Target Center green-roof bids are “on target,” as expected. It is unfortunate that Weiner went to press with the article before he and I were able to connect.

Cost estimate
The estimated cost of the vegetated roof option that was the base bid solicitation was $2.8 million, compared to $1.2 million for a conventional arena roof as reported to the Minneapolis City Council on Feb. 21, 2008 (see cost comparison matrix here, on page nine) (PDF). These cost estimates included only the cost to replace the main Target Center arena roof. The estimate did not include the cost to replace the other 29 Target Center roofs on five levels or to install lightning protection. These are necessary components of the roof replacement project that were included in the bid specifications; however, they were not part of the cost estimate analysis focused on the assessment of the feasibility of a green roof. While the bids received do not break down the costs into different elements, the consultant team that prepared the bid specifications indicated that the low base bid of $5.3 million for the entire project is consistent with the arena roof estimates presented in February.

Lifecycle costs
I must also correct Weiner’s statement that the vegetated roof would not pay for itself through energy cost savings as was expected. The cost savings of the vegetated roof over a conventional roof were never expected to be gained from energy efficiencies, as clearly outlined in the report to the Council (PDF) and on page five of the Kestrel Design Group report (PDF) that accompanied it, but rather, over the long term, by virtue of the fact that green roofs have a significantly longer lifespan than do conventional roofs that are exposed to UV radiation and other environmental stresses.

Conventional roofs have a typical warranty for a useful life of 20 to 25 years, whereas green roofs have been demonstrated to have a lifespan of 40 to 50 years. The green roof becomes more cost effective than a conventional roof at the point when the conventional roof must be replaced. In this particular case, due to the location of the air intakes for the building, the energy cost savings were not anticipated to be significant for a vegetated versus a conventional roof.

Potential for sponsorship
Weiner also states that the roof replacement will be entirely city financed. This is not necessarily the case. A large, innovative, highly visible and extensively publicized vegetated roof such as the one contemplated for the Target Center arena has the potential for sponsorship support and city staff is investigating sponsorship opportunities.

The city is conducting a review of the bids received, which includes a number of alternatives, and staff will present its recommendations to the City Council for a decision on the investment in the coming weeks.

Kristin Guild is manager, business development, Department of Community Planning & Economic Development, City of Minneapolis.

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