Which of the following is a challenge when implementing green roofs?

green roofs temporarily increase air pollutants.
green roofs need to be watered by hand constantly.
green roofs do not last very long.
green roofs can be expensive to install.

The correct option is D. Green roofs can be expensive to install.

Explanation:

There are two main disadvantages of green roofs.

Number 1: Green roofs are very expensive. Their installation takes twice the money of conventional roofs.

Number 2: The maintenance of green roofs is hard and expensive. And one might need to hire workers for it. Hence, increasing the expense again.

Apart from this, the green roofs can also cause leakage and hence have to be checked at least once every year.