21 these types of foundations would be thicker around the perimeter and then steel mesh applied in the slab. This type of foundation should be reviewed by an engineer to ensure it can sustain the required loads and that is built to code. Importance of drainage with a concrete foundation As you can guess, you need proper drainage underneath the greenhouse. You will want to make sure that the water comes out and is sent away from the structure and doesn’t pool underneath. Many customers choose a simple center drain and add standard plumbing pipes to move water away from the greenhouse. Taper the concrete down and towards the grate for easy drainage. A concrete foundation. thresholds with concrete foundations If your greenhouse has our upgraded storefront door, we suggest extending the concrete foundation by two inches to provide more support for the threshold of the door. In addition to this, some customers choose to build a stoop or landing area in front of the greenhouse for container plants and easier access. Ensure that this landing has a slight slope away from the greenhouse to prevent water pooling into the greenhouse.