If you want to fit a basement subfloor over a drainage area, you will need to make sure that you take a lot of care. It is not just a matter of fitting a floor over your drain, as you need to make sure that you have carefully tilted flooring, in order to prevent dampness affecting the basement subfloor.
Use a Moisture Barrier
You could use a moisture barrier, which will protect your basement subfloor from water seepage. This material is very expensive, so you may choose a compromise where you fit the moisture barrier around the drain area, and then use other insulation material on the rest of the floor.
Add Channels
Another solution to the subfloor is to add channels. These channels will help to direct water moving around the basement subfloor toward the drain. Also, slightly tilt the floor, so that it points in the direction of the drain. This involves adding an extra inch to the raised side of the flooring, and then building the floor down to meet the drain.
Use Plastic Sheeting
Take a little of the plastic sheeting, which is used as a vapor barrier, and place it around the edges of the drain. You can then apply the basement subfloor over the surface.
Source: www.DoItYourself.com
