I recently bought an old (1905) house in Calgary, Alberta. The basement has been dugout and concrete was poured. I would like to insulate the basement, and possibly build a room.

The walls have an offset about 4' off of the floor, the offset is 2'. The offset is to protect the orginal foundation. On this offset, there is plenty of loose concrete, and many holes that go right down to dirt. And there are some areas that are just dirt with no signs of concrete ever covering it.

I plan on vacuuming up any loose concrete, and then filling the holes with a concrete patch, in order to prep it for insulation and framing.

We had a big rain last week and I didn't see any signs of water leaking into the basement. But the holes do allow spiders and other bugs in (which I would like to avoid).

Is the vacuuming and patching a good idea or a waste of time?

This website says it for 'homebuilding professionals', and I am far from that.