Insulation, Radiant and Vapor Barriers - Insulating basement question....

Ok...I am getting ready to insulate the space above my sill plate. In the process I discovered a place where I am getting a good amout of cold air in. Hopefully I can describe this in a way that is not too confusing.

My home is a rectangular ranch. In the center of the basement there is a block on each end that is turned sideways and it runs floor to ceiling. The main center support beam sits on the these blocks at each end of the house. The tops of the blocks are open and there is cold air coming in the open space.

Is there any way to seal that space and is it even a good idea to do so? I was thingking that If I trap the cold air in the empty space I could get condensation and mold!

Spray foam will take care of this.

Spray foam will take care of this.

My concern was trapping the cold air in there. Will it cause issues?

No. How is cold air supposed to support mold growth? Also worrying about condensation--after you foam it the only place where condensation might occur is on the warm side of the wall not the cold side. Since you are going to insulate anyways after airsealing its not going to be an issue. Btw I did my sill plate as well but foamed the whole thing not just places where I had big gaps. Its a good idea to do this as all the small hard to see leaks will add up. I just used a foamgun and a few cans of foam along with cut 2 inch xps pushed into the rim joist area all around and sealed.

No. How is cold air supposed to support mold growth? Also worrying about condensation--after you foam it the only place where condensation might occur is on the warm side of the wall not the cold side. Since you are going to insulate anyways after airsealing its not going to be an issue. Btw I did my sill plate as well but foamed the whole thing not just places where I had big gaps. Its a good idea to do this as all the small hard to see leaks will add up. I just used a foamgun and a few cans of foam along with cut 2 inch xps pushed into the rim joist area all around and sealed.

I'm new to this so I just wanted to make sure I wasn't sealing up something I shouldn't.

I am going to foam the sill plate and outer joist.

What is 2 inch XPS?

Its extruded polystyrene and comes in pink or blue, Can be found at the big box stores in 4X8 foot sheets. The 2 inch thick kind is R10 and is good for foundation/basement work. Basically you can put it anywhere you put fiberglass and unlike fiberglass it will insulate but also function as an air barrier when the seams or edges are caulked or foamed. If you are insulating the band joist you can cut pieces of it and push it back against it then do your foam. The amount of foam needed to do your job will be greatly diminished.

cool...thanks I'll check it out!