[Hockeyplayr999]

Hello,

I am slowly working on finishing my daylight basement. (I think that is what it is called, it has a block wall for the bottom half and a framed and insulated wall for the top half with a 6.5" ledge)

I believe I have the framing down (My plan is to use a 2x8 as a top plate and mount it to the top of the blocks with a treated 2x4 as the bottom plate and studs up against the wall in-between)

My questions are:

1. My block wall was insulated (with spray foam) and waterproofed on the outside prior to the foundation being back filled. With that being the case, is there any need to insulate or vapor barrier the inside? I live in MN and even the last few weeks it has stayed comfortable downstairs with only 2 vents for the whole basement.
   
   
2. Because the block is insulated, should I still use a treated board for the framing that will be placed on top of the block?

Hope that makes sense. I will take pictures tonight if needed.

Thanks

 

[cleveman]

I am guessing that you mean that your concrete wall has some foam board on the outside.

Yes, insulate the stud cavities on the inside and use a pt bottom plate. I would bet that your concrete wall has a maximum of 2" of xps, so you can all another r-13 everywhere. Not a large cost.

 

[slackcc]

Not certain on the vapor barrier but with the treated board I wouldn't think you'd need it for the top of the block. I did something similar, but in a full concrete basement, a few years ago and the inspector had no issue with regular lumber on top.

The main issue would be wether any water is getting up there, one trick is to take a piece of plastic wrap at least 12" x 12" or so, duct tape it tightly on all sides to the area of the block you're looking at and let it sit for a few days to a week, take a look and see if there is any condensation inside, if there is then water is getting in there, if it's dry then you're probably good.

 

[Hockeyplayr999]

Thanks for the responses.

Clever - I do not mean foam board, I mean spray foam. They foam the outside of the foundation and then cover it with polyurea, should be about R13 right now.

Slack - I might give that a shot, we have been in the house almost three years and there has been no dampness that I have noticed.

 

[giterrdone]

Definitely going to want to go with the spray foam

 

[carpdad]

I still would use vapor barrier, or use materials that are inorganic.

 

[GottaFixIt]

If you have a vapor barrier outside, do not install one inside. Any additional insulation you add should be vapor permeable. Rockwool is a good choice for inside the stud cavities or XPS against the wall. If you choose spray foam, it should be open cell.

Doesn't matter if you verify vapor migration now, you have to leave one side unblocked to dry and since you have a vapor barrier on the outside, it's going to be the inside.

PT lumber is required where it touches concrete. Use a sill gasket under the bottom plate even though it will need to be pressure treated.