Will be finishing my basement, and have been reading so far. Have only gotten more confused and seem to be getting very different ideas depending on what posts or articles I read....

As of right now, I have a concrete block foundation, with a dry basement system installed. I still do get a small amount of moisture coming through the blocks on the walls in a few areas. Not enough to run down the walls, but simply just enough to show up. I have a dehumidifier, which is pretty much constantly running. Basement is heated, with a hot water boiler system.

The plan is to, hopefully, simply, install 1x3s, for framing on the concrete blocks. On top of the framing, place foam insulation. I was thinking the Super TUFF-R R3.3 1/2 inx4x8 foam boards. Then on top of the insulation, simply run vertical rough cut lumber.

Question is, some articles say that I need a vapor barrier. Articles then vary on the idea that it would go directly on the concrete walls or on the inside of the insulation. So is this needed and where would it be placed?

For a vapor seal, if necessary, I was thinking SimpleSolutions Moisturbloc 700 sq. ft. 70 ft. x 10 ft. 6-mil Film Vapor Barrier .

Am also reading in some articles that insulation should be facing certain ways or some can even be used as a barrier....

Any insight would be greatly appreciated. Thanks in advance!

 

Hi drmk and welcome to the forum,
It is a tough subject as every basement is different along with the climate and landscaping. From what you posted, you have both vapor and water issues. You only see the vapor after it is trapped by some plastic or other vapor barrier or when it drains out of your dehumidifier. The moisture you are seeing is water. Even though it is a small amount it is a huge problem when you consider covering it to finish the basement. Your first place to start is outside to ensure all steps have been taken to divert the rain from the roof well away from the house. Extend and direct gutters well away. Correct any slope problems where water collects against the foundation. Ensure above and below grade drainage is dumping that water somewhere else. One inch of rain on a 2,000 ft² area is over 1,200 gallons of water.

Also, today you may see just a little water, but on the worst day that may be much more. A basement is a hole in the ground and whether it is mother nature or a broken washer hose, they can fill up with terrible results. Be sure you have a sump and pump installed.

Now, once you get things dried out to where you are comfortable to proceed, that moisture vapor will still be there, migrating through the concrete. Install a vapor barrier and it will stop the moisture and allow it to accumulate until the inside matches the outside, that's wet.

No wood against the concrete, wood is food for mold. Your 1/2" of foam is a bit low for NY for the area above grade and down about a foot. You want that area to stay warm enough to not form condensation from inside humidity. Putting the foam directly against the foundation will reduce the convective air flow on the inside surface.

Here's some reading. Photo #4 is where I would head.
BSD-103: Understanding Basements — Building Science Information

Bud

 

Hello and thank you for your reply.

As far as drainage outside, my gutters are pointed and drained away from the house. I do live on a hill, which does have an impact on water levels, but previous owners of the house put in drainage to divert water around the house. I do have a sump pump installed with the dry basement system. This also includes a ridge drain in the corners between the slab and walls, which the vapor barrier can be installed into.

I can always go up to 1 inch or 1.5 for the insulation, and most likely will go for at least 1 inch with r value of at least 5.

But I think I just answered my own question...because I already have a ridge drain in the bottom of the walls, it would make the most sense to put a vapor barrier on the concrete walls, framing on top of that, followed by insulation and then the rough cut wood.

...Unless this isn't needed? "Putting the foam directly against the foundation will reduce the convective air flow on the inside surface." That is not something that I would want....right?

 

Convective air flow in the winter within that gap you propose (top to bottom) will circulate the warm moist air from below up to the very cold surface above where the concrete is exposed to the elements outside, causing condensation or even frost. And, since you have insulation between the gap and the heat in the basement, it will be cold. By placing the rigid foam directly against the concrete you stop the convective flow on the surface of the concrete and provide a warmer surface inside that will be less likely to form condensation. The photo #4 I pointed to above does exactly what I just described.

One link even describes applying the adhesive in a closed grid pattern to further reduce any circulation behind the foam. The 1 inch of rigid (not foil faced) will still have a permeability sufficient to allow some drying to the inside, preventing an accumulation of moisture behind the foam. Add your framing up against the rigid, then insulate without a vb and finish on the inside. No vinyl wall paper or oil based paints as they can act like a vb as well. Not sure which ones are best to avoid being a vb, I always seem to be looking for ones that are.

You can stop the rigid foam above the drainage at the floor. However, if you are still dealing with actual water coming through the block wall, I'm not sure what you can use. I have read about membranes that provide drainage channels on the back to allow water to drain to a channel below, but unsure where to find such a product.

Bud