The product you are referring to is Membrain, which changes permeability with changes in the ambient humidity. It has met Minnesota standards for Energy Code Building Foundation Rule Proposal Final Report. (And it has been approved for use in Canada based on computer modeling of above-grade construction.) But the University of Minnesota study Evaluation (See link below) was limited to a certain type of assembly in one soil type.

If your soil conditions and foundation construction differ from those in the evaluation, you might want to give it a second thought.

From the Minnesota study:

"All the conclusions apply to full-height, hollow core masonry block walls with an 18" above-grade exposure located in a well-draining group I soil (medium sand) with a very low water table. The exterior wall surfaces are bare and are in direct contact with the soil.

1. Full-height, bare masonry block walls with no more than 18" of the wall above grade that are insulated with unfaced fiberglass batts and covered with an interior, air-sealed PA-6 vapor retarder meet the performance requirements of the MN Energy Code Building Foundation Rule Proposal Final Report, specifically, they conservativelya satisfy the following criteria:

On the interior side of the water separation plane, the system has:
* a stable annual wetting/drying cycle
* no visible or olfactory fungal or other biotic activity
* there is no accumulation of free water on the interior side of the water separation plane and the above-grade portion of the foundation wall system does not exceed 17% of the foundation wall system height."

Here is a link that might be useful: Membrain Study

Thanks for the response. I told the contractor I wanted unfaced insulation in the walls. He told me how no one uses that and I should consider dry right because of the membrain. I read their website and posted here to be safe. I knew the membrain was too good to be true. I don't know if my type of basement fits into the criteria of the study but I would rather not take the chance. I called him back and told him I decided on the unfaced insulation to be on the safe side. He wasn't happy because he had to order it.

Maybe I was too wordy (as usual). The Membrain worked well in: "full-height, hollow core masonry block walls with an 18" above-grade exposure located in a well-draining group I soil (medium sand) with a very low water table. The exterior wall surfaces are bare and are in direct contact with the soil."

In other below-grade conditions, there have been no evaluations.

My basement does fit that profile but I feel better with the unfaced insulation. I may have to wait a bit to get it done though because 24" wide unfaced batts are hard to come from what my contractor told me. Plus it was about $120 cheaper for unfaced.

Insulation was finished today, now on to the next step, drywall.

What do you have on the walls?

Your first post says: "using drylock and xps on the walls." On later posts, you mention "unfaced insulation."

Unfaced insulation by itself is a mistake, according to Building Science Digest 103. If you've combined it with XPS on the wall, it's fine. No separate vapour barrier is needed.

The walls were drylocked. Then 1" xps was used on the walls, then unfaced r-13 between the studs.

Perfect, according to Building Science. I have to put in vapour barriers to meet Code, but Lstiburek says it's irrelevant at that point. I still use mechanical dehumidification.

I was considering cutting vents into my central heating and cooling system and installing them in the ceiling. Would this be adequate for dehumidification purposes?

In a well-insulated home, ac alone is usually insufficient to reduce basement humidity levels to below RH 50%. That's because it's not on long enough to affect the basement much. I have always used mechanical dehumidification. Not surprisingly, visitors remark it "doesn't feel, i.e., "smell" like a basement." (See page 9 in linked article.)

Low level heat registers work better in a basement. And if you're now conditioning the space you should also use returns.

Here is a link that might be useful: Basement Insulation Systems

Thanks for the link. I planned on having returns also. I will read the article, I will consider a dehumidifier also.

I have a hygrometer for my cigar humidors. I put in the middle of the basement and after 24hrs the rh is about 48% in winter. The summer it can go as high as 65-70%. I planned on putting vents and returns in the ceiling for heat to save money, rather than hire a contractor to run vents in the walls. I will use the money to purchase a good dehumidifier. I also planned on adding more unfaced insulation the rim joist area above the block once the sheetrock is done.