Well plans changed, i was hoping to build a new house, but we found an already built house 1.5 years old for a lot cheaper than it would have cost to build, so we went that route instead.

So one of the first areas i'd like to address is the interior of the basement. Currently there is 2" of foam board insulation with a foil backing on it (i am assuming it is polyiso) on the top 4' of the interior concrete wall.

I was wanting to seal the concrete walls with UGL drylok masonry latex waterproofer. My concern is if i apply the drylok under the foam board, could it cause future moisture problems? To the best of my knowledge the exterior foundation walls are just damp proofed with the spray on tar, not waterproofed or anything like that.

Thanks, Tim

There are no mop-on/paint-on sealers that come anywhere close to the vapor retardency of a foil facer. A single coat of UGL Drylok Latex runs ~4 perms, making it class-III vapor retarder. Multiple coats can bring it down to about 1 perm which would slow down the rate of drying but would still allow ample rates of drying toward the interior. It's a sealer designed to block the capillary draw of liquid moisture, but allows water to be released as water vapor. So water wicking up from the footing can dry just fine toward the interior through the lower half of the wall, without being forced to dry solely via the above-grade exterior.

Being relatively new construction I'd assume there is a sill gasket between the top of the foundation and the sill plate, which would usually be enough to limit capillary draw from the concrete to the susceptible wood even if the concrete had a fairly high moisture content. Even if you made the lower half of the wall as vapor-tight as the upper half (with the foil), if there is 18-24" of exposed foundation above grade on the exterior it would usually provide enough drying, as long as it's not getting a lot of splash-back from the drip line or the grade directs moisture toward the foundation rather than away from it. Using a concrete sealer on the exposed exterior to inhibit wicking up dew & rain splash would usually do more good than harm too, as long as it doesn't go too low in vapor permeance. (1-4 perms is fine, 0.2 perms maybe not.)

Bottom line, go ahead- it won't create a problem despite the very low-perm insulation on the upper half.

If you intend to insulate the foundation further, using 2" unfaced EPS (more breathable than XPS) on the lower half and adding 2x4 studwall with unfaced R11-R13 batts and latex-painted gypsum would give you a decently high-R foundation of ~ R22 after thermal bridging on the upper half, ~R18 on the lower half. This works from a moisture point of view almost anywhere in the lower-48 of the US (and most of Canada.) Whether it's "worth it" depends on your climate and heating/cooling energy costs.

I agree. I researched this subject in great detail before deciding to put 2" pink board XPS on the basement walls. We had all kinds of water and mold damage previously so I wanted to be certain I do the right thing.
First of all my basement is now the warmest area in the house in the winter! Location MD. The previous winter with no insulation on the cement block unit we were freezing and the heat was on almost all the time.
I think you should NOT use foil faced insulation ever. The thing is you want vapors to go both directions if need be. If any moisture does come through the wall it must dry inwards or you get mold. My basement was black mold infested because the previous owner apparently didn't care/understand the need to ventilate and insulate correctly.

check this http://www.buildingscience.com/documents/reports/rr-0309-renovating-your-basment
the buildingscience website is a brilliant resource on this subject

the key is xps at 2" has 0.5 perms I believe which eventually will allow moisture through to dry. you'd need to check if the foil faced insulation you have now does a similar job.
I have seen fiberglass insulation foil faced causing mold so I am now careful with vapor barriers. When I see foil backed fiberglass installed below grade in new construction, I run away from that property!

Unfaced EPS is even more vapor permeable, which makes it preferable to XPS for insulating the bottom half, given the vapor tightness of the foil-faced goods higher up.

Foil facers are actually pretty good in some applications, but any time you use a foil facer on it you'd better be sure to analyze the moisture drives for the assembly. For example, as a final exterior layer of insulating sheathing under a 3/4" rainscreen gap it improves the thermal performance of the assembly, blocks summertime vapor drives, and makes air sealing easy using FSK tape. But it could also spell disaster if there isn't sufficient R to the exterior of the structural sheathing to prevent wintertime moisture accumulation in the wood, or if there is a poly vapor barrier on the interior side of the assembly, creating a moisture trap.