Drylock isn't going to be a problem (it's still somewhat vapor permeable even though it blocks liquid moisture) but the insulation might be.

With masonry-embedded joists it's safer to leave some clearance around the wood with no insulation so that the embedded wood stays warmer (=drier) in winter. Leave at least an inch of clearance. It'll be a cold spot in the wall/floor, but the floor joist ends are less likely to develop rot issues.

Don't use XPS- it's only warranteed to R4.5/inch (read the fine print), and is blown with severely climate damaging HFC blowing agents. Polyiso will do better inch-for-inch, even reclaimed 2lb fiber faced roofing polyiso, at less than 1/3 the cost. Look for sources here:

https://chicago.craigslist.org/search/sss?query=rigid+insulation

https://rockford.craigslist.org/search/sss?query=rigid+insulation

https://quadcities.craigslist.org/search/sss?query=rigid+insulation

IRC code min for basements in zone 5 & higher is R15 continuous insulation, which would take 2.75" of roofing polyiso, which can be mounted to the wall with 1x4 furring through-screwed with 4.5-5" masonry screws. The foam needs a timed fire barrier such as half-inch gypsum between the indoors & foam, which can be mounted onto the furring. If you'd prefer, the same performance can be had with 1" of polyiso and an R11-R15 fiberglass insulated non-structural 2x4 studwall, no vapor barriers. Don't skip the exterior foam, or the above grade portion can collect enough moisture/frost over the winter to create a mold problem- it needs to be at least R5 to keep the fiberglass & studs warm enough to prevent that. If the basement has a history of flooding stop the polyiso a bit above the high tide mark and continue down with EPS. (EPS and polyiso are blown with enormously friendlier pentane.)

If studwall, put an inch of EPS under the bottom plate of the studwall and the slab. This keeps the stud warm enough to prevent summertime moisture accumulation in the wood from contact with the colder slab. With an inch of EPS under the plate it doesn't have to be pressure treated, since EPS won't wick ground moisture either.

With leaving a gap between the foam and the joists, how should I approach the insulation in the joist cavities? I was planning on installing fiberglass batts for noise insulation and to keep the upstairs as warm as I can. I would assume then not to shove the batts all the way up to the foam?

The XPS ship has already sailed as the previous owner had already installed quite a bit (albeit incorrectly) and also left behind some extra as well. I will probably stick with it because I don't want to figure out how to get rid of it or waste it all.

I plan to do the stud wall with R13 batts. Even with a guaranteed R4.5 that should still get me over the requirement correct? I might have enough 3/4in XPS leftover to go over the 1in, if necessary.

Any thoughts on sealing the gaps between the brick and the joists? Leave them open for drying or seal them up to keep the warm air from entering?

With structural brick walls you need to assess how wet they get (or are going to get).

You don't just want to do something like cover them in spray foam and let it go. Because it basically cuts off part of the brick's drying mechanism.

During the summer it isn't as much of a problem, because it's usually sufficiently warm and dry to allow the brick to dry fully (if not evenly).

During the winter though, you get problems with bricks staying damp on the inside, then being destroyed through differential expansion/contraction in successive freeze-thaw cycles, as there isn't enough heat coming through the wall to allow it to offload moisture in the "back" of the brick.

Posted By msells21 on 18 Oct 2018 01:41 AM
With leaving a gap between the foam and the joists, how should I approach the insulation in the joist cavities? I was planning on installing fiberglass batts for noise insulation and to keep the upstairs as warm as I can. I would assume then not to shove the batts all the way up to the foam?

The XPS ship has already sailed as the previous owner had already installed quite a bit (albeit incorrectly) and also left behind some extra as well. I will probably stick with it because I don't want to figure out how to get rid of it or waste it all.

I plan to do the stud wall with R13 batts. Even with a guaranteed R4.5 that should still get me over the requirement correct? I might have enough 3/4in XPS leftover to go over the 1in, if necessary.

Any thoughts on sealing the gaps between the brick and the joists? Leave them open for drying or seal them up to keep the warm air from entering?

For the existing XPS derate it to R4.5/inch for dew-point control purposes. So it takes more than an inch on the exterior of a 2x4 batt-insulated walls for dew point control in a US climate zone 5 location, but would have some marging at 1.5" (x R4.5/inch = R6.75, which is more than the R5 minimum.)

There's almost no point to insulating under the floor once the basement walls are insulated. In a tight basement with insulated walls, a 55F slab and a 65F subfloor above it will usually stay above 60F unless leaking a lot of air from the outdoors. Insulating the subfloor between the joists will make the basement colder, but won't move the needle much on the total heating energy use. If there is a heating system down there insulating between the joists can even increase energy use, since the distribution & standby losses to the basement no longer accrue to the heat load of the house upstairs.

Insulate the foundation walls between the joists with the same XPS, leaving a 1.5-2" clearance from the foam to the joists. Stacking it up to get R15 using foam board construction adhesive may or may not be "worth it", but get it to at least R10-ish.

Hi, i'm new to home renovation service. I started a course few months back which has been a DIY course mainly. And now i'm noticing my basement leaking out moisture due to lack of insulation. So, i am thinking of insulating it myself, though i read a couple of tips share by https://pickmythings.com/basement-encapsulation/ as a clue to basement insulation but still skeptical about it DIY. But if i have to hire a professional i would spend more and that's another big consideration for me. My question, should i do it myself or hiring a professional best?
Pls, i need assist on the way forward......