New basement workshop: Batt Insulation required by code

[Roger Feeley]

I'm told by the builder that when they turn the basement over to me, the walls will be all silver from the moisture barrier in the giant rolls of R10 insulation they are going to have to hang. that doesn't sound very useful to me. I'm either going to have to just take it all down (wasteful of insulation) or frame in a wall in front of it (wasteful of space).

What I would like are wood studs fastened to the concrete with insulation in between.

Any experts in building codes out there that can advise me before I call the city?

[Anthony Whitesell]

What are they hanging the insulation from?

[Chris Padilla]

That is my question, too: How are they hanging the R-10 batts if not snugging them between stud bays?

If you can afford it and it makes sense, I'd go with spray foam insulation. Surely you have some kind of choice here? Is the code that basement must be insulated?

[Paul F Franklin]

I think you'll find that your code requires insulation in the basement, probably at least R10. I think you'll also find that it doesn't have to be fiberglass batts, and the builder is using those because it's the cheapest way to meet code. Usually they staple it between the foundation plate and a furring strip fastened to the wall near the floor. It's a lousy way to insulate a basement and IMO, should not be allowed.

I think best practice is 2" of rigid foam against the walls, then stud walls with fiberglass or preferably, mineral wool insulation between the studs. The foam ensures you won't have any condensation against the cooler walls and the fiber or mineral wool adds R value inexpensively. Why not talk to the builder. I'm sure there would be an upcharge but you'll be a lot happier with the results.

[roger wiegand]

The code requires r10, how you get there is up to you. R10 should be considered the barest minimum. My new basement has 2" of waterproofing spray foam on the outside, 2" of rigid foam on the inside, then 2x4 wall with fiberglass batts. (4" of rigid foam under the floor) It's the most comfortable basement I've ever experienced, by a lot.

[Clay Crocker]

I think I have seen what the OP is talking about in my sister's house in VA. Their builder covered their exposed concrete basement walls with insulation that must have come in giant rolls; insulation on the concrete facing side and a silver vapor barrier facing out. No bats. The finished result makes the walls look like the top of a JiffyPop after you pop the popcorn. IIRC, they fastened it to the wall with a hammer shot nailed into a large plastic washer every so often. This is fine if you never plan to have a finished wall, but I can see where you would either have to build a stud frame wall away from the concrete wall or remove the sheet insulation, and frame the wall in next to the concrete wall and then install bats of insulation in between the studs. Full disclosure, I have no idea what the OP's local code requirements are. I would think the easiest thing for the OP to do would be to pay a little extra to have the builder frame in the walls and install bat insulation (if permitted) since it sounds like the house is still under construction. Just my two cents.

[Marty Tippin]

Personally, I'd just frame the stud walls in front of the insulation, there's no need for an interior wall to be fastened to the concrete basement wall; just nail to the concrete floor and to the overhead joists (using a stringer between joists if the wall runs parallel to the joists). You won't lose more than 3" of space, and you'll have better insulation with a continuous barrier rather than one interrupted by the (essentially zero R-value) wood studs every 16 inches.

[Steve Peterson]

Personally, I'd just frame the stud walls in front of the insulation, there's no need for an interior wall to be fastened to the concrete basement wall; just nail to the concrete floor and to the overhead joists (using a stringer between joists if the wall runs parallel to the joists). You won't lose more than 3" of space, and you'll have better insulation with a continuous barrier rather than one interrupted by the (essentially zero R-value) wood studs every 16 inches.

A typical 2x4 has an R-value of about 5, so it allows slightly more than 2X the thermal loss of the fiberglass between the studs at R11. The average R-value of the combination of wood and fiberglass is probably around R9.

I agree, that the best option would be to just add a simple frame wall in front of the required insulation. Let the builder do the cheapest option that satisfies the code. Asking him to make changes will probably be much more expensive than anything you do yourself after he is finished.

Steve

[Paul F Franklin]

You really don't want fiberglass insulation against concrete walls, assuming they are below grade. You get moisture diffusing through the concrete from the outside that has no where to dry to because of the vapor barrier. And because the vapor barrier is never perfect you get moisture from the inside air condensing on the cold wall surface. It's only a matter of time until you have wet insulation which both kills its insulating value and provides an environment that can support mold growth. You can get away with it if conditions are just right, but they almost never are (at least not year 'round) and you won't know until it's too late.

[Roger Feeley]

OP here:

Haha! I like the Jiffy Pop description. I will be using that.

My understanding of the codes is that R10 is required. I worked with my builder for some kind of rigid insulation with furring strips to which I can attach some sort of wall covering. I'm thinking either OSB or I could get funky and collect pallet wood for the next 8 months.

I'm a little concerned about venting that rigid insulation. Any moisture coming through the concrete would be trapped in there.

[mark mcfarlane]

OP here:

Haha! I like the Jiffy Pop description. I will be using that.

My understanding of the codes is that R10 is required. I worked with my builder for some kind of rigid insulation with furring strips to which I can attach some sort of wall covering. I'm thinking either OSB or I could get funky and collect pallet wood for the next 8 months.

I'm a little concerned about venting that rigid insulation. Any moisture coming through the concrete would be trapped in there.

If you are thinking about rigid foam, here is a good read on ants and termites. It's not entirely conclusive, but does raise some concerns worth considering at this early point in the history of rigid foam insulation.

[Dan Hintz]

I think I have seen what the OP is talking about in my sister's house in VA. Their builder covered their exposed concrete basement walls with insulation that must have come in giant rolls; insulation on the concrete facing side and a silver vapor barrier facing out. No bats. The finished result makes the walls look like the top of a JiffyPop after you pop the popcorn. IIRC, they fastened it to the wall with a hammer shot nailed into a large plastic washer every so often.

The Jiffy-Pop description is quite apt This is what I have in the basement. When I'm finished putting up the stud walls (with a 3" gap to the concrete), I plan on ripping out the JP rolls having someone spray a couple of inches of closed-cell foam.

[Prashun Patel]

If the builder has not completed their work yet, why don't you pay them to frame out against the concrete wall, and to lay the barrier/insulation between the bays?