Your basement isn't cold because it's being heated. Indeed, an uninsulated basement accounts for up to one-third the heating cost of an average home, according to Building Science Corp. Still, if no permits are required--other than plumbing--you probably won't have to add insulation.

However, the problem will arise in cold weather when the warm air of your basement hits the above frost line portions of your foundation and condensation occurs. The water will feed mould growth on the foundation wall and the back of the drywall. That's the typical "musty" scent of so-many basements. If you have ac, in the summer you'll have the cool basement air hitting the hotter foundation and rim joist area, again creating condensation in the confined space.

The International Energy Conservation Code 2012, which will eventually be implemented in most US states, calls for a minimum of R15 continuous insulation for basements in your climate zone--Zone 5.

Thank you Worthy. I've passed your info on to my husband. I'm wondering, would this mold growth only happen because the walls are closed up with draywall now, so the condensation has no where to go? Because right now, as unfinished walls, we never have condensation or any mold. You can see the stains from where water came in at one time (before we owned the house), but it has been dry for over 3 years. Here's a picture of one of the corners.

Removing duplicate post.

This post was edited by deb52899 on Tue, Mar 19, 13 at 9:49

When you build a finished wall, you're inhibiting the inward vapour drive. So the foundation wall won't dry as well as it does now. Also, the foundation wall will be cooler in winter than it is now, again making it more susceptible to condensation.

The few hundred dollars you spend now on insulation will quickly payback in energy savings and comfort.

In any case, you would be advised to repair those form-tie hole leaks before you do any finishing. Whatever temporary patches were done will eventually fail. The most common permanent repair is the use of non-shrinking urethane foam. Swell plugs are another method.

Here is a link that might be useful: Building Science Corp.: Renovating Your Basement

This post was edited by worthy on Tue, Mar 19, 13 at 13:42

Thanks again Worthy. So if I read Building Science correctly, the XPS should've gone on before the studs? My husband and son-in-law don't think we need insulation. I'm not worried about the heat, I'm just worried about mold later on. Part of the walls are framed already. I just read about plugging the holes too - never saw that before. Thank you!

So if I read Building Science correctly, the XPS should've gone on before the studs?

Correct. As per the pic below from Building Science Corp. I hope at least they put something under the baseplate to keep the moisture off the framing, such as 6 mil poly.

I sense the dynamic: Instinctive male knowledge vs. bothersome female with her smartass "booklearning."

This post was edited by worthy on Tue, Mar 19, 13 at 16:21

Worthy - can you help me? What size xps do I need? Is 1" ok?

I think from what I read 1" is fine - that's why our guy is buying this morning. Also, he can't find the foil tape anywhere and 3 building supply places told him that Tyvek is fine. I read that Tyvek said not to use their tape for this application, but that's all he can find so please confirm that it will be ok. Thanks!

One inch--R5--will work well to keep the wall above dewpoint; added fibrous insulation between the studs will give you better energy savings. (But unless you take care of those form-tie holes, avoid the fg.)

Tyvek tape is not suitable for taping extruded polystyrene (XPS) according to the manufacturer.

The linked article below mentions some that are. I use Tuck Tape, but it's not available everywhere. Look for a similar housewrap tape.

If you use shiplap XPS--especially the four foot wide boards-- you won't need much tape at all.

Simplest installation method: use concrete screws or percussive fasteners to fix the boards to the wall and temporarily prop tight. Frame the lumber (or lightweight steel) wall tight and shim as necessary. Any areas that don't sit tight to the wall can be foamed with Great Stuff, for example. Neatness doesn't matter.

Good luck!

Here is a link that might be useful: Sheathing Tapes

This post was edited by worthy on Wed, Mar 20, 13 at 10:31

My husband thinks the holes were already filled.

My guy is already working and using Tyvek tape. I looked up Tuck Tape and it appears to be available in Canada only. The article says to use housewrap tape, and when I search for that, Tyvek comes up (even though in the next paragraph Tyvek says not to). I think I have to let it go with the tape.

Installation, my husband does not want to put holes in the concrete walls to fasten the foam. They will glue and then the 2x4 frams will go up against them.

Thanks for your help!

my husband does not want to put holes in the concrete walls to fasten the foam. They will glue and then the 2x4 frams will go up against them.

A half-inch penetration into an eight or ten-inch concrete wall won't compromise it. I've never had good luck with glue on poured walls--just too many irregularities. Once you glue it, you can run a couple of lengths of one by two or one by one horizontally across a wall of the insulation to hold it, then frame against that. The important thing is to keep the XPS tight against the foundation wall so it can prevent the conditioned interior air from hitting the foundation.

The tape is not all that critical in this application, vs. exterior sheathing; too bad you couldn't find the shiplapped boards. Sometimes you have to look past the familiar Big Boxes.

my husband does not want to put holes in the concrete walls to fasten the foam. They will glue and then the 2x4 frams will go up against them.

A half-inch penetration into an eight or ten-inch concrete wall won't compromise it. I've never had good luck with glue on poured walls--just too many irregularities. Once you glue it, you can run a couple of lengths of one by two or one by one horizontally across a wall of the insulation to hold it, then frame against that. The important thing is to keep the XPS tight against the foundation wall so it can prevent the conditioned interior air from hitting the foundation.

The tape is not all that critical in this application, vs. exterior sheathing; too bad you couldn't find the shiplapped boards. Sometimes you have to look past the familiar Big Boxes.

Glad to hear the tape is not critical here. No one has said I'm crazy ot my face, but I think our builder might have told the store people that :) He is taking down what he already did, putting up the foam board and basically starting over for me. What are shiplapped boards? The XPS we got is tongue and groove, not square edges.

In this context, shiplapped and t&g are the same thing.

Good for not being intimidated!

The amount of outdated, uninformed information on building science never ceases to amaze me. Especially when with the click of a few keys you can get the state of the art from Building Science Corp., Building America, the National Research Council of Canada etc., etc.

I appreciate your help very much!