Framing and Insulation question

[James Conrad]

Some pics of the walls/area would be helpful, what region do you live in as well. You could use foil backed tape, or any non-permeable permanant joint tape, BORGs should have it.

If it were me, I would rip it all out, save the framing lumber and adhere 2" closed cell rigid foam to the walls, floor to cieling, maybe add 2 layers, reframe and leave the joist bays empty of any other insulation. I don't think fiberglass insulation is useful in a basement wall, it does not stop air movement and it will hold moisture, Roxul is a better option if you don't want to rip it all out.

[James Conrad]

To support my no fiberglass
review this article

http://www.buildingscience.com/docum...t%20insulation

Good articles, worth reading!

[Shaun Wesley]

Some pics of the walls/area would be helpful, what region do you live in as well. You could use foil backed tape, or any non-permeable permanant joint tape, BORGs should have it.

If it were me, I would rip it all out, save the framing lumber and adhere 2" closed cell rigid foam to the walls, floor to cieling, maybe add 2 layers, reframe and leave the joist bays empty of any other insulation. I don't think fiberglass insulation is useful in a basement wall, it does not stop air movement and it will hold moisture, Roxul is a better option if you don't want to rip it all out.

I am in DC. The more I look at other sections of my basement and take the faceplate off the cable outlet I have noticed the entire basement was done with faced batt insulation and there is no visible vapor barrier. Meaning drywall, batt insulation and I can see the concrete foundation. Having spoke with my neighbor who had his home built at the same time this one was built by the same builder he instructed me the basement walls below grade have some form of black sealant on the foundation and foam boards applied on the exterior walls.

Does this account for why there is no visible vapor barrier on the interior walls? For the walls above grade, obviously there is nothing on the exterior side of the wall, is it fine the interior side only has batt insulation separating the concrete and drywall? Since the home is only a few years old it is hard for me to believe this passed inspection if it was not ok for there to be no vapor barrier..? Does this account for why the foil backed insulation in the unfinished area was no taped at the seams because it did not matter? Thoughts?

[James Conrad]

If the house was built in 2009 most likely the 2006 code was being followed, possibly 2003. At that time there was no requirement for insulation if the basement was unconditioned space. The black coating is a moisture barrier to help stop any exterior water from migrating through the wall, depending on how well it was applied, not a vapor retarder as used in other construction methods. The thing is with a concrete basement wall is that it is a giant heat sink allowing hot/cold and dry/wet to pass back and forth as conditions in the basement change and with the seasons. To mitigate this you need to isolate it from the conditioned space, one of the best methods is closed cell spray or rigid foam. Using that type of product stops thermal bridging and most of the concerns of condensation occurring in the wall cavity because you have isolated that heat sink. As mentioned before, fiberglass faced or unfaced does not sufficiently stop air movement. While it may not violate code then or now, it does become a matter of best practices. The articles that Phil points to have very good diagrams showing how to follow best practices.

To answer questions about vapor retarder, it was most likely not code required, and how we use and view vapor retarder has changed even from 2009. Against a basement wall, a vapor retarder is useless without insulation and vise versa. If you stop air movement and not the transfer of heat/cold, you will get condensation as it hits the concrete wall or the back of your drywall with enough temp difference. If you just use fiberglass, you are not stopping air movement... That is why rigid foam is so good for this application - it's a vapor retarder, insulator and if moisture does arise it won't breakdown or hold it.

[Ole Anderson]

Not uncommon to use PT on the plates in contact with the concrete floor, and untreated studs. Just in case you get some wicking or spills on the floor. Watching Mike Holmes in Canadian episodes, seems they reverse the vapor barrier and put it against the cool wall. I recall him saying that he felt that was one area where the Americans had it right.

[Bob Betker]

Shaun: I'm in the DC area as well. My in-laws have a similar setup on their house which was built about 10 years ago. In essence, they have put the vapor barrier on the exterior walls as you guessed. The black stuff is a type of mastic and it is meant to be a waterproofing material, primarily to stop water from wicking through voids in the concrete (hydrostatic pressure). The foam boards are designed to be a thermal barrier to the cold ground so that the walls don't sweat. This type of exterior insulation/waterproofing is good for 20-30 years before it fails.

If you were starting from scratch and money wasn't a problem, putting 2" XPS on the interior walls would be the best approach, it insulates and is moisture impermeable so no interior moisture would get to the concrete walls and condensate. Inside your stud walls, you can insulate with a batt insulation. I'd go with Roxul since it doesn't have the mold problems that occur if your fiberglass insulation somehow gets wet. That would get you to about R-30 range for the walls and the basement should be pretty comfy.

There is moisture-resistant, mildew-resistant drywall that you can purchase. I used it on my workshop and it only costs a buck or two more than regular drywall.
Lastly, make sure you check your rim-joist for insulation and air infiltration. Sealing that can make a big difference in how the house feels.
Good luck, Bob

[Shaun Wesley]

I picked up the Roxul insulation and have some followup questions.

I was going to pull down the foil backed batt insulation because I figured it defeats the point of using Roxul, since Roxul is mold resistant. I don't think it would be smart to leave fiberglass insulation pressed up against the concrete wall. Do I need to put a vapor barrier against the Roxul? This is in an unfinished room and only three walls are framed. The fourth wall is obstructed by the HVAC and water heater so it will be left exposed (covered by the foil backed batt). I figured if the Roxul is resistant to mold then what is the point of a vapor barrier? These walls are solely for holding the electrical and drywall and are not load bearing. Is there a benefit to having a vapor barrier if it doesn't cover the 4th wall anyway?

If you recommend using the vapor barrier how do I seal the electrical outlets? Can I just spray foam the holes in the box where the wires enter and tape the plastic vb over the front of the wall?

Thanks.

[phil harold]

your wood studs will mold if the roxul wont
you could use a borax solution applied to the studs to resist molding

yes foam the boxes

remember it is vapor retarder not vapor barrier
vapor is still going to travel thru you are only going to be able to slow it down
seal it the best you can
good luck with your project