Basement insulation plan

[ouchmythumb]

Hi All,

I want to insulate my basement, I would like to do it right so I would love to have comments on what I plan to do.

I read the following:
http://www.buildingscience.com/resources/foundations/renovating_your_basement.pdf

Here is what I have:

I am in a townhouse, I have two concrete block walls, I am an end unit and the houses are offset so the shared block wall has 6ft of outside exposure. My house is 1ft lower than my neighbor so on the shared wall 1ft has dirt on the other side of it. On the end wall the earth slopes, so at the walkout end there is no dirt and at the front end there is 8ft of dirt. Part of the end wall has a finished stairway and I will not do anything to that, I think it is sheetrock on thin wood strips with a vapor barrier and no insulation. There is 6 to 8 feet of dirt on the other side of that part of the wall.

Here is my plan:

On the end wall I will have 1 inch of extruded polystyrene insulation (XPS) right up against the concrete block with no air gap, then 2X4s right up against the XPS holding it in place. The bottom will be pressure treated with sill plate foam under it. I will put fiberglass between the 2X4s right up against the XPS. All the R-13 I have seen is faced, can I buy unfaced R-13 somewhere or even unfaced R-11? On this I will put no paper sheetrock, is the material on the no paper sheetrock a vapor barrier? I don't think I can use any kind of a vapor barrier.

I will treat the shared wall the same as the end wall except I will only insulate the 6ft that are exposed + 2 more feet since the wall is likely to be cold, I will also insulate the bottom 2 feet of the wall to take care of the 1ft that has dirt on the other side of it. I will not insulate the rest of the wall between my house and my neighbor's, no point as their house is probably warmer than mine anyway.

I will not put any kind of additional vapor barrier anywhere on any of these walls but the no paper sheetrock might be a barrier.


The front wall is in an unfinished utility room, 8 feet of dirt behind it, I will have the 1inch XPS then wood strips then .5 inch of whatever the code requires, probably sheetrock without paper but plywood if it is allowed.

The last wall has walk out glass doors, I will have R-13 glass and .5 inch of foil covered foam on that wall, then sheetrock right against the foam.

The concrete block wall extends up to my first and second floor and I will treat them the same as the basement walls.

I will glue 2 inches of XPS against the rim joist. No vapor barrier.

Can I use paper covered sheetrock on any of these walls or on the basement ceiling? I like the 12 and 14ft sheets as they have fewer seams but I don't like mold and the mold seems to like the paper.

Thank you for any comments.

[Timothy]

You wrote:
"The last wall has walk out glass doors, I will have R-13 glass and .5 inch of foil covered foam on that wall, then sheetrock right against the foam."

Foil covered anything is a vapor barrier. I would not cover the R13 FG with this in the basement. Why are you considering foil covered foam in this one location when you're already planning on using the XPS elsewhere?

The building Science website is an excellent resource. There was an article on basement insulation in Fine Homebuilding within the past two years, excellent, detailed article. I'd consider buying the article online or getting it from the library.

You mentioned 12' and 14' drywall. Have you considered whether it will be difficult to get it into the basement (perhaps it's not an issue for your basement, for most it would be). I'd think the no paper drywall manufacturer's web site would indicate if it's a vapor barrier or not, or call the manufacturer.

[ouchmythumb]

The wall with the glass doors is a conventional stud wall with wood siding. I had thought that a vapor barrier was a good thing on such a wall. Should I have no vapor barrier anywhere in a basement? Should I just have the paper covered fiberglass on that wall with 3/4 inch of expanded or extruded polystyrene covering it and the studs and then 1/2 inch sheetrock over that? How about on my first and second floors?

The glass doors are 4ft wide and 6.5 ft tall, I can get anything I want into my basement, it is kind of nice.

[Wgoodrich]

The outside walk out wall would be treated as any other wall of a house most commonly insulated with friction batt non paper back insulation then plastic sheeting installed as a vapor barrier.

The basement walls below grade all depends on how they were built. YOu need to dig down along the bassement wall outside to find if insulation was installed and if black tar or other type of water proofing or water resistant material was installed making a vapor barrier outside. Then no paper back insulate only friction style non paper back insulation is installed in the studs on those subsurface walls. No bisquine or paper should be installed. Remember the styrofoam against your masonry wall serves as a vapor barrier unless you buy the type styrofoam that can breathe. You paper style drywall will perk moisture and is not considered a vapor barrier.

Sounds like you have a pretty good plan but check outside to find how those walls were protected below finished grade and if with vapor barrier such as the tar painted on the walls outside. This will change you work design inside.

I agree the building Science website is an excellent resource of knowledge on the subject. We pretty well parallel what they are saying on their web site believing pretty well the same as they suggest in our minds. Good web site to read.

Good luck

Wg

[ouchmythumb]

I'm in an end unit townhouse, I checked the foundation of the concrete block wall on the end, it is black below grade, I suppose that is waterproofing, it looks very thin, I wouldn't be surprised if it was too little to do any good. Above ground just paint.

The other concrete block wall is mostly shared with my neighbor, about 6 feet of it is painted and has my neighbor's shed right up against it. My house is lower than my neighbor's so about 1 foot of my shared basement wall has dirt on the other side of it. My neighbor has a shed that covers to the end of the wall and his house covers the rest so I can not dig very much on that side. I did reach under the shed and dig a bit and found that 8 inches below grade there was NO waterproofing. There is paint, perhaps there is waterproofing farther down or farther in, no way to know, but at least part of that wall below grade has no waterproofing at all.

Question 1.
Can you tell me if 3/4 inch XPS right against the block, then 2X4s with fiberglass is still a good plan?

Question 2.
Can you also tell me if I can put 3/4 inch XPS between the shared wall and the 2X10 joist? It is either open air or my neighbor's conditioned house on the other side of that wall. The 2X10 would be flat against the XPS, it is so much wider than a 2X4 that the rules might be different.


Note:
I am using 3/4 XPS because this paper:
http://www.buildingscience.com/resources/walls/Vapor_Barriers_Wall_Design.pdf
says that XPS 1 inch or thicker is vapor semi-impermeable and is therefore more of a vapor barrier than my wall can likely tolerate right up against the block.

I am also not going to use the foil faced foam on the inside of my walk out wall as my basement is cold in the summer and I am concerned about condensation inside the wall from the hot humid air outside infiltrating as far as the foil. I will use 3/4 XPS on the inside of that wall as well, covered with painted sheetrock. I am using the foam to stop the thermal bridging from the studs, I figure I have the whole place torn apart anyway and I don't mind losing the 3/4 inch of space.

[Wgoodrich]

xps styrofoam against the masonry walls is fine with or without waterproofing outside. At this point waterproofing is not sure but you discribe not much if any. I would install the xps styrofoam against the masonry wall then frame a wall against the inside of that styrofoam. Then install friction style without paper fiberglass insulation to fill the stud walls then install drywall as a finished product on the three subsurface walls. This is regardless of location of adjoining wall of neighber finishing that wall the same as above. All the products above will breathe out moisture into the room keeping the wall healthy. The styrofoam will perk moisture but if wet happens behind the wall it will be contained against the concrete that wicks moisture in or out as the subsurface water appears or dissipates to dry anyway. This styrofoam is you best choice against the masonry to protect the studs. Yes treated bottom plate that is agains the concrete floor.

The above grade wall build same as any other wall built in the house. Friction batt fiberglass insulation without paper in the stud space then plastic sheeting over the studs then drywall against the plastic sheeting.

Good Luck

Wg