Insulating Basement Walls

[Anonymous]

Posted by: Zimsky (old forum transfer)
Posted - 03/06/2002 : 09:43:09

I am finishing a heated basement which is entirely below grade. There are no water leaks in the block but I have noticed some minor florescence coming from the mortar joints around 6-8 blocks in a corner wall. Is this a concern?

I have also installed a 6 mil poly vapor barrier followed by 2" x 4" framing around the perimeter walls. I was planning on using standard R-13 fiberglass insulation with the kraft paper vapor barrier facing out. Is the best type of insulation for this application (i.e., with a vapor barrier), or would I be better served with non-faced fiberglass or perhaps an isocyanurate product like Celotex?

Thanks

Dave

[Anonymous]

Posted by: Wgoodrich
Posted - 03/06/2002 : 21:53:06

I am a bit confused on your statement of flourescense. Do you mean you can see some daylight through some cracks in the morter joints or are you saying that you have a subsantance giving off light such as a type of organic mold?

You are creating a problem or two concerning trapping moisture. If you have a basement that is below ground and if your building was built origianlly to meet Code then the outside of your basement walls were probably waterproofed with a form of barrier such as waterproofing pitch on the exterior of your basement walls. Then you are installing a plastic vapor barrier on the inside of that same wall. In my opinion your are creating a trap of moisture in between those two barriers blocking the walls from ever drying out inviting mold and mildew at the least. Then you again are installing a vapor barrier on the other side of your 2 x 4 wall again creating a second trapped area that can not breath trapping the moisture agian within the stud walls now making a double trapped area both inviting mold and mildew and now rotting can occur also with the wood studs.

In my opinion you need to use friction bat fiberglass insulation in the studs spaces allowing the cement and wood wall to breath and emit any moisture that may occur. This would limit concerns of rotting, mold and mildew. The friction style insulation will squeezin into the stud spaces creating your insulating desired without trapping moisture that can cause you long term and expensive damage.

The cracks in the morter if you can see daylight obviously your cracks are above finished grade. I wouldn't worry about the cracks unless the cracks are spreading showing movement in your footing or wall. If the cracks are opening up then you may have a concern of settling of you footing or movement of your wall. This could be a concern.

Hope this helps

Wg

[Anonymous]

Posted by: Zimsky
Posted - 03/07/2002 : 07:45:59

What I mean by "florescence" is a common term used to describe a white powder substance (i.e., calcium carbonate) that concrete block typically emits on the interior side of a below grade wall. I believe it is caused by the capillary movement of moisture through a block.

As far as the vapor barrier is concerned, I have seen this used in on "home show" programs for below grade applications, especially on floors, but your reasoning certainly makes sense.

I am still concerned about using a fiberglass insulation product. With the inherent moisture in all basements, wouldn't you recommend a foam board product?

Thanks

Dave

[Anonymous]

Posted by: Wgoodrich
Posted - 03/07/2002 : 13:25:38

As long as you have a dry basement you should be fine using the fiberglass insulation. However if you are concerned with the fiberglass getting wet wouldn't you also be concerned about the drywall getting wet. You can use the blue board type styrofoam installation board if you like. The R value would not be as high as the 3 1/2" friction style fiberglass stud batts but it would work fine.

The white powdery substance that you are discibing can be nothing to be concerned about but it also may be a health concern. That question should be easily resolved by scraping a sample into a clean small class container and taking it to your local Board of Health for testing. They should be able to rapidly tell you the results as to whether it is a concern to health or not. This test is something you should do for safety and piece of mind before you cover it up.

Let us know what you find and good luck

Wg

[Anonymous]

Posted by: HandyRon
Posted - 03/07/2002 : 20:27:20

Effloresence is leakage of (I think) lime from the motor/concrete from water penetration.

Ron

[Anonymous]

Posted by: Wgoodrich
Posted - 03/07/2002 : 21:56:23

HandyRon while I agree with what you said am also aware of molds that act in the same manner and look similar. I felt it to be safe than sorry later.

Just playing it safe

Wg

[Anonymous]

Posted by: kleecs1
Posted: Sat Jul 27, 2002 12:21 pm

There is a fundemental problem with insulating basements because of the moisture problem. Efflouresence is usually caused by moisture pushing through brick and bringing salts with it. Even if that is what is happening here, it should not be a big problem and there is not much to be done about it from inside the basement. If there is no appreciabe moisture present, then this should not drive the decision making.

The real problem here is the moisture barrier and trapping moisture in the wall as noted by Wgoodrich. The problem is that moisture barriers HAVE to be on the warm side of the insulation. If you install insulation with no vapor barrier, then the nice warm (and by definition) moist air will migrate through the insulation until it reaches a cold spot and then the moisture will condense. Over time, this condensation will cause the insulation to get matted down and will encourage the growth of molds and rotting of the structure.

As a result, there is no easy way to insulate a basement from the inside. Personally, I would avoid doing it because it covers up a potential source of problems in the house. You only find out about the mischief behind your drywall when really bad things are happening.


That said, if you have to do this, I would suggest that the best way would be to install a vapor barrier right on the face of the block (trapping moisture in there, but what can you do about that). Then I would install rigid insulation (not Isocyanurate because it offgases slightly and deteriorates over time). I would use MEPS or XEPS which is readily available and more environmentally friendly. It is something like Expanded Polystyrene. The key is to make sure that there are no gaps in the insulation so that you don't get any cold spots for condensation.

After installing the insulation, I would build out a stud wall inside the room leaving a small gap behind the insulation. And then, I might consider providing some vent holes in the drywall (top and bottom) to make sure that the cavity breathes. That way, the drywall cannot inadvertently start to function like a second vapor barrier.

One thing to keep in mind. If the basement is entirely below grade, the block temperature should be around 50 degrees F. This means that if your air is somewhat dry in the winter, you might not hit the dew point and so condensation risk is minimized. A typical problem area, however, is that the basement walls typically project above grade at some point and then the wall gets much cooler. You might have insulation in the outside wall at that point however. No matter what, you will have a small concern in the area where the insulation moves from the inside face of block to the outside face. In that area, there is something called a thermal bridge where the cold can move diagonally across the block and bypass the insulation. Your best bet is to try to overlap these areas so that the diagonal path is lengthened as much as possible.

That's my two cents. Good luck. It is not a problem that I would want to have to solve.

[Anonymous]

Posted by: Wgoodrich
Posted: Sat Jul 27, 2002 4:15 pm

kleecs1, well said. Your thoughts are accurate and impressive.

My hat off to your reply !

Wg

[highballer99]

Well hello all, I am in Canada, I was thinking maybe i could shead some light onto this, I have been working with an inspecter on finishing my basement, It has been studded, insulated with r-20 insulation, Now he suggests that you may use poly 6mm on the inside of the wall, but the better thing to do is tar the basement walls,so the whole basement was tarred below 2 feet grade level,{below your windows} this allows the moisture to still pass above, and gives a better seal! That said i too have the problem of that sulfer coming thru the walls, bleach does help but basically in olde homes they never added the requirements to stop the alkoliod, the cement you get now adays had this additive, So basically it will eat your walls out, but long after i am dead, so anyways after i tarred, i staudded the walls, insulated, then i am going around the walls with 6mm poly, and you have to seal all unfinished edges with the accoustical celent this traps the air out, this is the way the government of canada goes and does this through grant programs, so i am quite positive that it is a good solution, if they are footing the bill, any questions get back on this board, thanks, Dawn