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Yet Another Basement Wall Question


lilfos's Avatar
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08-10-05, 02:56 PM   #1  
Yet Another Basement Wall Question

Man, are there are lot of different opinions about the absolute right or absolute wrong way to finish exterior basement walls. I know that everything depends on climate and existing conditions, so everyone's opinion is probably valid for at least one home out there.

My hope is that I can describe my situation and see what folks think my best approach should be.

Climate: Washington DC area - mid 90's and high humidity much of the summer, 30's and 40's much of the winter with occasional cold snaps in the teens or single digits. Perfect weather during the spring and fall.

Exterior conditions: Grade level ranges from 5' above basement floor to ~7'. Known groundwater issues, mitigated with a full perimeter interior french drain and sump pump about 18 months ago. Basement has been very dry since, with the exception of one crack in the wall that leaks maybe one drop of water per hour during very heavy rains. The sump pump definitely runs during rain storms and sometimes for a day or two afterward (very intermittently).

Existing wall construction: Built in 1938. Concrete block with a few sections of brick (I think for extra support in specific areas). House is block with brick veneer. Some parts of the interior basement walls have what looks like DryLok, but it could just be flat white paint. Some areas were previously finished in the 60's with pine paneling and have an off-white paint that does not feel like DryLok. These areas have since been painted with latex paint for aesthetic reasons. The entire perimeter has an 8" vinyl "baseboard" installed with the french drain and designed both to let any wall moisture drip down into the drain system, and to keep the backfilled hydraulic mortar from filling up the holes they drilled in the base of each vertical channel in the block walls.

For half of the year, the inside of the basement is the warm side. When it's hot out, the sections of wall above grade switch to being warm on the outside.

Even without insulation or registers, the basement is very comfortable year round. The HVAC and ductwork is likely responsible, except on days when no climate control is necessary and the earth is doing all the work.

Whew...I think that's all. Now, some things I've been thinking:

The french drain contractor said that I could line the walls with plastic and tuck it behind the vinyl "baseboard;" however, I'm hesitant to create such a nice place for mold to thrive.

The basement is small, so I'd like to avoid dedicating 4+" to wall construction. The previous pine paneling hung from furring strips that I have since removed. I was thinking about using 2x3s or 2x4s turned sideways on 2x2 pressure treated sole plates. The plates (regardless of the size I choose) would be adhered to the floor with Liquid Nails to avoid giving hydrostatic pressure a few dozen places to relieve itself onto my floor. While some have said you should avoid letting wood studs touch exterior walls, there seems to be more people advising not to leave a gap.

I have read about gluing 2" closed cell foam with taped seams to the wall to act as a vapor retarder and insulator. Supposedly, the foam breathes enough to dry itself out, and is thus not a barrier. The tape is to avoid heat transfer, not moisture movement. I have also read about people gluing drywall directly to the foam and calling it a day. This is a very attractive idea, if it works. I'll just use mollies for my wall hangings. I've considered putting the 2" foam between the aforementioned 2x3s or 2x4s, but this might be useless unless I seal it to the studs really well. In either of these situations, I'd have to cut channels in the foam for the electrical, and the boxes might penetrate all the way to the block wall.

Finally, in addition to requesting your general opinions, I have a question: If the agreed-upon solution is to use a vapor barrier or retarder on the inside of the wall, is it ok to penetrate it with electrical boxes, or should I force the box in place, pushing membrane a couple inches into the wall.

Many thanks to anyone who takes the time to read this and offer a possible solution!

 
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em69's Avatar
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08-11-05, 05:04 AM   #2  
[QUOTE=lilfos] I have read about gluing 2" closed cell foam with taped seams to the wall to act as a vapor retarder and insulator. Supposedly, the foam breathes enough to dry itself out, and is thus not a barrier. The tape is to avoid heat transfer, not moisture movement. I have also read about people gluing drywall directly to the foam and calling it a day. This is a very attractive idea, if it works. I'll just use mollies for my wall hangings. I've considered putting the 2" foam between the aforementioned 2x3s or 2x4s, but this might be useless unless I seal it to the studs really well. In either of these situations, I'd have to cut channels in the foam for the electrical, and the boxes might penetrate all the way to the block wall.[/QUOTE]


This is why batt insualtion works best when insualting between studs...the batts fill the space between the studs mich better and it is easier to work with.


Posted By: lilfos Finally, in addition to requesting your general opinions, I have a question: If the agreed-upon solution is to use a vapor barrier or retarder on the inside of the wall, is it ok to penetrate it with electrical boxes, or should I force the box in place, pushing membrane a couple inches into the wall.

The electrical boxes must be sealed as well. There are two ways to do this. You use the same 6 mil poly you use of the walls by wrapping the boxes and then overlapping the excess onto on the VB. Then apply VB tape. Or, you can purchase the pre-formed plastic wraps for the electrical boxes, then you just need to tape of the edges.

 
lilfos's Avatar
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08-18-05, 09:30 AM   #3  
Thanks for your response.

I've heard mixed opinions about putting batt insulation up against the exterior walls. Do you think this would trap moisture in the fibers and against the studs, which are sealed in by the kraft facing?

I'm realizing the issue at hand is that there is moisture on both sides of the wall. Any wall system I use needs to be able to breathe to dry out, but not transfer much heat. Is this realistic?

 
Concretemasonry's Avatar
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08-18-05, 09:48 AM   #4  
Yet Another Basement Wall Question

Moisture will affect the insulating value of Fiberglas. I have read that something like 1% can can cut the R-value by 30 to 50%. It seems to make sense to keep it dry.

For what its worth-

Dick

 
em69's Avatar
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08-18-05, 11:37 AM   #5  
Posted By: lilfos Thanks for your response.

I've heard mixed opinions about putting batt insulation up against the exterior walls. Do you think this would trap moisture in the fibers and against the studs, which are sealed in by the kraft facing?

I'm realizing the issue at hand is that there is moisture on both sides of the wall. Any wall system I use needs to be able to breathe to dry out, but not transfer much heat. Is this realistic?

I wouldn't recommend putting batt up against the cement...it is a recipe for disaster. You should install what's called a moisture barrier (typically 6 mil poly or tar paper) up against the concrete, which starts at grade and goes all the way down and then sealed to the base plate. Your vapour barrier (6 mil poly) should then be sealed to this, therefore sealing the insulation. If it's done properly, all cracks sealed including electrical boxes, the batt will stay dry.

Now if moisture becomes present behind the wall cavity, it can escape through the upper portion of the wall...which is why the moisture barrier must only start at below grade.

My basement wall construction was done as per the National Research Council and CMHC specifications and I feel confident it is the best for my climate.

 
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08-18-05, 11:45 AM   #6  
Thanks again.

Would this work if the exterior wall is concrete block with a DryLock and/or Latex paint coating? I wonder if the moisture would not be able to escape in this case. I can imagine that a fair amount of moisture will rise up from the french drain system since there is that vinyl bumper at the base of the wall, allowing the drain trench to breathe.

 
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08-18-05, 11:51 AM   #7  
Yet Another Basement Wall Question

Keep in mond there are many source of moisture than can ruin the insulating value of pink stuff. This is why it is fragile and must be protected.

There is leakage through a wall, some vapor transmission and condensation. DryLok and other coatings do not affect the condensation. If the surface is below the dew point there will be condensation that will be transferred to the insulation.

Dick

 
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08-19-05, 04:21 PM   #8  
Posted By: lilfos Thanks again.

Would this work if the exterior wall is concrete block with a DryLock and/or Latex paint coating? I wonder if the moisture would not be able to escape in this case. I can imagine that a fair amount of moisture will rise up from the french drain system since there is that vinyl bumper at the base of the wall, allowing the drain trench to breathe.
I wouldn't apply the drylok above the grade level as it would prevent any moisture from escaping thus rotting the wood and creating mold.

 
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09-17-05, 07:05 AM   #9  
Thanks for all the input. While the stuff that looks like DryLok is already on the walls, it's good to know that I shouldn't put it above grade in future applications.

I think I'm going to go with 1 1/2" rigid foam glued to the block walls with 2x3 studs turned sideways. This should:
- make for a 3.5" finished wall
- let me true the walls a bit with the framing
- prevent wood from contacting the exterior wall
- serve as a vapor retarder that can still breathe
- give me a little space to run wires (which can carve into the foam a little behind each stud)
- prevent electrical boxes from penetrating all the way to the block wall

 
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09-19-05, 06:37 AM   #10  
dmeg
One more opinion

Your right there are many opinions. I researched alot before finishing my basement and this was my solution. I live in new England so my climate is pretty similar to the DC area.

First I repaired concrete issues with hydraulic cement. Even little cracks that were not leaking because you'll never get a chance to do it again. Then I coated the walls and floor with drylock (there are some other products on the interent as well). I know some people do't think much of this step but i have been a big fan of this product for some time.

Then we used standard 2x4 studs (not resting on the concrete walls) and a PT base plate that was wraped in 6 mil plastic as it was in contact with the floor. I used rolled fiberglass paper facing the finished room with standard drywall over that.

It has worked great, been 3 years. i run a dehumidifier as everyone does in the summer. Only thing I did not do was install a plywood floor, I decided to carpet a synthetic pad over the cement. I was told by numerous sources that wrapping the walls caused more harm than good.

Hope this helps







Posted By: lilfos Man, are there are lot of different opinions about the absolute right or absolute wrong way to finish exterior basement walls. I know that everything depends on climate and existing conditions, so everyone's opinion is probably valid for at least one home out there.

My hope is that I can describe my situation and see what folks think my best approach should be.

Climate: Washington DC area - mid 90's and high humidity much of the summer, 30's and 40's much of the winter with occasional cold snaps in the teens or single digits. Perfect weather during the spring and fall.

Exterior conditions: Grade level ranges from 5' above basement floor to ~7'. Known groundwater issues, mitigated with a full perimeter interior french drain and sump pump about 18 months ago. Basement has been very dry since, with the exception of one crack in the wall that leaks maybe one drop of water per hour during very heavy rains. The sump pump definitely runs during rain storms and sometimes for a day or two afterward (very intermittently).

Existing wall construction: Built in 1938. Concrete block with a few sections of brick (I think for extra support in specific areas). House is block with brick veneer. Some parts of the interior basement walls have what looks like DryLok, but it could just be flat white paint. Some areas were previously finished in the 60's with pine paneling and have an off-white paint that does not feel like DryLok. These areas have since been painted with latex paint for aesthetic reasons. The entire perimeter has an 8" vinyl "baseboard" installed with the french drain and designed both to let any wall moisture drip down into the drain system, and to keep the backfilled hydraulic mortar from filling up the holes they drilled in the base of each vertical channel in the block walls.

For half of the year, the inside of the basement is the warm side. When it's hot out, the sections of wall above grade switch to being warm on the outside.

Even without insulation or registers, the basement is very comfortable year round. The HVAC and ductwork is likely responsible, except on days when no climate control is necessary and the earth is doing all the work.

Whew...I think that's all. Now, some things I've been thinking:

The french drain contractor said that I could line the walls with plastic and tuck it behind the vinyl "baseboard;" however, I'm hesitant to create such a nice place for mold to thrive.

The basement is small, so I'd like to avoid dedicating 4+" to wall construction. The previous pine paneling hung from furring strips that I have since removed. I was thinking about using 2x3s or 2x4s turned sideways on 2x2 pressure treated sole plates. The plates (regardless of the size I choose) would be adhered to the floor with Liquid Nails to avoid giving hydrostatic pressure a few dozen places to relieve itself onto my floor. While some have said you should avoid letting wood studs touch exterior walls, there seems to be more people advising not to leave a gap.

I have read about gluing 2" closed cell foam with taped seams to the wall to act as a vapor retarder and insulator. Supposedly, the foam breathes enough to dry itself out, and is thus not a barrier. The tape is to avoid heat transfer, not moisture movement. I have also read about people gluing drywall directly to the foam and calling it a day. This is a very attractive idea, if it works. I'll just use mollies for my wall hangings. I've considered putting the 2" foam between the aforementioned 2x3s or 2x4s, but this might be useless unless I seal it to the studs really well. In either of these situations, I'd have to cut channels in the foam for the electrical, and the boxes might penetrate all the way to the block wall.

Finally, in addition to requesting your general opinions, I have a question: If the agreed-upon solution is to use a vapor barrier or retarder on the inside of the wall, is it ok to penetrate it with electrical boxes, or should I force the box in place, pushing membrane a couple inches into the wall.

Many thanks to anyone who takes the time to read this and offer a possible solution!

 
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