Basement mold and expanding foam insulation

[Velvet Elvis]

Hey guys,

Got a little bit of a quandary and wanted to expert advice. My house is only 5 years old and we are just starting to finish the basement. Recently we ripped out the insulation (was there by code) to do some wiring and found MANY places with mold due to condensation on the cement walls. The people who have looked at it (a half dozen or so contractors etc now) said that its nothing significant and should go away once there is drywall up. We of course cleaned it all and such first.

A couple people told us to fill the walls with expanding foam insulation prior to putting the drywall up because it will seal ALL air that is causing the condensation.

This would be fine, except some of the areas are studio walls where I was planning on putting rockwool.

Here's my question. The outer leaf is the concrete wall. The inner leaf will be 2 layers of 5/8 drywall hung on RC. Would the foam be a BAD thing? It seems like it would help the mold issue, but hurt the isolation/STC of the wall.

The other thing is the sill on top of the foundation seems to be where the suspect the air is coming from. The foam would completely encase that, which stops the air... but would this be good for sound as well (vs attempting to caulk and backfilling with rockwool along the sill)? Some areas I CAN'T get to for rock wool, but the foam would be able to.

I've read that the foam is worthless from an STC perspective, but I'm wondering if its worse/better/indifferent than rockwool when used in a decent two leaf wall?

Any comments would be great - we need to let contractors know what we want to do TOMORROW (Monday). Grrr... stupid timelines and house problems!

Jim

 

[Rod Gervais]

Hey guys,

Got a little bit of a quandary and wanted to expert advice. My house is only 5 years old and we are just starting to finish the basement. Recently we ripped out the insulation (was there by code) to do some wiring and found MANY places with mold due to condensation on the cement walls. The people who have looked at it (a half dozen or so contractors etc now) said that its nothing significant and should go away once there is drywall up. We of course cleaned it all and such first.

And what was the vapor barrier used - and how was it installed?

When you have condensation - you have a breach in your vapor barrier........ period - otherwise there isn't any warm moist air to condense on that cold surface.

A couple people told us to fill the walls with expanding foam insulation prior to putting the drywall up because it will seal ALL air that is causing the condensation.

First of all - comments like that bother me - because it shows anyone with experience that the people talking don't know anything about the problem - yet they are talking as if they do - which could really screw people up.

Air movement has nothing to do with condensation - nor does air in general.

Condensation is an issue of vapor molecules (which are much smaller than molecules of air) and the fact that they will migrate from high pressure areas to low pressure areas.

The problem is created when those high pressure areas have a temperature differencial between the high and low pressure areas that is perfect for creating dew point - at which time the condensation appears.

The correct answer to the problem is to lower the humidity levels within the space until they are around 45% - and to maintain a proper vapor barrier so that the warm vapor can't make it through to that cooler surface.

This would be fine, except some of the areas are studio walls where I was planning on putting rockwool.

Why are you throwing money away on rockwool - it is no better for you that stamdard fluffy insulation.

Here's my question. The outer leaf is the concrete wall. The inner leaf will be 2 layers of 5/8 drywall hung on RC. Would the foam be a BAD thing? It seems like it would help the mold issue, but hurt the isolation/STC of the wall.

The foam would be a very bad thing if it were to bridge the face of the cement wall with the stud cavity of the inner framed wall. Do I understand correctly that you are building a wood frame wall inside of (and not touching) the cement wall - and then insulating that prior to installing RC and then drywall?

If the answer is "yes" - then you are throwing money away here too - the RC isn't helping you any - in fact it will lower the TL value of your wall in the Lower Frequency range - it is not needed in isolated frame construction.

If - on the other hand - you are installing RC directly to the face of the concrete - then you won't have all that much isolation anyway (much too small an air cavity to be of any real use).

The other thing is the sill on top of the foundation seems to be where the suspect the air is coming from. The foam would completely encase that, which stops the air... but would this be good for sound as well (vs attempting to caulk and backfilling with rockwool along the sill)? Some areas I CAN'T get to for rock wool, but the foam would be able to.

Understand that expandafoam (unless you go for the real deal commercial products) is a joke and breaks down over time - plus the fact that it is lousy for sound isolation.

You would be much better off caulking the perimiter of the sill to the foundation.

Sincerely,

Rod

 

[Velvet Elvis]

Rod,

Thanks for your answers.

The break in the vapor barrier is because the vapor barrier only goes the height of the wall... right now air can flank over the top of the wall (via the ceiling) where the sill meets the foundation, because its all open.

The current vapor barrier is 6 mil visqueen (sp?) applied on the interior (warm side) of the studs. I live in the Midwest (Iowa) and that seems to be the preferred method.

The condensation was only appearing on places where the basement wall was above grade and facing the north/northwest, which is where the majority of the cold winds blow toward here (we live in the country somewhat).

The product they were wanting to use "Sealection 500"... I know nothing about whether it is commercial grade or not.

Humidity levels in the room don't seem to be the problem. In fact humidity (checked with two different devices) shows ~25-40 %. Of course, this mold could have begun back in the summer when it would have been higher.

The 4x4 windows in these rooms have steel bucks, which are a condensation nightmare. We are trying to get those replaced right now and wonder if that might also curb the problem some.

Other than that, there is no source of leaking water or anything of the sort. Its simply exposed foundation in a harsh climate meeting inside airi flanking over the top of the insulated wall via the ceiling.

RE: the rockwool on the walls of the studio area. I was under the impression that though it wasn't huge, there was some benefit to have the denser product in the walls. I needed to buy more insulation anyhow, so I thought that would be a wiser choice. Is that not the case? What about for the ceiling? Would you do rockwool there or regular fluffy stuff? (ceiling and walls will both be 2 layers of 5/8 on RC).

Thanks again Rod... you're a wonderful asset to this board!!

Jim

 

[Velvet Elvis]

The foam would be a very bad thing if it were to bridge the face of the cement wall with the stud cavity of the inner framed wall. Do I understand correctly that you are building a wood frame wall inside of (and not touching) the cement wall - and then insulating that prior to installing RC and then drywall?

If the answer is "yes" - then you are throwing money away here too - the RC isn't helping you any - in fact it will lower the TL value of your wall in the Lower Frequency range - it is not needed in isolated frame construction.

If - on the other hand - you are installing RC directly to the face of the concrete - then you won't have all that much isolation anyway (much too small an air cavity to be of any real use).

Let me clarify this part... the interior framing does not touch the concrete, but it does touch the I-beams and hold up soffit framing etc around HVAC. Knightfly and John had said that if your wall is coupled anywhere, you need the RC. If its not, then you don't. Since mine is coupled (even though its away from the concrete), I would think I'd need the RC.

Does that make sense?

Thanks,
Jim

 

[Rod Gervais]

Let me clarify this part... the interior framing does not touch the concrete, but it does touch the I-beams and hold up soffit framing etc around HVAC. Knightfly and John had said that if your wall is coupled anywhere, you need the RC. If its not, then you don't. Since mine is coupled (even though its away from the concrete), I would think I'd need the RC.

Does that make sense?

Thanks,
Jim

Jim -

Yes it does - although it's a shame - it's so easy to keep the walls isolated that loosing LF isolation due to flanking problems really doesn't make sense.

BUt it is what it is...............

Sincerely,

Rod

 

[Rod Gervais]

The break in the vapor barrier is because the vapor barrier only goes the height of the wall... right now air can flank over the top of the wall (via the ceiling) where the sill meets the foundation, because its all open.

Bring the vapor barrier all the way to the underside of the deck above - staple & tape it to the floor joist as you go........... this is after you caulk the building sill of course.

The current vapor barrier is 6 mil visqueen (sp?) applied on the interior (warm side) of the studs. I live in the Midwest (Iowa) and that seems to be the preferred method.

Sure nuff is.......

The condensation was only appearing on places where the basement wall was above grade and facing the north/northwest, which is where the majority of the cold winds blow toward here (we live in the country somewhat).

The product they were wanting to use "Sealection 500"... I know nothing about whether it is commercial grade or not.

Humidity levels in the room don't seem to be the problem. In fact humidity (checked with two different devices) shows ~25-40 %. Of course, this mold could have begun back in the summer when it would have been higher.

Condensation is one thing - you can have condensation with RH levels of 10% given the right conditions - Mold is a totally different issue........ the vast majorities of mold spores will not generate in levels at (or below) 40% RH.

The 4x4 windows in these rooms have steel bucks, which are a condensation nightmare. We are trying to get those replaced right now and wonder if that might also curb the problem some.

That might very well help.

If you have active areas of condensation - then keeping the warm moist indoor air from reaching them is critical in solving the problem - again the need for an effective vapor barrier between the warm inside air and the cold surface of the outside concrete walls.

Rather than see you try to insulate the inside of the walls (still leaving any hairline cracks subject to the problem - the better solution would be to insulate the OUTSIDE face of the concrete walls with a foam insulation - and then perhaps a fake stucco (Dryvit) finish -

This would allow the wall itself to maintain heat gain generated by the indoors - and would take dew point out of the picture on that wall surface.

Other than that, there is no source of leaking water or anything of the sort. Its simply exposed foundation in a harsh climate meeting inside airi flanking over the top of the insulated wall via the ceiling.

Understood

RE: the rockwool on the walls of the studio area. I was under the impression that though it wasn't huge, there was some benefit to have the denser product in the walls. I needed to buy more insulation anyhow, so I thought that would be a wiser choice. Is that not the case? What about for the ceiling? Would you do rockwool there or regular fluffy stuff? (ceiling and walls will both be 2 layers of 5/8 on RC).

From 50Hz to 200 HZ you are talking pretty much less than 1 dB of isolation difference - with some benefit on the side of the fence for either product dependant upon frequency - so really - no benefit at all if there is any cost difference between the 2 products.

Sincerely,

Rod

 

[Velvet Elvis]

Fantastic information as always , Rod. Thank you.

With your comments on Rockwool, would you advise not using Rockwool for interior walls either? (Same construction).

RE the isolated or RC walls on the outer perimeter: They are attached to the concrete floor as well as touching the ibeams at the ceiling. The ceiling (due to height) has to be hung off the ibeams using RC. I didn't have to option of building a freestanding ceiling, so I'm guessing the RC flanking problems would have been there regardless of what I did with the side walls. Would you agree?

Thanks again.
Jim

 

[Rod Gervais]

With your comments on Rockwool, would you advise not using Rockwool for interior walls either? (Same construction).

Elvis,

I wouldn't waste a single dollar on rockwool if that was all the extra it cost me - if it has a zero cost benefit - why spend additional funds?

By the same token - if you could buy rockwool for less money than fluffy insulation - I would say that it was the way to go (historically this isn't usually the case).

Anyway way you look at it - there is no real benifit to one over the other - thus no reason to spend more than you have to.

RE the isolated or RC walls on the outer perimeter: They are attached to the concrete floor as well as touching the ibeams at the ceiling. The ceiling (due to height) has to be hung off the ibeams using RC. I didn't have to option of building a freestanding ceiling, so I'm guessing the RC flanking problems would have been there regardless of what I did with the side walls. Would you agree?

No I wouldn't agree..... at least no to the same degree.

If you have my book you see exactly what you're talking about - walls sitting on concrete decks that aren't floated - 1" air space from concrete walls - but ALWAYS some means to isolating the walls from the ceiling above.

Why impart to the deck above any more sound than you have to.

Why add flanking to build-up with the air-borne transmissions.

isolating the walls from the ceiling makes perfect sense - it takes a LOT out of the transmissions to the space above (and conversly - from above to below)

Nope - you can't sell me on that one.

Sincerely,

Rod

 

[Velvet Elvis]

Rod,

Ok... so in your opinion, what would you do?

I've got walls tapcon'd to the floor, but spaced off from the outer concrete walls (this is a basement). There might be a gap from the framing to the ibeams of ever so slight proportion. The ceiling also has soffits around HVAC stuff etc.

So would you use RC on the ceiling only (since it hangs on the ibeams) and then rock the side walls right to the studs even though it is coupled with the floor?

No drywall has gone up as of yet - so I have options.

Thanks again for your expertise!!

Jim