In issue #169, page 78, it was suggested that by applying rigid foam board directly to the foundation wall it would not trap moisture and prevent mold. I moved some foam board today that I had stored next to one wall in preparation for this process and was overwhelmed by the smell of mildew! Should I go another way in my basement or am I just missing something?
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It depends on the type of foam you moved. Expanded polystyrene (looks like coffee cups) will allow the passage of water vapor. Extruded polystyrene (usually blue or pink) will not. Anything with a foil, kraft, or other facing will also block this passage of water vapor.
Justin Fink - FHB Editorial
Your Friendly Neighborhood Moderator
Thank You Sir! What I bought was the pink stuff! Well it's back to Home depot, now where's that receipt?
No trouble at all, I've got some basement remodeling in the squishy part of my brain right now, so the information was easily recalled.
Fill in your profile, stick around and keep posting. We love new faces....and you will likely run into more questions as you go. Justin Fink - FHB Editorial
Your Friendly Neighborhood Moderator
Questions? OH, I've got plenty! The next being; The article used only the foam board for insulation, would it be detrimental to fill the framing with un-faced fiberglass as well? I hate cold, damp basements and want to make these rooms as warm as possible!
Unfaced fiberglass batts will allow moisture to pass, but they will also absorb and hold water. Rigid foam won't.
If it were me, I wouldn't use FG batts on a wall that is up against concrete.
Others may have a different opinion, however.
Justin Fink - FHB Editorial
Your Friendly Neighborhood Moderator
Edited 10/3/2006 12:22 pm ET by JFink
Fill in your profile, stick around and keep posting. We love new faces....and you will likely run into more questions as you go.
Is that just because you're tired of dealing with the old faces around here?
The difference between stupidity and genius is that genius has its limits. -Albert Einstein
No event in American history is more misunderstood than the Vietnam War. It was misreported then, and it is misremembered now. --Richard M. Nixon, 1985
by the way, you should also avoid polyisocyanurate insulation - sometimes yellow with a foil facing. Just stick with the white stuff - I think Home Depot sells Polar Guard brand.Justin Fink - FHB Editorial
Your Friendly Neighborhood Moderator
I've read the "don't use extruded" somewhere before, but reading for my own planned redo of a basement, I ran across a statement at the Building Science website that seems to recommend either expanded or extruded polystyrene as being able to transmit vapor. http://buildingscience.com/resources/foundations/renovating_your_basement.pdf
I note that the article above is dated 2003, so I'm wondering if you have a more recent reference.
Right, Building Science does allow XPS but limits it to 1" thick on the floors. It is more rigid that EPS so I find it easier to work with.
Billy
When you say it's more rigid and easier to work with, do you mean that you find it distributes floor weight better? Because I haven't heard of problems with EPS in flooring applications.Justin Fink - FHB Editorial
Your Friendly Neighborhood Moderator
Hi Justin,
I meant that I like the rigid better for both flooring and walls, but for different reasons.
For flooring, the EPS does have some give and I find it is too compressible in the corners of the room, making the floor dip in the corners (and a bit around the perimeter). This isn't a big problem though and it can be controlled by being careful when tightening screws. But it's not an issue at all with XPS.
For walls I find that it's easier to work with the rigid panels. They don't flop around and it is easier to glue them to the wall. To the extent you need to hold the panels against the wall while the glue sets, this is easier to accomplish with rigid panels. The tongue & groove edges lock together well with XPS.
Just stay away from the XPS panels with the "skin" on them which will defeat the vapor permeability.
Plus they don't get damaged as easily in a construction environment.
Billy
You know, that article is pretty confusing in some places...and my source is probably not any more updated. In fact, I know Andy Engel (who wrote the no-mold basement article for FHB) took much of his information from Building Science Corp.
Anyway...
I was wrong to say that extruded polystyrene (XPS) is a true vapor barrier. In truth, it's a semi-permeable vapor barrier, but it only has a perm rating of about 1. For those who don't know - The higher the perm rating, the more easily the material will allow water vapor to pass (Tyvek, for example, has a perm rating of 58. 6-mil vinyl has a perm rating of .06).
Expanded polystyrene (EPS) has a perm-rating of between 2 and 5, so it's much better at allowing water vapor to pass.
So in a basement where they are trying to allow the passage of gaseous h2o, I'm not sure why they would recommend XPS rather than EPS. The only thing I can think of is that XPS offers a better R-Value (R-5 per inch vs. R-4 per inch).
Beyond that, I'm open to suggestions...Justin Fink - FHB Editorial
Your Friendly Neighborhood Moderator
I agree with you on the "confusing" part! Every time I think I'm starting to figure this out, I run across a statement that makes me go read some more.
The higher permeability rating of EPS does make a case for it being a better choice.
Thanks for the response.
My understanding from the reading I've done is that you want LESS of a perm rating. The goal is to prevent moisture from the INSIDE getting to the wall to condense, hence the recommendation of extruded.But that, of course, assumes a fairly dry wall to begin with.If the goal is to let water from the wall into the inside, I'd say that it might be better to build a vented wall. In the end, I still haven't found *the* basement insulation solution.
You and I are talking about two different approaches. The most common, and the one that you are explaining, is to isolate the cold exterior foundation walls from the warmer air in the basement - thus no condensation problems.
I'm talking about a system that allows water vapor to pass, relying on the HVAC system (or a dehumidifier) to pick up the extra slack and condition the basement. Justin Fink - FHB Editorial
Your Friendly Neighborhood Moderator
Justin,
My take after a careful reading of the Building Science material is that the goal is not to have as much vapor permeability as possible in the insulation -- if this were the goal then unfaced fiberglass insulation would work well, and we know that it doesn't.
The goal is to allow some water vapor to pass but not too much or too quickly. Their material states that both EPS and XPS meet this goal. If XPS did not meet the goal then they certainly would not recommend it, would they?
It's a good discussion and you are right to raise this issue. It would be interesting to hear what Joe Lstiburek has to say. In fact, you can read what he has to say in his May 2006 paper about basements here http://www.buildingscience.com/resources/foundations/Understanding_Foundations.pdf
Check out page 6 where he talks about perm ratings and insulation. An important factor that you overlooked in the discussion about EPS and XPS is that the vapor permeance depends in part on the THICKNESS of the insulation. Therefore, both EPS and XPS are fine, but you can use a thicker slab of EPS than you can of XPS to meet the vapor permeance requirements for "good" basement construction. He says that walls can take up to two inches of XPS (R-10) or up to four inches of EPS (R-16), which is interesting because it means that although XPS has a higher R value per inch, in a basement application you can get a higher R value from EPS and still get the benefits of drying if you are willing to pay the expense and give up the space. You have to balance that against how much R value is cost effective in a basement that is underground and does not see the indoor/outdoor temperature differentials of above-ground construction.
Also see the photo which clearly shows him using pink XPS insulation.
As long as you meet the design goals in terms of water vapor control, I still like working with the rigid XPS instead of the floppy EPS (and Viagra won't help it ;-) ).
Good discussion -- thanks. Now you can write a column in the next FHB "What's the Difference?"
Billy
Edited 10/4/2006 10:19 am ET by Billy
Edited 10/4/2006 10:20 am ET by Billy
Edited 10/4/2006 11:15 am ET by Billy
two different approaches...hence the perpetual confusion with basement finishing. ;o)Yea, there are two camps...assume it's wet, make sure it all has a place to go vs. assume it's wet, don't let it go anywhere.On the extremes, one argument is to vent the walls completely. You end up with radient insultation, but sstill have airflow behind the wall to properly vent. The other argument is a full and complete vaport barrier from mudsill to floor to other wall to other mudsill and trap all water on the outside of the VB.Both of those seem pointless to me.So that leaves that less extreme methods that we're both talking about. I'm not convinced either is best and the more I research this, the more I concede that the two options are either a) insulate a new basement properly on the outise or b) if an old basement, keep it a basement and don't bother finishing it. ;o)
I really think the best option is to use materials (insulation, drywall, floors, walls, everything..) that won't hold moisture. Let the moisture come in, but set it up so that the HVAC picks up the slack.
These guys who are trying to set up these remodels to keep all water out are just being stubborn. Water will get in - either liquid, or vapor - and then you have to figure out what to do with it. Let the HVAC handle it.
That, or like you said, don't try to finish basements... but where is the fun in that?Justin Fink - FHB Editorial
Your Friendly Neighborhood Moderator
"On the extremes, one argument is to vent the walls completely. You end up with radient insultation, but sstill have airflow behind the wall to properly vent."That completely ignores the issue of internal moisture. And can make the problems much worse from internal moisture.That is the problem with basements. You can have moisture drive in either direction.
"That is the problem with basements. You can have moisture drive in either direction."Bingo.
How where they stored?
I suspect that they where next to the wall, but not sealed against it.
Allow realatively moist air to get between the foam and the wall. The foam keeps heat from warming the wall. So you get condenastion.