I've got a question on basement insulation theories for finishing a poured basement  in zone 5 (Southest michigan)  It seems as though Building Sciences has published conflicting accounts on what's recommended in insulating your basement, though what's probably happened is I don't quite understand the distinction being made in the two reports.

Back in 2006 under the digest, the analysis pointed to this conclusion:
BSD-103: Understanding Basements By Joseph Lstiburek
"Basement walls should be insulated with non-water sensitive insulation that prevents interior air from contacting cold basement surfaces – the concrete structural elements and the rim joist framing. The best insulations to use are foam based and should allow the foundation wall assembly to dry inwards"

Bolded element is mine, but it's specifically saying to keep some vapor permeability in the insulation layer.  Choosing a 4" of EPS or 2" of XPS closedcell foam insulation to 3" and opencell to 10"

But then later in 2010 a comprehensive article is published analyzing basement insulation.  Note This study is limited to basement and foundation systems for cold climates (Minnesota zone 6)
Building America Special Research Project: High-R Foundations Case Study Analysis Research Report - 1003 20 August 2010 Jonathan Smegal and John Straube
http://www.buildingscience.com/documents/reports/rr-1003-building-america-high-r-foundations-case-study-analysis

The 2 recommended approaches actually seal the interior of the basement from both air and vapor.  They were recommended based on a variety of factors but actually were chosen mostly for wetting/drying issues and humidity control.

Case 5: uses 2" XPS (perm of .55) and then 2" PIC (perm of 0 effectively)
Case 7: uses 6" opencell 0.5pcf lowdensity foam

and then a third case was shown to be a very good choice if cost wasn't a factor.
Case 6: uses 3.5"closed cell 2.0pcf foam.

These were all top choices where they are advocating to limit both air and vapor movement.  Specifically mentioning that high moisture content in the concrete is fine since it isn't moisture sensitive
"The relative humidity between the concrete and spray foam is maintained at approximately 100% but neither material is moisture sensitive"

and later hinting they do not feel inward drying is good.
"Case 10 – 6” 0.5 pcf open cell foam with 2x4 framing offset 2” from foundation:
 No simulations were conducted on Case 10 because it will perform the same from a moisture perspective as case 7 as it also has 6” of 0.5 pcf open cell foam. In Case 10, the inward moving moisture may increase the wood moisture content of the framing."

So did Building Sciences change direction and are now saying we should limit inward drying inside basements for cold climates and that a vapor barrier when included with foam products on the interior of the basement is a good practice?    I don't quite understand as the inward and outward movement of vapor changes in summer and winter but I guess with the vapor barrier and air barrier there isn't any risk, but it seems that argument would also apply to poly sheeting.  Can anyone provide some more insight into basement insulation practices?

Alan

Some opinions on why breathable to the interior is better than a non fully adhered vapor barrier:

a) more moisture is more likely to grow mold against the concrete and this might release odors into the interior (air sealing is never perfect).

b) even more moisture and it might pour down the wall and exit at the floor.

I recommend that you also consult sources other than BuildingScience.com.

I'm trying to address similar issues in an 1920s house with a stone foundation, also in zone 5 and I've researched many of the similar references.  I've also spoken to a number of people who have successfully finished their basements after successfully addressing their moisture issues.  I think everyone has a different opinion, but what seems to have been the common themes is that everyone did their very best to make sure they dealt with their moisture issues 1st, ideally on the outside of the house, then whatever they did afterwards, they made sure to monitor their moisture levels after the fact and ran a dehumidier set for a safe humidity.  The people who have been most successful seem to have minimal humidity (dehumidifier only runs on the most humid summer days and not at all the rest of the year).  Interestingly none of them insulated below grade foundation walls (old school thinking, I guess).  My sense is that you have to take a scientific approach (constantly measure) and be able to adjust things if they're not working as planned (active, not passive).  The one thing that struck me in all my research was the point made in one article I read where one family lived in a house for many years without any mold problems, but another family lived differently and ended up with mold.  What I took away is that every house is different, everyone lives in their house differently, and houses are complex systems where one change can affect other aspects of the house.

I'm leaning towards vapor barier on the floor with EPS on top of that, open cell on the walls.  Closed cell foam just scares me too much (hard to remove, permiability of 0.8 perms vs 16 perms for open cell, cost).  The question I would ask is how confident are you that there would be any moisture behind whatever insulation you put up and what would happen to that moisture if it sits there.

Don't know if that helps, but I too would like to hear some professional opinions.

Moisture is not an issue for me at the moment which is good. I am leaning towards putting 2" XPS on the wall, then putting R-15 roxul in the studs. The cost of the spray foam (closed cell for sure, open cell not as much) is high enough that I'm not sure I can stomach it and the hard to remove aspect is a bit troubling. Though for the XPS I'll have a 'hard to install' problem in caulking, foam sealing and having to use tapcons. Maybe ease of install should be weighted heavier since it's definite it will have to be installed, but in terms of ease of uninstall it's likely it wouldn't have to happen. But in all, I am similar in having reservations on the spray foam.

One thing I'm trying to decide though is how thick to go on the XPS. If I go thicker on the XPS the permeance goes down and if that's the main thing to worry about then I'll stick to 2".

Thanks for the making my thread your first post. Appreciate it!

Alan

Posted By alang on 20 Mar 2012 04:16 PM

One thing I'm trying to decide though is how thick to go on the XPS. If I go thicker on the XPS the permeance goes down and if that's the main thing to worry about then I'll stick to 2".

Alan-

If you wanted to go thicker than 2", you might consider using glass fiber faced polyisocyanurate.  Different from XPS and EPS, polyisocyanuarate is said to be so permeable that the effective permeance is determined by the facing materials.  According to Peter Baker's (of Building Science Corp.) report at http://www.buildingscience.com/docu...-enclosure, the permeance of XPS is 1.10 perms for one inch, so presumably 0.55 perms for 2".  The R-value is given as 5.0 per inch.  For glass fiber faced polyisocyanurate, the permeance is rated at 1.0 to 3.0 perms depending on the facing properties, but that should not decrease a significant amount with increases in thickness.  The R-value is given as 5.0-6.0.  Dana1, who often contributes to this forum on moisture issues, used 3" of glass fiber faced polyisocyanurate on his basement is Massachusetts, and he said the water table is close to the bottom of his basement, so he does worry about potential moisture problems.     

Foil faced polyisocyanurate has a very low permeance rating of about 0.03 perms depending on the thickness of the foil, so it is not interchangeable with the fiber faced in terms of moisture properties.

Polyisocyanurate is less flammable than XPS (http://pima.org/BulletinFiles/tb202.pdf), I think charring rather than burning, but I think building codes in many areas would require gypsum board over either one to meet fire codes.  I have not worked with polyiiso personally, but was thinking of using some on a relative's basement in the future. 

Hmm. I'll have to look around for the glass fiber Polyiso, I usually see the Dow Super-TuffR stuff only. One thing I saw mentioned here and there is that polyiso is sensitive to moisture and using it below grade is not recommended. Now I'm pretty sure it's only sensitive due to bulk water intrusion, but those comments around sites like GBA made me leary.

Though the question still remains, is low permeable or high permeable good for a basement? The two research reports I mentioned are highly referenced, yet each gives different recommendations. The 2006 article mentions keeping it vapor permeable yet provides no empirical data. The newer report recommends limiting vapor permeance and backs it up with data measurements. What's the deal? I have been reading and following the trends and really put stock in that 2006 research. Then just a few days ago I stumbled upon the 2010 high-r article from posts over at GBA and was dumbfounded. I'm not quite sure what caused me to miss that newer article in the past, but it is at least bothering me that it doesn't mention the 2006 report and explain a little more.

As you are aware, the Dow Super Tuff-R is foil faced. The glass-fiber faced polyiso seems to be used mostly under roofing of commerical buildings, and, upon the recommnedation of Dana1, I looked and found the reclaimed material at a place that sells reclaimed foam. I have not purchased it, but am considering it. The reclaimed material sells for about $14 for 2"x4'x8', $20 for 3"x4'x8', and $28 for 4"x4'x8'. So this might be about 40% of the new material?

Concerning below grade use of polyiso:
From http://www.greenbuildingadvisor.com/community/forum/green-building-techniques/18728/can-i-use-polyiso-foam-internal-basement-wall-insula:
"You're correct that polyiso should not be used below grade and it should not be used interior to the concrete foundation since the foundation must be able to dry to the interior." But this particular comment obviously applies to the foil faced, since the permeance of the glass fiber faced is higher than XPS. Maybe the XPS is a safer bet?

I am also perplexed by the different recommendations on impermeable versus semi-permeable insulation for basements. The idea of a completely impermeable covering that seals in moisture between the concrete and the foam sounds undesirable to me (I keep thinking of the green slime), so I am leaning toward the semi-permeable approach, but not based on any real experience.

In cold climates, Basement walls and floors should NOT dry to the interior. There is simply too much moisture in the ground; it will (and does, in unfinished basements) overwhelm the moisture content of the house. The overall goal in basement insulating is to make the basement DRY and WARM.

I happened to be at a Building Science seminar yesterday where Dr. Lsiburek went into some detail on finishing older damp basements. The basic recommendation for walls was to spray about 2" or more of closed cell spray foam on the old foundation, be it rubble, stone or concrete. They have found that in (older) concrete basements over 2' deep, moisture wicking up the walls will escape to the exterior above grade so that no capillary break is needed at the sill (as it would be in very shallow foundations). Where there is water penetration through the wall, a drainage material (such as Enkadrain) should be used under the foam to allow the water to drain to below the floor.

On the floor, the poly should be above the foam so that in the event water rises to the level of the foam it will drain and dry out. If it gets wet with poly under the foam, it will never dry and the foam will never insulate properly.

http://www.buildingscience.com/documents/insights/bsi-045-double-rubble-toil-trouble/view

http://www.buildingscience.com/documents/reports/rr-1003-building-america-high-r-foundations-case-study-analysis
see page 53

Polyiso can be used on the walls in place of CCSF, but needs to be sealed top & bottom. It does absorb water so cannot be used under the slab.
Fiberglass faced polyiso is sold by commercial roofing suppliers.

Bob I
PS: There were 60-80 people at the seminar, and as usual only a minority of people who actually build. A very sad commentary on the building industry. At $50 for the day, the cost cannot be blamed. But the main casualty is that this information does not get out into the wider community.

Bob-

Thanks for the information. A disadvantage of the closed cell foam is that the blowing agents usually used are very bad as greenhouse gases (GHG), and some say from a climate change perspective, they are a net negative compared to the energy saved. Some open cell foams use water as a blowing agent, so much better from a GHG standpoint, but they are water vapor permeable.

The report mentioned by the OP, Building America Special Research Project: High-R Foundations Case Study Analysis Research Report - 1003 20 August 2010 Jonathan Smegal and John Straube, recommneds either the open approach (case 7) or the 2" XPS + 2" PIC (polyiso), their case 5. However, for the open cell foam approach, they recommend first sealing the rim joists with XPS or foil-faced polyiso to avoid condensation on the wood, and the above grade portions of the basement wall in very cold climates.

Well, I'm still a bit confused. Thanks for posting the information about keeping the basement Dry and Warm. I still not quite sure if that means sealing it all up with polyiso or similar low perm board. So at this point I leaning towards 2" XPS and then 2x4 stud wall insulated with R15 roxul stone wool insulation.

The 2" XPS will give .55 perms for vapor diffusion. I think that will be ok.

I'm also thinking of putting 1" or .5" XPS on floor then OSB ontop. Not quite sure I've got the background of whether to put a 6mil poly on the floor under the XPS. It sounds like I don't need one if using XPS, though at .5" it may still be needed due to it have a fairly high vapor permeability.

So at this point I leaning towards 2" XPS and then 2x4 stud wall insulated with R15 roxul stone wool insulation.

If you do this, I would consider putting a layer of Tyvek over the stone wool to make sure that no air can circulate and reach the foam (which could be below the dew point).

Interesting comment.  Foam is an air barrier if taped/caulked at the seams.  Why would I need to stop the air from hitting the foam when it already is an air barrier?  It's the same concept as using the foam as a WRB on the outside, but there's little environment effects in the basement to cause the sealing and taping to degrade as might be the case on the outside of the house. 

I should probably just stop reading articles because the more I read the more I can't determine what direction I should go.   I just read another one from Building Sciences by Joe Lstiburek (recent article about closed cell spray on the sill) that stated for above grade basement walls you should use foil faced polyiso  insulation since the wall should and can dry to the exterior.  The grade on my house isn't flat it slopes to one side meaning that the North side is mostly below ground (40" above ground) and then the south is mostly exposed (6 feet).  If I include the frost line, then on the south side It's almost all exposed and the articles mention using polyiso will block the vapor/air and then it will just dry to the outside.  This wall is also exterior brick veneer so it's probably better to deflect it out to limit the amount of solar vapor drive after rains.

Alan

Why would I need to stop the air from hitting the foam when it already is an air barrier?

Assuming you are talking about the foam next to the concrete, the issue is if warm moist air travels through the stone wool and then hits the cooler foam. There it condenses and wets the stone wool/studs and/or runs out the bottom of your wall. You never want air to be able to move in a wall. Tyvek helps with that. So does air sealed drywall.

Hi:
Since 1993, especially trying to heat retrofits with 21-to-64,000 btuh systems of total net heating capacity before ELEC Backup,
we have found in the areas of OH , like N of Detroit, where -15 and even -20 is hit and usually -10 to -12 below... (8% colder than Cleveland, annually)
that
NORTHWESTERN OHIO PRODUCTS had a great simple solution in 700- 2200 sq ft basements: Not to the floor, but you can decide on moisture abatment, etc---
just 3-5 ft below grade... and additionally over the plate above wall edge.. (BSMT generally)
5/8" foil with a tough white plastic backing against wall, and THEN studs for finish , 2x 2 if possible to tolerate, to drywall with JUST DEAD AIR SPACE, and in NEW CONST that GC's do not insultae floor slabs other than barrier of plastic... or 1/8th inch something...(!) when padded and carpetted...
or in old homes, again, that "thing" white fowma was all that is needed and even passes the r-19 built-up code for walls here, with the drywall.

I am glad to see all the moisture concerns addressed
I will be posting VerticalAirStabilization systems of 1984-to-date that work, soon, but a pic here in a few days of ducted 6" fan handling 30-ft ceilings, saved JC Penny in NY and many others and GSA, IRS buildings a bundle over ceiling fans.

AIR movement by turning INWARD the diffusers, if tolerable, like a garden hose adjusted to a stream around button-head at nozzle,,, WILL DO A LOT to keep molds and moisture in the air for filtering/DeHum, etc. now especially OK with the ecm blowers and Hi-Eff floor fans available...

When this was used in Dec 2006, the basement was 2200 sqft
under 2600 with 2nd story 1800

DURING JAN 2007 winter
with the 5/8ths foamboard and NO drywll, and first floor wet cellulose drying that week and 2nd story rough drywalled---
in construction,
NO finished wood

a single 10kw strip heater of ~ 34000 btuh held 1st and basement at 64 by 8AM mornings in 10-deg to 0-deg days, stick frame.

2200-2300 cfm blower had ECM-Electronic Hub shorted by June from dust, and was replaced (GCand the owner were warned).