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Old 02-07-2016, 02:44 PM   #16
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A good read, download this; http://buildingscience.com/documents...nsulation/view

“The lowest risk approaches for interior insulation of basement walls use non-moisture sensitive
semi-vapor permeable materials at the interface between the concrete and the insulation
(Lstiburek 2006). Alternately, in foundations known to leak liquid water, insulation assemblies
specifically designed to safely drain this water can be retrofitted to the interior.” From pp3of25

“Goldberg has tested a variety of interior basement insulation configurations at a Minnesota test
facility. After testing frame walls with fiberglass insulation (Goldberg and Huelman 2001), she
recommended an assembly with polyethylene on both sides of the stud bay, as adopted by the
Minnesota building code. However, a 2002 addendum provided warnings against using this assembly
in “superficially dry” basements, which would accumulate moisture behind the exterior polyethylene.
Tests were also run using a variable permeability vapor control layer made of polyamide-6 (PA-6)
(Goldberg and Gatland 2006). The PA-6 wall experienced minimal condensation during the
summertime, and was able to dry inwards, unlike similar polyethylene walls. The PA-6 had similar
monitored performance to Kraft-faced batts. In addition, some walls were constructed with a latex
elastomeric waterproofing on the concrete surface. These walls had noticeably higher wintertime
condensation than the uncoated concrete walls (which largely showed only surface dampness), due to
the elimination of the storage capacity of the hygroscopic material, by the hydrophobic
dampproofing layer.” From pp. 4of25 -------- So don’t ever use Drylock or similar product inside, unless you have an interior drainage system.

“The plot shows that moisture accumulation roughly corresponds to the vapor resistance of the
assembly. The polyethylene roll blanket shows the highest sustained RH levels: near saturation in
fall, spring, and summer, dropping to ~90% RH in winter. The XPS wall has vapor permeability an
order of magnitude higher, and shows RH levels in the 80-90% range. The frame/latex paint wall
has permeability an order of magnitude higher than XPS, and shows the lowest humidity levels,
indicating drying of the assembly. In this wall, RH values are at their peak during winter when the
concrete wall is coldest. The frame/polyethylene wall shows relatively low calculated RH levels; after
replacement of the damaged RH sensor, this relationship will be verified.

Framing Moisture Content: When assessing the risk of a wall assembly, the danger is not
necessarily condensation per se, but mold growth and damage to moisture-sensitive portions of the
wall, such as the framing. The moisture content of the framing at the upper portion of the wall is
plotted for the monitored period in Figure 6. Moisture contents were measured at the inboard and
outboard edges (3/8” or 9 mm from the faces) of the stud. The summertime increases in the
frame/polyethylene wall are seen at the interior side, similar to the moisture content wafer; however,
peaks are roughly 17% MC, which is still in the safe range. A similar rise in wintertime moisture
content is seen at the outboard side of the frame/latex paint wall; again, the MC remains within the
safe range (15% peak). Overall, moisture contents at all of these upper framing locations presented
minimal concern for mold growth; based on over a year of data, these cycles appear to be stable.” From pp 11of25

“In the frame/fiberglass/latex paint wall, there was no visible staining or mold growth on the
insulation, framing, or wafers. Moisture contents were in the 9-11% range throughout the wall. One
concern with omitting a polyethylene layer in assemblies is that inward vapor drives might cause
mold growth on the back of the drywall, due to accumulation at that location. Monitored data
showed that there was negligible accumulation; a visual inspection of the exterior side of the drywall
showed no damage, discoloration, or mold growth.” From; pp 12 of 25. ------------ So use some non-paper backed drywall.


IMHO, if the basement is dry, add some building paper with the fiberglass insulation. Interestingly, there have been no follow-ups on this cheap solution, squashed by foam manufacturers or others, possibly…. ------------- “Swinton and Karagiozis (1995) examined the phenomenon of condensation on the exterior
side of the polyethylene vapor barrier during spring and summertime, at the above-grade portion of
the wall. This problem is caused by inward vapor drives from the damp concrete; when there is an
inward thermal gradient, the moisture moves inwards and condenses on the polyethylene. They
replicated this problem using two-dimensional hygrothermal modeling in a Montreal climate and
demonstrated that using semi-permeable materials (building paper) on both sides of a fiberglass batt
cavity had the best overall performance. Although removing the interior polyethylene layer
eliminated the summertime problem, it resulted in moisture accumulation at the concrete-insulation
interface during the winter.” From pp 3of25. ------Bold is mine.

Pages 20-23 mention IF you have AC, you may have different summertime results and possible future mold problems… I thought the paper was code in Canada before they switched to poly... lol.


Gary
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Old 02-07-2016, 09:52 PM   #17
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If you have moisture getting through your foundation you need to address it before you do any remodeling. Stop the moisture infiltration and then you can use whatever insulation you choose.
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Old 02-07-2016, 10:14 PM   #18
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@throrope I have difficulty recommending all of that plastic and don't think I did with my posts. The more recent advice from the research groups will generally avoid plastic vapor barriers in favor of allowing some drying to inside through the rigid foam.

You may not be having problems with your installation, but it is still an example of one and that is why we like to follow the advice of organizations that have tested and measured their results on many homes in many climates.

A true vapor barrier as in a layer of plastic as opposed to a vapor diffusion retarder allows zero moisture to pass, as water or as a vapor. The result is, everything to the moisture side will slowly equalize until that side of the VB is just as wet as everything outside of it. In some soil conditions that may not be a problem, but in many it is.

Some reading: http://buildingscience.com/documents...ts?full_view=1

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Old 02-08-2016, 09:43 PM   #19
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A follow-up on my previous post; "
The use The use of building paper instead of polyethylene
sheetisheeting as a vapour barrier in case B5 provided the
opoptimum results. The permeability balance on both sides
of tof the cavity resulted in a steady, low moisture content
which fell below all other strategies" from;https://www.cmhc-schl.gc.ca/publicat...ech/95-207.pdf

Gary
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Old 02-10-2016, 11:02 AM   #20
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Quote:
Originally Posted by harpua728 View Post
Thanks, Bud. Would rigid insulation on it's own (with a higher R value) be good enough to use without batts, or do I need both?

Still looking for help on this....Instead of buying both rigid foam and fiberglass batts, could I get the same result by just using rigid foam boards with a higher R value?
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Old 02-12-2016, 04:44 PM   #21
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Hi harpua,
I didn't go back and reread the entire thread so I risk some confusion, but in your climate zone (4) link below a foundation wall (2009 IECC codes) says r-10 continuous or r-13 cavity. Now that isn't the best advice IMO because we shouldn't be installing batt insulation directly against the concrete. But you question about using more rigid is yes. Now, to qualify that, I'm looking at those 2009 codes and some areas have moved on to even the 2015 codes and I have not looked at the 2012 or 2015 requirements. Thus, you would need to determine what codes are applicable at present.

If you want to leave the rigid exposed, then you could use Dow Thermax only. It has a foil facing that has been approved to meet requirements without the drywall. Not cheap, but it can eliminate studs and drywall. Their 1.5" sheets are rated at just under r-10 close enough to meet most codes. $41 a sheet last I priced it.

IMO, the hybrid approach is still best, 1" rigid, stud walls against that, then fill with batt insulation. the minimal amount of moisture coming through will easily be handled on the inside and you are retaining some drying to the inside.

If I missed anything, let me know.
Bud
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Old 02-22-2016, 07:55 PM   #22
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Check the codes, for sure as the 2012 allows you to count both insulation types for a total, earlier does not. Also, using the 3 coldest months for your location (first county- second is colder); http://longisland.about.com/od/neigh...Ny-Climate.htm, with basement at 68*F the foam (1") could condense water vapor from dirt on the inside face at 39% relative humidity as the temp there is 43*F. So you would have condensation at the wood stud edges next to the foamboard for 3 months--- above grade and to "frost line"; Jan., Feb., and Dec., hopefully the HVAC can handle it to not cause mold.

Gary
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Last edited by Gary in WA; 02-22-2016 at 07:56 PM. Reason: sp
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