# Foamular XPS Rigid Foam Question



## Jalopy (Jan 25, 2017)

I am in the planning stages of finishing a bi-level ("walkout") basement. I am planning to use 2" of XPS rigid foam on all walls from slab to joists (and fitted into the joist cavities). This would mean I'll be fastening the rigid foam to both the below-grade concrete sections of the wall and the above grade sections which are studded and have R20 batts in them. I currently have poly over the stud/batts sections, but was going to remove the poly and then affix the rigid foam directly to the studs as Todd Fratzel does in his DIY Basement Insulation video on youtube. 

Finally my question. I can get a pretty ridiculous deal on some salvaged 2" rigid foam that is marketed for roofing. The brand is Owens Corning Foamular 350. I can get it for about $6 per 2-inch 2'x8'. Would this be suitable for below grade applications? Is it essentially the same thing as the Foamular C300? So far, I've been unable to find anything on using it in a basement interior.


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## akjose (Jan 1, 2013)

"Owens Corning Canada LP
does*not recommend rigid
extruded polystyrene (XPS) board
in the following locations:
• In soils that may contain
hydrocarbons and other
petroleum derivatives, and all
other products that may cause
corrosion and deterioration of the
polystyrene boards.
Consult soils investigation reports
and an Owens Corning Canada
regional technical support
representative."

Found Here

Not sure what that means for you.


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## Gary in WA (Mar 11, 2009)

--------Welcome to the forums!----------------------------

Could you describe the above-grade wall make-up of materials, please.

Gary


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## Jalopy (Jan 25, 2017)

The house is 8 years old. The areas that are above grade were studded by the builder and filled with white R20 insulation and a poly vapour barrier over them. Below that area, I have cement wall covered with builder's R12 pink wall wrap (picture attached). 

In regard to using roofing XPS in a basement application, I decided to write Owens Corning and they replied the following:

_Both the Foamular roofing rigid foam and the Foamular C300 are closed cell extruded polystyrene insulation. Both would be acceptable to use as insulation in the basement against a concrete wall as they have the same R-Value, R-5 per inch. The only difference that you are looking at performance wise would be the compressive strength of the product. We would recommend checking your local building codes._


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## Gary in WA (Mar 11, 2009)

Local code rules...
a good read; ftp://ftp.cmhc-schl.gc.ca/chic-ccdh...ngual/Vapour_Permeance_Volume_1_Web_sept5.pdf

Questions later..

Gary


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## Jalopy (Jan 25, 2017)

Thanks for the link. It was a very interesting read, but it was not my local code rules. It was actually a study that was done to determine the effectiveness of poly vapour barriers in above and below ground applications in Ontario and more generally in Canada. 

It certainly was applicable to my situation as my walk-out basement has both above and below grade portions. The study suggested that ABOVE-GRADE in WINTER, poly works well and XPS works excellently, but in SUMMER the use of poly is problematic.

Interestingly, BELOW GRADE, the study found: _that interior vapour control at the lower portion of the basement wall is unnecessary or inhibits drying. These locations experience temperatures that are similar to geographic locations that require no vapour control layer. The monitored data shows that an interior impermeable layer at this location reduces drying and results in longer periods of elevated humidity at the concrete-insulation interface. _

While this seems to suggest that using 1.5-2" of XPS against the below grade concrete would actually be a bad idea, the study goes on to say: 
_The wall with extruded polystyrene (XPS) showed excellent performance, due to its combination of vapour resistance and insulating value. However, high humidity was measured on the exterior side of the XPS, and the wall was never taken apart to confirm the actual condition. The presence of high humidity in this location should not present any risks if it is not connected to the interior environment. _

So it's all very confusing for my basement planning. For the above-grade section, XPS (in the pre-existing stud bays I suppose) or a poly vapour barrier seems to be the way to go (but only in the winter, not in the summertime!). And for the below grade concrete wall, the best bet is to leave the concrete alone altogether. The ideal solution seems to be to use a poly barrier for the above-grade but not for the below-grade, but I'm not sure how you would keep the two sections separate. All very confusing since the general trend in Ontario seems to be to use XPS on the concrete below-grade, and don't worry so much about the above-grade sections.


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## Gary in WA (Mar 11, 2009)

Yes. And there are those who use some P- 6 "smart vapor retarder"; https://www.google.com/url?sa=t&rct...sg=AFQjCNFihWruFRtcUxT69Jt2X7jykMDFpA&cad=rja

But, I have a test done with that that was wetter than an bare stud wall, no vb, just insulation, need to find it for you...

Why did they ever leave ('95) just adding builders paper on both sides of fibrous insulation and forget all the $$$ for testing and $$ foam board; https://www.cmhc-schl.gc.ca/publications/en/rh-pr/tech/95-207.pdf

Since it is no longer allowed in basement walls, seem to me someone could bond a paper facing to both sides like asphalt coated paper faced insulation; 
"Warning"---- below 6.2.3; http://www.nrcan.gc.ca/energy/effic...keeping-the-heat-in/basement-insulation/15639

Gary


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## Jalopy (Jan 25, 2017)

I was actually researching Doug Tarry's use of that Certainteed Membrain "smart" barrier yesterday.... (now that I've bought a bunch of XPS foamboard).

My plan now is to affix the 2" XPS to the cement portions of the wall (following instructions I've read in your other posts), and then place XPS fitted into the above-grade stud bays and rim joists, sealed in with canned spray foam. Then frame against the foamboard and use batt insulation between the new stud wall to get to my required R20. 

I'm still not sure if I then need to use a poly vapour barrier between the inside of the framing and the drywall -- or if poly there, in conjunction with my use of XPS, creates the dreaded "double vapour barrier." I will be asking my local building department this question to figure out what exactly the inspector wants to see there.


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## Gary in WA (Mar 11, 2009)

No poly sheeting at all; http://www.buildingfoundation.umn.edu/OCBasementSystem/ProjectReview.htm

Also; https://buildingscience.com/documen...rm=interior%20coating%20on%20basement%20walls


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## Gary in WA (Mar 11, 2009)

Your Code allows foam board that meets both "Interior damp-proofing" and "Vapor diffusion Control" with interior insulation systems; http://www.nrc-cnrc.gc.ca/ctu-sc/ctu_sc_n70

Notice also under "Air leakage control" that drywall, with ADA finish, meets "sheet/panel and gaskets/sealants" for the air barrier. ADA; http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach/

Gary


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## Jalopy (Jan 25, 2017)

Thanks again for the great links. I am convinced after all this research that I don't _want_ to use a vapour barrier in conjunction with the 2" of rigid foam. However, I called my building inspector and they _do_ want to see poly on the warm side of the wall regardless as it is code in Ontario. Based on some other posts I've read in this forum, I'm not the only one who has run into this. 

I've been delving into the Ontario Code (it's HERE if anyone reading this has had difficulty locating it) to try to get around this. The issue with my rigid foam AS a vapour barrier appears to be 9.25.4.2. Subsections (1) & (6). (see picture attached below)

I've read that 2" of XPS has a permeance of 0.55, I'm just not sure how this converts to ng/(Pa·s·m2). Is it less than 60 ng/(Pa·s·m2)? I have also read that rigid foam is considered a "vapor retarder, not a vapor barrier." 

I'm definitely not well enough versed in this area to argue with a building inspector. So unless I try to figure out the route of using "a coating...applied to gypsum board to function as the vapour barrier" (as in 9.25.4.2. Subsection (5)), I may have to go against my better judgement and use poly between the studs and drywall to satisfy building code.... despite all the evidence online that it is not a good idea.


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## Jalopy (Jan 25, 2017)

Further to my last post, the data sheet on Foamular350 has the Water Vapour Permeance as 0.60 perms, and 35 ng/(Pa·s·m2). This would suggest that the XPS foam will satisfy the code requirement as a vapour barrier being less than 60ng/(Pa·s·m2). I will have to wait and see if the building inspector agrees.


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## Gary in WA (Mar 11, 2009)

What did he/she say?

Converting 60ng to US perms multiply by .0174784 = 1 US perm which XPS is at 1.1 perm per inch thickness; http://us.henry.com/fileadmin/pdf/data/techtalk/TechTalk_Conversions_11122013.pdf

Gary


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## Gary in WA (Mar 11, 2009)

*6.2.4 Frame wall with batt insulation and rigid board insulation*

This method involves gluing rigid board insulation to the foundation wall and then covering it with a frame wall incorporating batt insulation. The result is higher insulation values with less loss of interior space, a very good reduction of thermal bridging and no need for an additional moisture barrier. It works best if the basement wall is even and vertical (i.e. poured concrete or concrete block) as the board is fairly rigid. Use only moisture-resistant board insulation such as extruded polystyrene or Type IV expanded polystyrene.
*Preparation*
Follow the preparations required in Section 6.2.1, How to insulate inside the basement using only rigid board insulation.
*Installation*
Using rigid board insulation with at least RSI 1.76 (R-10), secure and seal it to the foundation by applying foam-compatible adhesive around the perimeter of the foam board before fastening it to the wall. If any mould were to develop behind the insulation it would be contained. Air sealing the foam board to the wall creates an air and moisture barrier somewhat equivalent to spray foam. Special mechanical fasteners can be used if you have any sensitivity to the glue. Install the insulation snugly to eliminate air circulation at the edges. Use urethane foam sealant and technical tape to seal all joints and intersections of the foam board.
Next, install the wood-frame wall directly in contact with the rigid board insulation. Follow the techniques detailed in Section 6.2.3, Frame wall with single or double layer of batt insulation.
*Adding additional insulation*
The frame wall can now be roughed in for any wiring and plumbing and insulated as noted previously in Section 6.2.3, Frame wall with single or double layer of batt insulation. For details on treating the joist area, see Section 6.2.6, Joist header space.
*Finishing*
Do not use a polyethylene air and vapour barrier with this approach, as there is a risk of creating a double vapour barrier with the foam board. Instead, use either the smart barrier *or the ADA method.*
If you are using smart barrier, leave enough of the film at the top to connect to the air barrier in the joist space.
If you are using the ADA method, pay strict attention to proper air and vapour sealing, *including a layer of vapour barrier paint.* Any exposed foam insulation may require fire protection as per code requirements.' Bold is mine...


He/she has to accept this, from; http://www.nrcan.gc.ca/energy/effic...keeping-the-heat-in/basement-insulation/15639

As it fills #1 and #6 in 4,2 and ----------- #3 in 4,3 above.


Gary


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## Jalopy (Jan 25, 2017)

I won't know what the inspector says until I actually book my inspection.... which could be quite awhile away based on my current rate of progression*. But I've definitely got at least some of the knowledge now to argue my case if they do insist on poly. Thanks very much for the National Resources Canada link.

* Fitting the rigid foam into every single rim joist and stud bay is pretty time consuming in my walk-out basement. And I'm also rerouting the odd piece of plumbing and ductwork where necessary as I go to jive with my renovation plans. Just doing this with whatever spare time I can find outside of work and young family.


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