Exterior foam around basement wall

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Old 05-18-15, 05:02 AM
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Angry Exterior foam around basement wall

I am wanting to use a rigid foam (XPS) around my basement wall before the backfill. Should I have the concrete contractor apply his waterproofing and then come in with foam and silicon or liquid nail that against the wall...or would it be better to glue the foam to the wall and use a waterproofing over that instead?
 
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Old 05-18-15, 05:15 AM
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The insulation protects the membrane, and dirt holds it tight to the wall. Shiplap panels and seam tape help hold it together. The thicker the foam the better. A few 2x4's leaned against the foam here and there might be needed to hold it back to the foundation until you backfill. Backfill to within about 12" of the top then sealant goes across the joint, then finish backfilling.

http://building.dow.com/~/media/buil...gdfsmsect.ashx
 
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Old 05-18-15, 04:24 PM
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Why would it not be recommended to have the foam go all the way up to the sill plate? The other thing is, I have a walkout basement...so what am I to do with that exposed foam on the walkout wall? Thanks!
 
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Old 05-18-15, 04:52 PM
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Hard to say without seeing a picture or knowing where your grade will be.

Generally the thinking is that the foam is simply a thermal break between the ground (which is a fairly constant 50F) and the interior (which people generally want to keep around 70F). The foam is not durable and does not have exterior finish, so if it goes above grade you would need to protect/finish it somehow. Like maybe with fiberglass mesh and Dryvit. And if you use 2" foam, it would surely be thicker than any siding that is above the sill plate, so it would create a problem where the two meet.

Foam almost always stops anywhere it is going to be exposed above grade so that you don't have to figure out how to finish/cover it. Your primary insulation is on the interior walls of your basement.
 
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Old 05-18-15, 06:31 PM
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Here is some more information on rigid insulation in basements. Even in my northern climate, Maine, insects are a major issue on the outside, they just love to live in foam.

BSD-103: Understanding Basements — Building Science Information

Bud
 
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Old 05-18-15, 09:02 PM
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XSleeper, my apologies for not getting a drawing. I guess I always thought the foam above grade did just as much good as it does for an above grade, timber framed wall. I suppose the most economical approach is just to use it for below grade application to prevent cool soil temps from constantly thermal bridging into and through the basement wall (along with damp/moisture).

I was imagining in my head that the foam was acting as an energy efficiency boost, and that it was going to be most valuable to me on the walkout side of the basement because that side has no insulation against frost/heat like the sides with soil against them. Guess it's sort of beneficial, but not the main reason for using foam on the outside, then.

I will have an unfinished basement for some time. I was thinking I would not need to insulate the interior of the basement walls if I had foam on the outside. Suppose that's not an accurate assumption. Insulation in the basement on the inside behind drywall scares me. Moisture being trapped, leaks not being seen, bugs making hangouts, etc. Would I be better off to scratch the idea of any exterior foam use and just use foam on the interior if and when the time comes to work on finishing the basement?

Bud - I will read that link tomorrow when I get off work. I may have already stumbled upon that in the past, but it will be good to refresh as the house build is finally approaching.
 
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Old 05-19-15, 04:38 AM
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"I was thinking I would not need to insulate the interior of the basement walls if I had foam on the outside." That's not wrong, just that there are options.

Depending upon the code your location is following, there are different levels of basement insulation required. Here is an article referencing the 2012 International Residential Code which shows NE as requiring r-15 for the full height of a basement wall. This article also directly addresses the question of inside or outside.
How to Insulate a Basement Wall | GreenBuildingAdvisor.com

Now, if you are starting from the ground up with that basement and house, there are specific steps that can give you a dry basement. But it starts underneath everything, footings, slab, and then exterior of foundation. Combine that with a well planned perimeter drain system and well landscaped property and you might be able to omit the dehumidifier in the basement. But few contractors are up to speed on building a dry basement. That coat of tar on the outside or even a rubber membrane doesn't ensure "dry". Moisture can wick up from the soil below.

Are you at the planning stage?

Bud
 
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Old 05-19-15, 05:36 AM
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IMO completely covering the foam on the inside would be better, yes. But if you aren't going to drywall right away you would need to use a fire rated foil faced product like Thermax, and tape seams with foil tape. Regular Dow r-board (blue) or the yellow Celotex or pink OC shouldn't be left exposed inside.

IMO, 2" insulation is always best if you can afford it, not just for the r-value. Its more rigid and so its easier to install because it doesn't want to warp away from the wall.
 
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Old 05-19-15, 02:20 PM
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Bud -
I bookmarked that article. It's coming back to me that I was going to try some acrylic stucco product on the walkout portion of my basement (and exposed foam elsewhere that was above grade). I have been planning and researching for a couple years, so the information gets lost and I forget

I am currently planning, yes. More so planning as I go which is a no-no, but it's how I run. The insulation decision needs to be made soon, but I will have a while to decide whether inside or outside or maybe neither? Was hoping to hear first hand from someone who has used it. Unfortunately many builders around here are not up to snuff with energy saving ideas. I am trying to, without breaking the bank. My region is actually back on 2003 or 07 IIRC code, so the R15 does not apply. I honestly think houses are being build without the insulation at all right now unless it's those who use the ICF's with foam automatically.

XSleeper -
I am not fond of foam on the inside due to chemicals and the case of a fire. The chemicals worry more than the fire issues. I am aware XPS foam actually 'off-gasses' over time which in turn means it loses a little R-Value. Those gasses are what I am concerned about more than the loss of R-value. This is one of the reasons I will not be using spray foam. Way too many stories about how it went wrong, the smell, and the gasses. I know if it's done proper it is great, but I think foam board is good enough for me.

--
I am not sure at this stage whether to use XPS up to the soil grade, XPS on the entire wall (maybe 2" down from the sill plate for an inspection point/line), or XPS/ISO on the inside of the basement a few years from now *since code is not 2012 here. Any personal suggestions? Something I may not be considering or missing? The house is 30x44 so it's not a ton of foam to use. But still a 2k decision + my labor. Is there a certain method to follow for walk-out basements?
 
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Old 05-19-15, 07:21 PM
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Since you are still in the thinking stage and you are not alone with your concerns about foam insulation, have you looked at Roxul. In addition to the batt insulation they have a somewhat rigid bat they use for walls and from what I'm reading, even basement walls.

Now, since the experts have changed their minds AGAIN, about vapor barriers on basement walls, you might consider this sequence on the inside. Concrete, Vapor barrier, studs, cavity filled with r-15 Roxul. The flaw in this approach is warm humid inside air finding its way through the insulation to a cold foundation wall. Thus the typical advice of covering the concrete with a layer of rigid foam. I still like that approach and the combined cavity fill plus the rigid easily meets the r-values. But, if the wall is well air sealed to keep air from reaching the concrete, then you could consider omitting the rigid.

I would have to search, but I believe I have read articles using this approach. Before you lock in this advice, be sure to confirm as I'm basically guessing. I really don't have a vapor barrier answer since they changed their thinking. But I do like what I'm hearing about Roxul and I have used their batts.

Just more FYI.

Bud

Bud
 
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Old 05-23-15, 07:24 AM
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Bud, I have liked Roxul but it is pricey & not available unless I drive 4 hours out. Menards is nearby (70 miles) and they sell what is called Thermafiber Ultrabatt Mineral Wool. Not sure if it's as good??

I was doing some Q&A on GreenBuildingAdvisor's website....Although the EPS or XPS foam on the outside would be beneficial, especially on the part of my basement that has no soil to insulate the walls...I may decide to do no exterior foam. Crazy? Especially since I have the chance before backfill? I started to worry about moisture and bugs. Bugs apparently love the foam, I don't know how they would damage my concrete wall, because that's all the further they would get to after the foam, but apparently they are bad enough to convince people not to use foam outside or even ICF's for that matter when building.

I am strongly considering just a waterproofing on the areas which will have soil next to them (1/2 of basement) and using Poly-ISO or EPS on the interior later on since code doesn't seem to require any insulation here. Any word on Poly-ISO 'off gassing' like XPS? Otherwise EPS is significantly cheaper but less R-Value. Eventually I would want to use a mineral insulation after the foam but that is way out of my building budget for now. XPS offers the best R-value in per dollar when trying to not have too thick of wall. Poly ISO does it just as good or better but costs more money and EPS is cheaper but does half the R value performance. XPS also has been said to off-gas, which may not be toxic but it does lessen the R Value.

I don't think I would use a Vapor Barrier in the basement. If I did I would do the plastic bag test first. It may not be a problem in a walkout basement, but to my knowledge the concrete does need to breath and the VB would prevent that. So would the foam in a sense? Upstairs on the main level I plan on using 2" XPS outside and then Dense Fiberglass or mineral wool in the wall cavities. I will not be using a vapor barrier, just drywall over the studs so the wall can breathe since the XPS outside will be taped off and serve as my air and vapor barrier according to Green Building Advisor.
 
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Old 05-23-15, 01:40 PM
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I think your concerns about XPS offgassing are totally off base and are probably the result of either misinformation, media hype or confusion about the various types of foam insulation. Sure it will probably "offgas" if there is a fire, but so will every other building material in your house... the carpet, the pad, the glue, the caulk, the vinyl siding, the laminate floor, the wood, etc, etc, etc.

ISO (isocyanate) is the material that has been the subject of most articles about offgassing and losing r-value, so maybe you have your types of foam mixed up a little. I have heard it said that ISO foam may start out with a higher initial r-value than XPS but that as it ages, that r-value (as compared with XPS) may even out over time, so that in the end, ISO and XPS are pretty even as far as r-value per inch is concerned. ISO foam usually excels over XPS in that ISO foam generally has a foil facing and thus can be a better vapor barrier, plus it can carry a fire rating, whereas XPS does not, and thus can't be left exposed.

XPS does not lose r-value. Remember that X stands for "extruded" so those are the rigid foams like Dow r-board/blue board. ISO is soft, usually yellowish with very small closed cells that can contain chemicals from the chemical process used to create it. Thermax and Tuff-r are examples of ISO, along with most spray foam products. And as you know, EPS is white styrofoam, where E stands for Expanded polystyrene, which has lower r-values per inch, but that is generally offset by thicker products that help you achieve the same numbers.
 
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Old 05-23-15, 02:09 PM
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XSleeper,

I may have read a bit into the hype about XPS, but what is funny is your example between ISO and XPS is the EXACT difference between XPS and EPS. EPS generally uses Pentane, which has a very low Global Warming Potential and results in a stable R-value over time. XPS uses HCFCs as the blowing agent, which has a high Global Warming Potential. XPS also loses some of its R value over time, as the gas slowly escapes. - See more at: XPS versus EPS Foam

I have not read much about PolyISO besides that is is a good performance per inch in R-Value and that when it gets cold it is not as effective.

XPS loses R value over time and apparently is just above or about the same R-Value as EPS foam after 5-10 years.

PolyISO is not to be used outside where it will get wet, and if it is foil faced generally people do not have to cover it with sheetrock like they would with XPS or EPS because of the fire hazard and toxic fumes.
 
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Old 05-23-15, 02:22 PM
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The internet is a terrible thing when it comes to this sort of thing. There is way too much conflicting information out there. You also can visit web sites that seem authoritative but where marketing comes into play and one company skews their information in a biased effort to make their product appear good and their competition look comparatively bad.

There are also many "Types" of each kind of insulation. You can't categorically say that one type is better than another. A high grade of EPS may perform better than a low grade of XPS and vis versa. Its understandable when people are confused by the glut of information out there and end up overthinking every decision.

There may be some type of XPS (like Foamular) that loses that much r-value but if you stick with Dow square edge (type IV) or similar, there is no appreciable loss in r-value. Dow's own warranty for their Type IV XPS states that 1/2" to 3/4" insulation is warrantied to not lose more than 10% of r-value in 15 yrs... 1" insulation for 30 yrs... and 1 1/2" insulation for 50 yrs. So you can take that for what it's worth.
 
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Old 05-23-15, 02:46 PM
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True, that's one thing that is horrible about the internet and marketing. A lot of studies are backed by one company to persuade the test results.

I think I will try to use XPS on my exterior walls on the main floor and insulate the concrete basement walls on the inside later on. I just hope the 2" of XPS on the outside is a good move and that it won't cause moisture problems.
 
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