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Discussion Starter #1
Is XPS rigid foam sufficient enough to insulate a basement in NJ? I believe 2 inch has an R-value of about 10, or even 1 inch, which is R value of 3-5? Would I need additional on top of that, such as fiberglass? Does anyone know what the code is? Or what would be comfortable?
 

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Discussion Starter #3
Sorry yes, it will be framed out and used for extra living space, ie wreck room, gym, playroom. The foundation is poured concrete, no water even after hurricane sandy
 

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" Would I need additional on top of that, such as fiberglass? Does anyone know what the code is?" Code, where? Zone 4 or 5,4M?; http://energycode.pnl.gov/EnergyCodeReqs/index.jsp?state=New Jersey They both require R10 FB OR R-13 if still under the 2009, not 2012... you could have condensation in cavity on the FB if the location is cold enough and you use too much cavity insulation to stop the room air from warming it... eg.; Sussex county average temps for Jan., Feb., Dec. is 27.83*
minus the Delta T times the cavity insulation value= 1. R-5 XPS with R-15 cavity Roxul= only good up to 31% Relative Humidity in room. 2. R-10 alone with dead air space in cavity= good to 86% RH 3. R-10 XPS with R-15 Roxul= good to 39% RH without condensation on your foamboard face in cavity- wetting the insulation- fiberglass will lose about 60-70% of R-value when wet.Hopefully you searched our "XPS in Basement" threads also, it requires air-tight, same as rims mentioned by WoW. FB under bottom plate, tape/mastic FB joints, full contact with concrete, ADA the drywall, etc. The more cavity insulation, the colder the foam will be, less RH capable handling. Gary
 

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Discussion Starter #7
This is way too technical for me. I'm in climate zone 4 non-marine. In layman's terms, what thickness in XPS should i get, 3/4 inch? 1 inch? and then batt non liner insulation as well?
 

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Gary point was that by filling the cavity with insulation, you would so the heat loss to the foam board and therefor lower its surface temperature (hence raise the condensation potential).

I prefer 2" will a batt fill and airtight drywall approach.
 

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Use R-10 XPS air-sealed tight against the concrete wall for handling up to 86% Relative humidity (very, very wet) without any cavity fill insulation. R-10 + R-15 Roxul = 39% humidity, and the worst is R-5 + R-15 R. IMO, R-10 and no cavity insulation is premium.

Give a city name and I will figure minimum FB needed. Gary
 

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Discussion Starter #10
Use R-10 XPS air-sealed tight against the concrete wall for handling up to 86% Relative humidity (very, very wet) without any cavity fill insulation. R-10 + R-15 Roxul = 39% humidity, and the worst is R-5 + R-15 R. IMO, R-10 and no cavity insulation is premium.

Give a city name and I will figure minimum FB needed. Gary
Cherry Hill, NJ.

r10 is prob 2 inch thickness on the foam board??
 

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With your 3 coldest months average temp for Camden, R-5 (1" XPS) + cavity insulation will give only 30% RH and 38*F. It all depends on if you are meeting code (R-10; 2" XPS) or not. Will you be at 35% RH or less down there, the average when figuring RH? IF above the average 35, you need more foam or dehumidify it when the temps drop below your average used. With 2" XPS alone, empty cavity (not a problem = no convective loops as some assert), good to 79% RH and 63*F at foam face. With 2" + cavity insulation, good to 38%RH and foam at 43*F. With R-5 (1") and no cavity fill, 65% RH and a colder 58*F on the foam face. IMO, meet code with R-10 and no cavity fill, your climate doesn't warrant it. Gary
 

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Discussion Starter #12
Thanks Gary. I think I will go with 2" XPS and no additional cavity insulation. What about insulating the floor when I get to it? What do you recommend?
 

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While the condensation numbers are much higher, I would still fill the cavity if it were me.

39% RH with an outside temp of 28 degrees is high and if you have that kind of humidity level in the basement, the numbers are going to be even higher on the upstairs floors (i.e. where most of the humidity is usually generate unless you have slab or foundation wall issues) and your home is going to be sweating like a Richard Simmons exerciser at that point.

I would fill it the cavity and make sure the drywall is airtight. Put putty pads behind the outlets, seal the drywall as part of installation, and call it a day.

So little moisture will be moving through the drywall as a result of diffusion through a primed and painted sheet of drywall that the likelihood of condensation is supremely low.

Gary does know his science and application and those numbers are 100% accurate. As a matter of fact, I have been trying to get him to show me is magic formulas as well.

I am just not sure I have ever seen a basement wall with condensation issues that was done properly with 2" of foam.

As far as your other question, very little heat is being lost through the slab with the exception of the corners. Insulate if you want but ceiling height is usually a premium so most opt not to.
 

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I'm near NYC and did R5 1" xps with R15 Roxul over it. I haven't noticed any issues yet, but I think what Gary is saying is that this isn't good. Not sure if I should worry, but so far so good.
 

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If the drywall is tight and you keep reasonable humidity levels, you won't have any issues.

39% (and even 31%) is a good bit inside a home at the dead of winter. Again, unless you have slab or wall moisture making it into the basement, a majority of the humidity will be concentrated in those areas nearer humidity generation (i.e. baths, kitchens, etc.).

Depending on the heat source, you will generate some via combustion as well.

Certainly the RH will circulate via the conditioned air, however, you should have that much in the basement unless you are making a bunch of it.

Buy a humidistat and see what you have.
 

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Discussion Starter #16
I do have a humidistat in the basement, I'll take a look and see what it's registering. I put it down there a couple of days ago, wanted it to acclimate.
 

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As we wait for the results.... I wasn't saying you get humidity with 2" of foam, it can handle any exterior diffusion from the wet soil (bar an outright leak/flood/downspout) and (IF) any interior sourced moisture within reason (water heater/boiler, wood stove). Possible condensation from interior in springtime, but only after subtracting your slab depth; http://www.buildingscience.com/documents/bareports/ba-0309-renovating-your-basment With your mild climate I can't justify R25 in a basement wall (buried portion) while protected from the above-grade elements by the 6-8" thick concrete wall and tons of soil. I expect 1/2 the R-value required for your above grade wall (mass; R-10), when R-10 would work (and meet code), spend the extra money on other energy saving areas.

R-5 is fine (add more for less gain) for the slab/under bottom plate, though biggest savings are at perimeters. Slab will always be 5-10*F (depends on depth) warmer than ambient air, with a 25-30 day lag. http://www.google.com/url?sa=t&rct=j&q=deep%20ground%20temperature%20under%20a%20basement%20slab&source=web&cd=1&cad=rja&ved=0CC8QFjAA&url=http%3A%2F%2Facademic.udayton.edu%2Fkissock%2Fhttp%2FEEB%2FLecturesAndHomework%2F05_RoofsFloorsBasements%2FFloorsBasements.docx&ei=Yw4-UYKTMsS8qAHJvIGIDQ&usg=AFQjCNGFRE18JlhiYyqfhj_I6fU2ymaUSA

Or do you just want warm feet.... and, another link; http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_05fb/0901b803805fb824.pdf?filepath=styrofoam/pdfs/noreg/179-70015.pdf&fromPage=GetDoc

Could also save 2" floor space using 2x2 wall studs on top the FB with a shallow box for electrical (1-1/4"). OR, 1" XPS + cavity fill = dryer concrete wall to reduce the chance of wetting/spalling concrete and saturated mudsill plate wicking to rim joist above-grade for drying because of the low perms of 2"XPS, while 1" is 1/2 that.
Good read; http://aceee.org/files/proceedings/2006/data/papers/SS06_Panel1_Paper27.pdf

An early present for WoW; http://www.buildingscience.com/documents/digests/bsd-controlling-cold-weather-condensation-using-insulation/view

And; follow the links here, also; http://www.greenbuildingadvisor.com/blogs/dept/musings/are-dew-point-calculations-really-necessary

Gary (You never asked, Erik....)lol.
 

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Discussion Starter #18
As around 7pm this evening, my basement is 64 degrees F and 35% humidity. It's is currently 40 degrees outside and a light rain. Should I continue mapping the temp and humidity for a couple of days? I'm looking to only use FB insulation without cavity insulation. Should I use XPS 1" (R-5) or 2" (R-10). I'm not overly concerned about losing an inch of interior space once i frame the walls. I just need a clear cut answer and whatever will meet code for R-value.
 

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Code; "Basement Wall R-value c 10/13"

footnote "c";c. "15/19" means R-15 continuous insulated sheathing on he interior or exterior of the home or R-19 cavity insulation at the interior of the basement wall. "10/13" means R-10 continuous insulated sheathing on the interior or exterior of the home or R-13 cavity insulation at the interior of the basement wall." From; link on previous page; http://energycode.pnl.gov/EnergyCodeReqs/index.jsp?state=New%20Jersey

Your choice, Gary
 

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Discussion Starter #20
There is a 2 inch space between the rim joists and the top of the concrete foundation in my basement. When I install the FB, should I have it go only up to where the concrete stops, or all the way up to the rim joists? Sorry if this is a stupid question, but thanks for all your invaluable help! I really appreciate it! :thumbsup:
 
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