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Old 01-17-2016, 10:05 AM   #1
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2 1/2" EPS basement wall ?


i am thinking about insulating my basement walls.
EPS is what i would like to use because of cost.
i have an area by the stairs and back door that i need to keep as wide as possible.

my idea.
1" EPS , 2x4 sideways/flat 16" OC, treated bottom plate on 1"(?) EPS under that. then 1 1/2" cut to fill the cavity, then drywall. all air sealed(or not ?)

am i asking for problems ?
thanx
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Old 01-17-2016, 10:11 AM   #2
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EPS does not have great compressive strength.

Don't put the bottom plate on that. You aren't loosing that much energy through there anyway.

Any wires in that wall? Going to have to figure out another way if so.
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Old 01-17-2016, 10:27 AM   #3
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Originally Posted by Windows on Wash View Post
EPS does not have great compressive strength.

Don't put the bottom plate on that. You aren't loosing that much energy through there anyway.

Any wires in that wall? Going to have to figure out another way if so.
ok. how about xps ?

no wiring. though, i am thinking, IF i changed my mind, i could run conduit to the top of the wall, then romex down to an outlet. bad idea ? i don't have to have hiden electric, but it would look a bit cleaner. its a basement = future man cave.


anyway, what i am really wondering. would my EPS idea cause/promote mold or cause any other problem i can't think of right now ?

the basement is 50deg right now. and i may want to heat it.
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Old 01-17-2016, 10:43 AM   #4
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XPS is better and has more R-Value. I would go that route.

Are you really going to miss the 2" of floor space?
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Old 01-17-2016, 11:00 AM   #5
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i was saying use the xps under the bottom plate, not the whole wall = i would go broke.

yes, 2" would make a difference. there isn't much room there as it is.
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Old 01-17-2016, 12:23 PM   #6
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I know what you were saying about the foam placement. EPS is not suitable for that compression in my opinion.

If you switch to XPS, should be good.

http://foamular.com/assets/0/144/172...63215bea18.pdf
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Old 01-17-2016, 07:49 PM   #7
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ok, thanx.

things may change, but it looks like i am going to go with this. menards has the stuff on sale.
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Old 01-18-2016, 10:06 PM   #8
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Go with the EPS with a compression rating of 5# psi (per INCH) and a facer (or poly plastic) under the plate. http://www.greenbuildingadvisor.com/...-building-code Regular stud wall is 7# per square inch- using 3" x 1.5" plate as bearing load but you should add two fasteners mid-stud or they will warp/bow with added drywall later. Fasten them through the foam to concrete wall. Be sure to sight/shim where needed for a straight plane of all studs to meet drywall 1/8" variance (code-required). The Type XI is only 1/2# EPS, IMHO, not suitable for the wall application, as the better grades have higher comp. strength, though as said, - only bearing on bottom plate is itself. BUT way more importantly is the "water absorption %" of different FBs, EPS is only for a dry basement or at least use the 2# rated one, if using this product. http://www.buildwithplymouth.com/eps...spec_sheet.pdf XPS is 0.9% water absorption, if I remember correctly....

Add the FB under the plate unless your slab has (code-required perimeter insulation last 15 years) for a $1-3 savings times 10 years will pay for the FB, be sure to run a bead or two of caulking for the all-important air seal; http://www.google.com/url?sa=t&rct=j...hj_I6fU2ymaUSA

Otherwise, your wall is warm on top/middle and cold feet thermally through conduction to earth temp about 10* warmer than ambient and a few weeks lag time. Nice heat sink... 24/7. The perimeter wall insulation will save you some money if you are missing the slab insulation (though not quite as much); http://www.google.com/url?sa=t&rct=j...7c2C4A&cad=rja

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Old 01-19-2016, 09:42 AM   #9
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Go with the EPS with a compression rating of 5# psi (per INCH) and a facer (or poly plastic) under the plate. Regular stud wall is 7# per square inch
Why would the foam want to be of a lesser compressive strength than he stud wall?
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Old 01-19-2016, 10:20 PM   #10
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Gary, thanx.

i am working to digest your info. but in the mean time.
the DOW link. it says r-10 is a good bang for buck solution. would you agree with this ?
my foundation is a hearty block and is 1/2 below grade.

the inside of the wall, as the blocks were set, is not smooth. there are dimples and humps in a lot of places. 1/4" plus/minus. is this an issue i should deal with ? or just leave it and seal the parameter and joints.

no slab insulation. who knows how old the slab is. but it is in pretty good shape.


oh. the other day i did some temp checking. it was 23 outside. outside foundation temp 27. inside foundation temp, same exact blocks, 46 deg.

no direct heating
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Old 02-08-2016, 09:45 PM   #11
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Sent you a one-on-one... Gary
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Old 02-08-2016, 10:25 PM   #12
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Sent you a one-on-one... Gary
thanx Gary, just sent a reply.
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Old 02-12-2016, 05:24 PM   #13
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I will read it next....the forum automatically tells me. Adding a frame wall with drywall is about 35# per 16"on-center for 8' tall wall divided by 16" (bottom plate) times 1.5' (24) width of plate = -1.5# per inch on the foam; no contest even with 10# (ESP @0.5 density) when using a bottom plate, even if cut into 16" pieces (no added strength from wood fiber bending/deflection rating). Earlier figure was 3" X 1-1/2" point load if you read again... conclusion; anyone who has actually framed a wood wall knows the weight involved.... very ignorant to add a framed/drywalled wall and heat it while the slab it is on has basement earth temps, especially at the perimeter where major heat is lost; http://www.house-energy.com/Insulati...Insulation.htm

Granted, it's only 24 square inches per 16" x 50' lin.ft. basement wall (eg)= 900/144= 6-1/4 sq.ft. of thermal bridge (like a 3x2' window open); http://buildingscience.com/documents...-bridges-redux

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