# XPS or Polyisocyanurate for basement



## BlueBSH (Oct 29, 2009)

I'm about a few weeks away from starting my insulation project in the basement... was just about to order the rigid foam and noticed that polyisocyanurate foam is strangely cheaper... I was always under the impression it was more expensive..... anyways which of these would you buy? Keep in mind I am going to put a 2x4 wall infront of this and add R-13 to that in addition to this foam board....

*Dow STYROFOAM 3/4" x 4' x 8' R4 Insulated Sheathing *$17.72 per sheet

http://www.lowes.com/pd_14545-46086- 202059_4294858106_4294937087?productId=3125297&pl=1&currentURL=/pl_Insulated%2BSheathing_4294858106_4294937087_?rpp=15$No=15

or


Dow 3/4" x 8' x 4' R-5 Polyisocyanurate Rigid *$12.98 per sheet* 
http://www.lowes.com/pd_42821-236-2...Sheathing_4294858106_4294937087_?rpp=15$No=15


----------



## Gary in WA (Mar 11, 2009)

http://www.buildingscience.com/docu...rol-for-new-residential-buildings?full_view=1

Be safe, Gary


----------



## BlueBSH (Oct 29, 2009)

Not really sure that answers my question on which one to use... I already know how to insulate for my situation, just not sure if it matters which one I use or not


----------



## rustyjames (Jul 20, 2008)

BlueBSH said:


> Not really sure that answers my question on which one to use... I already know how to insulate for my situation, just not sure if it matters which one I use or not


For a basement use the XPS.


----------



## Gary in WA (Mar 11, 2009)

Sorry. The article brings out to use non-faced foam board. Poli is faced, three layers of : http://docs.google.com/viewer?a=v&q...4y-WgP&sig=AHIEtbTbbGN1fwF6N8aVdtkIjjvMMJW5yA

You want the water vapor to pass through the board and dry on the room side. Only latex paint, no v.b., no air space, sill sealer under p.t. plate for thermal/capillary break.
More recent studies suggest minimum 2" foam board for thermal protection against condensing.


Be safe, Gary


----------



## High Gear (Nov 30, 2009)

XPS tongue & groove


Owens corning 1" XPS 150 T&G is around $10.00 +/- $1 around here.

2" is $20.00 +/- ( Menards )


----------



## BlueBSH (Oct 29, 2009)

:confused1: ok I guess one last question... since I am framing a 2x4 wall infront of this and filling it with R-13 fiber glass insulation, should the be faced or not? some stuff I read says yes, some says no the XPS is the vapor barrier (which isn't it semi permiable? doesnt some vapor still get through?)


----------



## High Gear (Nov 30, 2009)

http://www.buildingscience.com/documents/reports/rr-0202-basement-insulation-systems

Particularly page 9 /10 / & 14 but read it all if you like.

Probably won't find unfaced R-13 , just take the paper off .


----------



## BlueBSH (Oct 29, 2009)

High Gear said:


> http://www.buildingscience.com/documents/reports/rr-0202-basement-insulation-systems
> 
> Particularly page 9 /10 / & 14 but read it all if you like.
> 
> Probably won't find unfaced R-13 , just take the paper off .


amazingly my local lowes has R-13 batts unfaced available


----------



## High Gear (Nov 30, 2009)

Good deal its always nice the less glass dust you stir up.

I have 1" foam with r-13 glass , I will be calling the 

plasterer this week.


----------



## BlueBSH (Oct 29, 2009)

when the foam board says "sheething" does that imply it has a facing? I know that means it can be used like plywood sheething is on the outside of the house when it is SIS but you wouldnt use that in a basement would you?


----------



## leungw (Apr 20, 2009)

BlueBSH, I am doing about the same thing as what you are describing. I am using Owens Corning 2" XPS. My local Home Depot has them. About $15 for 2ft x 8ft.


----------



## Gary in WA (Mar 11, 2009)

Looking good! Remember required egress from a basement: http://illowaicc.org/uploadedFiles/Illowa/Codes/Emergency Escape Rescue Openings.pdf

Foam board the rim joist: http://www.rd.com/57548/article57548.html

Sill sealer under the p.t. plate, a capillary and thermal break: http://www.greenbuildingadvisor.com...ressure-treated-sill-plates-and-building-code

Be safe, Gary


----------



## BlueBSH (Oct 29, 2009)

GBR in WA said:


> Looking good! Remember required egress from a basement: http://illowaicc.org/uploadedFiles/Illowa/Codes/Emergency Escape Rescue Openings.pdf
> 
> Foam board the rim joist: http://www.rd.com/57548/article57548.html
> 
> ...


 
I just finished 90% of my rim joist job... hit some snags with it though, some joist cavities had hvac riser ducts going into them for the 2nd floor and they where right against the wood it seemed like... so made it almost impossible to do.... for those ones I just spray foamed around the joints to seal it up then fiberglassed it with R-30 that was about 7 joist bays out of the ~110 joists I had to fill.. currentlu struggling with one 30 ft wall that is one long cavity (its running parallel with the joists) on one end the space is about 3 inches open (due to the basement wall beign framed in 2x4's and drywalled already I lost about 5 inches of space to get into it) so I had to find a way to get it up into there which wasnt hard but foaming around the gaps has been an interesting challange... made myself a longer flexable tube wand to stick up in worked great so far... but the problem is the other end... the gap is only about 1" so I can get the foam in but then I cant see a thing and the gas line comes in there and there is a water faucet... so im stumped on that end on what to do.... once I get that done im done with rim joists..... yay!


now my problem...... XPS in my area doesnt seem to come in toung and groove at lowes..... just "square edge" and lowes is really the only easy to get to lumber store around here anymore...... use to have an 84 lumber but that went away... any problems with using square edge and bonding the pieces together with glue then taping them or what would you do in this case?


----------



## BlueBSH (Oct 29, 2009)

what is the tape called you use on the joints? we always called it tyvek type (yea i know thats a brand... but we always just called it that)... is it just normal housewrap tape? I'm having a heck of a time finding it at lowes....... i can find houe wrap just no tape....


----------



## Gary in WA (Mar 11, 2009)

http://www.lowes.com/pd_135512-5629...tk=i_products&ddkey=http:SearchCatalogDisplay

http://www.lowes.com/pd_96179-1410-T96A_0_?productId=3047970&Ntt=clear+plastic+sealing+tape&Ntk=i_products&pl=1&currentURL=/pl__0__s?newSearch=true$Ntt=clear%20plastic%20sealing%20tape$y=0$x=0 

Be safe, Gary


----------



## BlueBSH (Oct 29, 2009)

ah thank you, was looking for the wrong stuff then!


----------



## leungw (Apr 20, 2009)

The tape that I use is indeed made by Tyvek. My local Home Depot has them. I have seen a similar product made by Lowes, but haven't actually tried it.

http://www.lowes.com/pd_103366-210-T255LWCS_0_?productId=3006052

I also have ducts running in some of the rim joists. I used fiberglass in those. The rest I used XPS.

The XPS that I am using have tongue/groove. I don't find them particularly useful as they don't always line up. Probably it is because my basement has concrete blocks and they are not perfectly flat. I am using tape on the joints anyway.

Check if your town requires fire blocking. If so, I would suggest doing that first after you seal all the rim joists.


----------



## High Gear (Nov 30, 2009)

Caulk the groove full of PL , you won't need tape.

I glue the heck out of the foam , air gets around it you've gained nothing IMO.


----------

