Replies

1. 
   Sphere | Jan 27, 2007 07:27pm | #1

   I have used a LOT of Ext. v. Beaded styrofoam and I will tell you, bugs won't get into the EXt. if that is a concern. I also went with Polyisocyanurate foam to save some cost..it is a bit less pricey.

   I have done this with a log home, where I scribed the foam sheets to fit between the logs and sealed with liquid foam sealant.  Time consuming for sure.

   Anyway, I'd steer away from the white coffee cup foam panels, and I really have no scientific reason why.

   Sorry.

    

   edit for typo...I mean extruded foam is better than expanded..pink or blue..not the white. Polyiso is yellow.

   Spheramid Enterprises Architectural Woodworks

   The secret to a long life is knowing when its time to go.  M. Shocked

   
   

   ---

   Edited 1/27/2007 11:29 am ET by Sphere

2. 
   dovetail97128 | Jan 27, 2007 07:57pm | #2

   The white expanded styrofoam will absorb water and bugs love the stuff.
   The extrudued foam, (pink or blue) will not absorb water and bugs don't seem to be able to tunnel thru it.
   I have seen what we call "sweat bees" and ants out here tunnel into the polyiso foam and I personally don't trust it in buried enviroment. I know the manufacturers tell us it works , won't absorb water etc. .. but.. my own tests, (bucket of water and pieces of different foams left to sit for a week or so ) tell me that only extruded styro is really water proof.
   get some samples and run your own test.

1. 
   MikeSmith | Jan 27, 2007 08:26pm | #3

   EPS  ( bead board ) will absorb water... but not enough to be of concern

   also.. EPS, to my knowledge is the only foam available in a  vermin  treated form ( treated with Borates ), usually under the trade name of  PerformGuard

   http://www.branchriver.com/eps.html

    

   all of the other foams will support vermin.. i've used polyiso, pink board ( Foamul-R ) , green board ( Amoco ), blue board ( Styro-SM )

   i've found carpenter ants  and other boring vermin in all of them

   as to the OP

   EPS is a lower cost per BF, with a slightly lower R-value  (3.4  to 4.8 / inch depending on the density of the EPS )

   some other foams will get close to R-7

   you have to do a cost analysis and make your own decision .. those r-values listed above would result in a thru the foam value of about 12  for the lowere R-value  to 24 for the higher R-value

   the net wall r-value has to be reduced by the thermal bridging of the studs and framing , which only has an apx.R-value of  3  to  4

   also.. if you use foam sheets you have to seal the sheets with a canned foam , or you will have so much edge loss that the foam is compromised to the point of being useless

    

    Mike Smith Rhode Island : Design / Build / Repair / Restore

1. 
   Hannah | Jan 27, 2007 09:51pm | #4

   If we added a continuous thin layer of foam, 3/4" (?), over the whole wall after foam is installed between the studs, would that be enough of a thermal break? Also, if this was well-sealed, would a vapor barrier be necessary?

1. 
   MikeSmith | Jan 27, 2007 10:01pm | #5

   adding a 3/4 foam over the studs would REDUCE the thermal bridge, but not eliminate it

   and the 3/4 foam is a pain in the neck for trim and trying to keep everything in the same plane

   some places you will crush the foam , other places you won't

   there is a technique called the "Airtight Drywall System "  ( or something like that )

   Gene Leger is a big proponent of it..

    anyways.. with the ADS, there is no  movement of air.. so no vapor of measurable amount gets into the walls.....

   if you  thouroughly seal your foam with a foam gun, you will acheive the same thing... no air movement, so no need for a vapor barrier

   if you were using dens-pak cellulose , you could also elimiante the vapor barrier, because of the lack of air movement and the ability of cellulose to diffuse the moisture

   but hey, whadda i no ?Mike Smith Rhode Island : Design / Build / Repair / Restore