Replies

1. 
   mike4244 | Sep 23, 2004 03:02am | #1

   Cold weather won't affect the sheetrock. If the board gets wet it will get moldy. Ordinarily an unheated , but otherwise dry cabin will be fine to sheetrock. If there is no vapor barrier in the wall , add a vapor barrier or buy sheet rock with a foil back.

   Many builders install plastic ( polyethelene, viscreen, etc) on the studs. I never do, I use 30lb felt paper. Plastic becomes brittle in a few years. Do not install two vapor barriers on the same wall, this could lead to mildew problems. Styrofoam cannot be used for insulation unless it is surrounded by 1/2" rock on all sides, this is the code where I live. Why not use fiberglass batt insulation  with a vapor barrier on it. This solves that problem easily. If you think you will get more insulating value with styrofoam, you probably do. Insulating the ceiling joists well is more important than the extra R value in the walls.Even 2x6 studding with insulation is not that much more effective than 2x4 walls with insulation.

   mike

1. 
   Piffin | Sep 23, 2004 05:35am | #2

   I hope you don't mind if I correct a couple of erroneous statements here.

   Plastic becomes brittle from exposure to the UV rays in sunlight. When it is covered and protected from same, it dopes not lose its pliability or become more porous.

   Foam does not need to be encapsualted on all sides. It only needs to be separated from living space by the firestop barrier that sheetrock can provide. That means that placing sheetrock over it on the inside of the wall will serve safely.

   Two vapor barriers become on if together on the same side of the wall. it is when there isa VB on each side of the wall that moisture can be trapped between in the middle of the wall that mildew - and worse rot - can occour.

   Fibreglass batts are the poorest kind of insulation available today. This is because they allow convection currents within the stud cavity to transfer heat to the outer surface of the wall to be conducted away. Foam is by far the best R value in insulation, especially when sealed well.

   I agree that in Idaho, there will be no difficulty allowing the SR to remain unheated or to heat and cool it multiple times, other than a possible hairline crack in the seams. There ar eclimates wehre this is not adviseable though. 

    

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1. 
   Mitremike | Sep 23, 2004 09:40am | #4

   Hey piffin

   couldn't he use Homosote instead of SR . The stuff is tougher . and It has square edges that he could apply battens to to cover the seams. Thus elimating any cracking. good call on the insulation.

   One point I am not sure about is the double up VB acting as one.

   Around here you need to slice any VB like kraft before using poly and they don''t like to see Green board over VB either. Personally I think Green Board is a marketing ploy just like that anti-mold stuff. Seems like trying to make and sell a product that deals with the symptom while ignoring the problem in the first place.

   You know what they say about advice---" It is worth exactly what you paid for it" Mike

1. 
   Piffin | Sep 23, 2004 08:04pm | #7

   I don't acre for homasote myself on exposed surfaces bwecause it is hard to pain, hard tp clean and if left unpainted, it will harbour moisture and mildew - and I don't believe it would meet fire code for oer the foam. Persoanlly if this were mine, i would use pine T&G V-groove to panel the interior, but that might be outside the budget.

   rthat idea about slicing the kraft faces is something a few of the inspectors dreamed up that has no basis in fact and really does nothing but waste time and satisfy the inspector's ego.

   Greenboasrd over VB - green board is moisture reistant sheetrock but there is something about the nature of it that when it does take on moisture, it loses more of it's strength so a ceiling of GB is more likely to sag just enough to notice. Or so I've heard. That may be why some places would disallow it directly over VB 

    

   Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

1. 
   Mitremike | Sep 25, 2004 03:52am | #11

   Didn't realize that about Two VB touching but I don't use Kraft faced so It is a moot point for me.

   as for Greenboard . Most of the newer houses around here have 24" OC floor trusses to tuck the mech. and GB isn't found in anything but 1/2 so the ceiling gets regular rock and by the time you order 8 sheet for the walls it is more work than its worth .

   Beside a good oil primer seals the board and the seams equally and IMO the substrate of GB is nulified. Then again I am going off my personal experience and my rockers. Mike

2. 
   mike4244 | Sep 26, 2004 07:41pm | #12

   Pippin, I agree that plastic exposed to sunlight degrades it quickly. From my expierence it also degrades behind sheetrock and under concrete. Years ago I removed sheetrock from a house that suffered water damage. The plastic behind it was brittle, like parchment paper. Every slab that I have seen that was removed with a plastic vapor barrier also had degraded.As far as the styrofoam being enclosed on all sides, I mentioned that the code enforcers in my town do not allow styrofoam in walls unless the stud cavity is enclosed with sheet rock. This is for fire purposes I imagine.

   mike

2. 
   expressn | Sep 24, 2004 02:55am | #10

   Thanks for the advice. Is just a small building, used once in a while. Will heat with wood , and know there will be leakage. Will have fiberboard, and t-111 on outside. styrofoam is dock material, and is free! fits well between studs, and figure will be better than nothing. Linda

2. 
   DaveMason2 | Sep 23, 2004 09:32am | #3

   No

3. 
   dIrishInMe | Sep 23, 2004 03:39pm | #5

   On a little tangent here, you said: "We are insulating with styrofoam panels".

   Do you intend to install the styrofoam between the wall studs/ceiling joists, or will it be attached to either the inside or outside face of the studs?  The reason I ask is that if you intend to install it between studs/joists, it will be very difficult to get it to fit well such that there is not significant air leakage around the edge of the pieces of the styrofoam - unless you use "foam in a can" to air seal each piece of styrofoam.  An important concept when insulating is that it is important to stop air leakage, since if heat/cold is transferred fastest via air currents.  In other words, rigid foam board is normally not used as wall cavity insulation, but rather as an inside or outside enhancement to the wall cavity insulation. 

   Another question - did you really mean styrofoam or perhaps another type of rigid foam?  Around where I live, styrofoam is sometimes used for insulation under a concrete slab, but not usually used for walls.  XPS - extruded polystyrene or polyisocyanurate are more typical for rigid wall insulation/sheathing.  I know that may sound like a bunch of technical mumbo-jumbo, but an easier way to look at it is that Styrofoam is usually white and is formed of many small, but easily visible beads or pellets.  XPS is normally blue, green or sometimes pink and is fairly stiff, and the polyiso is usually kind of a mustard yellow color and somewhat soft with a separate skin applied.  Depending on the type of rigid foam selected, it can act as a vapor barrier too.

   This may be more detail that you were really interested in for a "three season house" but you do want to make effective use of whatever money you do spend on insulation, and you also do not want to build in a possible problem possibly trapping moisture in the wall.
    

   Matt
1. 
   BillHartmann | Sep 23, 2004 04:24pm | #6

   "Another question - did you really mean styrofoam or perhaps another type of rigid foam? Around where I live, styrofoam is sometimes used for insulation under a concrete slab, but not usually used for walls. XPS - extruded polystyrene or polyisocyanurate are more typical for rigid wall insulation/sheathing. I know that may sound like a bunch of technical mumbo-jumbo, but an easier way to look at it is that Styrofoam is usually white and is formed of many small, but easily visible beads or pellets. XPS is normally blue, green or sometimes pink and is fairly stiff, and the polyiso is usually kind of a mustard yellow color and somewhat soft with a separate skin applied. "

   Wrong.

   Stryofoam is a brand name for whatever product that they want to put it on.

   The green XPS "logs" that hold up my dock and the sheets of blue XPS at the building supplies stores with Stryofoam stamped on it indicates that it is not limited to EPS.

   And now since Dow bought the foam operation of the old Celotex company they make polyiso that is also stamped Styrofoam.

1. 
   dIrishInMe | Sep 23, 2004 09:39pm | #9

   Thanks for the clarification.  I didn't know that Styrofoam was a brand name.  I think though when most people say styrofoam, they mean EPS - that white stuff that coolers are made of.  I have not seen the other products with the Styrofoam name on them, but I'm sure I will soon. Matt

2. 
   Piffin | Sep 23, 2004 08:07pm | #8

   Good points. I had made the mistake of assuming that the foam panels would run on the face of the studs. To do otherwise would be a waste of time and resources 

    

   Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!