Replies

1. 
   maverick | Feb 15, 2005 12:59am | #1

   PVA primer is not a substitute for a vapor barrier.

   Given a choice between kraft faced batts and continous plastic sheeting over fiberglass I would take the kraft paper. A house needs to breath a little.

   Todays houses are built too darn tight IMO

1. 
   zendo | Feb 15, 2005 01:16am | #2

   Thats weird. PVA primer is just your average primer paint for drywall.  it doesnt have anything to do with your vapor barrier. 

   See post #2.

   -zen

2. 
   lisakk | Feb 15, 2005 01:57am | #3

   Last time we built in 1998 I don't remember anyone installing vapor barrier on the walls, but I suppose the drywallers might have put it up before I saw.  I didn't exactly hang over their shoulder while they worked, which I'm sure they appreciated.  I'll just put both the primer and the vapor barrier on my spec list.  

   Is it considered standard to do three coats of joint compound?  If I want as little texturing as possible, without the expense of a smooth finish, do I just ask for lightly textured?

    

1. 
   MikeSmith | Feb 15, 2005 02:20am | #4

   lisa... i'd check out  buildingscience.com  for your part of the country..

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

1. 
   BarryE | Feb 15, 2005 02:28am | #5

   Seems like I've read that all paint is a form of barrier. PVA has a permeability of about 3.5 to 5 or 6 and in some climates is considered as a form of, She is in Seattle, this is from the Oakridge National Laboratory done for the city of Seattle:Insulation and Interior Finishes: The computer modeling
   suggests that under high interior RH conditions, a vapor retarder should be used on the inside face of the
   wall to limit vapor diffusion into the wall. Well-sealed
   kraft-faced batt insulation, unfaced batts with poly vapor
   barrier, or use of a PVA primer is recommended.Choice of Vapor Control Strategy on Interior Side of
   Wall: If RH is generally maintained at less than 60%,
   the computer modeling showed that more semi-permeable
   vapor retarding materials are preferable, i.e.
   materials with a permeability between 1 and 10 perms,
   e.g. latex primer and paint. If RH is maintained above
   60%, the modeling indicates that more vapor control is
   needed, i.e. materials with vapor permeability around 1
   perm, e.g., vapor retarding primer and latex paint, or
   kraft-faced batt insulation.1 If RH is maintained higher
   than 75%, the modeling indicates that a vapor barrier
   would be required, i.e. materials with a permeability
   around 0.1 perm or less, e.g., 6- or 4-mil poly.
   • Effect of Mechanical Ventilation: The net effect of
   mechanical ventilation, in combination with wind and
   stack effects, causes periods of air infiltration and
   exfiltration. The computer modeling predicted a net
   increase in the moisture load on a south-facing exterior
   wall. However, the study showed that vapor semipermeable
   assemblies were generally able to manage the
   additional moisture load, i.e., these assemblies were able
   to store and release moisture as needed, provided
   interior RH generally remained below 60%.2http://www.cityofseattle.net/dclu/news/moisture_study_summary.pdf

   Barry E-Remodeler

    

1. 
   MikeSmith | Feb 15, 2005 02:34am | #6

   good post..

   until we switched to Dens-Pak cells.. our typical spec would have been

   R13 friction fit batts and 6mil poly vapor barrier..

   Gene Leger  used to post here quite a bit.. he was a big advocate of the air-barrier drywall approach.. which i think had a lot of merit..

   now..  we watch our potential water sources ( crawl spaces, slabs, basements )

   and Dens-Pak our walls , seal our attics , and use  good mechanical ventilation for baths, kitchens, & clothes dryers... we also use an R-60 attic insulationMike Smith Rhode Island : Design / Build / Repair / Restore

1. 
   BarryE | Feb 15, 2005 03:19am | #7

   Years ago I looked at the ADA approach, thought about going the whole 9 yards and buying the gaskets. Seems like most remodels it doesn't pay when the majority of the house is built to minimum.I've been interested your dense pak method since you've started posting about it. I may have found the right project to give it a try, especially after we got the bid for foam. <g>

   Barry E-Remodeler

    

2. 
   MikeSmith | Feb 15, 2005 03:43am | #9

   i know what you mean.. i always get interested in foam... then i get the sub's price..

   lemme tell ya... the DP is pretty labor intense.. but most of the labor is prep.. the actual blowing takes about two days for two guys...

    the rest of the time is spent on making dams at the plates to keep the insul out of the soffits... installing  propa-vents to vent the attic.. building dams around the scuttle to keep the insul in the attic..

    and installing and gluing a lot of insulmesh for the walls and the denspak rafter areas 

   if you have full control of the job , some of these things can be done easier and faster if they are done in the right sequence... but if you have to go in and prep after a lot of stuff is in the way, it becomes more  time

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

2. 
   lisakk | Feb 15, 2005 03:20am | #8

   Thanks for the info.  I always wondered why we needed to use T & G plywood and PVA primer as a vapor barrier.  The only time I've ever seen visqueen used is in crawlspaces.