Which side to put vapor barrier on?
I don’t know which is the proper side of the insulation to install a vapor barrier?
I am building a 12’X12′ tack room and office for my wife in her horse barn here in southern Louisiana. The room will be framed with 2×6 studs 24″ OC with 2X8 joists 16″OC. I plan to insulate with fiberglass batts or rolls. It will be the only area in the building heated and cooled. On two walls the outer wall is the metal sheathing of the main building, the other two outer walls will be covered with 1/2″ plywood. The inner walls and ceiling will be either plywood or beadboard panels
I don’t know whether it would be better to put the vapor barrier next to the inner walls–inside the insulation–or next to the outer walls–outside the insulation. This part of Louisiana is pretty warm and very humid. We get about 2 months of cold weather but the rest of the year is warm and the summers are 85-100 and high humidity. I would really appreciate your help. Thanks
Replies
It depends on the number of days you require heat vs. days you require cooling. If more heat then cooling then the vapor barrier goes on the inside, if more cooling then heat it goes on the outside. I believe the Department of Energy has done a number of studies and they are available on their site http://www.eere.energy.gov/buildings/homes/insulatinghome.cfm . I remember from some research I've done that Southern Lousiana would require the vapor barrier on the outside.
Mastor
Thanks a million. What you say makes sense. Since I guess the idea is to keep the barrier on the warm side to prevent condensation inside the insulation. I'll check those links too. Thanks again.
Russ
local bldg dept would be able to tell you, thats if you have one.
CBD Builder:
Thanks, that's a good suggestion. I'll give them a call.
What little I know has always said that it goes on the warm side of the insulation.
You could make a good argument for not using a VB in that climate and situation, but my leaning is to putting on the oputside if you will be using air conditioning.
Excellence is its own reward!
To play devil's advocate, is there a 'right' answer regarding what side to put the VB on when you live in a climate like MN? Admittedly, we have more heating months than cooling (about 5 months heating, 3 months cooling). The cooling months also bring immense humidity.
I live in an old house...no vapor barrier at all, but I see a lot of tyvek wrapped, central air homes go up around here.
If you use air conditioning, it's a tossup. If you open the windows in summer, the vb needs to be on the inside.
edit - I'm changing that from tossuip to definitely put it on the inside. For sake of discussion with a devil's advocate, here's why,
sippose that you have three months of summer weather with temps averaging 90° and that you have three months of winter heating with outdoor temps averaging ten degrees. now assume that your HVAC system is designed and set to keep the indoor temp at 70°F
Your summer cooling degree days is 1800
Your winter heating degree days is 5400
So you therefore have more heat driving moisture out than driving it in.
These are all based on assumptions for the discussion's sake.
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Excellence is its own reward!
Edited 5/1/2003 10:52:02 PM ET by piffin