vapor barrier
#1
11-01-03, 02:09 PM
vapor barrier
When building exterior basement walls, what type of vapor barrier should I use. I live in SE Wisconsin and I've heard it all from no vapor barrier to a barrier over the concrete block wall AND directly under the drywall. What's the rule of thumb? Do I want the wall to breath with no vapor barrier or do I need one behind the wall or right under the drywall?
thanks in advance for your advice!!
thanks in advance for your advice!!
#2
11-01-03, 04:19 PM
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plyers22,
This is an article I wrote, use what you think is applicable to your project,
I guess this is the best and most economical way to construct walls that would be placed on the exterior. I prefer to see 2x4 but as mentioned by others they can get 2x3's. You still need that W/T BOTTOM PLATE. The best way is to attach WOOD TREATED BOTTOM PLATE to the concrete is to use either...
Concrete nails - Sometimes this is hard and time consuming!
Tapcon Screws - Relatively easy but again time consuming!
Hilti Gun with ramset nails - Rent the gun, buy nails and charges - Very fast and holds great! - No adhesive is needed.
Doing the wall framing 16" O.C. provides a solid base for your 1/2" drywall. If using traditional framing method, frame your new wall 1" from the vertical block/masonry surface if using R-13. The reason to keep the wood out from the walls is the moisture that could damage them. If using insulation like R-19 and only 2x4 studs, the insulation would touch the walls. I have stated before that if a homeowner did put thicker insulation in, and the wall was only 1" from the masonry surface, I have recommended hanging a vapor barrier between the back of the wall and masonry surface. This doesn't allow for the insulation to touch the wall and air movement is not restricted but at least you won't create damage to the insulation or wood.
Vapor barrier should be placed directly under the drywall. The warm inside air containing water vapor can get past the wall finish and insulation and condense inside the colder wall cavity. If enough of this happens, and the water cannot escape, wood rot, mold, and other moisture-related problems are likely to occur. For this reason, building codes often require installing a vapor diffusion retarder on the warmest side of the wall cavity. This is what is required in Minnesota;
"A 4 mill poly vapor barrier must be placed against all concrete or block exterior foundation walls prior to applying furring strips for full height of the wall. Another 4 mill poly vapor barrier must be placed over furring strips and insulation prior to covering with finish materials. (State Energy Code Requirement)" - MINNESOTA CODE
***PLEASE NOTE THAT YOU MUST MAKE SMALL SLICES AT GRADE LEVEL ONLY FOR WEEPING IN THE POLY IF POLY IS PLACED AGAINST THE BLOCK - ATTACH THE POLY WITH STAPLES TO YOUR JOISTS/FOUNDATION SILL PLATE***
If you do want to increase the R value, move the wall out further or use the R-13 and then apply a rigid insulation over the studs (warm side) then drywall (not paneling) *Code advises a 15 minute fire rated material over any rigid insulation - 1/2" Drywall*..
Kraft Faced insulation is fine to use in the above scenario. No need for the poly and you can do everything easily. You may find this easier and I would do this versus unfaced and vapor barrier because I don't like to play with it any more than I have to.
Let me add one other thing, RIGID insulation used on a concrete/masonry surface is fine. Considerations to make in using this is;
1. If you are just using 1 1/2" rigid and furring strips - A. You need W/T strips to protect the wood. B. The strips can be adhesively applied but they must be solid - mechanical anchors may have to be used to insure that if shelving is installed it will hold. Problem with this is, the penetration into a sealed concrete/masonry surface is damaged and subject to leaking. C. Any electrical boxes will have to be shallow - sometimes makes it hard to wire. D. You must use a fire retardant material over this as per Code.
(Most books, articles about rigid and furring strips fail to say anything about the use of W/T and this will get destroyed and be a good source for mold/mildew with the slightest hint of moisture)
2. Alternative which does add cost is to apply full rigid sheets to the concrete/masonry walls, adhesively applied, then place frame wall against the rigid, then insulate between studs and cover with drywall. The Rigid insulation does then act as a the vapor barrier. Do not tape/seal the seams. This allows it to breath and dry up any condensation that may form.
Hope this helps!
This is an article I wrote, use what you think is applicable to your project,
I guess this is the best and most economical way to construct walls that would be placed on the exterior. I prefer to see 2x4 but as mentioned by others they can get 2x3's. You still need that W/T BOTTOM PLATE. The best way is to attach WOOD TREATED BOTTOM PLATE to the concrete is to use either...
Concrete nails - Sometimes this is hard and time consuming!
Tapcon Screws - Relatively easy but again time consuming!
Hilti Gun with ramset nails - Rent the gun, buy nails and charges - Very fast and holds great! - No adhesive is needed.
Doing the wall framing 16" O.C. provides a solid base for your 1/2" drywall. If using traditional framing method, frame your new wall 1" from the vertical block/masonry surface if using R-13. The reason to keep the wood out from the walls is the moisture that could damage them. If using insulation like R-19 and only 2x4 studs, the insulation would touch the walls. I have stated before that if a homeowner did put thicker insulation in, and the wall was only 1" from the masonry surface, I have recommended hanging a vapor barrier between the back of the wall and masonry surface. This doesn't allow for the insulation to touch the wall and air movement is not restricted but at least you won't create damage to the insulation or wood.
Vapor barrier should be placed directly under the drywall. The warm inside air containing water vapor can get past the wall finish and insulation and condense inside the colder wall cavity. If enough of this happens, and the water cannot escape, wood rot, mold, and other moisture-related problems are likely to occur. For this reason, building codes often require installing a vapor diffusion retarder on the warmest side of the wall cavity. This is what is required in Minnesota;
"A 4 mill poly vapor barrier must be placed against all concrete or block exterior foundation walls prior to applying furring strips for full height of the wall. Another 4 mill poly vapor barrier must be placed over furring strips and insulation prior to covering with finish materials. (State Energy Code Requirement)" - MINNESOTA CODE
***PLEASE NOTE THAT YOU MUST MAKE SMALL SLICES AT GRADE LEVEL ONLY FOR WEEPING IN THE POLY IF POLY IS PLACED AGAINST THE BLOCK - ATTACH THE POLY WITH STAPLES TO YOUR JOISTS/FOUNDATION SILL PLATE***
If you do want to increase the R value, move the wall out further or use the R-13 and then apply a rigid insulation over the studs (warm side) then drywall (not paneling) *Code advises a 15 minute fire rated material over any rigid insulation - 1/2" Drywall*..
Kraft Faced insulation is fine to use in the above scenario. No need for the poly and you can do everything easily. You may find this easier and I would do this versus unfaced and vapor barrier because I don't like to play with it any more than I have to.
Let me add one other thing, RIGID insulation used on a concrete/masonry surface is fine. Considerations to make in using this is;
1. If you are just using 1 1/2" rigid and furring strips - A. You need W/T strips to protect the wood. B. The strips can be adhesively applied but they must be solid - mechanical anchors may have to be used to insure that if shelving is installed it will hold. Problem with this is, the penetration into a sealed concrete/masonry surface is damaged and subject to leaking. C. Any electrical boxes will have to be shallow - sometimes makes it hard to wire. D. You must use a fire retardant material over this as per Code.
(Most books, articles about rigid and furring strips fail to say anything about the use of W/T and this will get destroyed and be a good source for mold/mildew with the slightest hint of moisture)
2. Alternative which does add cost is to apply full rigid sheets to the concrete/masonry walls, adhesively applied, then place frame wall against the rigid, then insulate between studs and cover with drywall. The Rigid insulation does then act as a the vapor barrier. Do not tape/seal the seams. This allows it to breath and dry up any condensation that may form.
Hope this helps!
#3
11-04-03, 01:50 PM
Vapor Barrier NOT recommended
Building Science Corp has done extensive research on just this issue. check it out at:
http://www.buildingscience.com/resou...on_systems.pdf
The bottom line is that when retrofitting basements in cold climates with insulation, a vapor barrier will cause more harm than good. The double vapor barrier is the worst possible way to go.
The reason being is that concrete is porus and "breathes" water vapor, depending on the time of the year. When a vapor barrier is installed, this essentially prevents this "breathing" from occuring. The vapor barrier becomes a surface on which condensation will form. Once you get condensation, you get mold.
Without a vapor barrier, in the winter, relative humidities indoors in cold climates where heating dominates are low enough that condensation inside the wall is not a concern. In the summer, condensation is a concern, and this concern is usually delt with by running a dehumidifier, or central air conditioning, or both.
Building Science Corporation recommends that a continuous layer of extruded polystyrene be applied to the entire concrete wall, followed by your studs with insulation in the stud bays, followed by drywall. This does add some expense to the whole cost of finishing a basement, but in the final analysis, percentage wise, it is a very small portion of the total.
Good luck with your project.
http://www.buildingscience.com/resou...on_systems.pdf
The bottom line is that when retrofitting basements in cold climates with insulation, a vapor barrier will cause more harm than good. The double vapor barrier is the worst possible way to go.
The reason being is that concrete is porus and "breathes" water vapor, depending on the time of the year. When a vapor barrier is installed, this essentially prevents this "breathing" from occuring. The vapor barrier becomes a surface on which condensation will form. Once you get condensation, you get mold.
Without a vapor barrier, in the winter, relative humidities indoors in cold climates where heating dominates are low enough that condensation inside the wall is not a concern. In the summer, condensation is a concern, and this concern is usually delt with by running a dehumidifier, or central air conditioning, or both.
Building Science Corporation recommends that a continuous layer of extruded polystyrene be applied to the entire concrete wall, followed by your studs with insulation in the stud bays, followed by drywall. This does add some expense to the whole cost of finishing a basement, but in the final analysis, percentage wise, it is a very small portion of the total.
Good luck with your project.
#4
11-04-03, 04:15 PM
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plyers22,
Although MusicField seems to always bring up BSC, there is a need to conform to certain laws and codes within this country. Understand that I don't always agree with all of them either but in my business, I can't do what I want just because I read an article that said there's a better way which is not approved yet.
We have Building Codes which are to provide the standards in which we implement new or improve existing structures. Granted, these Codes may be a minimum in some areas and overkill in others but they are there for us to adhere to in order to protect the consumer and ensure structure safety and longevity.
Regardless of the BSC studies or findings, you should follow the guidelines that are enforced within your municipality. This may go against the grain of any article written or studies done, even if the data may be good. It is not any good if they are not placed into the Code for others to follow.
Until there is a change in the Building Code, based on location of a property which is being built or improved, the best advice is to follow those guidelines set forth by your municipality.
The article that I wrote has excerpts from the Minnesota code which for the most part are similar, if not the same, in Wisconsin. When you read the article completely, you'll clearly see how applications are done based upon material used.
Hope this helps!
Although MusicField seems to always bring up BSC, there is a need to conform to certain laws and codes within this country. Understand that I don't always agree with all of them either but in my business, I can't do what I want just because I read an article that said there's a better way which is not approved yet.
We have Building Codes which are to provide the standards in which we implement new or improve existing structures. Granted, these Codes may be a minimum in some areas and overkill in others but they are there for us to adhere to in order to protect the consumer and ensure structure safety and longevity.
Regardless of the BSC studies or findings, you should follow the guidelines that are enforced within your municipality. This may go against the grain of any article written or studies done, even if the data may be good. It is not any good if they are not placed into the Code for others to follow.
Until there is a change in the Building Code, based on location of a property which is being built or improved, the best advice is to follow those guidelines set forth by your municipality.
The article that I wrote has excerpts from the Minnesota code which for the most part are similar, if not the same, in Wisconsin. When you read the article completely, you'll clearly see how applications are done based upon material used.
Hope this helps!
#5
11-05-03, 10:09 AM
I'm going to chime in here with a link to research done recently by the University of Minnesota's Building Foundation Research Program--links below. There is some very interesting information available. The bottom line: what you do to insulate your basement depends on what is already in place, what type of materials have been used, where you're located, and so on.
Overview/Contents:
http://www.buildingfoundation.umn.edu/MainPage.htm
Insulation for "Wet" Walls
http://www.buildingfoundation.umn.ed...etWallProp.htm
Rim Joist Insultatoin Report:
http://www.buildingfoundation.umn.ed...st/default.htm
-patrick
Overview/Contents:
http://www.buildingfoundation.umn.edu/MainPage.htm
Insulation for "Wet" Walls
http://www.buildingfoundation.umn.ed...etWallProp.htm
Rim Joist Insultatoin Report:
http://www.buildingfoundation.umn.ed...st/default.htm
-patrick
#6
11-05-03, 11:23 AM
Don't get me wrong, Doug, the vapor barrier IS the best thing going when you use it above grade where the wetting and drying dynamics of construction materials are very different than those that are below ground surface.
The research in the field has shown that the double vapor barrier required by some codes to be the absolute worst method of construction.
Doug, we've discussed this issue before, and again I will re-iterate that building codes lapse well behind the state of research for many reasons, most of which have to do with the influence of the building industry on the code development and enforcement agencies. I know this to be a fact, because I am employed by a code enforcement government agency.
If I lived in Minnesota and were finishing a basement, I'd be requesting a variance from the code. And you know what? I bettcha that many, many local building inspectors would agree.
The research in the field has shown that the double vapor barrier required by some codes to be the absolute worst method of construction.
Doug, we've discussed this issue before, and again I will re-iterate that building codes lapse well behind the state of research for many reasons, most of which have to do with the influence of the building industry on the code development and enforcement agencies. I know this to be a fact, because I am employed by a code enforcement government agency.
If I lived in Minnesota and were finishing a basement, I'd be requesting a variance from the code. And you know what? I bettcha that many, many local building inspectors would agree.
