Simple basement build-out question
#1
11-23-05, 06:58 PM
Simple basement build-out question
I am looking to semi-finish my basement. It's mostly below grade (just the top foot or two is above ground. I don't know what the walls are made of (I assume cinder block), but they appear to have been mortared over and painted. We have had no problems with water or leaks of any kind down there since moving in (about 2 years ago).
My question is, if I chose to put up some drywall over those walls (possibly with some insulation), do I need to do something special? I have heard of needing to put plastic up as some sort of vapor barrier or something, but don't know if it's necessary. Also, is there a minimum amount of space I should leave between the "cement" and the drywall?
I live in the Chicago area (seasonal temperature changes).
Thanks for any help!!
My question is, if I chose to put up some drywall over those walls (possibly with some insulation), do I need to do something special? I have heard of needing to put plastic up as some sort of vapor barrier or something, but don't know if it's necessary. Also, is there a minimum amount of space I should leave between the "cement" and the drywall?
I live in the Chicago area (seasonal temperature changes).
Thanks for any help!!
#2
11-27-05, 05:09 PM
Hi, If you are going to build a 3 1/2" wall, i usually leave at least 1/2" between stud and concrete. This will allow air to flow behind the wall keeping it dry and you can keep your wall plumb even if the concrete isn't. I feel that using a vapor barrier in this situation is optional, i usually dont unless asked to do so.
#3
11-28-05, 05:34 AM
Do not leave an air space between the insulation and the concrete. Follow this link which will give you the scientific explanation.
http://www.joneakes.com/cgi-bin/getd...als.cgi?id=743
You should also install a moisture barrier (6mil poly) from grade level down to avoid the insulation from contacting the concrete wall.
http://www.joneakes.com/cgi-bin/getd...als.cgi?id=743
You should also install a moisture barrier (6mil poly) from grade level down to avoid the insulation from contacting the concrete wall.
#4
11-28-05, 06:00 AM
Originally Posted by em69
Do not leave an air space between the insulation and the concrete. Follow this link which will give you the scientific explanation.
http://www.joneakes.com/cgi-bin/getd...als.cgi?id=743
You should also install a moisture barrier (6mil poly) from grade level down to avoid the insulation from contacting the concrete wall.
http://www.joneakes.com/cgi-bin/getd...als.cgi?id=743
You should also install a moisture barrier (6mil poly) from grade level down to avoid the insulation from contacting the concrete wall.
The link doesnt work. why would not want an air space between? poly between the stud and concrete will only promote mold growth. the air gap is there to prevent this. How do you keep your wall plumb if the wall is tight to the concrete and the concrete isn't plumb? if your careful to insulate the stud cavity only, no insul/concrete contact will be possible. jmo.
#5
11-28-05, 07:45 AM
Forgive me, but I've become a little confused. I want to put drywall up over two concrete walls, with some insulation.
I will build the wall and raise it into place. Do I put plastic over the concrete wall, then fill in the spaces between the studs with insulation?
OR, do I put plastic over the wall and leave a space between the concrete and the insulation?
It seems as if there may be a few schools of thought here. What are your experiences with both?
Thanks again for your help!
I will build the wall and raise it into place. Do I put plastic over the concrete wall, then fill in the spaces between the studs with insulation?
OR, do I put plastic over the wall and leave a space between the concrete and the insulation?
It seems as if there may be a few schools of thought here. What are your experiences with both?
Thanks again for your help!
#6
11-28-05, 09:35 AM
I follow the specifications which have been created from years of scientific research by those who decide our building code regulations.
It is a myth to leave an air space between the wall and concrete. Here is the scientific explanation in laymans terms:
An air space behind basement insulation will not solve condensation problems. It can, in fact, cause condensation problems -- and create new problems to boot. The CMHC is so clear on this question that they even advise that if you are going to glue insulating panels to the wall, you do not dab the glue on the wall but apply it in a closed grid pattern that will prevent the formation of a circulating air space -- even one as thin as the glue. Here's why.
-- The concrete of a basement wall insulated on the inside will have a very large temperature difference between the top of the wall and the bottom of the wall. The top is exposed to the cold outdoors and the bottom is insulated by the earth.
-- Air in a space between the insulation and the concrete wall will become cold and heavy at the top of the wall and tend to drop to the bottom.
-- It is almost impossible to ensure that there is absolutely no space between the front of the insulation and the drywall. This space becomes the primary route for warm air to be forced up to the top of the wall by the pressure of the falling cold air in the back. Hence we find a very strong convection current that loops around the insulation.
-- This same mechanism does not happen in such a serious way with an ordinary wall totally exposed on the outside because you have an evenly cold exterior, not the large temperature differences that exist from the top to the bottom of an internally insulated basement wall.
-- The convection loop will draw moisture both out of leaks into the wall from the house and out of the lower portions of the concrete itself. This concentrated accumulation of moisture then tries to escape through the small portion of the wall that is above the ground level (and probably freezing cold).
-- Hence the above ground portion of a basement wall that has an air space between the wall and the interior insulation can easily become saturated with water. Wood in contact with this wall can easily develop dry rot -- including your floor joists. Repeated freeze/thaw cycles can cause spalling or flaking of the outer surface of the basement wall. Structural breakup of the wall could result with unsound walls.
-- Convection loops around your insulation will essentially eliminate their insulating effect, carrying the heat around the insulation to the cold wall behind.
Insulation pushed directly against the basement wall (for cautions about moisture proofing the wall first, search keyword "Basement" for the title "DO I NEED TO MOISTURE PROOF THE BASEMENT WALL BEFORE INSULATING?") will effectively prevent these air convection loops. With no air currents, the only moisture that can get through the wall is what can diffuse slowly up to the top of the wall and out through the wall without causing saturation conditions.
Heavy condensation discovered behind insulation that is snug against the basement wall is a sign of either a very poor job of sealing the warm side of the wall or of a need to damp proof the foundation wall. This is one case where ventilation cannot help us.
Killer,
It is recommended to place 6mil poly overtop of the concrete wall (moisture barrier) from grade level down to the slab. The reason it starts at grade level is so that any vapours can escape through the upper portion of the wall. Without this, your ceiling joists would rot as moisture would get trapped.
Insulate the wall cavity and then install 6mil poly overtop of the wood stud structure (vapour barrier) and seal it to the moisture barrier.
Make sure you use either pre-formed wraps for your electrical outlets, or just use the poly. It is important to prevent air transfer through the outlets.
It is a myth to leave an air space between the wall and concrete. Here is the scientific explanation in laymans terms:
An air space behind basement insulation will not solve condensation problems. It can, in fact, cause condensation problems -- and create new problems to boot. The CMHC is so clear on this question that they even advise that if you are going to glue insulating panels to the wall, you do not dab the glue on the wall but apply it in a closed grid pattern that will prevent the formation of a circulating air space -- even one as thin as the glue. Here's why.
-- The concrete of a basement wall insulated on the inside will have a very large temperature difference between the top of the wall and the bottom of the wall. The top is exposed to the cold outdoors and the bottom is insulated by the earth.
-- Air in a space between the insulation and the concrete wall will become cold and heavy at the top of the wall and tend to drop to the bottom.
-- It is almost impossible to ensure that there is absolutely no space between the front of the insulation and the drywall. This space becomes the primary route for warm air to be forced up to the top of the wall by the pressure of the falling cold air in the back. Hence we find a very strong convection current that loops around the insulation.
-- This same mechanism does not happen in such a serious way with an ordinary wall totally exposed on the outside because you have an evenly cold exterior, not the large temperature differences that exist from the top to the bottom of an internally insulated basement wall.
-- The convection loop will draw moisture both out of leaks into the wall from the house and out of the lower portions of the concrete itself. This concentrated accumulation of moisture then tries to escape through the small portion of the wall that is above the ground level (and probably freezing cold).
-- Hence the above ground portion of a basement wall that has an air space between the wall and the interior insulation can easily become saturated with water. Wood in contact with this wall can easily develop dry rot -- including your floor joists. Repeated freeze/thaw cycles can cause spalling or flaking of the outer surface of the basement wall. Structural breakup of the wall could result with unsound walls.
-- Convection loops around your insulation will essentially eliminate their insulating effect, carrying the heat around the insulation to the cold wall behind.
Insulation pushed directly against the basement wall (for cautions about moisture proofing the wall first, search keyword "Basement" for the title "DO I NEED TO MOISTURE PROOF THE BASEMENT WALL BEFORE INSULATING?") will effectively prevent these air convection loops. With no air currents, the only moisture that can get through the wall is what can diffuse slowly up to the top of the wall and out through the wall without causing saturation conditions.
Heavy condensation discovered behind insulation that is snug against the basement wall is a sign of either a very poor job of sealing the warm side of the wall or of a need to damp proof the foundation wall. This is one case where ventilation cannot help us.
Killer,
It is recommended to place 6mil poly overtop of the concrete wall (moisture barrier) from grade level down to the slab. The reason it starts at grade level is so that any vapours can escape through the upper portion of the wall. Without this, your ceiling joists would rot as moisture would get trapped.
Insulate the wall cavity and then install 6mil poly overtop of the wood stud structure (vapour barrier) and seal it to the moisture barrier.
Make sure you use either pre-formed wraps for your electrical outlets, or just use the poly. It is important to prevent air transfer through the outlets.
#7
11-28-05, 11:09 AM
em69, i have to give it to you, thats one heck of a point you make. few things though, and please dont take this as an arguement, i just like others opinions.
Where does the moisture between the poly and the concrete go?
What temp diffrences from top of the concrete wall to the bottom of the concrete wall do you experience in your area?
How wet are these concrete walls you refer to? (prior to construction)
Where does the moisture between the poly and the concrete go?
What temp diffrences from top of the concrete wall to the bottom of the concrete wall do you experience in your area?
How wet are these concrete walls you refer to? (prior to construction)
#8
11-29-05, 04:54 AM
No worries...ask whatever questions you want.
Where does the moisture between the poly and the concrete go?
If there is any moisture in the wall cavity, it escapes through the top of the concrete wall just above grade. If you are talking about water, then you have some major issues that you need to deal with in a different way.
What temp diffrences from top of the concrete wall to the bottom of the concrete wall do you experience in your area?
I have no idea. In my parts, the frost line is 42 inches during the winter months.
How wet are these concrete walls you refer to? (prior to construction)
What do you mean by wet? This technique is used on drywall walls only. If you have wet concrete walls, then you need to deal with that prior to finishing the basement.
Where does the moisture between the poly and the concrete go?
If there is any moisture in the wall cavity, it escapes through the top of the concrete wall just above grade. If you are talking about water, then you have some major issues that you need to deal with in a different way.
What temp diffrences from top of the concrete wall to the bottom of the concrete wall do you experience in your area?
I have no idea. In my parts, the frost line is 42 inches during the winter months.
How wet are these concrete walls you refer to? (prior to construction)
What do you mean by wet? This technique is used on drywall walls only. If you have wet concrete walls, then you need to deal with that prior to finishing the basement.
#9
11-29-05, 11:50 AM
When you say that the moisture (condensation) escapes through the above-grade portion of the concrete wall, do you mean that it goes through the concrete to the outside? Wouldn't it just keep rising into the ceiling (of the basement) and then into the joists (I'm not talking about any water. My concrete walls are sealed)?
It seems to me like the plastic would act like a sort of chimney for the moisture. Once it arrived at grade-level (where the plastic stops), it would just spread out (into the insulation and the "ceiling").
On the other hand, if I used plastic all the way to the ceiling, I would imagine that I'd face a similar problem.
And, with no plastic, any condensation would go into the insulation.
I am quite thoroughly confused as to the best course of action.
It seems to me like the plastic would act like a sort of chimney for the moisture. Once it arrived at grade-level (where the plastic stops), it would just spread out (into the insulation and the "ceiling").
On the other hand, if I used plastic all the way to the ceiling, I would imagine that I'd face a similar problem.
And, with no plastic, any condensation would go into the insulation.
I am quite thoroughly confused as to the best course of action.
#10
11-29-05, 02:01 PM
Good luck with that. I am in the middle of finishing my basement,and I faced the same questions as you 6 months ago. The more I asked around and researched, the more I realized that there is no one solution that is generally recognized as the best.
After considering the many options, I decided to do the following:
what I started with: 8 month old poured concrete foundation, dry basement, with a little bit of leakage in one area. Located in upstate NY.
what I did:
1. Put rain gutter extenders on, since there were none.
2. caulked outside in 1 area where rain was sometimes blown from my front porch slab, to under my siding, then down 8" to my sill plate.
3. made sure all areas sloped away from house. (one part sloped toward, a couple were a bit even.
4. put a sealer on the concrete, kind of for "just incase"
5. put aluminum backed stuff insulation boards all around the foundation walls. (on the inside) taped the boards together with aluminum tape. this acts as extra insulation and a vapor barrier.
6. put studs with fiberglass insulation and sheetrock right over that.
I hope my approach works, cause I am sinking 20-25K into a finsihed basement! My local town inspector recommended the aluminum backed stiff boards, and I had read about that somewhere.
After considering the many options, I decided to do the following:
what I started with: 8 month old poured concrete foundation, dry basement, with a little bit of leakage in one area. Located in upstate NY.
what I did:
1. Put rain gutter extenders on, since there were none.
2. caulked outside in 1 area where rain was sometimes blown from my front porch slab, to under my siding, then down 8" to my sill plate.
3. made sure all areas sloped away from house. (one part sloped toward, a couple were a bit even.
4. put a sealer on the concrete, kind of for "just incase"
5. put aluminum backed stuff insulation boards all around the foundation walls. (on the inside) taped the boards together with aluminum tape. this acts as extra insulation and a vapor barrier.
6. put studs with fiberglass insulation and sheetrock right over that.
I hope my approach works, cause I am sinking 20-25K into a finsihed basement! My local town inspector recommended the aluminum backed stiff boards, and I had read about that somewhere.
#11
11-30-05, 05:36 AM
Originally Posted by Killer V
When you say that the moisture (condensation) escapes through the above-grade portion of the concrete wall, do you mean that it goes through the concrete to the outside? Wouldn't it just keep rising into the ceiling (of the basement) and then into the joists (I'm not talking about any water. My concrete walls are sealed)?
It seems to me like the plastic would act like a sort of chimney for the moisture. Once it arrived at grade-level (where the plastic stops), it would just spread out (into the insulation and the "ceiling").
On the other hand, if I used plastic all the way to the ceiling, I would imagine that I'd face a similar problem.
And, with no plastic, any condensation would go into the insulation.
I am quite thoroughly confused as to the best course of action.
It seems to me like the plastic would act like a sort of chimney for the moisture. Once it arrived at grade-level (where the plastic stops), it would just spread out (into the insulation and the "ceiling").
On the other hand, if I used plastic all the way to the ceiling, I would imagine that I'd face a similar problem.
And, with no plastic, any condensation would go into the insulation.
I am quite thoroughly confused as to the best course of action.
Lol...now you are getting technical on me and I am no scientist. I believe moisture is drawn out. It naturally goes from a warm space into a cold area. So, it goes from inside your house where it is warm, to the outside where it is cold. It is for this reason that you do not want to block it from escaping. By the leaving that area above grade open, the moisture can escape. If you extend the moisture barrier all the way to the ceiling, then yes, you are trapping the moisture in the wall cavity.
Just so you know, I am not shooting this idea off the top of my idea. This is actually the Building Code in my area. The Code in my parts requires insulation on the foundation to 24" below grade. In addition, our Code requires that you apply a moisture barrier on top of the concrete wall to prevent the insulation from coming in direct contact with the concrete.
If you want to improve your insulation (which is highly recommended in colder climates) in the basement, you would extending the insulation all the way to the floor. You must then also extend your moisture barrier AND your vapour barrier.
Before I finished my basement, I was just as confused as others with all the information out there. So, I decided to speak to those who write our Codes and just improve on what is required. The Code is a MINIMUM requirement.
#12
11-30-05, 06:58 AM
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Make sure you check your local building codes.
My city requires a 1" space between the wall studs, and the concrete walls.
They also require that any wood in contact with concrete be pressure treated.
My city requires a 1" space between the wall studs, and the concrete walls.
They also require that any wood in contact with concrete be pressure treated.
#13
11-30-05, 09:12 AM
Member
Simple basement build-out question
Keep in mind that a code is a minimum. Despite that is frequently written as a prescriptive standard, you can vary from it. You are always allowed to do it better.
Unfortunately, the local code officials are frequently not qualified or knowledgable enough to make a judgement, so the process to do something better is difficult. Also some officials won't spend the time or effort (or are afraid) to make a judgement.
The problem with prescriptive language is that not all situations are the same. The right of a locality to have a stricter standard than the national (IBC, IRC) is allowed, just as the right to do it better is allowed.
"Your are not wrong going by the letter of the code, but you may not be right".
Dick
Unfortunately, the local code officials are frequently not qualified or knowledgable enough to make a judgement, so the process to do something better is difficult. Also some officials won't spend the time or effort (or are afraid) to make a judgement.
The problem with prescriptive language is that not all situations are the same. The right of a locality to have a stricter standard than the national (IBC, IRC) is allowed, just as the right to do it better is allowed.
"Your are not wrong going by the letter of the code, but you may not be right".
Dick
