I am located in mid South Carolina. Very hot and humid summers, winter low temps may dip into the low 20’s.
I have a slab room about 500-600 sf on the end of my brick house. The rest of the house is a crawl space. The room has very dark 1/4″ paneling and I am planning on sheetrocking to lighten up the room. My question is should I remove the paneling and install a poly vapor barrier or just sheetrock over the paneling. There is 3-1/2″ insulation behind the paneling, but I do not know how good it is.
The slab room has a heat pump dedicated to just this room for heating and cooling and it also has a laundry room attached to one end. Any ideas would be appreciated.
Edited 11/8/2003 11:23:43 AM ET by tiger
Replies
Tiger,
You are in what's known as a mixed climate...one where there are both heating seasons and cooling seasons. This presents a problem regarding vapor barriers--which are supposed to be on the warm side of the wall. That is so that when water vapor hits the barrier, the temperature of the vapor barrier will be above the dewpoint, and you won't have any condensation problems. If the vapor barrier is on the cold side of the wall, when water vapor hits it, if the temperature differential is great enough, and the mumidity is high enough, you will get condensation on the vapor barrier, which is a bad thing.
During the winter in your climate you want a vapor barrier on inside of the wall, and in the summer you want it on the outside of the wall.
So the answer is obvious: every spring and fall you must totally remodel your thermal envelope, relocating the vapor barrier from inside to outside for the summer, and back inside for the winter!
If that is not within your budget, your walls should be as airtight as possible (most moisture moves into and through the thermal envelope on bulk air movement), yet the wall should also be as vapor permeable as possible to both sides, so that whatever moisture does get into the wall will have every oportunity to dry via diffusion to whichever side it can, rather than hitting a cold, impermeable surface to condense upon.
In short, no vapor barrier on either side is best for your climate.
For a detailed look at what kind of wall assemblies will accomplish this outcome, I recommend "Builder's Guide to Mixed Climates" by Joe Lstiburek (a Taunton Book).
Steve
Steve, I appreciate your input on this subject.
Other than the extreme southern band of the USA, where do we not have 80 deg temperature swings from season to season, often within just a few days?
That fact would suggest that most of the country does not have the barrier in the right place for at least part of the year, and that the real first line of defense is the elimination of air movement in the wall. Do you agree? PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
Hi Paul,
I agree that the most important thing to do to control moisture movement through framing cavities is to create an effective air barrier. It's also the best way to avoid paying to heat the great outdoors.
If the air barrier is good, The VB becomes superflous at best, IMO. If the air barrier is not so good, or you are relying on a totally impervious VB to create an air barrier, there is the potential for moisture to accumulate when the VB is on the cold side of the wall.
Gabe asked (rhetorically)where the moisture will come from and how it will get to a condensing surface. Moisture moves from wet to dry, from hot to cold, and from high pressure to low pressure. But as Gabe's meatlocker metaphor illustrates, it depends on how cold the cold side is, how hot and how moisture-laden the air on the hot side is, and what the pressure dynamics of the given situation are. Gabe said there are no conditions short a meat locker where a VB on the inside will cause a problem. I think that's debatable.
That said, we build with vapor barriers on the wrong side of the wall in ways we rarely think about. Plywood and OSB on the outside of the wall in a northern climate is, in theory, a bad thing. In practice, it doesn't seem to cause too much trouble unless there are aggrevating circumstances. And there are certainly plenty of air-conditioned houses in the south with impermable surfaces on the inside that fare just fine. But I think these practices can contribute to problems in the presence of additional aggrevating factors.
I don't thinks it's cut and dried, but I try to avoid poly in the walls. It's not as problematic in colder climates, but I would definately try to build air-tight and vapor-permeable in a mixed climate with humid summer conditions. I try build on the assumption that sooner or later moisture will make it's way into the framing cavities, either via leaky cladding details or vapor pressure. I think it's important to expect that and build in such way as to allow it to get back out as quickly as possible under as varied conditions as possible.
There are lots of ways to try and achieve those goals. I prefer to rely on dense-packed cellulose or sprayed-in-place foam to minimize air movement. After that, I don't think a vapor barrier matters much one way or the other in my (northern) climate, though I would rather leave the poly out.
I build my exteriors on the assumption that doors and windows will leak and flash the openings with tyvek flexible flashing and sub-sils that bevel outward at the bottom to deal with that. I rely on mechanicle flashing details that will shed water without the use of sealants. I don't caulk my siding joints--I put tarpaper splines behind them that lap over the piece of siding below. I have yet to build with a full drainage plain behind the cladding, but that is what I think I will do on the next project I get where that is practicle.
I'm just a humble remodeler trying to make sense out of all the conflicting information out there myself. Lstiburek's books make a lot of sense to me. I subscribe to Home Energy magazine, which has pretty good, if somewhat dryly written and poorly packaged information on this and other energy related topics. If you know any other good sources, I would love to know of them.
Apologies for the long missive.
Steve
I would recomend craft facing on your insulation. It changes womewhat to keep moisture out in the summer and keep it in in the winter.
You get out of life what you put into it......minus taxes.
Marv
I would remove the panelling regardless.
Examine the back of the panels for water marks and double check your insulation, caulk and seal around windows.
If you have water stains, install a poly vb and then the drywall.
If you don't have any water stains, install a poly vb anyways, it's cheap insurance and then install the drywall.
BTW I would double check the laundry area specifically for water stains. Do you have the laundry room ventilated with an exhaust fan?
Gabe
If you have water stains, install a poly vb and then the drywall.
If you put the Vapor barrier behind the drywall, in the summer the moisture will condense on it and dampen the insulation. I would not recommend for very humid climates.You get out of life what you put into it......minus taxes.
Marv
If you put the Vapor barrier behind the drywall, in the summer the moisture will condense on it and dampen the insulation. I would not recommend for very humid climates.
Don't be silly and get out of that antiquated mindset.
The moisture from where will condensate where and do what to the insulation?
Unless your house leaks like a sieve and you live in a refrigerated home used as a meat locker you ain't got nothing to worry about your insulation getting wet from outside.
Gabe
Gabe,
VB on the inside of an air-conditioned house in a hot humid climate can lead to moisture problems. I remember reading an article with photographs (though I can't remember where--home energy mag most likely) of US gov't issue prefab modular office units that were built with vinyl wallpaper on the inside. They performed fine in norhern climates. A bunch were shipped to southern US locales. The all grew mold behind the wallpaper very rapidly. The problem was traced to the impermeable wallpaper on the cold side of the wall, hot humid air on the outside, driven into the wall by sun, getting to the cool wallpaper and condensing. They were re-done with no vinyl paper and no vb on the inside and all was fine after that.
Steve
Steve,
Put aside what you read and think about what you know.
We have a exterior wall that is 5" thick.
If the outside ambiant temperature is 35 C and the inside temp is 22 C, the outside has vinyl siding over Tyvek over 1/2 osb, the wall cavity is insulated with 3 1/2 inches of FG, the inside wall is VB'd with poly covered in drywall with good quality paint, where will the condensation plane be? On the outside, on the inside, 1 inch into the wall, 2 inches into the wall, 3 inches into the wall, 4 inches into the wall?
Same wall composition except that the poly is not installed, where will the condensation plane be?
Same wall composition except that poly is installed instead of the Tyvek, where will the condensation plane be?
Time to come for a little ride outside the box, Steven.
Gabe
Gabe -
This I know.... given proper conditions, the condensation will take place at the point where the temperature reaches the dew point for moisture laden air. Meaning ....
I've seen houses here in the Pacific Northwest that had to be completely re-roofed due to someone's fascination with exposed 2x6 T&G decking laid on exposed beams with a shallow built-up roof (no insulation) applied direcly to the deck. The moisture from the heated interior actually condensed at the dew point which in this case was within the thickness of the car decking. There wasn't anywhere for it to go since there was a waterproof, vapor proof barrief (the roofing) on the cold side.
I just recently moved north of Seattle to M t. Vernon area. This is a little higher in the mountains than where I have been living. We get conditions here where the garage floor (unheated space) actually sweats due to the condensation of the damp (warm) air on the cold concrete floor. Even with doors open on either end of the garage for air flow. And now, this is not water migrating from under the slab. In places where I've taped 6mil poly air tight to test moisture migration through the slab, it's dryer than the unexposed area.
I'm not supporting anyone's position on placement of, or the use or non-use of poly or any other vapor barrier. You asked the (rhetorical?) question "...where would the moisture plane be...". My experience thus far is that it would be at the point where temperature reaches the dewpoint. That is, of course, a dynamic situation since the dewpoint varies with atmospheric humidity and wetbulb vs drybulb temperatures.
...........
Dennis in Bellevue WA
[email protected]
Thanks for all the input on my situation. I will take the paneling down and examine the walls. Like I stated my house is 30 yrs old and at that time, in the south, building practices were very lax, so I may find the insulation sparse. Thanks again for the help. I will try to post some pics if possible.
Great articles here.
http://www.buildingscience.com/You get out of life what you put into it......minus taxes.
Marv
Tiger -
Like I said in my reply to Gabe - I'm not suggestng taking the paneling down, vapor barrier or not, or what type of insulation/vapor barrier. I live in the Pacific Northwest. A climate vastly different from yours. You need to consult with a qualified architect, designer, engineer or other design professional with experience in *your* area and climate in order to get proper advice on how to assemble your building enclosure. With 30+ years in construction and building design I've learned one thing: I don't have all the answers.
...........
Dennis in Bellevue WA
[email protected]
The real point of the exercise was that regardless of the location of the VB, the exact location of the condensation plane would still be the same.
What the purpose of the VB would be is to create a shield or barrier to prevent the crossing over of moisture laden air.
If the house is relatively well sealed, the ability for moisture laden air moving through the wall and depositing moisture anywhere is negated.
Gabe
Gabe,
I'm open to learning here. Where would that condensation plane be?
I'm assuming it will be at the first impermeable surface the moist air encounters that is cold enough to make the air in contact with it lose it's ability to hold the amount of moisture it is capable of holding at the ambient air temerature. ie: the first surface that is at the dewpoint for the current ambient air conditions.
A south-facing wall can have the moisture driven deep into the wall by the sun. Moisture moves from hot towards cold (outside to inside in this case, from wet to dry (outside to inside in this case). I think dewpoint may or may not exist somwhere within the wall cavity, depending on temperature inside, temperature outside, and the RH of the air w/in the wall cavity. If the inside wall is cold enough, the ambient air RH is high enough, and the ambient air temp is high enough, there is a chance that the first condensing surface will be the back side of the poly. I'm not enough of a scientist to know how cold the surface has to be to create a dewpoint for say a 90 degree ambient air temp with 90% RH. (anyone?)
From experience I know for a fact that a vapor barrier on the cold side of the wall in a heating climate wall will cause condensation if the interior air is allowed to move through the wall. I've peeled back lots of fiberglass in buildings with no interior wall surface and nothing to stop the air flow through the fiberglass to find quite heavy frost on the back of the plywood or osb. Admittedly, the temperature differntial is much greater in these circumstances, but it seems to me that the temperature differntial on a south-facing wall of a heavily air conditioned building could lower the temp of the poly to the dewpoint. It doesn't take freezing cold pipes to drip with condensation in a humid basement in the summer, only ambient cellar temps and an impermeable surface.
How else would you explain the example of the vinyl wallpaper incident that I read about?
Steve
>>If the house is relatively well sealed, the ability for moisture laden air moving through the wall and depositing moisture anywhere is negated.
exactly.
If it is well sealed, because "the ability for moisture laden air moving through the wall and depositing moisture anywhere is negated" there is no need for a vapor barrier (it is at best, superfluous, as I said before). If it is not well sealed, and the vapor barrier is in the wrong place, there could be problems.
Steve
Steve,
The vapour barrier can be the easiest air barrier to install and can be the least expensive to buy as well as the most effective.
The point us that the condensation plane being that point at which the dew point occurs. Yes on the sun side during the day it will be at a different point in the wall then on the shaded side. However, the location of the VB will not have an effect on it's location. The VB only forms a wall of protection and not only prevents the moisture from going any further but negates or reduces the air current or movement from acting as a carrier.
The biggest cause of moisture damage is as a result of air leakage via outlets and breaches in the envelope, causing an increased amount of moisture ladden air to flow through that specific area, passing through the condensation plane and losing or depositing water droplets along the way.
Gabe
Gabe,
We are really pretty much in alignment in our thinking.
You say: "the condensation plane being that point at which the dew point occurs".
Agreed.
You say: "on the sun side during the day it [the condensation plane] will be at a different point in the wall then on the shaded side. However, the location of the VB will not have an effect on it's location".
Agreed. I'm not saying the VB affects where the condensation plane is, only that if the VB is at a place in the all assembly where it is the first impermeable surface that the ambient air hits that is below the dewpoint, then that is where condensation may occur.
You say: "The biggest cause of moisture damage is as a result of air leakage via outlets and breaches in the envelope, causing an increased amount of moisture ladden air to flow through that specific area, passing through the condensation plane and losing or depositing water droplets along the way".
Absolutely agreed. No Question. In a heating climate. But is that still so in a cooling climate, where the interior air is at a lower temperature and usually at a lower RH than conditions outside?
You say: "The vapour barrier can be the easiest air barrier to install and can be the least expensive to buy..."
Absolutely. That is why it is the predominant way of doing things.
You say: "...as well as the most effective".
This is where I have to part ways with you. I think the poly vapor barrier is prone to flawed installation. I gets breached in a million ways in the construction process, as well as by unknowing remodeling, creating those problem infiltration spots. Once breached, intruding air is free to move thoughout the wall cavity, as FG insulation will do nothing to hinder its movement.
That's why I prefer foam or cellulose as the insulation and primary air barrier. Any breach in a wall with foam or DP cells will have literally no effect on the integrity of the overall air barrier beyond the immediate location of the breach.
Your discussion of moisture infiltrating the walls has still been primarily cold-climate centric (wonder why, eh?). And that is my primary concern as well, since that is my building climate. But I would like to have a good understanding of what works and doesn't in hot and mixed climates as well. After all, I may feel like moving to the Carolinas when I get tired of battling the elements up here.
I'm still under the impression that moisture from hot, humid exterior air can be drawn or driven into walls from outside because of the forces that I've mentioned in previous posts. Moisture gets into the walls from faulty flashing details all the time, as well as from doors and windows that leak (and all doors and window leak--there was yet another study that was recently released in which not a single door or window in study did not leak. It has the window mfgs. pretty hot and bothered). There is also wind driven rain, and just plain old exterior air infiltration though non-airtight exterior wall construction.
Once moist air is in a wall that is heated by the sun, it will move from the hot side of the cavity to the cold side of the cavity (moisture moves from hot-to-cold, from wet-to-dry, and from high-pressure to low-pressure.) When it hits the VB on the cold side of the wall, it may condense if the RH of the air in the wall is high enough, and the VB is cold enough. Whether this will cause damage, who knows. Not me.
In the case of the mobile office units with the vinyl wallpaper that got moldy behind the wallpaper, it seems that the moisture was driven from outside into the permeable drywall, and the vinyl wallpaper kept it there. If the interior wall surface was permeable, then there would have been continued diffusion of the moisture in the not-so-drywall to the even colder interior air (hot-to-cold), and the dryer interior air (AC dehumidifies, no?). Not that paint might not have also caused the same thing, but the point is, that when the units were rebuilt sans vinyl paper, the problem went away.
Granted poly on the back side of the drywall wouldn't have been as cold as the vinyl on the inside of the drywall, but it may still have been cold enough for condensation to occur, who knows? Not me.
I'll have to try and locate the article on the office units, as I don't remember all the details.
Steve
Edited 11/12/2003 7:47:46 PM ET by STEVENZERBY
Steve,
We's gettin close.
Absolutely agreed. No Question. In a heating climate. Not so in a cooling climate, where the interior air is at a lower temperature and usually at a lower RH than conditions outside.
You went back to what you read and abandonned what you know.
If we were discussing laboratory results on a plain wall composition dividing two controlled air spaces, you could be right.
But we're not.
A bathroom, kitchen or laundry room can easily have higher than average ambiant room temperature coupled with an elevated RH compared to outside.
Exterior walls commonly also have furniture against them, add-on uncontrolled space like closets, built-on cabinetry, etc. and that really screwws up the base formula you're hanging your theory on.
What I found in doing 6 or 7 years of technical audits was that failures in building envelopes were rarely the end result of ONE issue or item. It normally resulted from a multitude of wrong things being at the wrong place stories.
It's this experience that caused me to question the acceptable norm of conventional construction based on national codes and handed down theories and practices.
I'm not a fan of dense packed celulose and you dislike FG but we both agree on foam. Could it be that foam negates the problems associated with what you believe is wrong with fg and the same could be said about cels and me?
Gabe
Gabe,
You are pretty fast on the draw, I changed that sentence from a statement to a question within about a minute of posting it. After a few years of wrangling here at BT I know better than to state absolutely that which I don't know ;-)
"You went back to what you read and abandonned what you know".
That's just it. When it comes to cooling climates, I only know what I've read. I try to do a critical review of the literature that's out there, when I have no firsthand experience to draw upon.
Perhaps I shouldn't stick my nose into a thread where I can only regurgitate what I've read rather than what I've experienced.
As to fg/cells/foam, as guess we'll just have to agree to disagree on fg/cells.
Foam can have problems too, though. Witness the wholesale failure of SIP roofs in Juneau Alaska a few years ago. Leaky seam details (air leaky from inside, not water leaky from outside) under high pressure due to really large stack affect because of the extreme temperature differentials forced warm indoor air into the panels at the joints and roofs started growing mushrooms at the seams.
But I do like sprayed-in place foam a lot.
Edited to say that also, there are plenty of rooms in a house that are not laundry rooms, kitchens or bathrooms. Every case is different. I know you and I agree on that, and I agree wholeheartedly that it is rarely any one factor that leads to system failures. Complex systems fail in comnplex ways.
Steve
Edited 11/12/2003 8:38:53 PM ET by STEVENZERBY
Have a good evening, good discussion.
Gabe
Steve, I have been following this thread because VB seem to generate a lot of discussion, and the mistakes are costly.
About 6 yrs ago, I witnessed a discussion between the future owner of a house under construction, with a large developer/builder, the sheet rocker, and the manufacturer (a biggie) of the sheet rock.
The prospective owner had called them together because many of the houses in the development were popping sheet rock nails, and the builder was trying to stonewall corrections. The owner asked who was to warranty the sheetrock and the method to be followed for its installation.(He also said he wanted an energy tight wall.)
The manufacturer said "glued and screwed", and laid out the pattern. The sheet rocker said he would charge the builder more if screwed, but in no case would he accept a poly vapor barrier; it would be glued and nailed or screwed. The builder didn't want to pay for poly VB/labor, and knew the owner would be tough to fight if any nails popped, so he went with glued and screwed, and agreed to pay the screw upcharge.
To get the energy efficiency, the wall was sprayed with 1/2" poly foam, then fiberglass batt with the VB kraft flanges stapled to the inside edges of the studs, and then sheetrock glued and screwed to the studs, and latex painted. On the outside of the sheathing, there was 1/4" fanfold and Tyvek under the vinyl siding.(R-17-18) The house never had a "nail pop",and the utility bills are way below neighbors'.
Last year, a major portion of the south wall was removed for an addition. The wall interior looked fine, no evidence of any mold or condensation. Was the owner just lucky, or did the lack of air migration prevent condensate problems in this mixed climate, or is the VB kraft that good?(mid Atlantic, lots of cooling, heating and humidity swings)
What is your opinion on this wall configuration?
PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
Gabe -
Im actually agreeing with you even though it may not sound like it (grin)
I'm also getting a real time, real world lesson in how this stuff works. Or, in my case, doesn't work.
This house we recently bought which I've turned into a 'retirement project' has a massive brick chimney on one end of the gabled roof. We tore off some ugly field stone facing in the interior only to find that the framing behind the chimney was completely rotted out. The block filler was laid directly against the 3/8" plywood sheathing without so much as a layer of 15lb felt.
Later, It said to myself, "self, you better tear off some drywall upstairs and see what the framing looks like behind the chimney up there.
I quite literally took the plywood sheathing and 2x4 framing out by the handfulls. The damage went all the way up the gable end into the attic to .... where the insulatio stopped. There was 3 1/2" batt insulation in the stud spaces in the attic up about 3' then none.
No air movement, rot!. Air movement - no damage. My framer seemed to think the flashing at the roof had failed which also contributed to the problem but - the killer is, there was a pellet stove insert in the fireplace. The fireplace was actually built as a circulating type (Heat-a-lator kinda thing) but the warm air outlets for the masonry fire place had been walled off with the field stone facing. Any/all warm air from the units outlet was being shunted into the stud space. To make matters even more complicated, the guy that designed this house had some wierd idea about sucking air either out of the crawl space or from the hot air furnace system and back into the air distribution system. By the time we bought the house, the ductwork was falling apart under the crawl space so who knows how long the moist air from there was being drawn into the circulating fireplace, heated, and sent, basically, into the insulation and stud space above.
It's the most bizarre thing I've ever run across. And totally off topic. So please don't feel obliged to reply. It just helps having someone/somewhere to talk. (grin)
...........
Dennis in Bellevue WA
[email protected]
Have to go to work, would like to respond fully when I get home.
Gabe
Fascinating discussion, guys. I've read the article below
http://www.buildingscience.com/resources/mold/Design_Build.pdf
which has some interesting advice related to mold and allergy problems. The article says,
"No interior vapor barriers should be installed in basements- ever - because they trap moisture inside the (wall) assemblies."
This is a rather broad pronouncement, which follows from their belief that all wall systems should be designed to "dry to one side". In the case of a masonry wall below grade, the only side it can dry to is the inside.
Do people agree with that statement? If I have a below-grade masonry wall in a "mixed climate"- cold in winter (heating from October through March), hot and humid in summer (enough to merit A/C in July and August)- should I avoid the use of a vapour barrier on the inside of the internal (insulated) stud walls, even though I have some rigid foam insulation between the wall and the soil?
Haven't had time to read it all but from what I read, I wouldn't put too much crediability in that report.
They say for example that you mustn't install poly on exterior walls in basements but advocate the use of polystyrene rigid insulation behind the drywall.
I can assure you that there will be moisture trapped behind that assembly like you wouldn't believe.
The secret is in the exterior of the concrete wall and the integrity of the waterproofing to prevent moisture from permeating inward.
Walls do not and I repeat do not dry to the inside.
Not to mention that they forgot to include the greatest provider of water in modern homes is the occupants.
Aside from that, still not much good reliable information on that report.
Gabe
Walls do not and I repeat do not dry to the inside.
I repeat, moisture will travel right through a wall towards the inside or outside, according to moisture content. The only thing stoping it is the ability of each material (perm rate) in the wall to slow down or stop the flow.You get out of life what you put into it......minus taxes.
Marv
Any sealer paint will prevent the drying process.
Your house would have to leak like cheesecloth to allow enough air to pass through in order to complete the drying process and you would have to have all exterior walls free of paint, tile, wallpaper, shelves, cupboards, cabinets etc. to make your assumption even remotely accurate.
Like I said, walls do not dry to the inside.
Gabe
Gabe:
Last year I rented office space in a strip mall. On one wall (Brick over block, south facing) I stripped off vinyl wallpaper to find lots of mold and drywall with so much moisture in it that the paper facing was falling off. I skim coated with drywall compound and painted with latex paint and have not had any problems since.
The store next door had only paint on the block wall but showed no signs of water damage.
IMHO the vinyl wallpaper stopped the moisture from coming into the building and caused the moist drywall and mold. Now that it is covered in latex paint (permiable), I have no moisture build up.
How would you explain this problem and solution?You get out of life what you put into it......minus taxes.
Marv
Below grade is a different matter.
In a basement, I would want the VB right next to the masonry wall. Moisture is far more likely to come into the wall assembly through the [permeable] masonry than it is to ride into the wall on [moisture laden] interior air. You would also want a continuous thermal break to prevent condensation on the cold masonry surface, or anything it could conduct to...
"Do people agree with that statement?"
Molten...it sounds like we have similiar climates (I'm in MN).
I'm not a builder by any means. Just a homeowner. I do agree with that statement, though. That is based on a lot of reading (here and at buildingsciences), commentary from within these forums, and from talking to some Architect friends.
The more I read through these types of (quite fascinating, btw) vapor barrier discussions, the more I lean towards the 'breathable walls' is the better way. That or using CIPS or ICPs.
We're just about to go forward with our basement remodel. We'll be putting the pink foam on the walls directly, metal stud walls, and then sheetrock/panelling. I'll be making every effort to keep the walls NOT airtight.
Now, this is an old house, and that's a big part of the reasoning (we have heavy clay soil, and porous concrete block..it MY leak at some point and I might as well give it a place to dry to) and hot, humid summers (so we'll get condensation, and need it to dry to the inside as much as possible). If it were a new house, I think I'd invest in quality waterproofing on the outside and let that be the 'vapor' barrier.
The only catch is that local code dictates a full poly vapor barrier up against the foundation wall. I've been to a few recent remodels that have done that and It just seems like a great way to trap a lot of moisture where you don't want it. So, I may not be pulling a permit on this one... ;o)
Just next door in WI, I've watched a friend have their brand-new home's basement finished and the contractor didn't put any VB in at all.
All that said, Gabe added:
"I can assure you that there will be moisture trapped behind that assembly like you wouldn't believe."
And that is the only concern I have at the moment. Our walls are fairly rough (appears to be a heavy-sand rough coat of plaster on it) so I think we'll naturally gain a bit of an airspace behind the foam insulation to allow for some airflow. Is that maybe not enough? Better to go with FB? FB just seems very bug and mildew friendly (I've been rebuilding some windows on my house and have pulled out rather black FB while doing so).
The only catch is that local code dictates a full poly vapor barrier up against the foundation wall. I've been to a few recent remodels that have done that and It just seems like a great way to trap a lot of moisture where you don't want it. So, I may not be pulling a permit on this one... ;o)
That is what you want. Below grade, old house, clay soil...
These folks [above] are arguing about properties of above grade walls.
The moisture in the ground outside wants to come in. Masonry walls are like sponges, but air does not pass through them. You are not trapping water with a VB, you are encouraging it to go back into the ground where it came from. Once the wall is saturated, it will stop absorbing water. If you were to 'dry' the wall by evaporating some of the water into the inside air, more water from the ground will displace it. This can amount to tens of gallons per day for the rest of your structure to deal with. In the winter, this moisture load will travel on air to undesirable places. Similar to using a giant humidifier. Look into Tu-Tuf for below grade use.
"That is what you want. Below grade, old house, clay soil... "
Argh. You do realize that now I'll never get this basement finished because I can't make up my mind which way to do it. ;o)
OK, your comments make a lot of sense too. However, I'm not sure if we really that much water coming through where we need to 'block it and force it back out'. Even if the wall is saturated, that means it is damp, no? Isn't a cold, damp dark wall ideal for mildew? It sounds like it would be damp with or without the VB, and my gut feeling is that It'd make more sense to have some air movement back there in the summer since I'll be running a dehumidifier anyways.
The one house we recently visited that had a fully remodelled basement was an older house like ours, but with rock foundation. They built the perimeter wall about 6" from the foundation wall and blocked it with Poly. This floating wall then opened into a utility room in back. The place smelled of mildew even with brand new carpet+walls and a huge dehumidifier running. And this was in late, dry October...not the high-humidity of August or wet ground of April.
Right now, we use the basement in summer. It's humid (but so is everything) and we run a dehumidifier constantly. In winter, I'm not sure if we get much...if any moisture coming through. We're on a fairly high point (basement floor is above street level) so I don't think we have any water table issues and the ground above is frozen solid.
I guess I have more to think about...
"Even if the wall is saturated, that means it is damp, no? Isn't a cold, damp dark wall ideal for mildew? It sounds like it would be damp with or without the VB, and my gut feeling is that It'd make more sense to have some air movement back there in the summer since I'll be running a dehumidifier anyways."
Think about it this way. If the wall is cold, dark, and damp, but completely isolated from your living area, why would you care? The outside of the wall is all of those things too, but does it matter? The wall will attain equilibrium with the surrounding soil, instead of trying to attain equilibrium with your living space.
Air movement over the wall is a bad thing, particularly in the summer, when even warmer/moister air wants to condense on your cold masonry wall. This is where the continous thermal break comes in. The dehumidifyer is consuming energy to fight these forces of nature.
Moisture comes through in the winter as well, but the dryer interior air evaporates it away quickly, and the stack effect sends it up and out the top of your structure to condense there, and cause a new set of problems.
A wall 6 inches away with a VB is not pushing the moisture back into the soil at all. Moisture will still come in until the air is fully saturated. Some air is going to circulate back there, but it will never really dry out. This setup is just asking for trouble.
What you want is a continuous vapor barrier sealed tight to the top of the masonry wall with a continuous bead of high quality sealant. To get full benefit, the barrier would continue across the floor as well. Next would come a thermal break to prevent condensation, then finish materials.
"If the wall is cold, dark, and damp, but completely isolated from your living area, why would you care?"
Valid point. I don't know if I have confidence in completely sealing said VB around the perimeter of the basement, though.
"A wall 6 inches away with a VB is not pushing the moisture back into the soil at all. Moisture will still come in until the air is fully saturated. Some air is going to circulate back there, but it will never really dry out. This setup is just asking for trouble."
That's what I thought too.
I have been following this thread all of the way through and I must agree with csnow. Below grade the foundation must be sealed tight. If not outside, as per current code, then inside. Water will hit the barrier and stop. It will then travel some other route of less resistance. It would be nice to have a barrier under the concrete floor to stop the flow there.
I would also strongly recommend that any surfaces that are going to be covered that have been exposed for a while should be bleached. Kill off the existing spores and other organic nasties. I.E. window frames, ceiling joists, door jambs, and wall surfaces---blah blah blah.
I appreciate the discussion regarding vb above grade.
Curly
P.S. get the surface water away from the house as fast, and as much as possible.
Hand Hewn Restorations Inc.
Restoring the past for the future.
Darrel -
First let me qualify my submission by acknowledging that I live in the Pacific Northwest, or Pathetic Northwet as my wife refers to it. Meaning - the ground is wet most of the year. Even in the hot dry summer we had this past year.
Moist earth against a concrete or espectially a unit masonry wall will wick moisture al the way through from the cold side to the warm side. Here in our area, that's mostly in the winter and often in the summer as well. It's standard practice to put a vapor barrier on the *out* side of concrete foundation walls for occupied basements below grade. This is almost universally a fluid applied material rolled on after the forms have been stripped the concrete has cured to a specified point.
I personally think it would be cheap insurance to apply such a vapor membrane to the outside of the concrete walls if that's an option - that is, unless they've already been backfilled or if it's an existing below grade concrete wall.
...........
Dennis in Bellevue WA
[email protected]
The moisture in the ground outside wants to come in. Masonry walls are like sponges, but air does not pass through them. You are not trapping water with a VB.
I have to disagree. If I run my airconditioner for 3 months during the summer, and moisture comes in through the masonary, the VB is going to stop the moister and the insulation is going to get wet and possibly creat mold.
I think we have another problem in this thread. EVEN IF THERE IS NO AIR FLOW IN THE WALLS, VAPOR CAN AND WILL STILL BE A PROBLEM. Just like a paper towel will wick up a water spill (high perm rate), a wall will pull water through it. The amount of moisture passing through will vary with materials.You get out of life what you put into it......minus taxes.
Marv
"I have to disagree. If I run my airconditioner for 3 months during the summer, and moisture comes in through the masonary, the VB is going to stop the moister and the insulation is going to get wet and possibly creat mold."
Not sure we disagree. I was talking specifically about a below grade masonry wall in that post.
My opinion is that the vapor barrier should be applied in direct contact with a below grade masonry wall and sealed tight.
My first thought would have been the chimney/fireplace as being the main culprit.
Masonry has 10 times the perm rate of concrete and as such, unless properly sealed, will wick water everytime it rains.
Having the framing directly against it without a vb ends up trapping the moisture inside the walls where it can do the most damage.
If the flashings at the roof failed as well then the problem would be accelerated.
Like you said the rest is bizzare enough on it's own.
Gabe