I am thinking of using almost a second vapor barrier on basement walls
I am thinking of using almost a second vapor barrier on basement walls
(OP)
I just bought a bungalow built 1960 up north. The basement walls are cinder blocks. They are damp. I am thinking of breaking the slab on the inner perimeter and installing a french drain pumped out by a sump pump.
I am thinking of placing a vapor barrier on the cinder blocks (because they are so damp) From the top to the bottom of the french drain. I am then thinking of finishing the basement. Using wooden 2x4" and pink fiberglass matts covered with drywall. Since the vapor barrier should be behind the drywall, I am thinking of placing a second barrier there. Both barriers will drain into the french drains with spacers. The french drain would be covered with cement except the two spacers which will allow each barrier to individually drain. Both barriers will be sealed at the top and open bottom to remove trapped moisture. I think??
I am thinking of placing a vapor barrier on the cinder blocks (because they are so damp) From the top to the bottom of the french drain. I am then thinking of finishing the basement. Using wooden 2x4" and pink fiberglass matts covered with drywall. Since the vapor barrier should be behind the drywall, I am thinking of placing a second barrier there. Both barriers will drain into the french drains with spacers. The french drain would be covered with cement except the two spacers which will allow each barrier to individually drain. Both barriers will be sealed at the top and open bottom to remove trapped moisture. I think??





RE: I am thinking of using almost a second vapor barrier on basement walls
Before going too far with vapor barriers, determine why the walls are damp. You may be just having moisture from the floor area condensing on the cool walls, especially in summers. That's a common situation in some basements I have seen. What's the outside look like as to surface water drainage? Ground water flow?
Fiberglass insulation can take on water like a sponge. Mice like the stuff also. Pink closed cell extruded polystyrene won't take on water.
As to your "French Drain", do some reviewing of my advice found on those forums dealing with that term.
RE: I am thinking of using almost a second vapor barrier on basement walls
RE: I am thinking of using almost a second vapor barrier on basement walls
Please see attached.
I do not want to trap the moisture.
Bryan
PS:I changed my handle
RE: I am thinking of using almost a second vapor barrier on basement walls
The house has no surface drainage. I am correcting this with downspouts that remove most of the roof's water over 12 feet away. I will raise the slope on the outside perimeter.
The walls are damp even halve way up so I thing drainage is a big factor. But, I suspect that the slab might not have a vapor barrier below it??
I am installing the internal French Drain thinking it will catch all the water trying to get underneath the slab??
I am trying to hope that having the two barriers open to a bottom drain that the moisture will not build up??
Regards,
Bryan
RE: I am thinking of using almost a second vapor barrier on basement walls
RE: I am thinking of using almost a second vapor barrier on basement walls
RE: I am thinking of using almost a second vapor barrier on basement walls
You have replies from two old engineers who have seen a lot of problems out there, such as mold, law suits, wet basements, caved in basements, and varied personal experiences. From your replies, I'd guess you have not looked up French Drain forum discussions, nor have you considered some of the warnings. I assume you know how much water a sponge holds before it starts to release some.
In doing the outside slope work, there is a technique that many engineers, architects and landscapers do not know about; water proofing the ground surface. If interested I can give the details.
As to French Drains, my Master's Degree Thesis dealt with drainage of wet ground by subdrains. Conventional "French Drain" details can fail.
RE: I am thinking of using almost a second vapor barrier on basement walls
This link has some comments that may help explain my thoughts.
http://www.eng-tips.com/viewthread.cfm?qid=290956
RE: I am thinking of using almost a second vapor barrier on basement walls
I did read the French Drain stuff, but only found one thread on inside French drain. The problem was not the drain but an oil pipe installation?
The drain had no problem functioning.
I would like to hear your information on waterproofing the surface.
The walls have bowed in 2 inches. I was thinking of straightening them first. Then bracing 2x4's to retain the wall straight. I would like to use a vapour barrier to protect the wood.
Pink closed cell extruded polystyrene won't take on water, true but, if I have the wood every 16" and the extruded polystyrene between them, the wood would have mold & smell? That is why I am thinking of putting the barrier.
If I do not use a barrier, I would have to use the metal 2x4. But they conduct heat and I do not think as strong?
Bryan
RE: I am thinking of using almost a second vapor barrier on basement walls
Exterior ground surface can be made waterproof in this way. Assuming the surface is in its final position, then do this. Leaving walks and bushes, all the surface where fill was placed, strip the sod. Place a powdered bentonite (not the granuated kind) on that surface at a rate of about 3 pounds per sqauae foot. Powdered bentonite is available at plumbling supply houses in 50 pound bags from under various names for "driller's mud". One name is Volclay. It is a volcanic clay that has the particles made up of parallel platelets which electrically attract water. Given free acess to water it can swell 16 times is orginal volume. However, in soil it will fill voids and keep the soil moist and rather impervious. You mix that in with a rototiller about 3 inches deep. Thorough mixing is needed. If you feel ambitious, you use a concrete mixer or mix by hand in a wheel barrow. Then re-place the sod. If you use too much bentonite, it will turn the lawn to mush. It is a natural clay so grass now grows better. The required treatment distance out from the house is the whole zone of backfiliing to the basement. In may cases this is as much as 10 feet. If you do not know that fill width, at least as far out as the height of the wall. At cracks in walks next to a foundation, fill a mix of sand and bentonite.
With the wall buckled in some, that brings up a whole different picture. Sounds like frost has shoved the wall in. Very common with block walls. Insulate the wall and less heat goes out, making mister frost even more vicious.
Pushing the walls straight may be more than you want to try. There is earth out there. Some suppliers furnish a bracing system that at least keeps it in the present position. No way will ordinary wood or steel studs do that if more frost push is coming.
Here is one system:
http://www.aquaproof.com/structural-repair/gorilla...
Another:
http://www.permajackofstlouis.com/basement-wall-br...
I once saw a system that looked like a bow for bow and arrow. One even installs structural steel members.
If you really want to stop frost push, you need to do one of three things; remove cold, remove water, or change soil to non frost susceptible. Water can get there by capillary action, so draining the footings won't do it. Even the surface drainage fix won't fully do it, but helps. Insulating the outside can help, such as leaving snow there or a layer of fall leaves each season. On new jobs we even recommend burying a sheet of the pink stuff about a foot down, to 4 feet out.
Non-frost susceptible soil is sand with less than 5% passing the number 200 sieve (a size hardly visible to the eye).
Turns out to be quite a project, huh?
Reminds me of a village where they decided to avoid winter frost heaving of the new streets. They laid down a sheet of pink stuff, then the base and paving. In winter, the warmth in the ground was retained there and the pavement got colder than the roads in the country. A freezing rain came down in early winter. In the country the warmer road was just wet. In town it was glare ice. Those folks coming in from out of town sure got a surprise. Fixed one potential problem and caused another .
So you may fix one thing and cause a few problems you didn't expect. I hope our info helps. At least now it is more complicated.
RE: I am thinking of using almost a second vapor barrier on basement walls
I had assumed you were aware of the limitations of plastic vapor barriers. They are not that great. In addition to perforations such as nails and openings that are hard to seal, they do transmit moisture, even though slow. So your "seal is a good thought, but it won't fully stop moisture transfer. Your drainage openings at the bottom are obvious sources of vapor to go to cooler places, such as cold outside walls.
RE: I am thinking of using almost a second vapor barrier on basement walls
The more complicated, the more interesting.
Thanks for the great insight!
Regards,
bryan
RE: I am thinking of using almost a second vapor barrier on basement walls
RE: I am thinking of using almost a second vapor barrier on basement walls
Not sure if it was already mentioned, but because you have a bow in your basement walls, you may also have expansive clay. I would do a hand auger next to your walls and see what you have. A local geotech firm can do this test fairly cheap. At least then you know the soils you are dealing with and that same firm may be able to help you a bit more with your drainage/moisture solutions.
Also agree with Oldestguy and Ron. I think this is correct:
Ideally your moisture barrier would be on the exterior face of the wall, but I would stick with one good one on the interior. In areas with basements, there are usually specialty contractors that deal with this exact thing. It seems you are a DIYer, which I am too and so full respect, but this one you may want some additional expertise on. There may be membranes that if installed by a certified installer offer some type of warranty.
Ron- do you think once this is all done you would just leave an air cavity between the basement wall (now covered by a moisture barrier) and then frame out your interior wall, insulate and drywall with NO additional moisture barrier? So you would not use paper-backed fiberglass either. That way the wall can breath and the heat/AC system or dehumidifier would remove any excess moisture from the air. You could also treat this the way some crawlspaces and attics are now- frame your interior wall with several inches of void space and run your heat/AC system through it with a return and supply, constantly exchanging the air and pulling out excess moisture.
Keep us posted, this is a good case study.
RE: I am thinking of using almost a second vapor barrier on basement walls
RE: I am thinking of using almost a second vapor barrier on basement walls
Thank you all for your great insight!
I have decided not to double vapor barrier after Oldestguy's wise advise.
a2mfk,
The wall needs to be braced. Or, history might repeat itself? But, I could brace with carbon stripes every 4 ft.
My water surface drainage is bad. I am taking Oldguy's advise about the foam below grade. As well, I am greatly improving the surface drainage.
If I have expanding glay, can I not just brace the inside and forget about it?
Then, about your spacing design, do you think using pink fiberglass would be problematic in your design?
This vapor barrier drains to an interior French drain which is located beside the footing. (see sketch way above.)
I have broken the slab around the perimeter.I am presently testing for Radon. If radon is high, I would fear the spacer has to go?
If so, I am back at square one?
Best Regards,
Bryan
RE: I am thinking of using almost a second vapor barrier on basement walls
Now comes a question. Why any barrier at all? So moisture collects on the block wall. Maybe moldy I suppose. It also would collect on the barrier there. In this north country the main reason I see for a barrier is to keep water from collecting on the siding and in insulation there during winter. When I was a kid the outside walls had to be painted frequently due to that winter moisture collection ruining the paint adherence, but that was the main reason then for barriers. We had no insulation.
On the bentonite soil waterproofing treatment thing, the details came about due to a lot of lab work for landfill work. Also, it came from noting the layers of soil in most basement backfills sloping towards the wall and job problems resulting from that sloping condition directing infiltrating water. So, you treat the whole backfill area, even if slopes are good. No work on windy days. It really blows around.
My experience with expansive clays usually is reverse, with settlement from shrinkage. One job was compacted clay expansion aggravated by use of bentonite in the wrong place fed with roof water. I'd be interested in what experience home owners have when a basement waterproofer uses bentonite on the outside. None of these have come to my attention.
RE: I am thinking of using almost a second vapor barrier on basement walls
Basements are a bit outside my area of expertise, but I found this:
http://www.epa.gov/indoorairplus/technical/moistur...
I would consider using PT base plates too.
The bowed walls MAY go back more towards plumb if you have expansive clay soils that dry out. But a 1960s basement constructed with CMU probably is mostly unreinforced, and is probably not very elastic, so it going back into a vertical position may be wishful thinking. I am surprised you don't have a cracking problem. This is a separate structural issue and I would hire yourself a local PE with experience with basement walls in your area. Severely deflected unreinforced CMU scares me....
Your sketch also assumes the slab is down at the foundation level. I don't know what was/is common practice for basement construction in your area, but I would not be surprised if the wall was built first, and then the slab was built over the foundation, perhaps several inches above the top of the foundation. I also don't like the interior french drain idea and think it is a lot of work and creates its own set of issues.
I would do this project in phases, and see how each step improves your situation.
1. Drainage improvements- less moisture intrusion? Wall movements?
2. Structural assessment and repair of the wall
3. Once you have gone through your wet season, re-evaluate your moisture situation. The US EPA suggested detail makes a lot of sense, I would like to know what Ron thinks of it.
RE: I am thinking of using almost a second vapor barrier on basement walls
Thanks again for your advise.
If I use a foam sheet under the soil, Do I still need bentonite?
My property line is six feet. I am thinking of installing foam for the 6 feet.
Regards,
Bryan
RE: I am thinking of using almost a second vapor barrier on basement walls
Thanks for the info!
I am doing it in phases.
1- Fix surface drainage. + Start straitening the wall. + test for Radon.
2-examine Radon results.
If high, go the above epa route.
If low:
A- go with Vapor barrier against wall ending in French drain. I will have drilled holes in the bottoms of the bottom blocks. The above sketch is good.
(slab same level as footing). So water coming out of those holes has to be routed to the French drain.The vapor barrier would do the trick?
B- Modify epa system so the holes can drain. ie: start the barrier only inches above the hole and install the flute spacer for access to the French drain.
C- something I have not thought of yet?
Best regards,
Bryan
RE: I am thinking of using almost a second vapor barrier on basement walls
To satisfy my of morbid curiosity, can you give us an idea of how out of plumb or out of plane the walls are? Is it bowed two inches over 30 feet of length at the top of wall, bowed in two inches at mid-height everywhere, or does it lean in two inches from floor to ceiling?
What is next to the house? You say you have six feet to the property line, and I'm curious what is next door that could be a) dumping water onto your property (like the lot next to my house that sheds to my yard, and mine to the house downhill from me), or b) is there a huge pile of dirt/big building pressing down on the soil mass against your wall?
We might offer solutions based on these answers. But expect us to direct you to a local structural if it sounds like you need one. (You ALWAYS need one.)
RE: I am thinking of using almost a second vapor barrier on basement walls
Short answer. The buried foam should do the job. However,if problems are not all fixed, the surface work can come later.
RE: I am thinking of using almost a second vapor barrier on basement walls
bowed in two inches at mid-height everywhere, basically the full length of three walls. It is out of plum buy 1 to 2 inches.
The next house is 12 feet away. It is about 3 feet higher on an even slope. next door is dumping water onto my property.
Oldestguy,
Thanks again.
Regards,
Bryan
RE: I am thinking of using almost a second vapor barrier on basement walls
Bracing the wall takes consideration as to the top of wall situation. If it is not a bearing wall, that may explain the out of plumb. Any brace has to have a resistance up there and a non-bearing wall has little. The earth anchor alternative may be best and least complicated. That anchor needs to be beyond the zone of influence on the wall or it is like the boot strap analogy.
If bearing wall appears not fully capable of resisting the bracing load, add scabs under the joist ends (planks between the wall blocks (not only the plates) and the joists,). Do this at opposite ends of the house using the first floor as the strut.
RE: I am thinking of using almost a second vapor barrier on basement walls
Thank-you once again!
I am over 65 with a bachelor's and recently retired. I am OK with thermodynamics but forgot anything I knew about Vapor Pressure. Your help is greatly appreciated.
On the property line is a set of cedars. I have to build up to have a downward slope so much that I do not dig. At the property line, I am thinking of making the middle of the house the high point and I was thinking of sloping such that the low points are 10 feet away from the building. Since I cannot dig at the property line without cutting the roots, I think the swale would have to be a solid material? The insulation would end on top of the swale. Therefore, the cover over the insulation near the swale would be about 4-6 inches. At the swale I would cover with 3/4 inch gravel. Is this what you seem to be suggesting??
The bow is V shaped. The top and bottom of the walls kept there position. I do not understand how a basement wall of a bungalow can not be a bearing wall, according to my definition?
Earth anchor is not possible with only 6 feet distance?
I do not understand your scab. Are you referring to joist as planks? are wall blocks the cinder blocks composing the wall? Are plates the sill plate?
I am placing a wooden brace at every joist.(16 inches) there will be a brace at the opposite wall of the joist.
Best Regards,
Bryan
RE: I am thinking of using almost a second vapor barrier on basement walls
I think you have it.
I made a rough sketch of it called Wall Brace.
A bearing wall is the wall where the floor joists sit. That load is very useful in keeping the blocks from caving in. It does so by downward loading, as well as friction on the top of wall. An example of this downward load effect is take a stack of kid's toy blocks and carry one end in your hand with the other hand pressing the stack together. You can do all sorts of configurations with your two hands pushing together and the blocks don't fall. It is that compressive force that counters the tendency of the wall to cave in. However, the main thrust of my statement is that the joists sitting there also make a place for adding some resistance to prevent top moving in, in addition to the frictional ability of those joists and the plate (sill plate). So if you have light load, as where there are no joists, the downward compressive force in the blocks is much less, making the ability to resist caving in much less. There also is much less ability of the house above to resist that tendency for the wall top to move in by friction on top.
So at that lightly loaded wall, a good resistance to the top moving in is not there. How to add resistance there becomes more complicated. What is desired is to get that inward push tendency somehow into the floor system. Bridging between joists helps, but conventional bridging probably is not enough. Solid bridging is better. Many builders just take the same size plank, cut 14-1/2" long pieces and use that as bridging material. Braces have to reach to the block, not just to the sill. Double thickness plank is needed. Where I have done this, I use 2 x 4's and 2 x 6 with pole barn nails. By the way, I still am older at 85.
RE: I am thinking of using almost a second vapor barrier on basement walls
RE: I am thinking of using almost a second vapor barrier on basement walls
Thanks again,
Two of the three walls are bearing walls. Now, I understand what you are saying. Makes perfect sense.
Regards,
Bryan
RE: I am thinking of using almost a second vapor barrier on basement walls
Here is another article about moisture and basement walls:
http://www.buildingscience.com/documents/informati...
RE: I am thinking of using almost a second vapor barrier on basement walls
Interesting comment. Trouble is the walls are masonry block (he calls them cinder block). Pretty hard to do much structural calculations when you are just dealing with a bunch of individual blocks( probably not well glued together). When I was a kid they were cinder blocks made with coal ash cinders. For 1960 vintage I suspect they are of concrete. Still, since the original job likely was by amateurs, the mortar strength also might be questioned The structural part comes from transferring the earth pressure loads into the building and considering the wall as not much of a help. However, if the outside buried insulation work and better surface drainage comes about, it would be expected that frost action, pushing in the walls, would be less or not present. Then, just keeping things as found probably is the best that can be done, short of completely replacing the wall system. Of professionals, I'd guess a good carpenter would be the best fellow to have there. Earth pressures could be calculated, but I doubt that any of the constructors who do wall bracing do any calculations. lacking knowledge of what Mr. frost can or will do, a guy has to do the best he can. I don't know of a way to figure frost heave pressures that means anything. Earth loads yes, but not frost. Maybe someone can jump in with that.
RE: I am thinking of using almost a second vapor barrier on basement walls
I'll bring in an engineer for a visit and verbal advise.
His gut feel is worth the price.
Regards,
Bryan
RE: I am thinking of using almost a second vapor barrier on basement walls
Sorry I have to strongly disagree with you on this specific point. Structural engineers are not just here for new buildings, we work with rehab and renovation of historic structures all the time. There are lots of options and methods for strengthening older partially or unreinforced CMU walls, but you should not just experiment as a DIY'er or trust that a carpenter can understand the forces and stresses involved.
Since Steambryan said he is hiring an engineer, I will leave it at that. Get to the bottom of your drainage and soil problems, and then fix the wall. Hopefully some of the "bow" will go away once you have improved the site and soil conditions.
Good luck!
RE: I am thinking of using almost a second vapor barrier on basement walls
OK, let's see what the engineer says. Interesting how this thread has progressed from a simple question to a complicated thing. I still doubt that much of any new ideas will come forth, since the pushed in block walls are very common and the contractors that brace them don't engineer much of anything, other than to find "they work". Other than replacing fully caved in walls,I don't know of any one that has "pushed them back". I do recall one bridge job however, where compacting the heck out of backfill to a new bridge abutment that sat on piles caused the abutment to be pushed toward the lower roadway about a foot. They dug out the fill and some from the timber piles and pulled the thing back. Used a dozer and a grader with cables. Yes, the piles bent some first and came back straight. I would bet the "powers that be" didn't know of that. I was there for something else and just kept my mouth shut. No problems after that. No engineer involved (other than me). At this site, I suppose you could do the same thing. If it was my house, I probably would. But, I'd want to be on site for such a job.
RE: I am thinking of using almost a second vapor barrier on basement walls
He said I could use a breathable material on the inside brick wall. (waterproof but not moisture proof)
Best Regards,
Steam Bryan