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Owens Corning Basement System - Mold prevention in walls Virtual Instrument Plugins
Old 22nd March 2010
  #1
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Owens Corning Basement System - Mold prevention in walls

Hello,

I am about to finish my basement studio and I am curious about your opinions of the Owens Corning Basement Finishing system - or a similar "no-sheetrock" wall construction technique. Specifically, in regards to mold.

I just came back from a home show, and Owens Corning had a booth there, showing off their basement finishing systems.

The one interesting thing they said was that all of their products are 'inorganic', and not food for mold to breed. They claim that the paper backing on sheetrock is the perfect food for mold and it is only a matter of time before a basement finished with sheetrock (exterior) walls will have mold.

Their walls are simply these prefab rigid fiberglass boards with a decorative fabric adhered to them. They sit in between metal studs, and claim to be breathable, to prevent moisture buildup.

I don't have water problems in my unfinished basement, but it does seem moist, and we do keep a dehumidifier running at 55%. Maybe there is some benefit to their system, at least on the exterior walls. Interior walls could certainly be sheetrock, but the exterior walls, against the concrete block is what concerns me.

Does anyone have any opinions, or know any alternatives to this system, that will keep mold at bay on the exterior walls?

Thanks,
geelo
Old 22nd March 2010
  #2
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for finishing a basement in general - their product is a decent product - however - if you are looking for isolation - their product will do you no good......

everything begins with what your needs are........

BTW - FWIW - I would drop that humidistat to below 50% - 50% and above RH is an ideal humidity for mold production.........

I generally recommend (and design) with RH in the area of 43 to 45% - never ablve 45%.

Rod
Old 22nd March 2010
  #3
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Wow...an immediate answer from an authority! Thanks Rod! I've purchased and read your book religiously in preparation for this project.

I know the lack of mass in the Owens Corning walls would provide no isolation, and I would only see using them on the exterior walls, against the block. The interior walls, dividing the control room / tracking / iso booth would be sheetrock.

I'd prefer to use sheetrock for all walls, even double layer in some areas for greater mass/isolation. But with a humid basement (especially in the summer), will mold be an issue on the inside cavity of the exterior walls?

I wonder how other people have addressed this, since I am obviously not the only person with a humid basement, who wants to finish it.

I don't suspect dehumidifiers in the rooms would do much good since a sheetrock wall would create a sealed cavity.

Venting? Active exhaust fans/ducts?

Ahhh...the challenges of an underground space!
Old 26th March 2010
  #4
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I bet just painting the walls with standard waterproofing basement cement paint will help get the humidity down and be a mold preventer for whatever you buildout from there.
Old 28th March 2010
  #5
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Personally, i think it's a bad idea to attach anything directly over the concrete outer basement walls. If you put something over the wall that "breathes", then you are going to get humidity in your finished space, your dehumidifier will run continuously and barely be able to keep up.

If you seal the wall with a vapor barrier, then you'll have stuff growing behind it, or will have a damp / wet / stagnant situation one way or another which is not a good thing.

And, there is a lot of controversy regarding coating the concrete outer walls with a moisture proof paint... do a search and read up on it. Some say it's bad for the concrete and can cause the concrete to deteriorate over time, etc. Others say the paint can fail over time etc and is thus a waste. I have no idea, but this is what I read.

After studying all this, I decided to simply place my finished walls a good 16 inches away from the outer concrete walls. Yes, I've lost some square footage by doing this, but I now have a cavity behind my finished walls that I can actually walk through if need be, there is light coming in there from the windows, there's air space and air movement... nothing will be growing in there. And, I have added a good vapor barrier in my finished walls so that my finished space will remain dry when running the dehumidifier.

And no need to coat the concrete with anything that might possibly cause an issue. Basically, there is light and air space / air movement everywhere, thus no mold problems. Nothing is covered up.

As an added bonus, I can now easily get to all pipes / wires etc that run behind the finished walls.... nothing is buried. The 16" gap is plenty in order to get back there and service things if need be. I have doors that lead back there, I added simple light fixtures in there too. I plan on mounting a few small fans back there on a timer that perhaps go on once a day for maybe a half hour just to make sure there is adequate air movement. I will not be able to dehumidify the air behind the finished walls, but with good regular air movement and a good deal of daylight coming in through the windows, I don't think it's going to be a problem back there.

I do have sheetrock facing the concrete walls, but I bought mildew resistant paint and will soon be priming and coating all the sheetrock with this paint. This should prevent growth on the sheetrock paper.

If you have the space to spare, I don't think you can go wrong with this plan. Directly covering up concrete basement walls seems like an idea that will never really work out well. I've been in many basements where sheetrock or paneling has been placed directly over the concrete walls, and there's always been issues... mold growth, or an inability to keep the finished space dry, etc... almost always a bad mildewy odor in the finished spaces.

When in doubt, play it safe with basements... you definitely do not want mold issues or musty odor issues.

Keep that dehumidifier running at all times, set to, as Rod said, ideally 45% or so... important! I used to know someone that would turn on their dehumidifier only when they started noticing a mildew odor. Once you detect an odor, it's already too late... you need to keep the RH at 45% or so at ALL TIMES, and not just run the dehumidifier when you think you're starting to smell a mildew odor. Yes, the dehumidifier uses electricity... basement studios are more expensive than they would seem to be.
Old 28th March 2010
  #6
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The paint I'm talking about is for the INSIDE concrete wall, one brand is UGL. It is a cementous paint (adding a thin layer of waterproof cement to the wall). For the exterior, that is typically done during construction and would require alot of digging to re-apply something but for new constuction they have many different types of moisture barriers now including some with a mesh or plastic dimples to allow drainage of anything that gets through. For fixing basement wall cracks/leaks after the fact some companies will inject clay into the outside ground at the leak location. Sounds like you have enough ground water to keep the walls damp so the paint should be a good first step and cut down on the dehumidifier.
Old 28th March 2010
  #7
SAC
Registered User
 

So little specific information while desiring a simple and quick fix...
As without knowing the specific nature causing the problem, we can speculate all day long and never necessarily address the actual problem. But then, that does seem to be a tradition...

First, we have NO information as to what is causing the moisture problem. (Yeah, I know...moisture...heh ) And all we know is that it has been treated with a humidifier and that a proposed solution is the OC product that claims to help mitigate mold. Yet thus far no suggestion of identifying or mitigating the source of moisture ingress.

Is there an external source of water that proper slope, re-routing or relocating drains, and/or French drains cannot resolve? Is the outside of the wall below grade properly waterproofed? Is the wall fully below grade or partially exposed?

Lots of issues with an entire list of best practice solutions to be explored first...

And while a waterproof coating can help with moisture transmission through a porous surface, it will NOT address the more significant issues of seams and other entry points. As has been noted above, this is NOT simply paint! ...Unless you want to watch it peel - And as far as problems, that is the ONLY problem of which I have ever heard. And for a wall material (concrete) that does just fine fully submerged, I am not sure to what damage one might be referring... And be aware, that you may want to consider a waterproofing coating and not a sealer...

But the bottom line, the actual source of the ingress must be determined and addressed. Otherwise you are simply chasing and treating symptoms.

You might want to contact a local structural engineer who specializes in such issues to determine the cause and to identify appropriate measures as simply trying to use mildew resistant materials/greenboard, or even steel studs and cement Durock backer board, etc., without addressing the real problem which is the uncontrolled ingress of moisture will not solve the problem.

Do the due diligence to have the source of the problem accurately identified, and then you will be in a much better position to evaluate the various appropriate treatment options available.
Old 29th March 2010
  #8
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Quote:
Originally Posted by SAC View Post
So little specific information while desiring a simple and quick fix...
I'm sorry, did I imply that I was seeking a simple and quick fix? No need to put words in to my mouth.

I all seriousness, I do appreciate all the suggestions that I've received thus far.

As I originally stated, there are no actual water issues in the basement. Completely dry sump, no beading water on the walls, no leaks, excellent outside drainage/gutter system. There is just some overall humidity, that is resolved with a dehumidifier, but I am concerned with the sealed cavity that will be formed once I create a wall.

After talking with a contractor, one idea we came up with was to use a poly sheet on the studs before hanging the sheetrock - and also create an intake vent on one side of the room, and an exhaust fan on the other. This could be set on a timer or humidity meter, and theoretically maintain air movement in the wall cavity.

While this could be seen as a "band aid" - I think given the fact that there is no actual running water - the ventillation should be enough to keep the walls free from moisture buildup. The in-room dehumidifier would take care of the rest.

This idea would hurt isolation, but since it's only on the outside walls, and not the walls separating the rooms, I might be ok.

Unfortunately, there are several coats of paint on the walls at the moment. So I don't think those concrete sealers would be much help.

Thanks again for your feedback, and feel free to chime in on my my latest "vented exterior walls" idea.

Thanks,
geelo
Old 29th March 2010
  #9
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I thought I'd also update the post with some informative links that I've found at buildingscience.com. I can't believe how much contradictory information there is out there - even among supposed experts / professionals. This website seems to have some of the best resources.

BSD-103: Understanding Basements

http://www.buildingscience.com/docum...ting-basements (pdf)

Vapor Barrier Guidance

RR-0509b: Details for Avoidance of Mold - Foundations

I'll post again once I read through all this stuff, and hopefully draw a conclusion.
Old 29th March 2010
  #10
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Quote:
Originally Posted by gee_lo View Post

...I can't believe how much contradictory information there is out there - even among supposed experts / professionals....
This is why I voted to just leave a service space between my inner finished walls and outer concrete walls. Can't go wrong this way. There may always be some degree of a problem trying to go right up against the concrete with a finished system. I really wonder IF there is truly a "correct" way to do this at all.

I think I will try to go grab some pics of my basement walls / service space this afternoon so you can check it out. Nothing is covered, nothing is hidden, there is light and air movement everywhere. My inner finished walls DO have a layer of plastic sheeting right under the finished sheetrock to keep humidity out of the finished space.

But I think SAC has indeed provided some solid words of wisdom here: "...the bottom line, the actual source of the ingress must be determined and addressed. Otherwise you are simply chasing and treating symptoms."

In our cases where we do not have any major problems (such as serious water leaks or water beading on walls etc), just a "normal" degree of basement moisture / humidity (which is still "high"), I'm not sure what could really be done to truly "fix" this ("at the source") short of digging out all the earth around the foundation, perhaps covering the entire exterior of the foundation walls with a moisture-proof barrier, then backfilling with sand or whatever with an extensive drainage scheme etc... and this, for most people and situations, would not be practical. I know for me, it would be nearly impossible to do all this, would cost a fortune, I already have a lot of landscaping, trees, walls, driveway, etc all around my foundation, it would all have to be torn up and destroyed in order to access the exterior foundation walls from the outside, it's absolutely not practical to do this... for me. So I personally must resort to "chasing and treating symptoms" which I do by simply running a dehumidifier inside my moisture sealed finished "inner" basement room.

Old 29th March 2010
  #11
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Great points 666666,

I know your work is already done, and you've come up with a great plan. In my case, I don't think I can lose that kind of square footage, so I have to determine the best approach to build walls against concrete.

Have a read of that first link I posted ( BSD-103: Understanding Basements )

The author authoritatively states that rigid foam should be placed against the concrete foundation, prior to wall construction - and no poly barrier should be used.

Article quote:
" If basement wall systems are designed and constructed to dry to the interior – regardless of where insulation layers are located – interior vapor barriers must be avoided. This precludes interior polyethylene vapor barriers installed over interior frame wall assemblies or any impermeable interior wall finish such as vinyl wall coverings or oil/alkyd/epoxy paint systems.

If an interior insulation layer is used the indoor air should be prevented from reaching the concrete structural wall assembly or rim joist assembly (unless insulated on the exterior) in any significant volume. Rigid foam systems or spray-applied foams are recommended for this purpose, because they allow drying, are not sensitive to moisture damage, and do not support mold growth – essential characteristics for all materials which contact the basement wall and basement floor slab."





I am just glad I am doing the research now, before I build!

Thanks,
gee_lo
Old 29th March 2010
  #12
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Cool article.

Well, to sum up what the article is saying about interior moisture barriers... moisture barriers do not let moisture pass through and thus do not allow drying behind the finished wall and thus you get mold, rot, etc. Indeed.

In my build, I have used a plastic moisture barrier in my interior walls, but again, I have an 18" or so space between the interior wall and exterior concrete wall.... there is plenty of airflow around all walls for drying... and daylight (UV light) too which helps prevent mold growth. I've already gone through one super humid summer / lots of rain etc with this set-up, and there is no trace of mold or any other problems. Yes, there IS a bit of a musty odor in the "service gap", but not any worse than it ever was before the interior rooms were added. Actually, it seems much less now (probably because there is just less area and really good light in this space).

Pic below shows the area between the interior and exterior walls. Note: this particular room was not built to be "sound-proof" - this is the lounge area:



Pic below shows the view from inside the interior space. The work is not completed, measures will be taken to improve aesthetics. A "large" interior window was used to let a maximum amount of daylight into the finished space.



Pic below is of another section of the basement, early stages of my "sound-proof" room:



Old 29th March 2010
  #13
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Cool...thanks for posting the photos!

I think your "service gap" is a great idea. The fact that you can walk in there, and service any of your plumbing, etc, is a huge benefit. Great work, I'll share some photos when I start my job as well.
Old 30th March 2010
  #14
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Disjointed's Avatar
 

the second wall with a walkway is great if you have the space..

one common way is to line both the walls and floors with rigid polystyrene (the pink board), then tape all seams. (like as mentioned in the article)

if you do build directly onto the concrete floor, make sure to use treated lumber, composite lumber, or use a good barrier between it and the floor .... it will wick moisture.

gl
Old 16th May 2010
  #15
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once a roadie's Avatar
I think 666666 is onto something here with building the walls within the walls...

any comments from pro designers on this idea?

I'm thinking of doing the same!!!
Old 20th May 2010
  #16
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I have a couple of friends who installed the Owens Corning basement finishing product (not the entire basement) but a couple of rooms, and they love it. They never had water issues, so I can't comment on how well it rejects mold growth. I like the idea of puting an 18" access space between the sheetrock walls (in pics above), but some basements are a lot smaller and taking 3 feet off a room dimension can defeat the purpose of putting a room down there. If you have a big enough basement, thats a smart idea for future maintenance issues and any water problems.
Old 20th May 2010
  #17
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666666's Avatar
Quote:
Originally Posted by Insulation Man View Post

...but some basements are a lot smaller and taking 3 feet off a room dimension can defeat the purpose of putting a room down there. If you have a big enough basement, thats a smart idea for future maintenance issues and any water problems.


Indeed, the biggest or perhaps only problem with having an 18" "service gap" behind the walls is the loss of usable square footage.... and this can surely be in issue if your basement is not that large.

I'm lucky to have a basement that is "large enough" to allow a "service gap", the basement isn't gigantic, but I was willing to give up the square footage to have the gap, and the resulting room sizes are adequate.

I estimate that I have "sacrificed" nearly 100 square feet for my service gap in total (verses having put sheetrock right up against the concrete). To visualize 100 square feet, it's the same as a room 10 feet square... in one regard this is a LOT to give up!... though in my case it's less than 10% of the total area of the several basement rooms.

I guess my attitude is, I'd rather sacrifice square footage and have a 100% usable basement with zero issues, than to "maximize" square footage and then have possible problems and headaches (which might wind up making the basement nearly unusable as real-deal living space / studio use).

Pros and cons to everything, as always. I'm loving this service gap though, just the other day I was walking back and forth in there running a bunch of new wiring for the house etc, it's nice to have. And there is zero trace of mold etc. There IS a slight musty odor inside the service gap, but the rooms are nice and dry.

Old 22nd May 2010
  #18
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666666 - do you dehumidify only the interior rooms of the whole basement?

I'm looking to do something similar this fall
Old 22nd May 2010
  #19
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Yes, I only dehumidify the interior rooms. The interior rooms are well insulated with plastic vapor barriers, etc, so that once the dehumidifier drys the rooms, they stay dry and the dehumidifier does not need to run that much. The "outside" service gap space of the basement is not insulated at all, vapor pours through the concrete foundation walls, if my goal was to dehumidify the service gap, I'd probably need to have 5 dehumidifiers in there and they be running non-stop all summer long... and they'd probably barely keep the RH down. This wold get costly in terms of electricity... any typical dehumidifier is rated at about 5 - 6 amps.

What I DO plan on doing though is setting up some type of "air movement" system for the service gap, keep the air flowing. This will reduce / hinder mold and mildew formation. One thought is to place a mega-duty exhaust fan (blowing to the outside) on one end of the gap, and then add some type of intake port (from the outside) on the other end of the gap so that the exhaust fan will suck fresh air into and all around the service gap. With this type of set-up, I figure if I just manually turn the exhaust fan on once every few days during the summer, even for just 15 minutes, that will replace any stagnant, musty air in the gap.

One thing that I'm a little disappointed about so far... I have one new basement room with a porcelain tile floor, this particular room really needed tile (will be a playroom / party room)... I never gave too much thought to the vapor blocking characteristics of porcelain tile, but... I'm finding that the dehumidifier in this room has been running almost non-stop recently, constantly pulling out moisture. I'm fearing that porcelain tile does not block moisture, and thus I'm going to be doomed to having the dehumidifier run almost continuously all summer long. I have another room that is 100% surrounded by plastic sheeting (even on the floor, under a carpet) and once the dehumidifier dries that room, it STAYS dry for a while before the dehumidifier has to kick on again. It's still a little early to determine what's going on here, I hope to learn a lot more this summer now that almost all the basement rooms are completed, but the main point is, your goal should be to build a room, INSULATE it very well from MOISTURE (meaning surround the ENTIRE room with 6 mil plastic sheeting), and then dehumidify only that area.

So does anyone know offhand if porcelain tile is vapor-tight? I suppose I should have tried to figure this out before I put down the tile, but again, this room kind of "needed" tile anyway, carpet or laminate flooring would not have worked well, etc... there will be spills, etc.

Another side note... when planning your rooms, figure out where you will place the dehumidifiers and figure out a drainage system so that you need not empty the dehumidifiers by hand. One set-up that works, place your dehumidifier up on a stand, maybe 2 or 3 feet above the floor, then run a drain hose from the dehumidifier through the wall into the service gap, then you can have a condensate pump in the service gap on the floor that can pump the water outside. Definitely plan for this... because otherwise you'll be emptying your dehumidifier tank once every other day or sooner, it gets to be a real pain after a while, trust me, especially if you have more than one dehumidifier. And occasionally, the switch will stick on the dehumidifier (had this happen to me with several different brand units) and the unit will run continuously until water starts overflowing from the tank, all over the floor... so, you definitely want an automatic drainage system in place. Some new dehumidifier models actually come with built-in condensate pumps etc, or you can get external condensate pumps at Home Depot / Lowes, etc.
Old 22nd May 2010
  #20
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Mulmany's Avatar
Tile

666666, The top of the porcelain tile is water tight but the sides and the grout is not. You can try using a grout sealer to keep the moister from seeping though. The sealer is designed to keep the grout from absorbing and therefore staining when you drop food/liquid on the floor. I would suspect that if it keeps the grout from absorbing moister that it will keep the grout from giving up moister. You will want to put down several coats so that it penetrates deep into the grout.
Old 22nd May 2010
  #21
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Quote:
Originally Posted by once a roadie View Post
I think 666666 is onto something here with building the walls within the walls...

any comments from pro designers on this idea?

I'm thinking of doing the same!!!
If you have the space to lose and you want to do it then go for it -it makes a ton of sense if you have anything around the perimeter of the room that you might need to access one day but for the purpose of humidity control? Sorry - it doesn't gain you anything -

Nor would I recommend building a plastic wrapped box and then dehumidifying the interior.......


666 notes:

There IS a slight musty odor inside the service gap and he still has to deal with moving some air in through "gap"

Air can be run through the gap whether it's 1" or 18" - next - if humidity levels are as high as all that in the rest of the basement - then you have a room that is fine - and a basement that will have mold in it (the musty odor is the first sign).

The first attach should be to identify the source of the moisture (in some cases it is just the humidity levels of the outside air - and nothing to do with water issues i around the building) - remember - in the summertime (which 666 noted as when he would have to run the humidifier constantly) the outside air is hot and moist - and the temperature in most full basements would be around 50 to 70 depending on the location - and when hot moist air get cooler the relative humidity rises (same grains of moisture in a smaller area in volume (air expands when heated and contracts when cooled).

The correct answer is not to use special materials that will not support the growth of mold - especially seeing as the remainder of the construction they are hiding will - it is not to dehumidify one are and let the rest have their way - the answer is to maintain the entire area surrounding the room (so the whole basement) at a healthy humidity level - which will make it impossible for any room within that area to achieve a humidity level above the remainder of the space........

Rod
Old 22nd May 2010
  #22
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Hi Rod -

Sorry, I got lost on your last paragraph. If you ever get a minute to clarify that would be greatly appreciated.


"The correct answer is not to use special materials that will not support the growth of mold - especially seeing as the remainder of the construction they are hiding will - it is not to dehumidify one are and let the rest have their way - the answer is to maintain the entire area surrounding the room (so the whole basement) at a healthy humidity level - which will make it impossible for any room within that area to achieve a humidity level above the remainder of the space........"




thanks
Old 23rd May 2010
  #23
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I think what Rod might be trying to say is, control the humidity of the ENTIRE basement, not just a small inner portion only.

But the problem here is, in some or many cases, it is not practical to do the above.

I suppose if I removed all the earth from around the outside of my foundation, wrapped it in some type of moisture proof layer, then back filled with sand with drainage pipes below, maybe even with pumps and vents below etc, then strategically landscaped the top of the earth to push water away, etc ,etc, etc, I would perhaps not have serious humidity problems in the basement at all... and the entire basement would be controlled without having extra vapor proof walling in "front" of the concrete foundation walls.

But the reality is, if you have an existing structure surrounded by nice trees, landscaping, walkways, driveways, AC compressors, etc, it would be incredibly expensive / impractical to tear it all up just to deal with foundation vapor issues. I guess the point could be argued either way. What will I pay in electricity costs for dehumidifiers over the next 20 years? Maybe I SHOULD tear up my property now and do it "correctly"...? Or maybe I'll move in 5 years and thus such a massive project would prove to be a huge waste of money... a potential buyer of the house will not care whether or not I spent many thousands of dollars fine tuning my basement vapor issues. That money would never be recouped. Plastic sheeting along interior basement walls on the other hand is pretty cheap.

As Rod mentioned, one great reason for a service gap is to access things along the foundation wall (plumbing, electrical wires, AC cooling lines, etc)... for this reason I am happy to have it, I very much like being able to easily access and inspect all these things without ripping walls down... but I suppose if you really do not need a "service gap" and do not have the real estate to sacrifice, then perhaps you need to look into more extensive options.

I am 100% totally into the idea of digging out a foundation and doing it "right"... one of my neighbors back in Queens did this, he had a small house and he was digging for months, I've never seen a human being work so hard, then he coated his foundation with something, not sure what, tar perhaps, whatever... but this guy had the space and had the time... many others do not. Again, it's a practicality issue, situation dependent... choose what's best for you.

What I think is a bad idea personally though, is to have a basement that has NOT been treated properly from the outside, with high humidity levels, and then put up walling directly on the concrete foundation walls, with little or no space, light or airflow. This will lead to almost guaranteed mold issues behind the walls, possibly dangerous ones. It'll be in there and you won't know it until it becomes a serious problem. A "service gap" provides light and airflow, plus you can inspect this area any time, clean it, paint it, air it out, whatever. If a problem forms, you'll see it right away.

My dream is to build a custom building from scratch one day and truly do everything correctly... from scratch. That's the RIGHT way to do it. Trying to "improve" existing older structures can sometimes not be practical or cost efficient, again, it depends. If I live long enough and become really successful, I'll buy some nice property and plan on building a custom building / studio from scratch... and I'll give Andre, John Brandt and Rod a call first to make sure it's all planned out properly. But one step at a time, first I need to go practice my scales. heh

Side note... the RH in my basement right now is about 65% (and about 60% outside), but I am able to maintain 45% in my one porcelain tile floor basement room (which is pretty big). Yes, the dehumidifier has been running a lot, but not continuously... but maybe more than I'd like. I have to remember that it's a pretty big room, total square footage about 500 sq/ft or so... and the dehumidifier is not even that big... and there's actually one wooden door with no seals facing a humid area, have yet to seal that up and vapor-proof... so maybe I'm just being a baby, the fact that I can hold a steady 45% down there now is not bad, and it feels nice, cool and dry, zero musty odors, etc. It's "working" at the very least. How much electricity will I eat up on dehumidification over the next 5 or 10 years...? Probably not more than if this was an above ground room running an air conditioner. Somehow, if you're in the north-east, you have to pay to play no matter what.... extreme heat, extreme cold, extreme humidity, we got it all!!!

Old 23rd May 2010
  #24
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Quote:
Originally Posted by 666666 View Post
I think what Rod might be trying to say is, control the humidity of the ENTIRE basement, not just a small inner portion only.
I understood Rod to be suggesting that if you control the humidity in
your service space, you'll automatically control it for the room inside
that space. Where is your dehumidifier ?

If you have cold winters you must be losing a lot of heat through the
foundations if they aren't insulated. Where I live I'd have to insulate
the foundations before a service space so I wouldn't have the possibility
of seeing what's going on between the insulation and the foundation
anyway.

But access to the backside of the interior wall would still be a great plus.

Paul P
Old 23rd May 2010
  #25
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Quote:
Originally Posted by PaulP View Post
I understood Rod to be suggesting that if you control the humidity in your service space, you'll automatically control it for the room inside that space. Where is your dehumidifier ?
I agree. This is what I meant.

The whole problem here as I see it is insulating the concrete foundation wall from moisture. There seems to be no good, easy way to do this other than truly attacking the problem from the outside (digging out the foundation, installing drainage, pumps, vents, etc, huge expensive job). Or, some folks put some type of barrier over the concrete walls on the inside, but this can trap moisture, no light, no airflow, and thus almost guaranteed dangerous mold problems.

One of the main reasons I came up with the "service gap" idea was that it allowed me to INSULATE my living space room very well (framed walls with 6 mil plastic sheeting, and also R-15 batt insulation), while not having to cover up any of the concrete foundation walls. The "service gap" design allows light and air movement.

If I were to put a dehumidifier in the service gap area, it would run continuously day and night and would barely be able to make a dent in the RH since the vapor is just pouring right through the concrete walls / floor. However, when I put a dehumidifier in my insulated living space (inside the plastic wrapped room), the dehumidifier is able to reduce the RH and keep it at a relatively low desired level.

As far as heat... even in the dead of winter, my basement has never gone below maybe 48F degrees. My new rooms are all fully insulated with R-15 in the walls, these rooms hold heat very well. The service gap should never go below 48F degrees, and there's no wind in there, so the interior basement rooms should be VERY easy to keep warm. I'm already considering spending a lot of time down there when it's extremely cold out, I can turn down the thermostat on my above ground rooms and enjoy staying warm with very little fuel oil being used in the tight, well insulated, underground rooms.

In a perfect world, the "service gap" area would be treated for humidity and insulated. A lot of folks like to coat their concrete foundation walls (inside) with "moisture blocking paint", I'm not sure I'm sold on that idea, I've heard a lot of horror stories, maybe the stuff they sell now is better than in the past, I've heard a lot of reports of the stuff basically not working, peeling off after a while, etc. And there are articles that state that it's not a good idea to trap moisture in concrete anyway, it's not good for the concrete, breaks it down, etc.... not sure how true that all is, but that's what I read. Due to the assorted uncertainties about moisture blocking paint, I decided instead to just leave the concrete foundation walls ALONE (can't go wrong this way), create a service gap and frame walls with 6 mil plastic to be a 100% effective and reliable moisture barrier.

All basement rooms should be completed and will be in service before the summer is over, I'll report back on how it all goes. In August I expect to see RH of up to 85% in the unfinished areas of the basement, we'll see how the finished rooms hold up, how much the dehumidifiers need to run, how much, if any, mold growth or moisture related issues exist in the service gap etc. I'd say that if I am able to keep the finished rooms at 45% without having the dehumidifiers run 24/7, and if I do not observe any severe mold / mildew activity in the gap etc, then my "service gap" idea will have proven to be a success. At the very least it's a "poor man's" way of dealing with basement humidity... again, when I'm ready to build a new custom house / studio from scratch (right now only in my dreams), at that point I'll do things "right" and build a "moisture-proof" foundation system.
Old 23rd May 2010
  #26
SAC
Registered User
 

This topic is really not difficult to address. But I get the feeling that the wall itself and any appropriate treatment is not the source of what the 'problem' has become!

Thus far:
There is no immediate ingress nor externally applied water pressure, simply the movement of humidly through a masonry wall from an area of higher ambient humidity to an area of lower ambient humidity - and in this case, the movement is further driven by the humidifier that reduces the humidity level inside as there has been no barrier established between the outside and the inner space.

The problem: lack of a moisture resistant seal on the porous wall.

OK, you can build beau coup interior walls (for whatever additional practical use you like) and place plastic vapor barrier on the interior wall studs, etc., but in the end you will have only limited how far into the room the humidity will penetrate. But you will have done nothing to mitigate the fundamental ingress of the moisture through the existing wall. To me that is not much of a moisture solution.

And as noted, simply creating an additional sealed wall inside the room and running a humidifier in the gap will do nothing but exacerbate the movement of moisture into the space! Read up on the 'laws' regarding diffusion (not acoustical!) and of the subset regarding partial pressures!

If there is no hydraulic pressure on the exterior wall surface - meaning no water is actively trying to penetrate through the barrier, you can go so far as to apply similar mastic based waterproofing on the inside wall as is often applied on the exterior to waterproof the foundation; or for that matter, you can simply any of a multitude of reliable hydraulic waterproofing materials that effectively seal the wall relative to the ingress of moisture.

This is a relatively easily solved problem if there is no hydraulic water pressure driving the ingress!

Then you can simply paint or construct virtually any interior wall you like.

This has been suggested already by several persons, some of whom are 'experts' in this area, but for some reason some wish to simply avoid addressing the fundamental source and would rather continue to treat this more as an emotional issue.

Moisture ingress is neither new nor a mystical science, and every major city has several qualified engineering firms that specialize in just this issue! If this is such a complicated issue and the basic proven suggestions are not adequate, cut to the chase and contact them for an opinion. But I will also suggest that if you tell them that the problem is simply humidity with no external source of actual water, that they will tell you basically the same thing some here have told you - barring access to the exterior surface, apply an appropriate internally applied waterproof sealant - and deem it not even necessary to come out.

Then you can begin to think about acoustical treatment.
Old 23rd May 2010
  #27
Lives for gear
 
Rod Gervais's Avatar
 

Quote:
Originally Posted by SAC View Post
OK, you can build beau coup interior walls (for whatever additional practical use you like) and place plastic vapor barrier on the interior wall studs, etc., but in the end you will have only limited how far into the room the humidity will penetrate. But you will have done nothing to mitigate the fundamental ingress of the moisture through the existing wall. To me that is not much of a moisture solution.
This concept is not quite right either - no one has completely (at least to my satisfaction) proven that the moisture is migrating through the concrete wall.......

the fact that there is no water issue mentioned as entering the structure during rainy periods suggest that the outside of the foundation is indeed properly waterproofed - and note I said "suggests" - however - let us for a moment assume that the foundation itself was sealed in such a manner that it was physically impossible for moisture to migrate through it's walls........ would this solve the problem?

The answer (UNFORTUNATELY) is "no"

Sealing a foundation is a great way to deal with water penetration, but has little (or nothing) to do with a non water problem, and the reason for this is due to the construction of the rest of the building.........

You have a foundation - on top of this foundation (best case) is a piece of sill seal - to stop the free passage of air beneath the sill, then a wood sill, on top of which rests an outside member which is typically the same member used for the floor joists.......

Beneath the sill is not sealed against the passage of vapor - nor is the wood itself - so even if the concrete will not allow the passage of the moisture through it's body - the warm moisture that exists in the summer can still enter the basement - and once there it can still condense on the cooler surfaces of the concrete, and can still raise the humidity levels of the basement.

We dig up around buildings to handle issues with water entering basements - and sometimes that doesn't even get the job done (if the problem is with the level of the ground water table, sealing the foundation will not solve the problem) but when this is not an issue we deal with humidity levels by installing dehumidifiers............

One suggestion - and that is - if your humidifier is running 24 hours a day during the summer - then your unit is way to small to do the job......

You need to invest the money required to purchase an unit large enough to dehumidify the space quickly - and then you are maintaining the humidity rather than running a race trying to keep up with it........ with energy star rated equipment of the correct size - the cost of operating the equipment should not be an issue.......

Rod
Old 23rd May 2010
  #28
SAC
Registered User
 

A good point.

All of this points to the value of determining the actual source of the moisture. From there, an appropriate solution is much easier - than speculating endlessly over what might be the nature of the problem.

If he is simply dealing with ambient relative humidity in the house from the sills, it might be withing one's means to apply an exterior vapor barrier under exterior trim (depending upon the construction. Such surfaces as lap siding, etc. can be removed and reapplied rather easily - whereas such a finished surface as brick would be prohibitive. And if he owns the home and are planning to stay there, this might be a more expedient route to take as it would pay for itself rather quickly compared to the ongoing operation of a dehumidifier for an ongoing indefinite period of time.

Otherwise, if the moisture continues to ingress, instead of a dedicated dehumidifier, one might simply include an air return and vents for the air conditioning system in the basement as well as the rest of the house. A reputable HVAC firm should be able to easily configure such a system (including any necessary changes to the system assuming the new load).

If the humidity is entering via the rest of the house, it may seem a bit damper due to the cooler temperature in the basement, but the relative humidity will be approximately equal throughout the house if it is diffusing into the basement. But then one wonders what the air conditioning system is (not!) doing in the upstairs if it is not sufficiently mitigating the humidity prior to it becoming excessive prior to its diffusion into the basement if it is not coming from out of doors. And in that case, the upstairs has the same potential issue with mold as does the basement.
Old 23rd May 2010
  #29
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Rod Gervais's Avatar
 

Quote:
Originally Posted by SAC View Post

If he is simply dealing with ambient relative humidity in the house from the sills, it might be withing one's means to apply an exterior vapor barrier under exterior trim (depending upon the construction. Such surfaces as lap siding, etc. can be removed and reapplied rather easily - whereas such a finished surface as brick would be prohibitive. And if he owns the home and are planning to stay there, this might be a more expedient route to take as it would pay for itself rather quickly compared to the ongoing operation of a dehumidifier for an ongoing indefinite period of time.
Be careful with this sort of advice - because it is location sensitive...... in the wrong location it can cause more problems than it solves..... 6's location is one of those places........

He is located in NY - which (as he mentioned) has it all - hot summers - freezing winters - and it is the freezing winters where the problem begins.........

In the summer all of that humidity wants to come from the hot outside air into the cooler inside - thus the migration is from out to in.....

But - in the winter the exact opposite is the case...... the inside air is warm - the outside air freezing- and the migration is from inside to out - which is why in the northeastern US vapor ******ers are always placed on the inside of the structure - in fact they are mandated to be placed there by code....

If there exist on the outer face of the structure the moisture will hit the cold surface - reach dew point and condense - and THEN you are going to develop some problems, besides mold you will develop structural damage as the sill, box and joist begin to rot away.......

it is very difficult in the northeast to handle moist basements without dehumidification.

Quote:
Otherwise, if the moisture continues to ingress, instead of a dedicated dehumidifier, one might simply include an air return and vents for the air conditioning system in the basement as well as the rest of the house. A reputable HVAC firm should be able to easily configure such a system (including any necessary changes to the system assuming the new load).
Assuming that one has a whole house HVAC system - and that the Fan Coil Unit is located in the basement - and that the unit is oversized to begin with - this might well be a viable alternative....... but - assuming that everything else is in a workable position - if the unit is sized properly - necessary changes to the system would include a new fan coil unit and a new compressor unit - hardly a cost effective solution...... considering that cost along with the cost of the ducting - you can run a dehumidifier (which is all the cooling coil is doing) for a real REAL long time.........

Think about it - what is a dehumidifier?

It is a small HVAC unit - it has a compressor - and a cooling coil - it circulates air through the coil - and when the air is cooled the warm moisture condenses - exactly the same as air conditioning - except cheaper to operate because it is not trying to cool the entire space - just a very small piece of it in order to lower the humidity level in the space. Longer run times for the compressor actually lower operating costs because the largest expense of operating the compressor come at start up time.


Quote:
If the humidity is entering via the rest of the house, it may seem a bit damper due to the cooler temperature in the basement, but the relative humidity will be approximately equal throughout the house if it is diffusing into the basement. But then one wonders what the air conditioning system is (not!) doing in the upstairs if it is not sufficiently mitigating the humidity prior to it becoming excessive prior to its diffusion into the basement if it is not coming from out of doors. And in that case, the upstairs has the same potential issue with mold as does the basement.
I doubt very much that the humidity is entering via the space above - one of the reasons that we put vapor ******ers on walls but NOT on ceilings is because we want the vapor to enter a well ventilated attic - where it will then be mixed with outside air and leave the structure - I would be very VERY surprised to find that the house above was the source........

Also, the dehumidification of the upper level would insure that it was always the lower pressure zone - it would work against what ever enters that area from migration through cracks and crevices in doors, windows, the outer wall assembly and the basement..........

Rod
Old 28th May 2010
  #30
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666666's Avatar
Thanks Rod. Indeed it seems that the humidity is getting into the basement via the air, not necessarily through the concrete walls. I say this because when there is a spike in outside RH, there is a spike in the basement RH as well, and vise-versa... the basement RH seems to follow the outside ambient RH quite closely and quickly.... just noticed this over the past week or so. This would indicate that the humidity issue I have in my basement is due simply to ambient RH and not necessarily moisture issues from the concrete walls. Though I'd bet there is a bit of moisture coming in through those concrete walls too, probably a little bit of everything going on. But the walls are never "wet" and thus likely not the main issue.

I forgot to mention that my basement is lined with all sorts of things that cannot / should not be covered up with insulation, or would be hard to place insulation behind or near... such as waste pipes, water pipes, electrical wires etc, fuel oil tanks, furnace, AC cooling lines, etc... on the concrete walls and also up in the first floor plate area. As well, I plan to leave about 25% of the basement unfinished anyway, simply do not need it finished, no need to spend money dehumidifying, this space will be a workshop, opens to the garage... so with all this in mind, you can see why I came up with the idea of building insulated, isolated rooms within the basement and insulating / conditioning them only, as opposed to attempting to seal up the entire basement... what I have done is built up only the square footage that I need finished so I am not conditioning more than I need.... and not covering up important aspects of the building that may need to be accessed, such as pipes, wiring, etc.

The other night it was about 88% RH outside and 85% RH in the basement... and only 68F degrees (in the basement), extremely uncomfortable... you start to feel totally wet and sticky within minutes without even moving. But my one currently finished room in the basement, which has a dehumidifier running within, was about 48% RH but also 68F degrees.... wow, what a difference, it feels much colder (even though the temp is the same), and by comparison is EXTREMELY comfortable. The one "small" dehumidifier that I have in that finished room is actually doing a great job of keeping the room dry the more I think about it, and it's running maybe 60% or 70% of the time and filling it's tank (about 50 pints) maybe once every two days at this point... and the RH in there is at a rock solid 48% - 50% as measured at the opposite end of the room as the dehumidifier. Not bad for a room surrounded by an ambient RH of 85%+.

But I did notice that the basement RH goes up much faster than the RH of the first floor of the building (above ground), and that's with no conditioning on the first floor. When it was 88%+ outside and 85%+ in the basement, the first floor didn't get much above 65% surprisingly... and then I turned the central AC on at that point anyway. Then again, the building does have decent insulation, Anderson windows etc all around, etc...

But one key difference between the basement and first floor of course... the basement is lined with "cold" concrete walls and no direct sunshine. As Rod mentioned, warm moist air hits the cold concrete and condenses, perhaps raising the RH even higher, where as the first floor structure consists of above ground wood framed walls getting beaten by severe sunshine, these hot, "dry" walls may even help to reduce RH perhaps, in theory anyway.

All interesting stuff. But yeah, around here, the RH is a roller coaster ride... and in the summer it can get very high. Based on my observations so far, I should be able to keep all my basement rooms at a solid 50% RH with just a few 50 pint dehumidifiers running and ductless split ACs. Right now, my one existing basement room, at 68F degrees and 48% RH, is the most comfortable room in the whole building. I cannot get the first floor to stay that cool no matter how hard I try, the vaulted ceilings in direct sunlight kill me, even with a new dual compressor heavy-duty central AC system. The basement may wind up becoming the most desirable place to hang out in the whole building ironically.

And I bet the basement rooms will be super easy to keep warm in the winter also, will likely be nice and toasty in there being that the surrounding air temp never goes below about 48F degrees in the dead of winter, and no drafts, as opposed to the first floor above ground rooms that are sitting up there in the freezing cold harsh wind with outside glass and a measly R-13 in the walls etc. Damn, I may just move into the basement and abandon the first floor! Probably save well over 60% in heating / cooling costs while being more comfortable.

Anyway.... it seems that everything Rod mentioned is correct per my observations so far. All interesting stuff. Yeah, my region is a pain, if you're not heating and humidifying, you're cooling and dehumidifying, and the times when you can actually just open the windows and not have to condition, there is a severe pollen problem, forces you to keep the windows shut tight and condition anyway.
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