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Discussion Starter · #1 ·
I am in the process of hanging insul batts. But I am overly concerned about mold build up behind the wall that is adjacent to the foundation in the basement.


I don't have leak problem, however it is a basement and my average humidity is about 65%. Now closing off a couple of inches of space behind this wall made me think that over time there will be some mold pores build up. Putting up vapor barrier make matters worst IMO.


Any thoughts would be appreciated.
 

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Some years ago we remodeled a basement with minor moisture transmission. I installed a pair of small vents in each stud cavity. One just below ceiling line and one just above base board level. These a small round louvered vents that are normally installed in soffit for roof ventilation. With the correct size hole saw they were a snap to install. We painted them to match the walls and turned the bottom vent louvers down and the top lovers up. This particular install did not involve batts but if I were to use them in conjuction with fiberglass I would also install rafter vents "O/C Raftermates" to keep an air channel open. This was my own preventative trial for a job that had some minor mold involved as an unfinished area. The owners are friends of my wife and I have heard no mention of any problems. We did (as I usually do) bleach the whole job first to make sure any beginning mold was gone.
 

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The proposed solution about venting is a good one IF you don't care about sound transmission. I am about to start construction on my theater and I have similar concerns. I don't have any moisture, but that doesn't mean I won't 2 years from now.


Has anyone tried waterproofing the walls with the appropriate paint before putting up studs, insulation and drywall? There must be a tried-n-true way to handle this type of construction.
 

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Its suggested that when you frame up the interior walls against the foundation that you leave it sticking out about 1". Then when you put in your batts, there should be some space between them and the wall for air to circulate.


DougK
 

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How about spraying the walls, and all sides of the studs with a 15% clorox/Water solution?


A friend was required to pay a Licensed, State Certified Mold Inhibitor Technician $65/hour to spray all of the exposed wood surfaces before the outer plywood, and inner plywoood shear wall and drywall were installed, when he was having his house built .


The Licensed, State Trained Certified Mold Inhibitor Technician showed up with several gallons of Clorox bleach from Costco, and a $15 plastic bug sprayer. My friend said it looked like he was mixing about a 10% clorox to water solution. It took 4 hours to spray all of the exposed wood.
 

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Discussion Starter · #6 ·
Quote:
Originally posted by DougK
Its suggested that when you frame up the interior walls against the foundation that you leave it sticking out about 1". Then when you put in your batts, there should be some space between them and the wall for air to circulate.


DougK
Hi Doug, glad to see you posting.

I felt that the 1" gap only potentiating the mold issue. There must be a way for saturated air to escape, otherwise a gap's only function would be for decoupling structure.
 

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Quote:
Originally posted by DougK
Its suggested that when you frame up the interior walls against the foundation that you leave it sticking out about 1". Then when you put in your batts, there should be some space between them and the wall for air to circulate.


DougK
If you leave a space between walls that is devoid of insulation, doesn't this pose a theoretical fire risk (chimney effect)? I thought that was why you are supposed to frame in horizontal 2x4 pieces between the studs to act as a fireblock. Having a full height cavity behind a wall defeats this.


Regarding mold and moisture in basements, there was a long thread about this a few months ago (see here ). Be sure to read this pdf file . See especially figures 12-14. The consensus from the thread seemed to be to use a variation of extruded polystyrene insulation without a vapour barrier against outside walls below frost line, and polyisocyanurate foam above frost line, as this setup was much less prone to molds than the cheaper and more traditional fiberglass and vapor barrier. Hope that helps.
 

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I check last night and the humidity of my finished basement/HT is about 65%. Is this bad? Is there anything I can do at this point to lower the humidity?
 

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Most people that buy a dehumidifier have a stigma about how long it will run and how many times they will have to empty the bucket. There are homes that require 24/7 operation of a dehumidifier to maintain a suitable humidity level. There is nothing wrong with plumbing a line from the humidifier and letting the thing run 24/7 if it is rated for continuous duty.
 

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usehername

I haven't checked my basement humidity but it feels humid, and lately musty. If I plumb a line from the dehumidifier (need to buy one still) can I run the drain into the sump?...I'm guessing it's probably against code..... My drain to the septic is about chest high, would I need to tap nto the main drain with a pump to get it there? Thanks, I've been lurking awhile and your advice is usually right on track


Jerry
 

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First thing to do is to run it and see how much water you will have to handle. You may only need to empty the unit a couple times a week. Even daily is not a problem for a lot of people. If it is extreme most often it is a matter of a garden hose to a floor drain. I guess it is possible some municipalities might consider it a violation because you are introducing a water source into the treatment plant that you did not pay for. (Most sewage bills are based on water supply usage) I would argue that one but it is a thought. The result water is quite pure however. Anyway if the unit has to be in a finished area where you will spend any time then your concern would be noise and heat. There are some units that are quieter than others. All will produce some heat. Ideally you would keep it with the other utilities if possible.
 

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Thanks..


Sounds like time to research some dehumidifiers. I have my own well and septic so I don’t have to worry about paying for water/sewer, just have to worry about building code. I don't have a floor drain that I can find.


We just bought the house (built 1987) and the basement walls (poured walls) are already framed and drywalled. I will have to tear off the drywall on the 2 exterior walls in the future HT area anyway to pre-wire and insulate. I will definitely check for mold. The thread and pdf file referenced above were a good reads – more research needed, this is never as simple as it seems……


Is there such a thing as “plain†mold and “don’t smell/touch/expose yourself or it will hurt you†mold? Will I need to call in the guys with white suits?

:D


Jerry
 

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PLEASE take time to read the buildingscience site. Putting up a vapor barrier in a basement with fiberglass behind it in the cavity is just begging for mold problems.


The issue is that water vapor will condense as it hits the cold surface. The PDF referenced above talks about ways to minimize this.


Another important step is to control humidity. If your basement is damp/moist then dealing with humidity is key. The Sahara dehumidifier is a much better choice than a standard type - check into it. One link for this is:
Sahara Dehumidifier
 

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Quote:
If you leave a space between walls that is devoid of insulation, doesn't this pose a theoretical fire risk (chimney effect)? I thought that was why you are supposed to frame in horizontal 2x4 pieces between the studs to act as a fireblock. Having a full height cavity behind a wall defeats this.
Ok, I just started to do my basement finally. I first made sure that there was no problems with water seepage. Next I scraped down all the walls to remove anything loose and then went over it with a metal brush. Next I applied 2 coats of dry-loc.


I live the the Midwest and it gets COLD here in the winter so I desided to make my walls a solid 2x4 wide as apposed to using 1x2s against the walls. I felt this would allow me to add full insulation to all the external walls.


Because it’s an old house I needed to measure each and every 2x4 and install them individually. There is a ½ to 2 inch gap now all around the room and I planed on running a 4mill vapor barrier all around the INSIDE of the walls prior to adding the insulation.


This “chimney effect†has me concerned now. Is this something that I need to deal with or not. Any help please?


Ken
 

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I would seem that certain standard home theater construction practices, i.e., using acoustic caulk to make walls airtight, would encourage the formation of mold. In an other thread I was advised to caulk just the interior walls if the climate had a potential for mold.
 

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Just like wooden boat restorers use to treat wood before being painted, you can use a mixture of prop. glycol (anti-freeze) with borax and boric acid. As long as it is not leached out by lots of water, it should last as long as your house.

John
 

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A good site to visit concerning this is doityourself.com. That's where I learned about the techniques that I used to finish my basement. They have a forum dedicated to basements, where this topic is discussed quite a bit. There appears to be a lot of differant opinions on what is right. Also local building codes might have to be followed.


They recommend that as I said you install your framing away from the block 1" to allow airflow behind. Also this eliminates the chances of the studs contacting the concrete walls and possibly rotting. They also recommend that you don't use a plastic vapor barrier over your insuulation before drywalling. Just use a kraft faced batt and drywall over it.


DougK
 

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Sungen99,


Just a couple of points -


Have you / will you be getting a permit for this work? I ask only because of the potential consequences that can arise if the work is done without a permit. Hopefully it won't happen, but should you have a fire in the house, and you have done a substantial renovation without a permit/inspections, the insurance company may be able to deny paying your claim. This does, in fact, happen - after all, an insurance adjuster's job is not to determine how MUCH you should receive, but rather, it is to determine how LITTLE the insurance company needs to pay on your claim.


If you choose to get a permit for the work, the local building/construction official can tell you everything you need to know concerning firestopping regulations (this is to avoid the "chimney effect" you'd mentioned).


In any event, in my basement theater, I built 2x4 walls that are 3/4" away from the concrete block walls of my basement. To satisfy the firestopping regulations, I had to first secure 3/4" plywood to the underside of the ceiling joists from the point where the wall would touch the joists to the sill plate of the house.


Think of it this way - I took 4'x8' sheets of plywood, and cut them into 3 strips that are 16" wide by 8' long. Then, the long edge of the strip was butted up against the edge of the sill plate (the wood that sits directly on top of the foundation wall) and screwed the strip of plywood into the ceiling joist to hold it in place. Then, the theater wall was built in between the concrete floor and the strip of wood. The strip of plywood encloses the top of the cavity between the back side of the new wall and the inside of the foundation wall - so, no chimney effect.


Whether you choose to get a permit for this job or not, I'd strongly recommend that you build your walls in this fashion to help mitigate the risk of a fire spreading rapidly through the walls/floors of your home.


Personally, I get permits whenever applicable - it helps me sleep at night...


Dwight
 

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Thanks for the help here Dwight. I agree that permits are important as they are really only there to protect the home owner from poor workmanship. It’s just that I see all sorts of threads on- use a vapor barrier, don’t use a vapor barrier, use rigid insulation, don’t use ridged insulation.


Its just frustrating. The use of a vapor barrier is required by code for me so that’s a done deal then. but as far as the insulation goes. Well. They ask for a specific R-value but the choice is yours as far as the type. If its bat insulation its must not come in contact with the wall so then the vapor barrier should go on the inside then correct. If it IS rigid then it can go on the outside I guess.
 
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