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Basement Insulation / Steel framing and electric done - need help


dbldown768's Avatar
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10-22-12, 03:53 PM   #1  
Basement Insulation / Steel framing and electric done - need help

As a first time DIY basement, I have been working on finishing my basement for almost a year. I have steel studs and tracks up for all soffits and walls. I have already run electric for lights and outlets thought the studs. I was getting to the point of insulation. I originally thought about using spray foam insulation, but with a price tag of $1800, I wasnt sure i wanted to put all my money into this system. The biggest concern with this system is the fact that some people suggest they can smell the foam in their house and it has ruined it for them. Also i dont understand how the slab of the floor isnt going to let in moisture. I don't plan on having XPS on the floor and then a subfloor.

Because I am limited with what I can do with the walls and electric already in place, about the most I can do outside of spray foam would be to use fiberglass insulation with kraft or foil backing or slide in 1/2" sheets of XPS behind the wall. I was leaning towards the 1/2" XPS behind the wall, but it is my understanding that in zone 5 of IL, that 1" at 5 R value is required?

Is it worth putting in the 1/2" or do i really need 1"? Do i even bother with this approach or just go with batting? I cannot tear down all the walls, it would be way to much to start over again. what about a product like Roxul

 
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10-22-12, 04:34 PM   #2  
The biggest question is moisture/water? If the foundation was never constructed to be water resistant, and very few are, then you must (repeat must) plan on dealing with the moisture after it gets through. That moisture comes in 2 forms, water and water vapor. If you have or had water at any time, simply covering the walls without solving the problem is not advisable. If the soils outside are moist, you can grow grass, then that moisture will constantly be migrating through the foundation into that basement. Allowing it to continue through your new walls and evaporate inside the basement prevents it from accumulating behind a vapor barrier and causing problems. Dehumidification may be necessary in summer months, but better than mold.

Now, tell us about any moisture issues and we can continue.

Bud

 
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10-22-12, 05:11 PM   #3  
the house was built in 2005. it has 9' ceilings in the basement with the majority of the basement below ground. There has been some moister issues in the past with water coming over the sill plate. This moister would show some damptness on the wall. This issue has been address by lowering the soil along the foundation so that you can see approximately 4" of foundation. Other then the grading issue outside, there has been no other issues of moister in the basement.

Assuming that these issues have been address what would be the best approach to this problem. I simply cannot redo every wall in the bsement. the bottom steel tracks have been shot in the concrete slab. The walls are plum and straight and have between 1" to 2" space behind the studs. The biggest problem is trying to wedge the XPS behind them. Not only that i would have to wedge them behind it and somehow get glue on there as well.

Obviously my biggest concern is mold. I have family/friends that dont think FG batt will be and issue, but i know that can't be correct. My assumption is just that people dont realize mold might be behind the walls because no one looks. I would like to avoid the 1800 price tag not only because the money but for any possible health / allergy reasons. I know they suggested they are formaldehybe free, but talking to these foam contractors is worse then buying a car

 
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10-23-12, 05:17 AM   #4  
An 05 home has a better chance than an 1805 home in terms of maybe they tried to seal the outside and maybe they got the drainage right. The low free board and water over the sill doesn't sound like good planning as there should have been a minimum requirement, plus some slope out from there. Remember, frost can lift the soil 4' out up about 6" when it has a mind to. The soil next to the house will lift less now, but more after you insulate. Less heat, more frost.

You mentioned 1" with r-5 being required, is that in your codes or just the recommendation for your zone?

The most critical part of the foundation is the exposed area plus about one foot below. When someone cannot insulate everything, I advise just doing the upper portion. In your case, focus on the upper 4' and do your best below that. A 1/2" of foam may not sound like a lot, but sure better than nothing. If you have to cut and fit the foam into place, just seal the edges and get as close of a fit as possible.

You mention Roxul and although I have never tried it on a basement, worth considering. Check their web page.

IMO, if you can cover the wall with as thick a rigid foam as possible, and then fill with Roxul, you should be good to go. Recognize my experience with Roxul is limited. but it is very dense and will limit any air circulating and depositing condensation from the conditioned side. Cold walls and warm moist air can also provide moisture.

I added a link below and it has several other links listed. Photograph #5 will show you what happens with fiberglass when things go wrong and someone looks.

RR-0202: Basement Insulation Systems — Building Science Information

 
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10-23-12, 06:13 AM   #5  
Thanks! Part of the drainage problem was with the previous owner and the landscaping that was done in the front of the house. To large of a retaining was was build that trapped soil above the weep of the brick. This has all be fixed this summer after water was seeping in the front of the house.

I am not sure what exactly is code in my zone. I have looked and read on that building science articles about basement many times over. They suggest XPS foam, but they never suggest how much is really required for a vapor retarder. All i know is that in chicago is a zone 5. I'm not sure what exactly that means.

I think I could manage to cover all the walls in 1/2" xps and tape or great stuff around any areas. Its only an R-3 insulation, but as i stated before, i have more of a concern with mold then the issues of heat down there - the temperature stays pretty constant.

I dont know anything about roxul, except reading it from people on this site. If i had to rank the best ways to go about finishing the job based on your feedback i'm guessing it would be the following:

1. spray foam (walls and sill boxes)
2. 1/2 xps foam, great stuff, roxul
3. 1/2 xps foam, FB batt???

Also, couldnt the same theories be true for the basement slab. What i mean is, i planned on putting down carpet in a section of the basement floor. The padding will be on top of the slab with the possibility of growing mold? Or will there be enough circulation of air to prevent the carpet from holding moister.

 
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10-23-12, 08:11 AM   #6  
Way down south is Zone 1 and Alaska is zone 8, I think. So you are in cold country, but not the arctic .

There is a ratio between the rigid insulation that stops air flow and the fiberglass that ensures the surface of the fg will always be warm enough to not form condensation when inside humid air finds its way in through that insulation. Roxul helps because little if any air can get through.

Since you have very little exposed foundation, use the 1/2" and then Roxul at the top and 1/2" and fg for the rest. Do check to be sure Roxul is happy being used in a basement wall. I think it is.

For the floor, there will be moisture coming up through as well. Carpet pads can be food for mold, so more reading as there is a wealth of info on basement floors. The elevated drop in floor squares may be best and since you have plenty of height, no loss.

One more. Spray foam has a problem at the rim joist of encapsulating the area the termite inspectors want to see.

Bud

 
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10-23-12, 08:15 AM   #7  
The following quote was from another person. Does this make sense?

"I'm sorry to hear about your cart-before-the-horse problem. As you now realize, you should have installed a thick layer of rigid foam on your walls before you began installing your steel framing.
You won't get much thermal benefit from 1/2 inch of rigid foam. I don't recommend the installation of air-permeable insulation products like fiberglass batts or Roxul, because these types of insulation can allow warm, humid interior air to contact cold concrete (or the relatively cold surface of a thin layer of 1/2-inch rigid foam).
Here are your choices:
1. You could bite the bullet and pay for spray foam. (Even if you install spray foam, however, your steel studs are much too close to the concrete. You really want to have enough room for a thick layer of insulation between the cold concrete and the steel studs, which are conductors.)

2. You could disassemble your stud walls and insulate with a layer of rigid foam. Then you can put your stud walls back up."

"You are in climate zone 5. The minimum code requirement for basement wall insulation in your climate zone is R-10. That means at least 2 inches of XPS.

Your steel studs are much worse thermally than wood studs; they act like radiating fins, conducting heat through any insulation you install between them.
Somehow, you need to get at least 2 inches of foam insulation between the back of your steel studs and the concrete wall, or it's hardly worth insulating. That is the minimum code requirement."


I would basically have to dismantle everything to start the entire project over

 
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10-23-12, 10:21 AM   #8  
There is a difference between the stated code he is quoting and the code your jurisdiction is following. Always follow at a minimum what your town requires.

Now, as you said, two issues, heat loss and mold. Yes 2" is nice, but for the exposure you have, 1/2" would be an improvement over an 8" concrete wall which is rated at about r-1. The real issue is probably those steel studs and not forming condensation on them or the sheetrock attached in the basement. Roxul is extremely dense and I don't believe a much air will be flowing through it. Be detailed when you install it to get it tight together.

On the flip side, the 2" of rigid is much harder for the moisture vapor to migrate through. Your 1/2" (and in some places you indicated maybe 1") will dissipate the moisture from outside right through to the basement as you want. It won't be that much but you don't want it to accumulate in the wall.

If you are so inclined, starting over would be a better job. I'm just trying to make the best of what you have. I have ground off the heads of those nails and pulled up the bottom channel and it really isn't that bad of a job. Use a masonry drill and "tap cons" to re-install and you will avoid the gun. It is not like it is going anywhere. Install a moisture break underneath if they didn't. Then 2" of foam and you are done, as you won't even need the fg and you will have protected those metal studs.

Bud

 
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10-23-12, 10:30 AM   #9  
had none of the soffits, electric been already installed, i would definately consider moving the walls inward. The problem is, the soffits that are attached to the wall would also have to change.

The part i have in question is the 2" of foam. From my understanding here (Calculating the Minimum Thickness of Rigid Foam Sheathing | GreenBuildingAdvisor.com) R 10, 2" of foam is for Zone 7 and 8. I am in zone 5, which if i'm understanding correctly would require 1" foam, R-5. Now if 1/2" is R-3 and 3/4" is R-4, that is pretty darn close to the requirement. Now i understand it isn't was was 'required' but maybe enough to prevent a problem 90% of the time?? I'm just not sure where the R-10 2" foam is coming from. If its the report, the report took place in Minn. which is a Zone 7.

 
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10-23-12, 11:58 AM   #10  
Don't get too hung up on the numbers unless YOUR code requires something specific. There's 2007, 2009, 2012, 2013, and they are working on 2015 I think. In most locations, energy codes are guidelines as there is no national energy code covering everyone.

So what goes with guidelines? Your home. Yours has less than typical exposure. I've worked on basements with 8' exposed to the elements, they need 4", I'm in Maine. Others with barely 3", but dry. They can get by with much less.

Those metal studs will balance their temperature between drywall and heat on one side and 1/2" of foam or more and 8 + inches of concrete. Below grade the temperature doesn't sink like the wind exposed surface so 35 to 40. That means the stud will be warmer and conduce some heat to the above colder areas. Bottom line is $2 a month in extra heat loss for 3 months. Of course that's a guess, but it is no big deal.

Dr, Listiburek just posted a rant about too much insulation causing cold floors BSI-064: Bobby Darin and Thermal Performance — Building Science Information . Yes it was the energy efficient way to go, but warm floors at a minimal added expense was a better choice.

Just so you don't feel bad, I'm in the business and I find basements to be the most difficult area to pin down. On paper it's easy, but in the real world it gets difficult to match needs, desires, money, and efficiency.

I'm not uncomfortable with your reasoning and I'm sure whatever you decide to do it will be fine.

Bud

 
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10-24-12, 07:19 PM   #11  
so i did run out and pick up a bunch of 3/4" insulation to try and retro fit behind it. My friend that helped me get the foam just thought it was going to be a lot of extra work for nothing. he says my basement is dry and because most, if not all walls i'm putting up with have open ends and the top will be open because the drop ceiling that enough circulation would move around to keep mold from growing. That said, neither of us are experts at all in this area.

I guess my question is before i start this task, is will i be doing more harm then good by putting the foam back there? Because there might be less airflow between any FG insulation that gets put in after it, but it will be touching the foam instead of concrete if at all. I just dont want to go through this extra hassle to make matters worse. If chances are better or even the same, then I'm fine with doing the extra work to put this back there.

 
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