Best way to insulate basement wall?

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Old 01-18-18, 08:03 AM
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Best way to insulate basement wall?

Hey guys, I had some water damage ruin my basement wall. It had the pink stuff insulation before. What's the best way to insulate this other than spray foam. Can I use Ridgid foam? and do I need any vapor barrier behind the studs? If I use ridgid foam I would have to cut and cobble it it, since there isn't that much room between the studs and foundation.
 
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Old 01-18-18, 09:18 AM
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Given that you have the studs up already, I would go with Roxul. No vapor barrier but an assumption that you have all water problems resolved.
 
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Old 01-18-18, 09:40 AM
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So put the Roxul right against the concrete? And does it fit behind the studs?
 
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Old 01-18-18, 11:31 AM
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I'm not seeing any room behind the studs. If there is, then rigid foam might still be a good option.
 
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Old 01-18-18, 12:24 PM
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I have about an inch between studs and concrete. Should I use a 1" ridgid foam?
 
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Old 01-18-18, 12:48 PM
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I'd wait for Bud to chime in - the foam needs to be thick enough to form a thermal break to prevent the formation of condensation. He has the chart that says how thick the foam needs to be based on your location. What town/province are you in?
 
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Old 01-18-18, 12:55 PM
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I'm located in Toronto, Ontario.
 
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Old 01-18-18, 01:30 PM
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1" rigid behind the studs would keep them away from the concrete. Bottom plate should be pressure treated. If you are getting this inspected they may want that replaced if not. Not familiar with codes in Canada but they seem to want a vapor barrier over the concrete. Rigid might be acceptable or may still need the plastic covering.

As for how much rigid foam is needed I have no guidance from Canada but if we look across to Michigan we see climate zones 5 or 6 and they want r-5 or r-7.5 respectively, this link.
Calculating the Minimum Thickness of Rigid Foam Sheathing | GreenBuildingAdvisor.com

Now, that link is discussing an exterior rigid layer over an entire above grade wall. Some portion of your foundation is below grade and above grade we should be able to include the foundation itself. But logic rarely works on code officials.

Bottom line, IMO, slide the one inch rigid behind the current studs and install 3.5" Roxul then your drywall with no vapor barrier. Prevent all inside air fron getting through to the concrete.

Bud
 
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Old 01-18-18, 05:21 PM
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I did some measurements and I actually only have one or two studs that have 1" space between stud and concrete.

What can I put behind the studs with such a small gap?
 
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Old 01-18-18, 07:22 PM
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If you can't move the wall then fanfold is the thinnest I know of.

Bud
 
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Old 01-18-18, 07:31 PM
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Could I put something just to cover the back of the studs then cut and cobble Ridgid insulation? If so, what can I do to prevent moisture getting to studs?
 
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Old 01-19-18, 01:51 AM
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install 3.5" Roxul then your drywall with no vapor barrier. Prevent all inside air from getting through to the concrete
Water vapor moving to and from a basement wall is not the problem, it's when it gets trapped and can not be controlled (like using plastic) that causes problems.

What nobody has asked and you did not clarify, what was the initial water issue?
 
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Old 01-19-18, 03:29 AM
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The water issue was a broken dishwasher that leaked water into my basement. The foundation itself has been dry for the couple months that it's been exposed.
 
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Old 01-19-18, 09:49 AM
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So you've got the proof you need that you dont need to go to the extreme of installing foam insulation.

I am not knocking that process but it's very expensive and is not the ultimate requirement for a basement. Personally I would never go that route, just re insulate and wrap it up!
 
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Old 01-19-18, 10:30 AM
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Thanks Marq1. Sorry for all these questions. Last one I promise. So I can put Rockwool Comfortbat right in-between the studs touching the foundation and then put a vapor barrier over top? or put Ridgid foam between the studs without a vapor barrier?

So no need to worry about the studs being covered from the back?
 
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Old 01-19-18, 01:57 PM
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Marq1 and Stuspick, one of the purposes of the layer of rigid is to ensure that the first surface any basement air can contact will be above the dew point. Fiberglass insulation being very vapor open lets the air go right through and develop moisture at the wall surface. Roxul is much denser but still vapor open so a layer of rigid would still be recommended.

Because we can't start this project from scratch we are left with almost no space behind the existing studs. Here the issue is untreated wood in contact with the foundation. By installing a thin layer of insulation, like sill seal, behind each stud that problem can be eliminated except for the bottom plate.

If 1" rigid were cut and fit between all studs and caulked to prevent any basement air from reaching behind it most of the objective would be achieved. With the cold surface eliminated you could use fiberglass or Roxul. With the loss of 1" of depth the fiberglass might fit better but peeling some off of either will help.

Unknown whether this approach will meet Canadian codes and unknown whether an addition of a vapor barrier would be required. Current guidance would say not (US guidance).

Bud
 
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Old 01-19-18, 04:10 PM
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But, the OP has not experienced any issues with vapor transfer, he had a dishwater leak., so why reinvent the wheel.

Sealing up the concrete wall is fine or you just allow the water vapor to move through. around, or over the stud wall (which is how I control vapor) and address with adequate ventilation and/or dehumidification.

There is never a moisture problem until the vapor is trapped and pools.
 
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Old 01-19-18, 05:33 PM
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Marq, "There is never a moisture problem until the vapor is trapped and pools."
I agree and I like the 1" pink or blue as it has enough permeance to all some drying to the inside. They are vapor retarders as opposed to vapor barriers.

There are two sources of moisture, through the concrete (always present) and from the inside air. The one inch of continuous rigid is a very good solution for both, preventing condensation by ensuring the first inside surface and basement air can contact will be above the dew point yet allowing some drying.

Unfortunately Canada doesn't agree with the drying to the inside and insists on installing a vapor barrier, although I don't know where they want it, against the concrete or out under the drywall.

Bud
 
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Old 01-20-18, 05:03 AM
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The one inch of continuous rigid is a very good solution for both, preventing condensation by ensuring the first inside surface and basement air can contact will be above the dew point yet allowing some drying.

And again I am not disagreeing with the concept of using foam, BUT it is not a necessity. Should the OP tear out the wall, or the entire basement to change something that is not an issue he is experiencing?

II suspect you know what my answer is!
 
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Old 01-20-18, 06:12 AM
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Thanks everyone for all your help. Since I don't see moisture issues could I just put the roxul between the 2x4s without touching the concrete, then vapor barrier, then drywall?
 
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Old 01-20-18, 03:17 PM
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could I just put the roxul between the 2x4s without touching the concrete, then vapor barrier, then drywall?
Skip the vapor barrier of if it's faced make cuts.
 
 

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