# Help! Insulating concrete walls with french drains



## simonnyc (Mar 2, 2016)

I am in the early stages of planning to finish my basement. Before I think about framing the walls or anything else, I want to insulate the walls with rigid insulation. The issue I'm having is I have french drains around the perimeter of my basement and am unsure of how to attach the insulation. Everything I have read about installing the insulation is to completely seal off the insulation so air cannot get inside. My dilemma is I am not sure whether or not the insulation should stop above the miradrain board? Or do I put the insulation in front of the miradrain board and extend the insulation all the way to the concrete floor? What is the proper way of installing the insulation? I have attached some pictures for reference.

Here's a picture of what it looks like currently...









Is this the correct way of applying the insulation? (Stop right above the miradrain board)









Or do I extend the insulation all the way down to the concrete floor/lip to seal out any air from getting in?


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## Fix'n it (Mar 12, 2012)

do you ever get water past that type of drain ? looks interesting.

anyway. i would notch the botttom of the rigid so it goes on the wall flat and over that drain thing to the floor. glue that to the wall. frame on top of that and with roxul. use 2 bottom plates. don't put the drywall over the very bottom plate.

NO OPEN AIR !


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## simonnyc (Mar 2, 2016)

@fix Thx for the reply. In the 3 yrs that I've been living in the house, the basement has been bonedry. I should mention I have 2 sump pumps in the opposite corners of my basement. when I look down the sump pump hole, i can see a drain pipe that feeds into the sump pump pit from the perimeter drains (about 12-18 inches deep).

What do you mean by "don't put the drywall over the very bottom plate"?


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## Windows on Wash (Aug 30, 2011)

I would also add to put some foam under the bottom plate as well. Reading Gary's posts as well as Fix's posts have shown me the utility in that.


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## Bud9051 (Nov 11, 2015)

Hi simon,
I have a little different take on insulating basement walls of existing homes. 90% of the heat loss occurs in the upper half of the wall, maybe more. In order of importance, the area of the foundation that is exposed to the elements if the worst. Then, the first foot or two below grade. Below that the path for heat to escape to the air increases with depth and when you get near the bottom, the depth of soil is actually acting as an insulator. It may start out at 40° but as it absorbs heat it warms up and the heat loss slows down. The only heat actually lost is the small amount that conducts all the way to the surface. So, I vote for stopping the rigid above the drain grill.

As for the air gap, I agree with Fix'n, no gap, plus, you will want to enclose the back of the stud cavity to eliminate any air circulation through the insulation. 

Not sure what purpose the concrete lip is serving, but it is preventing water on the floor from reaching that grill until it is an inch or so deep. You may want to determine the function of what is there and either make it work of eliminate it.

One additional thought might be to elevate the wall, set on short studs, to stop above the grill. I'm just not sure how to deal with that lip.

Bud


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## Fix'n it (Mar 12, 2012)

simonnyc said:


> In the 3 yrs that I've been living in the house, the basement has been bonedry.
> 
> What do you mean by "don't put the drywall over the very bottom plate"?


lucky you. i have a little water problem.

when drywalling, leave the very bottom plate exposed.


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## Fix'n it (Mar 12, 2012)

Bud9051 said:


> Hi simon,
> I have a little different take on insulating basement walls of existing homes. 90% of the heat loss occurs in the upper half of the wall, maybe more. In order of importance, the area of the foundation that is exposed to the elements if the worst. Then, the first foot or two below grade. Below that the path for heat to escape to the air increases with depth and when you get near the bottom, the depth of soil is actually acting as an insulator. It may start out at 40° but as it absorbs heat it warms up and the heat loss slows down. The only heat actually lost is the small amount that conducts all the way to the surface. So, I vote for stopping the rigid above the drain grill.
> 
> 
> ...


Bud

in my case, my basement 1/2 below grade. and the wall is cold all the way down.


when i first saw it, i thought the same thing = that is an oddly placed grill.
but, its not a grill. its a membrane http://www.maxokc.com/products/media/400_48634_1.jpg?1357920120
installed, water runs behind it. down to the FD.
http://www.almightyconstructionllc.com/images/waterproofing/waterproofing4.jpg
that ledge. i also thought that to be odd. only thing i can think of = they busted out the floor for the FD. but the footing was in the way so the FD pipe could not go any deeper. so they just put the ledge there to cover it. 

once the wall is up, that ledge would be pretty much irrelevant.


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## Gary in WA (Mar 11, 2009)

Depends on how long you stay in the house, for full height insulation= 8% less heat loss, about $65 annual savings, Chart 2 and Table 4; http://msdssearch.dow.com/Published...foam/pdfs/noreg/179-70015.pdf&fromPage=GetDoc

The drain is continuously connected to the sump, do you want that moisture behind the frame wall... you would also create a horizontal chase, possibly against fire codes, check locally. For sure, the frame wall has to be fire-blocked every 10' horizontally and at ceiling; http://publicecodes.cyberregs.com/icod/irc/2006f2/icod_irc_2006f2_6_sec002_par017.htm IMO, add sticky window tape over the holes before running the FB down on to acoustic sealant at floor, also at joints and perimeter, not canned foam.

The PT is not required when using faced foam board under your non-bearing wall; http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_3_sec017.htm

Appears they left it open for basement flooding... all the pics show it covered with interior finish; https://www.google.com/search?q=mir...sAQINw&biw=1024&bih=615#imgrc=gCwO_eekhrXuwM:

Gary


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## adanders (Feb 6, 2018)

Simon,
Did you ever resolve your question regarding rigid foam over the perimeter drain in your basement? I have the same situation. Did you put it over the "egg crate" flap? 
Any help is appreciated.


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## simonnyc (Mar 2, 2016)

LOL....wow. This thread is 2 years old already? Life happened and I never got around to finishing my basement. It's something I actually just started on. Pull the flourescent lighting and installed recessed lights. Don't know how I'm going to insulate it yet.


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