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Insulate & frame foundation walls with membrane in basement

Insulate & frame foundation walls with membrane in basement


  #1  
Old 08-09-17, 11:51 PM
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Smile Insulate & frame foundation walls with membrane in basement

Our basement has interior drainage system with membrane covering up the foundation all the way from the floor to the ceiling, and any leaked water from foundation is supposed to run inside the membrane into the drainage system under the concrete floor.

I'm trying to finish the basement - framing, insulation and drywalls. Our house is in Seattle area.
Our city inspector adviced me 2 options.

1. An option is to attach 1 inch rigid foam (R-5) to the wall(to the membrane), then frame with 2x4s, then put fiberglass (R-13) between the studs, then cover up with drywalls.
2. Another option is to frame with 2x6s keeping 1/2" space from the wall(to the membrane) for air flow, then put fiberglass (R-21) between the studs, then cover up with drywalls.

I'm thinking about the option #1.
Is there anyone seeing problem with this option with the membrane? Something like potential vapor? #2 could be better? Or do you have another suggestion?

BTW, this seems to be the membrane by the tag.
https://www.armtec.com/product/platon-foundation-wrap/

Thank you for your advice in advance.
 
  #2  
Old 08-10-17, 06:35 AM
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If you stop the water from passing through the foundation, which is what should have been done in the first place, that would solve everything.
 
  #3  
Old 08-10-17, 08:18 AM
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As Shorty said, the membrane is a patch for a problem that should have been addressed when the house was built. But that message will take a few generations to reach the home owner population.

Option #2 fails to recognize the condensation potential when a cold wall is exposed to warm humid air. The #1 option addresses that issue by covering the wall with a layer of rigid insulation so that the inside surface will remain warmer and above the dew point. There is a balance where too little rigid or too much fiberglass can result in potential condensation.

Plus, the suggestion of leaving a gap has been shown to promote condensation and even ice under very cold conditions when moist air from the lower areas circulates up to the colder spaces above. I would avoid any space as much as possible and using the rigid foam allows the insulation to be placed directly against that wall.

Bud
 
  #4  
Old 08-10-17, 11:51 PM
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Smile

Thank you Bud and Shorty. I totally agree that if we ever see active leaking, that should be stopped first. In our case, that part has been addressed too. Our area had record breaking hard rain earlier in this year, and a lot of leaking happened to countless old houses in the city (I think many of them didn't have water issue for several decades). So we conducted comprehensive measure inside & outside. I don't know if any water will go into the interior drain system, but if that happens, hopefully the stopper does the job.

So, my concern was mainly, as Bud pointed out, about potential condensation. (I didn't have much knowledge around this, especially I had no idea for cases with membrane) Thanks Bud, sounds like the option #1 is the way to go. Your explanation makes sense to me!
 
 

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