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Insulation of Canadian basement according to CMHC

Insulation of Canadian basement according to CMHC


  #1  
Old 02-17-15, 11:09 AM
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Insulation of Canadian basement according to CMHC

I am getting ready to re-finish (and re-insulate) by basement. I thought the insulation part was going to be pretty straight forward, but it appears that there are 100 different ways to do this, with several people arguing the pros and cons and potential disastrous results of each. It is safe to say I am officially confused.

I ended up looking at the CMHC website (Canada Mortgage and Housing Corporation, the Government department in charge of these things), and these are the three approaches that they suggest:
A) lay polyethylene sheets or tar paper on the basement wall, build a stud
wall with batt insulation and seal the warm side with polyethylene;

B) use an approved, rigid-board insulation thick enough to give RSI 2.1
(R-12) and finish it with a fire-resistant material (e.g., gypsum board);

C) lay 25 mm (1 in.) of extruded polystyrene board insulation against the
basement wall, build a stud wall with batt insulation and finish with
gypsum board.
Personally, due to cost effectiveness, I would be tempted to go with Option A, but I don't think I saw anyone suggesting this. I saw a debate on whether a vapor barrier should be directly on the wall or between the framing/insulation and the drywall, but I don't think I read anything about placing a barrier in both places.

Long story short, I would really appreciate if someone could help me figure out the best approach here. I do plan to tape a piece of plastic to my foundation for a week to ensure that it remains dry before moving forward with anything.

As usual, your input is much appreciated!
 
  #2  
Old 02-17-15, 11:13 AM
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If used, the vapor barrier goes to the warm side, which is the inside for you. That said, vapor barriers should not be used on below grade walls, which I assume is what you have here.

Option C would be my choice, though Roxul (mineral wool) is superior to fiberglass insulation.
 
  #3  
Old 02-17-15, 11:27 AM
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"A" is kind of the standard around here.

I would not do "B" as it would be more challenging to install any electric now or later.

"C" is the best option and will give you warmest, best insulated wall. As you mentioned, it is also the most expensive, but really the only extra cost is the foam board.
 
  #4  
Old 02-17-15, 12:19 PM
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Canada has different climate zones so your particular area will affect the approach.

You can do the plastic test, but it is a negative results only test. In other words, it might tell you there IS a moisture problem, but it can't tell you there ISN'T a problem. Moisture problems occur top to bottom, season to season, and it might be dry for a few years, and then oops. Thus, the more frequent approach is to avoid the vapor barrier (plastic sheeting) and use the rigid foam board which, although it looks water proof, is rated as a vapor diffusion retarder. Option C with the 1" of rigid maintains a small amount of drying to the inside while keeping the inside surface of that rigid warm enough to not be subject to condensation.

So option C would be my choice and as stickshift suggested, I would opt for the Roxul, it is getting good performance reviews.

Always remember, even a perfectly dry basement is still a hole in the ground and I have helped clean up many due to one form or another of water.

Bud
 
  #5  
Old 02-18-15, 09:52 AM
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Alright fellas,

So what I am getting here is that there is different ways to do things in different basements and different climates, but if I go with option "C" I can't really go wrong.

That's good enough for me. Thank you so much!

Man, I love this forum!
 
  #6  
Old 02-18-15, 11:08 AM
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The difference for "C" in different climate zones would be the thickness of the foam and whether CA requires you to go all the way down. In the States we used to be able to just go a couple of feet below grade, but the new requirements increased the r-value and it has to go to the floor.

The primary risk is too little rigid with too much fluffy insulation. Excess fluffy would allow the rigid to get too cold, yet being fluffy air could seep through and condense on that cold surface. Each climate zone has a recommended ratio of rigid to fluffy.

Now, I'm being sarcastic calling it fluffy, because traditional fiberglass is very "air open". But, if you went with Roxul, its density and a neat installation would greatly reduce any chance of air sneaking through.

Enjoy,
Bud
 
  #7  
Old 02-18-15, 11:45 AM
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Hmmm

I guess I'm gonna have to figure out what the proper rigid to fluffy ratio in my area. As of right now there isn't much insulation at all. It's just framed, with weird composite cardboard stuff on top of the framing, and then brick paneling on top of that.

The basement is definitely colder than the top floor in the winter.

Also, I've been trying to read the code for my to find out what exactly I should be doing and I'm about to stab myself in the eye with a fork. Very hard to find a straightforward answer.
 
  #8  
Old 02-20-15, 10:51 AM
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All of the options are acceptable, but the key to option "A" is that your vapour barrier should only go as high as the outside grade on the basement. This will give any moisture that might get behind your 2x4 wall a place to escape. If you put the vapour barrier all the way up on the concrete, the water vapour will not be able to escape and condensate on the cold plastic, run down the wall and on the floor. If you only put the vapur barrier on the inside of your basement on the 2x4 wall, dampness from the concrete will fill the void beween your stud wall and basement wall faster than it can escape and will result in mould issues down the road.

I usualy will do option B or C. Only draw back with B is that it is harder to change any electrical down the road, but it also takes less floor space from your basement (the width of the stud wall).
 
  #9  
Old 03-01-15, 05:47 PM
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Great question Shivaya!

I have found it equally confusing as there are a ton of options out there. Spray foam is particularly popular right now as well which only add to the confusion. I'm leaning towards using 2" of rigid foam board (I live in Edmonton where it gets quite cold) on the exterior walls and then going with a stud wall and Roxul in all the walls and ceiling.

I hope you don't mind, but I have a question of my own. It has to do with the vapor barrier. I was planning on spray foaming my rim joists and not putting any poly or anything over the Roxul. My basement is partially above grade though- 4.5 feet below grade and 4.5 feet above grade. Do I need to be doing something different for the above grade portion of my basement?

Thanks in advance!!
 
  #10  
Old 03-01-15, 06:25 PM
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You can never go wrong with spray foam, it is great stuff in my opinion, just make sure you are getting a closed cell type for locations that require a vapour barrier.

Your vapour barrier ALWAYS goes on the warm in winter side. If you plan to put a stud wall up, you will need to put poly on that wall after it is insulated. If you plan to put 2" foam on the foundation wall first, you don't need to worry about poly on the foundation side, and you would run the foam right to the top of the wall.

Only if you were NOT putting the rigid foam first would you put a poly vapour barrier on the foundation wall, starting at the grade level, down the wall and 1 foot into the room. You would then frame your interior wall on top of that poly, and wrap it up the inside of the wall and seal it to the poly on the inside of your wall.
 
  #11  
Old 03-02-15, 08:16 AM
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Hey fellas!

I don't want to do spray foam because I know nothing about it, which means I would need to hire someone, which is probably going to be more expensive than I really need it to be. I also heard it was a real nightmare to work with if ever something happens to the foundation down the road and you want to fix it from the inside.

I spoke to some friends of mine who are in the field and they explained it how they do it here (I am in Quebec). It seems like option C is the way to go.

1 inch of foam glued directly to the wall and straight to the ceiling, all taped and sealed; framing on top of that; wool (or roxul) inside the framing; vapor barrier; drywall.

Unless somehow otherwise convinced, that's what I'm going to go with.
 
  #12  
Old 03-02-15, 08:31 AM
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Option C as you presented it originally did not have a vapor barrier and I would not use one below grade.
 
  #13  
Old 03-02-15, 08:37 AM
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Yep, that will work great, just remember to put something under your sill plates so they are not in contact with the concrete floor (use sill gasket or poly).
 
  #14  
Old 03-02-15, 11:32 AM
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Keith - Can I just use pressure-treated lumber for my bottom plate?

stickshift - it seems the norm in my area is to use a vapor barrier. I understand this seems to be a debatable subject, but unless otherwise convinced, I think I'm going to follow what my local guidelines are...
 
  #15  
Old 03-02-15, 12:05 PM
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Even pressure treated should not come in contact with concrete. Is it allowed? Yes, but it will still absorb moisture and lead to mold or rot.
 
  #16  
Old 03-03-15, 05:54 PM
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For what it's gonna cost, I'll just put something under them.
Thanks!
 
 

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